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Abstract The yield potential of large-panicle rice is often limited by grain-filling barriers caused by the development of inferior spikelets (IS). Photoassimilates, which are the main source of rice grain filling, mainly enter the caryopsis through the dorsal vascular bundle. The distribution of assimilates between superior spikelets (SS) and IS is influenced by auxin-mediated apical dominance; however, the mechanism involved is still unclear. In this study, the effect of auxin signaling on the grain filling of SS and IS was investigated in two large-panicle japonica rice varieties, W1844 and CJ03. Compared to SS, IS displayed delayed initiation of filling and a significantly lower grain weight. Furthermore, the endosperm development in IS remained stagnant at the coenocytic stage. The development of the dorsal vascular bundle in the IS was also slow, and poor sucrose-unloading was observed during the initial grain filling stage. However, the endosperm development in IS immediately started after the improvement of dorsal vascular bundle development. GUS activity staining further revealed that indole-3-acetic (IAA) was localized in the dorsal vascular bundle and surrounding areas, suggesting that the low IAA content observed in the IS during the initial grain filling stage may have delayed the development of the dorsal vascular bundle. Therefore, these results demonstrate that IAA may control sugar transport and unloading by regulating dorsal vascular bundle development, consequently affecting endosperm development in IS.

This study aimed to select suit glutinous rice varieties for the production of sweet rice wine. The wine was prepared by using 25 glutinous rice varieties harvest in Huaiyuan as raw materials. The basic components of glutinous rice, and the physicochemical properties the wine were compared. The sensory characteristics were investigated by using electronic tongue, electronic nose, sensory evaluation, the relationship among the basic components of glutinous rice, physicochemical properties, and sensory qualities of rice wine was established by correlation analysis. The results showed that the total starch content of 25 kinds of glutinous rice was 59.0~81.0 g/100 g, the amylose content was 1.0~3.5 g/100 g, and the protein content was 6.6~8.5 g/100 g. The alcohol content of 25 kinds of sweet rice wine was 0.8%vol~2.8%vol, the reducing sugar content was 15.5~31.8 g/100 g, and the total acid content was 0.29~0.66 g/100 g, which met the requirements of clear-juice type rice wine stipulated by industry standard. All rice wine presented antioxidant activity to some extent, while this made from 'Funuo 628' showed the best antioxidant activity, with DPPH free radical clearance and iron ion reducing ability reaching 71.3% and 15.7 μg VC/mL, respectively. The sensory of 25 kinds of rice wine had significant differences. 13 kinds of rice wine were significantly better than the commercial Xiaogan rice wine among them, while the others were similar to the commercial one. The reducing sugar and total acid contents dominated in determining the sensory scores. 'Funuo 628' exhibited the advantages of both high sensory quality and good antioxidant activity, which therefore was potential to develop sweet rice wine with unique flavors and functional properties.

Abstract Slow-controlled release fertilizers are experiencing a popularity in rice cultivation due to their effectiveness in yield and quality with low environmental costs. However, the underlying mechanism by which these fertilizers regulate grain quality remains inadequately understood. This study investigated the effects of five fertilizer management practices on rice yield and quality in a two-year field experiment: CK, conventional fertilization, and four applications of slow-controlled release fertilizer (UF, urea formaldehyde; SCU, sulfur-coated urea; PCU, polymer-coated urea; BBF, controlled-release bulk blending fertilizer). In 2020 and 2021, the yields of UF and SCU groups showed significant decreases when compared to conventional fertilization, accompanied by a decline in nutritional quality. Additionally, PCU group exhibited poorer cooking and eating qualities. However, BBF group achieved increases in both yield (10.8 t hm−2 and 11.0 t hm−2) and grain quality reaching the level of CK group. The adequate nitrogen supply in PCU group during the grain-filling stage led to a greater capacity for the accumulation of proteins and amino acids in the PCU group compared to starch accumulation. Intriguingly, BBF group showed better carbon–nitrogen metabolism than that of PCU group. The optimal nitrogen supply present in BBF group suitable boosted the synthesis of amino acids involved in the glycolysis/ tricarboxylic acid cycle, thereby effectively coordinating carbon–nitrogen metabolism. The application of the new slow-controlled release fertilizer, BBF, is advantageous in regulating the carbon flow in the carbon–nitrogen metabolism to enhance rice quality.

Abstract Background The intensified global warming during grain filling deteriorated rice quality, in particular increasing the frequency of chalky grains which markedly impact market value. The formation of rice quality is a complex process influenced by multiple genes, proteins and physiological metabolic processes. Proteins responsive to stimulus can adjust the ability of plants to respond to unfavorable environments, which may be an important protein involved in the regulation of quality formation under elevated temperature. However, relatively few studies have hindered our further understanding of rice quality formation under elevated temperature. Results We conducted the actual field elevated temperature experiment and performed proteomic analysis of rice grains at the early stage of grain filling. Starting with the response to stimulus in GO annotation, 22 key proteins responsive to stimulus were identified in the regulation of grain filling and response to elevated temperature. Among the proteins responsive to stimulus, during grain filling, an increased abundance of signal transduction and other stress response proteins, a decreased abundance of reactive oxygen species-related proteins, and an increased accumulation of storage substance metabolism proteins consistently contributed to grain filling. However, the abundance of probable indole-3-acetic acid-amido synthetase GH3.4, probable indole-3-acetic acid-amido synthetase GH3.8 and CBL-interacting protein kinase 9 belonged to signal transduction were inhibited under elevated temperature. In the reactive oxygen species-related protein, elevated temperature increased the accumulation of cationic peroxidase SPC4 and persulfide dioxygenase ETHE1 homolog to maintain normal physiological homeostasis. The increased abundance of alpha-amylase isozyme 3E and seed allergy protein RA5 was related to the storage substance metabolism, which regulated starch and protein accumulation under elevated temperature. Conclusion Auxin synthesis and calcium signal associated with signal transduction, other stress responses, protein transport and modification, and reactive oxygen species-related proteins may be key proteins responsive to stimulus in response to elevated temperature. Alpha-amylase isozyme 3E and seed allergy protein RA5 may be the key proteins to regulate grain storage substance accumulation and further influence quality under elevated temperature. This study enriched the regulatory factors involved in the response to elevated temperature and provided a new idea for a better understanding of grain response to temperature.

Abstract Poor grain-filling initiation in inferior spikelets severely impedes rice yield improvement, while photo-assimilates from source leaves can greatly stimulate the initiation of inferior grain-filling (sink). To investigate the underlying mechanism of source-sink interaction, a two-year field experiment was conducted in 2019 and 2020 using two large-panicle rice cultivars (CJ03 and W1844). The treatments included intact panicles and partial spikelet removal. These two cultivars showed no significant difference in the number of spikelets per panicle. However, after removing spikelet, W1844 showed higher promotion on 1000-grain weight and seed-setting rate than CJ03, particularly for inferior spikelets. The reason was that the better sink activity of W1844 led to a more effective initiation of inferior grain-filling compared to CJ03. The inferior grain weight of CJ03 and W1844 did not show a significant increase until 8 days poster anthesis (DPA), which follows a similar pattern to the accumulation of photo-assimilates in leaves. After removing spikelets, the source leaves of W1844 exhibited lower photosynthetic inhibition compared to CJ03, as well as stronger metabolism and transport of photo-assimilates. Although T6P levels remained constant in both cultivars under same conditions, the source leaves of W1844 showed notable downregulation of SnRK1 activity and upregulation of phytohormones (such as abscisic acid, cytokinins, and auxin) after removing spikelets. Hence, the high sink strength of inferior spikelets plays a role in triggering the enhancement of source strength in rice leaves, thereby fulfilling grain-filling initiation demands.

Controlled-release urea (CRU) is widely reported to supply crop nitrogen (N) demand with one basal application, thus effectively replacing split applications of urea without diminishing grain yield and N use efficiency (NUE). However, its use for replacement for high-yield split applications of urea (CK) for rice is untested. In addition, the degree to which greenhouse gas (GHG) emissions in rice systems are affected when CRU is substituted for CK remains unclear. During 2017 and 2018, we sampled plant growth and gas emissions in a rice paddy field treated with three CRU types (sulfur-coated urea [SCU], polymer-coated urea [PCU], and bulk blended CRU [BBU]) applied via two methods (surface broadcasting on the soil and subsurface banding at 5 cm depth), with CK as a control. The three CRUs led to different soil NH4+-N dynamics, and the N supply pattern under BBU was more beneficial for rice seedling establishment than under SCU and PCU, resulting in grain yield and NUE comparable to those under CK. CRU type showed no significant effect on either CH4 emissions or N2O emissions, and broadcast CRUs exhibited significantly higher total GHG emissions than CK. However, banded CRUs significantly reduced the total GHG emissions in comparison with broadcast CRUs, by 9.2% averaged across the two years. Reduced CH4 emissions, particularly during the period prior to the middle drainage, contributed largely to the GHG difference. With comparably high grain yield and low total GHG emissions, banded BBU showed a low yield-scaled GHG (GHG emissions divided by grain yield) comparable to that under CK in both years. Overall, our study suggested that N management synchronized with rice demand and contributing to a high NUE tended to minimize yield-scaled GHG. Broadcast CRU can hardly substitute for CK in terms of either grain yield or GHG emissions, but banded BBU is a promising N management strategy for sustaining rice production while minimizing environmental impacts.

Three-dimensional (3D) phenotyping is important for studying plant structure and function. Light detection and ranging (LiDAR) has gained prominence in 3D plant phenotyping due to its ability to collect 3D point clouds. However, organ-level branch detection remains challenging due to small targets, sparse points, and low signal-to-noise ratios. In addition, extracting biologically relevant angle traits is difficult. In this study, we developed a stratified, clustered, and growing-based algorithm (SCAG) for soybean branch detection and branch angle calculation from LiDAR data, which is heuristic, open-source, and expandable. SCAG achieved high branch detection accuracy (F-score = 0.77) and branch angle calculation accuracy (r = 0.84) when evaluated on 152 diverse soybean varieties. Meanwhile, the SCAG outperformed 2 other classic algorithms, the support vector machine (F-score = 0.53) and density-based methods (F-score = 0.55). Moreover, after applying the SCAG to 405 soybean varieties over 2 consecutive years, we quantified various 3D traits, including canopy width, height, stem length, and average angle. After data filtering, we identified novel heritable and repeatable traits for evaluating soybean density tolerance potential, such as the ratio of average angle to height and the ratio of average angle to stem length, which showed greater potential than the well-known ratio of canopy width to height trait. Our work demonstrates remarkable advances in 3D phenotyping and plant architecture screening. The algorithm can be applied to other crops, such as maize and tomato. Our dataset, scripts, and software are public, which can further benefit the plant science community by enhancing plant architecture characterization and ideal variety selection.

Drug delivery via intra-articular (IA) injection has proved to be effective in osteoarthritis (OA) therapy, limited by the drug efficiency and short retention time of the drug delivery systems (DDSs). Herein, a series of modified cross-linked dextran (Sephadex, S0) was fabricated by respectively grafting with linear alkyl chains, branched alkyl chains or aromatic chain, and acted as DDSs after ibuprofen (Ibu) loading for OA therapy. This DDSs expressed sustained drug release, excellent anti-inflammatory and chondroprotective effects both in IL-1β induced chondrocytes and OA joints. Specifically, the introduction of a longer hydrophobic chain, particularly an aromatic chain, distinctly improved the hydrophobicity of S0, increased Ibu loading efficiency, and further led to significantly improving OA therapeutic effects. Therefore, hydrophobic microspheres with greatly improved drug loading ratio and prolonged degradation rates show great potential to act as DDSs for OA therapy.

Nitrogen (N) fertilization increases rice yield, but inappropriate N fertilizer application increases N loss and the risk of environmental pollution. Short-term fertilizer postponing (FP) generally reduces N apparent surplus and increases rice yields, but the effects of long-term FP on N surplus and rice yields remain unknown. Our study was the first to investigate the impacts of long-term FP (11 years) on N apparent surplus and rice yields. FP effects in the short term (≤6 years) did not affect rice yields, whereas FP effects in the long term (>6 years) increased rice yields by 13.9% compared with conventional fertilization (CF). FP did not affect panicles per unit area, 1000-kernel weight, and filled-kernel rate, but spikelets per panicle increased over time due to spikelet formation stimulation. FP also reduced the N apparent surplus over time more strongly than CF owing to higher N accumulation and N utilization efficiency. FP effects in the long term also significantly increased soil organic matter, total N, and NH4+-N content. Our results were supported by a pot experiment, showing that rice yields in soils with a history of FP were significantly higher than those for soils without a history of FP, indicating that FP increased rice yields more strongly in later years mainly because of soil quality improvement. Our findings suggest that long-term FP can reduce N loss while increasing rice yields by improving soil quality.

Heat resilience and tolerance of rice crops is enhanced by manure amendment and could improve yield stability under projected climate change, suggest a meta-analysis and long term manure amendment experiments.

Interaction between the embryo and endosperm affects seed development, an essential process in yield formation in crops such as rice. Signals that mediate communication between embryo and endosperm are largely unknown. We used the notched-belly (NB) mutant with impaired communication between embryo and endosperm to investigate the effect of the embryo on developmental staging of the endosperm and signaling pathways in the embryo that regulate endosperm development. Hierachical clustering of mRNA datasets from embryo and endosperm samples collected during development in NB and a wild type showed a delaying effect of the embryo on the developmental transition of the endosperm by extension of the middle stage. K-means clustering further identified coexpression modules of gene sets specific to embryo and endosperm development. Combined gene expression and biochemical analysis showed that T6P–SnRK1, gibberellin and auxin signaling by the embryo regulate endosperm developmental transition. We propose a new seed developmental staging system for rice and identify the most detailed signature of rice grain formation to date. These will direct genetic strategies for rice yield improvement.

Despite growing interest in controlled-release N fertilizers (CRNFs) because of their potential for enhancing nitrogen use efficiency (NUE) and economic returns, their comprehensive impact on machine-transplanted rice remains to be understudied. To address this gap, here, we present a two-year field experiment that assessed the impact of CRNF using mechanical deep placement fertilization (DPF) on rice cultivation. The study involved three CRNF types (bulk blending fertilizer (BBF), polymer-coated urea (PCU), and sulfur-coated urea (SCU)) and two fertilization methods (DPF and broadcast application), with a high-yield split fertilization of urea as a control (CK). The results showed that DPF, especially with SCU, greatly enhanced soil NH4+-N concentrations, NUE, rice yield, and economic benefits compared to broadcast application. BBF consistently exhibited superior NUE and notable economic benefits, regardless of the application method used. Conversely, single-time application of PCU was less favorable for rice growth. In conclusion, for optimal economic benefits and NUE, DPF combined with single-time application of SCU is recommended. However, if deep application is not feasible and only broadcasting is possible in rice cultivation, BBF emerges as the ideal choice for both high NUE and significant economic returns. This research offers insights for improved nitrogen management in machine-transplanted rice, effectively optimizing yield, NUE, and profitability.

Elevated levels of atmospheric CO2 (eCO2) promote rice growth and increase methane (CH4) emissions from rice paddies, because increased input of plant photosynthate to soil stimulates methanogenic archae. However, temporal trends in the effects of eCO2 on rice growth and CH4 emissions are still unclear. To investigate changes in the effects of eCO2 over time, we conducted a two-season pot experiment in a walk-in growth chamber. Positive effects of eCO2 on rice leaf photosynthetic rate, biomass, and grain yield were similar between growing seasons. However, the effects of eCO2 on CH4 emissions decreased over time. Elevated CO2 increased CH4 emissions by 48%–101% in the first growing season, but only by 28%–30% in the second growing season. We also identified the microbial process underlying the acclimation of CH4 emissions to atmospheric CO2 enrichment: eCO2 stimulated the abundance of methanotrophs more strongly in soils that had been previously exposed to eCO2 than in soils that had not been. These results emphasize the need for long-term eCO2 experiments for accurate predictions of terrestrial feedbacks.

Accurate assessment of crop biochemical profiles plays a crucial role in diagnosing their physiological status. The conventional destructive methods, although reliable, demand extensive laboratory work for measuring various traits. On the other hand, nondestructive techniques, while efficient and adaptable, often suffer from reduced precision due to the intricate interplay of the field environment and canopy structure. Striking a delicate balance between efficiency and accuracy, we have developed the Bio-Master phenotyping system. This system is capable of simultaneously measuring four vital biochemical components of the canopy profile: dry matter, water, chlorophyll, and nitrogen content. Bio-Master initiates the process by addressing structural influences, through segmenting the fresh plant and then further chopping the segment into uniform small pieces. Subsequently, the system quantifies hyperspectral reflectance and fresh weight over the sample within a controlled dark chamber, utilizing an independent light source. The final step involves employing an embedded estimation model to provide synchronous estimates for the four biochemical components of the measured sample. In this study, we established a comprehensive training dataset encompassing a wide range of rice varieties, nitrogen levels, and growth stages. Gaussian process regression model was used to estimate biochemical contents utilizing reflectance data obtained by Bio-Master. Leave-one-out validation revealed the model’s capacity to accurately estimate these contents at both leaf and plant scales. With Bio-Master, measuring a single rice plant takes approximately only 5 min, yielding around 10 values for each of the four biochemical components across the vertical profile. Furthermore, the Bio-Master system allows for immediate measurements near the field, mitigating potential alterations in plant status during transportation and processing. As a result, our measurements are more likely to faithfully represent in situ values. To summarize, the Bio-Master phenotyping system offers an efficient tool for comprehensive crop biochemical profiling. It harnesses the benefits of remote sensing techniques, providing significantly greater efficiency than conventional destructive methods while maintaining superior accuracy when compared to nondestructive approaches.

Enhancing the photosynthetic rate is one of the effective ways to increase rice yield, given that photosynthesis is the basis of crop productivity. At the leaf level, crops’ photosynthetic rate is mainly determined by photosynthetic functional traits including the maximum carboxylation rate (Vcmax) and stomatal conductance (gs). Accurate quantification of these functional traits is important to simulate and predict the growth status of rice. In recent studies, the emerging sun-induced chlorophyll fluorescence (SIF) provides us an unprecedented opportunity to estimate crops’ photosynthetic traits, owing to its direct and mechanistic links to photosynthesis. Therefore, in this study, we proposed a practical semimechanistic model to estimate the seasonal Vcmax and gs time-series based on SIF. We firstly generated the coupling relationship between the open ratio of photosystem II (qL) and photosynthetically active radiation (PAR), then estimate the electron transport rate (ETR) based on the proposed mechanistic relationship between SIF and ETR. Finally, Vcmax and gs were estimated by linking to ETR based on the principle of evolutionary optimality and the photosynthetic pathway. Validation with field observations showed that our proposed model can estimate Vcmax and gs with high accuracy (R2 > 0.8). Compared to simple linear regression model, the proposed model could increase the accuracy of Vcmax estimates by >40%. Therefore, the proposed method effectively enhanced the estimation accuracy of crops’ functional traits, which sheds new light on developing high-throughput monitoring techniques to estimate plant functional traits, and also can improve our understating of crops’ physiological response to climate change.

Detailed observation of the phenotypic changes in rice panicle substantially helps us to understand the yield formation. In recent studies, phenotyping of rice panicles during the heading–flowering stage still lacks comprehensive analysis, especially of panicle development under different nitrogen treatments. In this work, we proposed a pipeline to automatically acquire the detailed panicle traits based on time-series images by using the YOLO v5, ResNet50, and DeepSORT models. Combined with field observation data, the proposed method was used to test whether it has an ability to identify subtle differences in panicle developments under different nitrogen treatments. The result shows that panicle counting throughout the heading–flowering stage achieved high accuracy (R2 = 0.96 and RMSE = 1.73), and heading date was estimated with an absolute error of 0.25 days. In addition, by identical panicle tracking based on the time-series images, we analyzed detailed flowering phenotypic changes of a single panicle, such as flowering duration and individual panicle flowering time. For rice population, with an increase in the nitrogen application: panicle number increased, heading date changed little, but the duration was slightly extended; cumulative flowering panicle number increased, rice flowering initiation date arrived earlier while the ending date was later; thus, the flowering duration became longer. For a single panicle, identical panicle tracking revealed that higher nitrogen application led to earlier flowering initiation date, significantly longer flowering days, and significantly longer total duration from vigorous flowering beginning to the end (total DBE). However, the vigorous flowering beginning time showed no significant differences and there was a slight decrease in daily DBE.

The green fraction (GF), which is the fraction of green vegetation in a given viewing direction, is closely related to the light interception ability of the crop canopy. Monitoring the dynamics of GF is therefore of great interest for breeders to identify genotypes with high radiation use efficiency. The accuracy of GF estimation depends heavily on the quality of the segmentation dataset and the accuracy of the image segmentation method. To enhance segmentation accuracy while reducing annotation costs, we developed a self-supervised strategy for deep learning semantic segmentation of rice and wheat field images with very contrasting field backgrounds. First, the Digital Plant Phenotyping Platform was used to generate large, perfectly labeled simulated field images for wheat and rice crops, considering diverse canopy structures and a wide range of environmental conditions (sim dataset). We then used the domain adaptation model cycle-consistent generative adversarial network (CycleGAN) to bridge the reality gap between the simulated and real images (real dataset), producing simulation-to-reality images (sim2real dataset). Finally, 3 different semantic segmentation models (U-Net, DeepLabV3+, and SegFormer) were trained using 3 datasets (real, sim, and sim2real datasets). The performance of the 9 training strategies was assessed using real images captured from various sites. The results showed that SegFormer trained using the sim2real dataset achieved the best segmentation performance for both rice and wheat crops (rice: Accuracy = 0.940, F1-score = 0.937; wheat: Accuracy = 0.952, F1-score = 0.935). Likewise, favorable GF estimation results were obtained using the above strategy (rice: R2 = 0.967, RMSE = 0.048; wheat: R2 = 0.984, RMSE = 0.028). Compared with SegFormer trained using a real dataset, the optimal strategy demonstrated greater superiority for wheat images than for rice images. This discrepancy can be partially attributed to the differences in the backgrounds of the rice and wheat fields. The uncertainty analysis indicated that our strategy could be disrupted by the inhomogeneity of pixel brightness and the presence of senescent elements in the images. In summary, our self-supervised strategy addresses the issues of high cost and uncertain annotation accuracy during dataset creation, ultimately enhancing GF estimation accuracy for rice and wheat field images. The best weights we trained in wheat and rice are available: https://github.com/PheniX-Lab/sim2real-seg.

The number of leaves at a given time is important to characterize plant growth and development. In this work, we developed a high-throughput method to count the number of leaves by detecting leaf tips in RGB images. The digital plant phenotyping platform was used to simulate a large and diverse dataset of RGB images and corresponding leaf tip labels of wheat plants at seedling stages (150,000 images with over 2 million labels). The realism of the images was then improved using domain adaptation methods before training deep learning models. The results demonstrate the efficiency of the proposed method evaluated on a diverse test dataset, collecting measurements from 5 countries obtained under different environments, growth stages, and lighting conditions with different cameras (450 images with over 2,162 labels). Among the 6 combinations of deep learning models and domain adaptation techniques, the Faster-RCNN model with cycle-consistent generative adversarial network adaptation technique provided the best performance (R2 = 0.94, root mean square error = 8.7). Complementary studies show that it is essential to simulate images with sufficient realism (background, leaf texture, and lighting conditions) before applying domain adaptation techniques. Furthermore, the spatial resolution should be better than 0.6 mm per pixel to identify leaf tips. The method is claimed to be self-supervised since no manual labeling is required for model training. The self-supervised phenotyping approach developed here offers great potential for addressing a wide range of plant phenotyping problems. The trained networks are available at https://github.com/YinglunLi/Wheat-leaf-tip-detection.

Background: Brief hypoxic exposures are increasingly applied as interventions for aging-related conditions. To optimize the therapeutic impact of hypoxia, knowledge of the sex-related differences in physiological responses to hypoxia is essential. This study compared hypoxia-induced hypoxemic responses in elderly men and women.Methods: Seven elderly men (70.3 ± 6.0 years old) and nine women (69.4 ± 5.5 years old) breathed 10% O2 for 5 min while arterial (SaO2; transcutaneous photoplethysmography) and cerebral tissue O2 saturation (ScO2; near-infrared spectroscopy), ventilatory frequency, tidal volume, minute-ventilation, and partial pressures of end-tidal O2 (PETO2) and CO2 (mass spectrometry) were continuously monitored. Cerebral tissue oxygen extraction fraction (OEF) equaled (SaO2–ScO2)/SaO2.Results: During 5 min hypoxia SaO2 fell from 97.0 ± 0.8% to 80.6 ± 4.6% in the men and from 96.3 ± 1.4% to 72.6 ± 4.0% in the women. The slope ΔSaO2/min was steeper in the women than the men (−4.71 ± 0.96 vs. −3.24 ± 0.76%/min; p = 0.005). Although SaO2 fell twice as sharply per unit decrease in PETO2 in the women than the men (−1.13 ± 0.11 vs. −0.54 ± 0.06%/mmHg; p = 0.003), minute-ventilation per unit hypoxemia increased less appreciably in the women (−0.092 ± 0.014 vs. −0.160 ± 0.021 L/min/%; p = 0.023). OEF fell with hypoxia duration in the women, but remained stable in the men.Conclusion: During 5 min hypoxic breathing, elderly women experience more intense hypoxemia and reduced chemoreflex sensitivity vs. their male counterparts, which may lower OEF stability in women despite augmented O2 dissociation from hemoglobin during hypoxia. These sex-related differences merit attention when implementing brief hypoxic exposures for therapeutic purposes.

Abstract Heat events during the reproductive stages of rice plants induce great yield losses. Cultivating heat-tolerant varieties is a promising strategy for guaranteeing grain security under global warming scenarios. Most heat-tolerant rice genotypes were identified under heat during the flowering stage, but it is unclear whether these currently screened heat-tolerant rice genotypes maintain stable high grain yields when heat stress occurs during the other reproductive stages. In the present study, two notable heat-tolerant rice cultivars, Nagina22 and Shanyou63, and one typical heat-sensitive cultivar, Liangyoupeijiu, were evaluated for their yield response and yield stability under heat treatments during the panicle initiation, flowering, and grain filling stages during 2010–2014. Our results revealed that rice cultivars respond differently to heat stress during different reproductive stages. Nagina22 was the most tolerant to heat stress during the flowering and grain filling stages but was susceptible during panicle initiation; Shanyou63 was the most tolerant to heat stress during panicle initiation and grain filling and was moderately tolerant to heat stress during the flowering stages. Genotype and genotype-by-environment interaction biplot yield analysis revealed that Shanyou63 exhibited the highest stability in high grain yield, followed by Nagina22, and Liangyoupeijiu exhibited stable low grain yield when experiencing heat stress across the three reproductive stages. Our results indicate that the heat tolerance of different rice cultivars depends on the reproductive stage during which heat stress occurs, and the effects manifest as reductions in grain yields and seed setting rates. Future efforts to develop heat-tolerant varieties should strive to breed varieties that are comprehensively tolerant to heat stress during any reproductive stage to cope with the unpredictable occurrence of future heat events.

Fertilizer management is vital for sustainable agriculture under climate change. Reduced basal and increased topdressing fertilizer rate (RBIT) has been reported to improve the yield of in–season rice or wheat. However, the effect of RBIT on rice and wheat yield stability and soil organic carbon (SOC) sequestration potential is unknown, especially when combined with straw incorporation. Here, we report the effect of RBIT with/without straw incorporation on crop yields, yield stability, SOC stock, and SOC fractions in the lower Yangtze River rice–wheat system region over nine years. RBIT with/without straw incorporation significantly increased nine–year average and annual rice yields but not wheat yields. Compared with conventional fertilization (CF), RBIT did not significantly affect wheat or rice yield stability, but combined with straw incorporation, it increased the sustainable yield index (SYI) of wheat and rice by 7.6 and 12.8%, respectively. RBIT produced a higher C sequestration rate (0.20 Mg C ha−1 year−1) than CF (0.06 Mg ha−1 year−1) in the 0–20 cm layer due to higher root C input and lower C mineralization rate, and RBIT in combination with straw incorporation produced the highest C sequestration rate (0.47 Mg ha−1 year−1). Long–term RBIT had a greater positive effect on silt+clay (0.053 mm)–associated C, microbial biomass C (MBC), dissolved organic C, and hot water organic C in the surface layer (0–10 cm) than in the subsurface layer (10–20 cm). In particular, the increases in SOC pools and mean weight diameter (MWD) of soil aggregates were greater when RBIT was combined with straw incorporation. Correlation analysis indicated that topsoil SOC fractions and MWD were positively correlated with the SYI of wheat and rice. Our findings suggest that the long–term application of RBIT combined with straw incorporation contributed to improving the sustainability of rice production and SOC sequestration in a rice–wheat system.

Carbon isotope composition (δ13C) of a plant organ is an inherent signature reflecting its physiological property, and thus is used as an integrative index in crop breeding. It is also a non-intrusive method for quantifying the relative contribution of different source organs to grain filling in cereals. Using the samples collected from two-year field and pot experiments with two nitrogen (N) fertilization treatments, we investigated the temporal and spatial variations of δ13C in source organs of leaf, sheath, internode, and bracts, and in sink organ grain. Constitutive nature of δ13C was uncovered, with an order of leaf (−27.84‰)

Abstract Background The initiation of flowering transition in rice (Oryza sativa) is a complex process regulated by genes and environment. In particular, drought can interfere with flowering; therefore, many plants hasten this process to shorten their life cycle under water scarcity, and this is known as drought-escape response. However, rice has other strategies; for example, drought stress can delay flowering instead of accelerating it. RICE CENTRORADIALIS 1 (RCN1) is a TERMINAL FLOWER-like gene that influences rice flowering transition and spike differentiation. It interacts with 14–3-3 proteins and transcription factor OsFD1 to form a florigen repression complex that suppresses flowering transition in rice. Results In this study, we explored the role of RCN1 in the molecular pathway of drought-regulated flowering transition. The rcn1 mutant plants displayed early heading under both normal water and drought stress conditions, and they were more insensitive to drought stress than the wild-type plants. Abscisic acid (ABA) signaling-mediated drought-induced RCN1 is involved in this process. Conclusions Thus, RCN1 plays an important role in the process of drought stress inhibiting flowering transition. It may worked by suppressing the protein function rather than transcription of HEADING DATE 3a.

Grain chalkiness is a key quality trait of the rice grain, whereas its underlying mechanism is still not thoroughly understood because of the complex genetic and environmental interactions. We identified a notched-belly (NB) mutant that has a notched-line on the belly of grains. The line dissects the endosperm into two distinct parts, the upper translucent part, and the bottom chalky part in the vicinity of the embryo. Using this mutant, our previous studies clued the negative influence of embryo on the biochemical makeup of the endosperm, suggesting the need for the in-depth study of the embryo effect on the metabolome of developing endosperm. This study continued to use the NB mutant to evolve a novel comparison method to clarify the role of embryo in the formation of a chalky endosperm. Grain samples of the wild-type (WT) and NB were harvested at 10, 20, and 30 days after fertilization (DAF), and then divided into subsamples of the embryo, the upper endosperm, and the bottom endosperm. Using non-targeted metabolomics and whole-genome RNA sequencing (RNA-seq), a nearly complete catalog of expressed metabolites and genes was generated. Results showed that the embryo impaired the storage of sucrose, amino acid, starch, and storage proteins in the bottom endosperm of NB by enhancing the expression of sugar, amino acids, and peptide transporters, and declining the expression of starch, prolamin, and glutelin synthesis-related genes. Importantly, the competitive advantage of the developing embryo in extracting the nutrients from the endosperm, transformed the bottom endosperm into an “exhaustive source” by diverting the carbon (C) and nitrogen (N) metabolism from synthetic storage to secondary pathways, resulting in impaired filling of the bottom endosperm and subsequently the formation of chalky tissue. In summary, this study reveals that embryo-induced metabolic shift in the endosperm is associated with the occurrence of grain chalkiness, which is of relevance to the development of high-quality rice by balancing the embryo–endosperm interaction.

There is a need to comprehensively evaluate the rice quality of different rice varieties under different nitrogen treatments. Therefore, in this study, we used twenty-one hybrid indica rice varieties and twenty-three inbred japonica rice varieties with three nitrogen fertilizer levels to investigate differences in rice qualities. As compared with hybrid indica rice, inbred japonica rice had lower coefficient of variation values for grain shape, mild rice percentage, and head rice percentage, but relatively higher coefficient of variation values for chalkiness traits, appearance, and taste value of cooked rice. A principal component analysis and membership function method were used to comprehensively evaluate the qualities of rice. The overall eating quality value by sensory evaluation and head rice percentage explained 61.3% and 67.9% of the variations in comprehensive quality of hybrid indica rice and inbred japonica rice across different nitrogen levels, respectively. We also found that rice comprehensive quality was better under low nitrogen levels for hybrid indica rice, while for inbred japonica rice, properly increasing nitrogen application could improve the comprehensive quality.

Ammonia (NH3) volatilization from paddy fields is a major issue which leads to poor fertilizer use efficiency and is considered a severe threat to the atmosphere. The previous research studies gave importance to the use of nitrogen fertilizers to mitigate NH3 volatilization, while very little emphasis was given to the role of other fertilizers, such as phosphorus (P), for the alleviation of NH3 volatilization in rice fields. Considering P importance herein, we conducted two consecutive field experiments using an innovative, controlled-release, phosphorus-blended fertilizer (CRPBF, with levels CRP0, CRP1, and CRP2). We compared CP0 (in which no fertilizer was applied), CP1 (112.5 kg P ha−1 P of locally recommended fertilizers), and CP2: (P and K blended fertilizers) to determine the best possible way to reduce NH3 volatilization without affecting the yield and quality of rice. The results of the study suggested that the yield of rice increased significantly with the application of CRP1 (11.11 t ha−1) and CRP2 (11.99 t ha−1). The addition of CRP1 and CRP2 to the rice field also enhanced yield-related components, i.e., panicle weight, total spikelets per unit area, spikelets per panicle, and above-ground biomass. CRP0 showed a lower yield and related components when compared to CP2. The addition of CRP1 and CRP2 demonstrated lower protein contents when compared to other treatments. The CRPBF application improved starch content and taste scores, and reduced the chalkiness of the rice grain during both years. The results showed a decreasing trend in NH3 volatilization from CRPBF amendments by improving the nitrogen use efficiency traits when compared to other treatments: CRP2, CRP1, and CRP0 reduced NH3 volatilization by 45%, 35%, and 15%, respectively. The results of this study indicate that, due to the episodic nature of NH3 volatilization, CRPBFs with 50% P and 100% P can markedly reduce NH3 volatilization from paddy fields without compromising the yield and quality of the crop, and could be a promising alternative to the ordinary commercial fertilizers used in rice fields.

A reduced basal and increased topdressing fertilizer rate (RBIT) can usually increase rice yield, but whether this practice alleviates the impact of poor weather on rice production is unknown. Thus, the effect of three integrated RBIT treatments (RBITs, including RBIT alone, RBIT in combination with straw incorporation (RBITS) or a reduced fertilizer rate (RBITR)) on rice growth and nutritional status under different weathers was investigated in a 9-year experiment. Conventional fertilization (CF) was the control. We found that daytime temperature and light (DTL) after heading were the main meteorological factors limiting rice yield increases. RBITs did not affect rice yield under High-DTL, compared with CF, but RBITS significantly increased rice yield under Low-DTL. Compared with High-DTL, the positive effect of RBIT and RBITR on the N concentration and proportion in vegetative organs under Low-DTL was higher than the K concentration in vegetative organs, but RBITS showed the opposite trend. Regression analysis indicated that the harvest index had stronger correlations with the N concentration (negative), K concentration (positive), and N/K (negative) in vegetative organs under Low-DTL than under High-DTL. Our findings suggested that RBITS could improve rice adaptability to daytime temperature and light changes after heading by balancing crop nutritional status (N/K).

The increasing trend of extreme heat events poses serious implications for rice production in China, especially when it coincides with the heat-sensitive reproductive growth period (RGP) leading to high temperature-induced spikelet sterility. (2) Methods: This study analyzed the long-term meteorological data of Jiangsu province, located at lower reaches of Yangtze River Valley, to ascertain changing trends in temperature extremes. Moreover, stress days and nights were derived from temperature extremes, during RGP as a proxy of rice sterility in the province. The stress days were defined in three ways, with higher daily maximum (≥35 °C, hot day, HD), and minimum temperature (≥28 °C, hot night, HN) and days with both critical limits (severe hot day, SHD). (3) Results: The analysis of data revealed that a definite warming hiatus period in the 1970s and a transitional phase in 1980s were evident for daily maximum temperatures (TMX) in the province. Warm phases since 1990s were evident for both day and night temperature extremes. Asymmetric warming of TMX and daily minimum (TMN) temperatures reduced diurnal temperature range (DTR) over time. The slight negative trend for TMX and HD were observed, while trends for TMN, HN and SHD were strongly positive in the province with regional variations. (4) Conclusion: Observed increasing trends of TMN, HNs, and SHDs, as well as the decreasing DTR during rice RGP can be a threat to rice production in the province. Rice crop in the Southern Jiangsu is more vulnerable to higher temperature extremes while in the northern Jiangsu, decreasing DTR can be crucial. These findings could have useful implications for improving rice yield under changing climate.

With the intensification of global warming, rice production is facing new challenges. Field evidence indicates that elevated temperature during rice grain-filling leads to the further deterioration of grain quality. In order to clarify the potential regulatory mechanism of elevated temperature on the formation of rice quality, the DIA mass spectrometry method under the background of field warming was conducted to investigate the regulatory effects of high temperature on grain development and material accumulation pathways. The results showed that a total of 840 differentially expressed proteins were identified during the grain-filling process under elevated temperature. These differentially expressed proteins participated in carbon metabolism, amino acid biosynthesis, signal transduction, protein synthesis, and alternately affected the material accumulation of rice grains. The significant up-regulation of PPROL 14E, PSB28, granule-bound starch synthase I, and the significant down-regulation of 26.7 kDa heat shock protein would lead to the component difference in grain starch and storage proteins, and that could be responsible for the degradation of rice quality under elevated temperature. Results suggested that proteins specifically expressed under elevated temperature could be the key candidates for elucidating the potential regulatory mechanism of warming on rice development and quality formation. In-depth study on the metabolism of storage compounds would be contributed in further proposing high-quality cultivation control measures suitable for climate warming.

To investigate the differential responses of super rice grain filling to low filling stage temperature (LT) and the regulative effect of nitrogen panicle fertilizer (NPF), physiological and molecular experiments were conducted with two super rice varieties (Nanjing 7th: N7 and Nanjing 9108th: N9108) on two different filling stage temperature treatments implemented by applying two sowing dates [Normal filling stage temperature (CK): Sowed on May 30, Tmean = 24.7°C and low filling stage temperature (LT): Sowed on July 1, Tmean = 20.3°C], and two NPF levels (0 and 150 kg N ha−1). In this study, LT, NPF, and simultaneous LT and NPF treatments suppressed the grain filling in all varieties with different levels. Under LT or NPF treatments, the reduction of grain weight, seed setting rate, and filling rate were closely associated with suppressed starch biosynthesis rate in inferior seeds, suggesting that reduced starch biosynthesis rate, expression, and activities of enzymes encoded by related genes, Floury endosperm-4 (FLO4), Starch branching enzyme-I (SBE1), and Starch phosphorylase-L (PHO-l), were responsible for the grain filling reduction. Under LT or NPF treatments, significantly higher grain filling rates and lower variance were found in N9108 compared to that in N7, which were closely related to their higher starch biosynthesis ability, related gene expression, and enzymes activities. One of the probable explanations of the grain filling difference was the variation in the relative amount of key regulative hormones, Abscisic acid (ABA) and 1-aminocyclopropane-1-carboxylic acid (ACC). These results raise a possibility that super rice with higher sink activities has superior adaptability to LT and NPF due to their higher sink activities.

The poor grain-filling initiation often causes the poor development of inferior spikelets (IS) which limits the yield potential of large panicle rice (Oryza sativa L.). However, it remains unclear why IS often has poor grain-filling initiation. In addressing this problem, this study conducted a field experiment involving two large panicle rice varieties, namely CJ03 and W1844, in way of removing the superior spikelets (SS) during flowering to force enough photosynthate transport to the IS. The results of this study showed that the grain-filling initiation of SS was much earlier than the IS in CJ03 and W1844, whereas the grain-filling initiation of IS in W1844 was evidently more promoted compared with the IS of CJ03 by removing spikelets. The poor sucrose-unloading ability, i.e., carbohydrates contents, the expression patterns of OsSUTs, and activity of CWI, were highly improved in IS of CJ03 and W1844 by removing spikelets. However, there was a significantly higher rise in the efficiency of sucrose to starch metabolism, i.e., the expression patterns of OsSUS4 and OsAGPL1 and activities of SuSase and AGPase, for IS of W1844 than that of CJ03. Removing spikelets also led to the changes in sugar signaling of T6P and SnRK1 level. These changes might be related to the regulation of sucrose to starch metabolism. The findings of this study suggested that poor sucrose-unloading ability delays the grain-filling initiation of IS. Nonetheless, the efficiency of sucrose to starch metabolism is also strongly linked with the grain-filling initiation of IS.

Aluminum (Al) toxicity inhibits root growth, while nitrogen is an essential nutrient for plant growth and development. To explore the effects of nitrate (N) on Al toxicity and accumulation in root of wheat, two wheat genotypes, Shengxuan 6 hao (SX6, Al-tolerant genotype) and Zhenmai 168 (ZM168, Al-sensitive genotype), were used in a hydroponic experiment with four treatments (control without N or Al, N, Al, and Al+N, respectively). The results showed that N increased the inhibition of root elongation and aluminum accumulation in root. The Al-sensitive genotype suffered more serious Al toxicity than the Al-tolerant genotype. Histochemical observation clearly showed that Al prefers binding on the root apex 7–10 mm zones, and the Al-sensitive genotype accumulated more Al in these zones. Compared with other treatments, the Al+N treatment had significantly higher O2−, superoxides dismutase (SOD), catalase (CAT), peroxidase (POD) activities, H2O2, Evans blue uptake, malondialdehyde (MDA), ascorbic acid (AsA), pectin, and hemicellulose 1 (HC1) contents in both genotypes. Under Al+N treatment, O2− activity, Evans blue uptake, MDA, and HC1 contents of SX6 were significantly lower than those of ZM168, but SOD, CAT, and POD activities and AsA content exhibited an opposite trend. Therefore, aluminum toxicity and accumulation in root of wheat seedlings were aggravated by nitrate.

Not enough attention has been paid to the comparison in yield performance and N responsiveness between hybrid rice and inbred rice using the large number of new cultivars released after 2000 under machine transplanting. Field experiments were conducted in 2017 and 2018; 48 widely planted rice cultivars included four groups, namely indica hybrids (IHs), japonica inbreds (JIs), indica-japonica hybrids (IJHs), and indica inbreds (IIs) that were transplanted by machine with three nitrogen fertilizer levels (0, 150, 300 kg ha−1). The average yield of the hybrids (IHs, IJHs) was higher than that of JIs or IIs with a higher crop-growing rate (CGR) during the total growth duration, regardless of the N application level; moreover, longer total growth duration was responsible for the higher yield in IJHs than in IHs. The IHs had a large gap yield which mainly came from the genetic improvement in the CGR during the grain-filling stage. The yield gap was relatively small in JIs, and longer growth duration combined with optimal daily mean temperature during the grain-filling stage was the critical factor for high yield. The JIs or IJHs had higher yield under the N300 level, while the response of IHs to nitrogen varied with different cultivars. Cultivars with higher CGR during the grain-filling stage had higher yield under the N300 level. In conclusion, this study suggests that high CGR during the grain-filling stage may be a vital trait for the development of rice with high yield and high N responsiveness at machine transplanting.

Our previous study has shown that nitrogen plays an important role in dealing with significantly increased chalkiness caused by elevated temperature. However, the role of nitrogen metabolites has not been given sufficient attention, and its regulatory mechanism is not clear. This study investigated the effects of high temperature and nitrogen fertilizer on the synthesis of grain storage protein and further explored the quality mechanism under the actual scenario of field warming. Results showed that increased temperature and nitrogen fertilizer could affect the activities of nitrogen metabolism enzymes, namely, glutamate synthetase, glutamine synthetase, glutamic pyruvic transaminase, and glutamic oxaloacetic transaminase, and the expressions of storage protein synthesis factor genes, namely, GluA and GluB, and subfamily genes, namely, pro14, BiP1, and PDIL1, which co-induced the changes of storage protein synthesis in rice grains. Furthermore, the increased temperature changed the balance of grain storage substances which may lead to the significantly increased chalky rate (197.67%) and chalkiness (532.92%). Moreover, there was a significant negative correlation between prolamin content and chalkiness, indicating that nitrogen fertilizer might regulate the formation of chalkiness by affecting the synthesis of prolamin. Results suggested that nitrogen application could regulate the related core factors involved in nitrogen metabolism pathways, which, in turn, affects the changes in the storage protein components in the grain and further affects quality. Therefore, as a conventional cultivation measure, nitrogen application would have a certain value in future rice production in response to climate warming.

Abstract Background Large panicle rice has a large sink capacity, but inferior spikelet filling is poor in this variety of rice due to asynchronous grain filling. The understanding of the factors that cause asynchronous grain filling will help to propose a model for how to regulate the rice inferior spikelets grain filling. Results In this study, two large panicle rice varieties, W1844 and CJ03, with the same sink capacity but with differences in asynchronous grain filling were used. The difference in the grain filling rate between superior and inferior spikelets in W1844 was much smaller than that in CJ03. We found that superior spikelet filling was initiated earlier in W1844 than in CJ03. The source-to-sink translocation rate of sucrose during the grain filling stage was more efficient in W1844 than in CJ03, and the gene expression levels of sucrose transporters (OsSUTs) were higher in W1844 functional leaves than in those of CJ03. In addition, carbon output, the transport ratio, and the contribution rate from the stem and sheath to the panicle were much higher at the early filling stage than at later filling stages in W1844. Conclusion Efficient sugar translocation can satisfy high sink strength, and also the strong sink activity can facilitate the sugar unloading in spikelets. All the above results indicate that an efficient sugar translocation rate at the early grain filling stage can improve sink strength and inferior grain filling initiation. Strategies to limit asynchronous grain filling in rice were also discussed based on our findings.

Salt stress severely restricts the growth of plants and threatens the development of agriculture throughout the world. Worldwide studies have shown that exogenous melatonin (MT) can effectively improve the growth of plants under salt stress. Through a meta-analysis of 549 observations, this study first explored the effects of salt stress characteristics and MT application characteristics on MT regulated plant growth under salt stress. The results show that MT has a wide range of regulatory effects on plant growth indicators under salt stress, of which the regulatory effect on root indexes is the strongest, and this regulatory effect is not species-specific. The intensity of salt stress did not affect the positive effect of MT on plant growth, but the application effect of MT in soil was stronger than that in rooting medium. This meta-analysis also revealed that the foliar application of a concentration between 100–200 μM is the best condition for MT to enhance plant growth under salt stress. The results can inspire scientific research and practical production, while seeking the maximum improvement in plant salt tolerance under salt stress.

With the intensification of global warming, high temperatures during rice’s growth and development could further lead to a deterioration in rice yields. Therefore, it is particularly important to further clarify the response of the rice booting stage to high temperatures, and to explore reasonable countermeasures on this basis to reduce yield losses. Methyl jasmonate (MeJA) is a derivative of jasmonates and is widely used for stress resistance. However, the role of MeJA in alleviating high temperatures during the rice booting stage has not been given enough attention. This study aimed to further evaluate the alleviation effect of methyl jasmonate on high-temperature stress during the key growth period of local conventional japonica rice. The results showed that high temperatures (37.5 °C/27.0 °C) at the booting stage had a significant impact on the antioxidant system of rice and also significantly reduced the photosynthetic capacity of the plant, resulting in a decrease in the final yields. The exogenous spraying of 0.1 mmol/L MeJA at the booting stage could effectively alleviate the influence of high-temperature stress on rice photosynthesis. Exogenous MeJA increased the stomatal conductance (Gs) of rice leaves under high-temperature stress, and correspondingly increased the transpiration rate (Tr) and decreased the organ temperature of rice plants, thereby reducing the damage to the actual photochemical efficiency (ΦPSII) caused by high temperatures. By increasing the carotenoid content (Car) and reducing the malondialdehyde content (MDA), the antioxidant capacity of the plants was restored to a certain extent under exogenous MeJA, and the yield factor showed an increase in the number of grains per panicle and the seed-setting rate of Wuyunjing 24, which alleviated the booting stage yield losses induced by high-temperature stress. In conclusion, the application of exogenous MeJA at the booting stage alleviated the negative consequences of high temperatures by enhancing the plants’ antioxidant and photosynthetic capacity. Therefore, MeJA may have a potential role in mitigating the challenges of global warming in rice production.

Large panicle rice cultivars often fail to fulfill their high-yield potential due to the poor grain filling of inferior spikelets (IS), which appears as initially stagnant development and low final seed weight. Understanding the mechanism of the initial stagnancy is important to improve IS grain filling. In this study, superior spikelets (SS) were removed from two homozygous japonica rice varieties (W1844 and CJ03) with the same sink capacity in an attempt to force photosynthate transport to the IS. The results showed that SS removal increased the grain weight, sucrose content, starch accumulation, and endogenous IAA levels of IS during the initial grain-filling stage. SS removal also improved the patterns of vascular cells in the dorsal pericarp and the expression levels of genes involved in sucrose transport (OsSUTs and OsSWEETs) and IAA metabolism (OsYUCs and OsPINs). Exogenous IAA application advanced the initiation of grain filling by increasing the sucrose content and the gene expression levels of sucrose transporters. These results indicate that auxin may act like a signal substance and play a vital role in initial grain filling by regulating dorsal vascular cell development and sucrose phloem unloading into caryopsis.

Plant growth rhythm in structural traits is important for better understanding plant response to the ever-changing environment. Terrestrial laser scanning (TLS) is a well-suited tool to study structural rhythm under field conditions. Recent studies have used TLS to describe the structural rhythm of trees, but no consistent patterns have been drawn. Meanwhile, whether TLS can capture structural rhythm in crops is unclear. Here, we aim to explore the seasonal and circadian rhythms in maize structural traits at both the plant and leaf levels from time-series TLS. The seasonal rhythm was studied using TLS data collected at four key growth periods, including jointing, bell-mouthed, heading, and maturity periods. Circadian rhythms were explored by using TLS data acquired around every 2 hours in a whole day under standard and cold stress conditions. Results showed that TLS can quantify the seasonal and circadian rhythm in structural traits at both plant and leaf levels. (1) Leaf inclination angle decreased significantly between the jointing stage and bell-mouthed stage. Leaf azimuth was stable after the jointing stage. (2) Some individual-level structural rhythms (e.g., azimuth and projected leaf area/PLA) were consistent with leaf-level structural rhythms. (3) The circadian rhythms of some traits (e.g., PLA) were not consistent under standard and cold stress conditions. (4) Environmental factors showed better correlations with leaf traits under cold stress than standard conditions. Temperature was the most important factor that significantly correlated with all leaf traits except leaf azimuth. This study highlights the potential of time-series TLS in studying outdoor agricultural chronobiology.

Grains located on different positions of the panicle differed in grain weight and quality performance, however, the comprehensive effect of sowing dates on physiological and quantitative characteristics of grains located on different positions still remains unclear. In this study, a field experiment was conducted with two japonica rice cultivars, Nanjing 9108 and Ningjing 7, under 3 sowing dates (S1, 30th April; S2, 30th May; S3, 30th June). Delayed sowing treatments increased before-heading mean temperature (Tmean), day temperature (Tday), night temperature (Tnight) and mean solar radiation (Smean) for 0.94 °C, 0.99 °C, 1.23 °C, and 1.04 MJ, respectively, while decreased growth duration (GD) for 13.4 days, with 30 days delaying sowing date. Elevated before heading thermal resources and shortened GD contributed to enlarged panicle size via enhancing number of grains on secondary branches (SG) and led to higher ratio of SG per unit area (SG%). Meanwhile, delayed sowing decreased after heading Tmean, Tday, Tnight and Smean by 0.84 °C, 1.23 °C, 1.13 °C, and 2.12 MJ, respectively, with 30 days delaying sowing, and further enhanced rice stickiness (ST), peak viscosity (PKV) and breakdown (BD), but suppressed hardness (HD), amylose content (AC), cold pasting viscosity (CPV), hot pasting viscosity (HPV) and setback (SB) of SG, whilst grains on primary branches (PG) di no significant differences. Elevated taste and cooking quality of SG under delayed sowing was regulated by slower grain filling rate, which is largely regulated by AGPase and GBSS. Compared to PG, SG has better physiochemical, texture properties and RVA profiles due to its slower starch biosynthesis. The above results suggested that physiological (starch biosynthesis of SG) and quantitative parameters (amount of SG) of the rice population should be referred simultaneously to improve rice cooking and taste quality.

The stress of transplanting injury adversely affects rice growth and productivity worldwide. N-acetylcysteine (NAC), the precursor of glutathione, is a potent ROS scavenger with powerful antioxidant activity. Previous studies on the application of NAC in plants mainly focused on alleviating the stress of heavy metals, UV-B, herbicides, etc. However, the role of NAC in alleviating transplanting injury is still not clear. A barrel experiment was carried out to explain the mechanism of NAC regulating the transplanting injury to machine-transplanted rice during the recovery stage. The results showed that NAC priming shortened the time of initiation of tillering and increased the tiller numbers within 3 weeks after transplanting. In addition, NAC priming increased the chlorophyll content, net photosynthetic rate, and sucrose content, thereby improving the dry weight at the recovery stage, especially root dry weight. At the same time, NAC priming significantly increased the activity of ascorbate peroxidase (APX), glutathione reductase (GR), catalase (CAT), and superoxide dismutase (SOD). In addition, it also regulated flavonoids and total phenols contents to reduce hydrogen peroxide (H2O2) and malondialdehyde (MDA) contents, especially at the initial days after transplanting. These results suggest that NAC priming improves the tolerance of rice seedlings against transplanting injury by enhancing photosynthesis and antioxidant systems at initial days after transplanting, thereby promoting the accumulation of dry matter and tillering for higher yield returns.

Nitrogen (N) plays a vital role in plant growth; however, the yield response to N fertilizer is regularly declining in the major cropping systems due to overuse and the upper limit of yields. Heavy losses of N are also documented due to its excessive use in the rice-wheat rotation system, resulting in low nitrogen-use efficiencies (NUE) and environmental problems. Therefore, a three-year field experiment was performed with different N managements to investigate the impact of reduced N input rates in this exhaustive cropping system. Reducing the N application rates did not affect the wheat and rice yields significantly, only during the second wheat season was the yield slightly reduced as compared to higher N input treatments. Decreasing the N input rates in the prior crop and present crop, and the interactions of both rice and wheat seasons (R × W) did not influence the yields of either crop. A reduction in N fertilizer had a considerable impact on dry matter production during the wheat seasons but demonstrated no effect during the rice season. The accumulation of N was significantly reduced during both crop seasons by lowering the rate of N application. In addition, the NUE indices were significantly influenced by N fertilizer application rates. In conclusion, N fertilizer input rates for both rice and wheat crops can be lowered as compared to present fertilization rates without any risk of yield decline. Lowering the N input increases the NUE and effectively reduces N losses, and soil N status can also be maintained.

What strategy of nutrient management can maintain the high and stable annual yield in rice–wheat systems under climate change? A 10-year term experiment was conducted in the rice–wheat system to investigate the effect of optimal nutrient management on crop yield and meteorological drivers of year-to-year fluctuations in rice and wheat yield. Treatments were as follows: conventional fertilization (CF, as control), fertilizer postponing (FP, with the same amount fertilization as CF and increasing rate and times of panicle fertilizer) with/without straw incorporation (including only straw returned in rice (W) or wheat (R) season, and both straw incorporation (WS), RFP (reducing amount based on FP) with/without organic fertilizer. Results showed that FP with/without straw incorporation increased 10-year average yields of rice, wheat, and annual by 4.5~6.5%, 3.8~7.2%, and 4.8~6.8%, respectively, while RFP with/without organic fertilizer did not markedly reduce wheat yield, compared with CF. Effect of optimal treatments on wheat and rice yield stability was different; among the annual yield stability in FP + WRS was the greatest due to increasing and a stable number of spikelets and dry matter accumulation (DMA) after heading. Furthermore, the coefficient of variation (CV) of DMA during rice jointing-heading (21.6~30.0%) and heading-maturity stage (20.1~27.9%) was higher than before jointing (13.9~16.7%), which were affected by day photosynthetically active radiation (explain: 26%) and the number of rainy days (explain: 34%), respectively, using Stepwise regression; in contrast, in wheat season, the fluctuation of DMA before jointing was the highest (CV: 83.8~109.9% (before jointing) vs. 61.1~97.4% (heading-mature stage) vs. 33.7~46.3% (jointing-heading period), 55% of its variations was impacted by day-night temperature differences, the number of rainy days and photosynthetically active radiation accumulation. Our finding suggested that nutrient management to increase and stable the DMA after rice jointing and before wheat jointing could maintain the high and stable annual yield in rice–wheat systems.

Embryo-endosperm interaction is the dominant process controlling grain filling, thus being crucial for yield and quality formation of the three most important cereals worldwide, rice, wheat, and maize. Fundamental science of functional genomics has uncovered several key genetic programs for embryo and endosperm development, but the interaction or communication between the two tissues is largely elusive. Further, the significance of this interaction for grain filling remains open. This review starts with the morphological and developmental aspects of rice grain, providing a spatial and temporal context. Then, it offers a comprehensive and integrative view of this intercompartmental interaction, focusing on (i) apoplastic nutrient flow from endosperm to the developing embryo, (ii) dependence of embryo development on endosperm, (iii) regulation of endosperm development by embryo, and (iv) bidirectional dialogues between embryo and endosperm. From perspective of embryo-endosperm interaction, the mechanisms underlying the complex quality traits are explored, with grain chalkiness as an example. The review ends with three open questions with scientific and agronomic importance that should be addressed in the future. Notably, current knowledge and future prospects of this hot research topic are reviewed from a viewpoint of crop physiology, which should be helpful for bridging the knowledge gap between the fundamental plant sciences and the practical technologies.

Rice culm carbohydrate transport can simultaneously affect grain filling and stem lodging resistance by regulating non-structural carbohydrate (NSC) and structural carbohydrate (SC) contents. However, the relationship between carbohydrate transposition and culm strength is not well documented. Accordingly, a high-yielding hybrid rice cultivar (Y Liangyou 2) was tested under different N fertilization regimes at two locations, Taoyuan (a special high-yield eco-site), Yunnan province and Danyang (a representative eco-site of the middle and lower Yangtze), Jiangsu province, China. Significantly higher grain yield and basal stem strength were found at Taoyuan than Danyang under all N rates throughout the two-year experiment. At heading stage, soluble sugars, starch, cellulose and lignin contents of the basal culm at Taoyuan were significantly 132.0%, 73.7%, 1.2%, and 62.7% higher than those at Danyang, respectively. At 20 days after heading, soluble sugars and starch content at Taoyuan decreased significantly compared to Danyang, but lignin content remained higher. Culm carbohydrate transport to kernels at Taoyuan was significantly greater than that at Danyang, and the proportion of soluble sugars and starch was correspondingly 62.9% lower. However, the proportion of lignin and cellulose was 22.7% higher at Taoyuan than that at Danyang. Soluble sugars and starch partitioning were significantly reduced under an increased nitrogen application rate, but SC partitioning was little affected. There were significant positive correlations between basal culm bending stress and dry weight and cellulose and lignin proportions at both locations under all N rates, suggesting that the higher SC proportion at 20 days after heading was primarily responsible for culm strength. These results suggest that high-yielding rice populations with greater culm strength require both moderate NSC transport and greater SC accumulation. Keywords: Rice, High-yielding, Lodging, Culm strength, Carbohydrate partitioning

Abstract The present study was conducted to determine if TRPC6 regulates glomerular filtration rate (GFR) and the contractile function of glomerular mesangial cells (MCs). GFR was assessed in conscious TRPC6 wild type and knockout mice, and in anesthetized rats with and without in vivo knockdown of TRPC6 in kidneys. We found that GFR was significantly greater, and serum creatinine level was significantly lower in TRPC6 deficient mice. Consistently, local knockdown of TRPC6 in kidney using TRPC6 specific shRNA construct significantly attenuated Ang II-induced GFR decline in rats. Furthermore, Ang II-stimulated contraction and Ca2+ entry were significantly suppressed in primary MCs isolated from TRPC6 deficient mice, and the Ca2+ response could be rescued by re-introducing TRPC6. Moreover, inhibition of reverse mode of Na+-Ca2+ exchange by KB-R7943 significantly reduced Ca2+ entry response in TRPC6-expressing, but not in TRPC6-knocked down MCs. Ca2+ entry response was also significantly attenuated in Na+ free solution. Single knockdown of TRPC6 and TRPC1 resulted in a comparable suppression on Ca2+ entry with double knockdown of both. These results suggest that TRPC6 may regulate GFR by modulating MC contractile function through multiple Ca2+ signaling pathways.

Abstract Background Large-panicle rice varieties often fail to achieve their yield potential due to poor grain filling of late-flowering inferior spikelets (IS). The physiological and molecular mechanisms of poor IS grain filling, and whether an increase in assimilate supply could regulate protein abundance and consequently improve IS grain filling for japonica rice with large panicles is still partially understood. Results A field experiment was performed with two spikelet removal treatments at anthesis in the large-panicle japonica rice line W1844, including removal of the top 1/3 of spikelets (T1) and removal of the top 2/3 of spikelets (T2), with no spikelet removal as a control (T0). The size, weight, setting rate, and grain filling rate of IS were significantly increased after spikelet removing. The biological functions of the differentially expressed proteins (DEPs) between superior and inferior spikelets as well as the response of IS to the removal of superior spikelets (SS) were investigated by using iTRAQ at 10 days post anthesis. A total of 159, 87, and 28 DEPs were identified from group A (T0-SS/T0-IS), group B (T0-SS/T2-IS), and group C (T2-IS/T0-IS), respectively. Among these, 104, 63, and 22 proteins were up-regulated, and 55, 24, and 6 proteins were down-regulated, respectively. Approximately half of these DEPs were involved in carbohydrate metabolism (sucrose-to-starch metabolism and energy metabolism) and protein metabolism (protein synthesis, folding, degradation, and storage). Conclusions Reduced endosperm cell division and decreased activities of key enzymes associated with sucrose-starch metabolism and nitrogen metabolism are mainly attributed to the poor sink strength of IS. In addition, due to weakened photosynthesis and respiration, IS are unable to obtain a timely supply of materials and energy after fertilization, which might be resulted in the stagnation of IS development. Finally, an increased abundance of 14–3-3 protein in IS could be involved in the inhibition of starch synthesis. The removal of SS contributed to transfer of assimilates to IS and enhanced enzymatic activities of carbon metabolism (sucrose synthase, starch branching enzyme, soluble starch synthase, and pullulanase) and nitrogen metabolism (aspartate amino transferase and alanine amino transferase), promoting starch and protein synthesis in IS. In addition, improvements in energy metabolism (greater abundance of pyrophosphate-fructose 6-phosphate 1-phosphotransferase) might be played a vital role in inducing the initiation of grain filling. These results collectively demonstrate that carbohydrate supply is the main cause of poor IS grain filling.

During its reproductive phase, rice is susceptible to heat stress. Heat events will occur at all stages during the reproductive phase of rice as a result of global warming. Moreover, rice yield traits respond differently to heat stress during panicle initiation, flowering and grain filling. The reduction in the number of spikelets per panicle of heat-stressed plants is due to the attenuated differentiation of secondary branches and their attached florets as well as the promotion of their degradation during the panicle-initiation stage but is not affected by heat stress thereafter. Spikelet sterility as a result of heat stress is attributed not only to physiological abnormalities in the reproductive organs during the flowering stage but also to structural and morphological abnormalities in reproductive organs during the panicle-initiation stage. The reduced grain weight of heat-stressed plants is due to a reduction in nonstructural carbohydrates, undeveloped vascular bundles, and a reduction in glume size during the panicle-initiation stage, while a shortened grain-filling duration, reduced grain-filling rate, and decreased grain width contribute to reduced grain weight during the grain-filling stage. Thus, screening and breeding rice varieties that have comprehensive tolerance to heat stress at all time points during their reproductive stage may be possible to withstand unpredictable heat events in the future. The responses of yield traits to heat stress are regulated by phytohormone levels, which are determined by phytohormone homeostasis. Currently, the biosynthesis and transport of phytohormones are the key processes that determine phytohormone levels in and grain yield of rice under heat stress. Studies on phytohormone homeostatic responses are needed to further reveal the key processes that determine phytohormone levels under heat conditions.

Straw-derived N (Straw-N) is an important organic N source, but its distribution in soil–rice systems regulated by water management and N fertilization is poorly understood. Therefore, a pot experiment using 15N-labeled wheat residue was conducted with conventional flooded irrigation (CF) and alternate wetting/drying irrigation (AWD) both with and without N fertilization. Results showed that the whole-plant straw–N recovery rate and the soil residue rate were 9.2–11.9% and 33.5–43.1%, and 10.2–13.8% and 33.7–70.2% at panicle initiation stage (PI) and mature stage (MS), respectively. There was no interaction between water management and N fertilization. Compared to CF, AWD did not affect whole-plant straw-N absorption and significantly changed its distribution in various plant parts, such as increasing the straw-N accumulation in roots at PI and decreasing it at MS. N fertilization addition markedly promoted the transfer of straw-N to the plant but reduced the contribution rate of N uptake by the plant. Furthermore, AWD or N fertilization addition allowed more straw-N to remain in the soil, and a positive interaction effect on the straw-N loss mitigation was found. These results suggest that AWD combined with N fertilization addition is a great measure to improve the efficient utilization of straw-N and avoid the risk of environmental pollution in a soil–rice system.