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Wheat ( Triticum aestivum L.) cv. Jimai22 was used to evaluate the effect of ethylene evolution rate (EER) and 1-aminocyclopropane-1-carboxylic acid (ACC) and their relations with photosynthesis and photochemical efficiency in plants well-watered (WW) and under a severe water deficit (SWD). SWD caused a noticeable reduction in the grain mass. The marked increases in both EER and the ACC concentration were observed under SWD; it was reversed effectively by exogenous spermidine (Spd) or amino-ethoxyvinylglycine (AVG). Thermal images indicated that SWD increased obviously the temperature of flag leaves, mainly due to the decrease in transpiration rate under SWD. Exogenous Spd or AVG decreased to some extent the temperature of the flag leaves. The strong decline in photosynthetic rate ( P) and stomatal conductance as well as the photodamage of PSII were also observed under SWD after 14 and 21 days after anthesis (DAA). Intercellular CO concentration was reduced at 7 DAA, but slightly increased at 14 and 21 DAA under SWD, indicating that the decreased P at 7 DAA might result from stomatal limitations, while the decline after 14 and 21 DAA might be attributed to nonstomatal limitations. Correlation analysis suggested that EER and ACC showed negative relations to photosynthesis and photochemical efficiency. Data obtained suggested that the effects of SWD were mediated predominantly by the increase in EER and ACC concentration, which greatly decreased the leaf photosynthesis and photochemical efficiency, and, therefore, reduced the grain mass. Application of Spd or AVG reduced the EER and ACC, and thus positively influenced photosynthesis and photochemical efficiency under SWD. [ABSTRACT FROM AUTHOR]

Low temperature is one of the most severe abiotic stress factors that limit chrysanthemum growth and development. Natural temperature changes are more complex, and cold stress from a laboratory incubator cannot accurately represent the natural temperature stress. Here, nine separate high-throughput mRNA sequencing technology (RNA-Seq) libraries were generated from the RNA sample of roots from different temperatures, including chilling (Ch), freezing (Fr), and control (CK). The 7 069 and 3 952 differentially transcribed genes were identified as CK vs. Ch and CK vs. Fr, respectively. The Kyoto encyclopedia of genes and genomes pathway (KEGG) enrichment analysis showed that significantly different flavonoid biosynthesis and linolenic acid pathways commonly appeared in CK vs. Ch and CK vs. Fr. Arginine and proline metabolism, lipid metabolism, fatty acid degradation, and fructose and mannose metabolism pathways were found in CK vs. Ch, and only in the CK vs. Fr enrichment metabolic pathway included steroid biosynthesis and monoterpenoid biosynthesis. The transcription of genes on differential metabolic pathways and MYBs were successfully validated using quantitative real-time PCR. At the same time, the antioxidant activity, malondialdehyde, and proline content were analyzed under low temperature. These datasets may aid in understanding and carrying out future studies on the molecular basis of cold stress and contribute to chrysanthemum breeding. [ABSTRACT FROM AUTHOR]

The occurrence of shade and drought stress either individually or simultaneously causes altered morphophysiological and molecular responses in crops. Nevertheless, responses of crop plants to combined shade and drought stress are unique as compared to those of individually occurring stress which urges need to study and identify distinctions, commonalities, and the interaction between responses of plants to these concurrent stress factors. In the present review, we outlined currently available knowledge on responses of plants to shade and drought stress on a shared as well as the unique basis and tried to find a common thread potentially underlying these responses. Then, we briefly described some plausible mitigation strategies to cope with these stresses along with future perspectives. A deeper insight into plant responses to co-occurring shade and drought stress will help us to generate crops with broad-spectrum stress tolerance and increased resilience to such stresses in high planting densities or intercropping systems, thus, ensuring food security. [ABSTRACT FROM AUTHOR]

An interactive effect of simultaneous shade and drought stress on drought-tolerant and drought-sensitive cultivars of soybean was studied. As drought stress intensified, the net photosynthetic rate decreased in both cultivars due to reduced leaf area, relative water content, transpiration rate, stomatal conductance, chlorophyll content, and Rubisco activity which ultimately led to yield reduction. Moreover, the chlorophyll fluorescence parameters also decreased. Interestingly, a moderate shade was found helpful in alleviating the adverse effects of drought stress, specifically in resistant cultivar N12 where seed yield improved significantly under moderate drought conditions in contrast to the cultivar C103. In summary, the effect of drought stress on soybean depended on the irradiance conditions and shade could enhance soybean drought resistance, although this resistance was cultivar dependent. With appropriate cultivar selection, a moderate shade can help optimize yield and improve the performance of drought-exposed soybean. [ABSTRACT FROM AUTHOR]

In order to explore whether leaf area of developing leaves was regulated by systemic irradiance signal from mature leaves, we investigated the leaf area, leaf anatomy, photosynthesis, auxin, gibberellin, and cytokinin contents of new developing leaves in soybean growing under conditions of shaded mature leaves (MS), shaded whole plants (WS), and under full sunlight (NS). The results showed that developing leaves under MS exhibited the higher leaf area and leaf mass than that of WS. Blade thickness, palisade tissue thickness, sponge tissue thickness, cell size, cell numbers, net photosynthetic rate, stomatal conductance, transpiration rate, and cytokinin content of developing leaves under MS were lower, while auxin and gibberellin contents were higher than that of NS. These results indicate that the leaf area, leaf anatomy, and photosynthesis of developing leaves were regulated by the shading environment of mature leaves. Growth hormones may possibly act as candidate signal substances to systemic regulation of leaf area development. [ABSTRACT FROM AUTHOR]

Our present work showed that the expression of genes encoding PTOX (terminal oxidase of chlororespiration) and PGR5 (one essential component of cyclic electron transfer) were stimulated by red and blue light, but the stimulation under red light was soon reversed by subsequent far-red light. The expression levels of PTOX and PGR5 under simulated light quality conditions in line with maize-soybean relay strip intercropping (SRI) were obviously lower than those under simulated soybean monocropping (SM), since the lower red:far-red ratio under SRI. Measurements on photosynthetic and chlorophyll fluorescence parameters suggested a decline of assimilatory power supply and a lower nonphotochemical quenching under SRI as compared to SM. In this case, weaker PGR-dependent cyclic electron transfer and chlororespiration under SRI, suggested by lower expression levels of PGR5 and PTOX, could be considered as means of reducing excitation energy dissipation to allocate more power toward CO assimilation. [ABSTRACT FROM AUTHOR]

Intercropping is a sustainable agricultural practice used worldwide for highly efficient utilization of resources. However, short crops often grow under the shade of the canopy of tall crops in intercropping systems. Plants evolved two main strategies to deal with shade: avoidance and tolerance. Soybean ( Glycine max), a legume crop, is often planted in intercropping. But little is known about a strategy that soybean may employ to deal with shade at seedling stage. Therefore, we determined morphological and physiological traits related to shade tolerance and shade avoidance in seedlings of two varieties. Generally, both varieties showed similar shade tolerance traits, such as increased specific leaf area and chlorophyll (Chl) content, and reduced photosynthetic capacity and the Chl a/ b ratio. The light-limiting environment eliminated the benefits of shade tolerance traits for the carbon gain, which led to similar real-time photosynthesis and biomass in intercropping. By contrast, two varieties expressed different changes in shade avoidance traits. The variety Guixia 3 exhibited clear preference of shade avoidance that resulted in a high main stem, hypocotyl elongation, and biomass allocation towards the stem. The variety Gongxuan 1 showed those traits less. We suggested that the genetic variation occurs within soybean, thus the shade avoidance related traits might be important for variety selection for intercropping. Hence, the evaluation of performance should focus on shade avoidance in soybean genotypes in future experiments. [ABSTRACT FROM AUTHOR]

Intercropping, a traditional and worldwide cropping practice, has been considered as a paradigm of sustainable agriculture based on complementary mechanisms among different crop species. Soybean ( Glycine max) is widely relay intercropped about 60 days before maize ( Zea mays) harvest in Southwest China. However, shade caused by tall maize plants may be a limiting factor for soybean growth at a seedling stage. In field research, we studied the ecophysiological responses of two widely cultivated soybean varieties [Gongqiudou494-1 (GQD) and Gongxuan 1 (GX)] to maize shading in a relay intercropping system (RI) compared with monocropped soybean plants (M). Our results showed that soybean seedlings intercropped with maize exhibited significantly downregulated net photosynthetic rate ( P) (−38.3%), transpiration rate (−42.7%), and stomatal conductance (−55.4%) due to low available light. The insignificant changes in intercellular CO concentration and the maximum efficiency of PSII photochemistry suggested that the maize shading-induced depressions in P were probably caused by the deficiency of energy for carbon assimilation. The significantly increased total chlorophyll (Chl) content (+27.4%) and Chl b content (+52.2%), with lowered Chl a/ b ratios (−20.5%) indicated soybean plants adjusted their light-harvesting efficiency under maize shading condition. Biomass and leaf area index (LAI) of seedlings under RI decreased significantly (−78.7 and −71%, respectively) in comparison with M. Correlation analysis indicated the relative reduction in biomass accumulation was caused by the decline in LAI rather than P, it affected negatively the final yields of soybean (32.8%). Cultivar-specific responses to maize shading were observed in respects of LAI, biomass, and grain yield. It indicated that GX might be a better cultivar for relay intercropping with maize in Southwest China. [ABSTRACT FROM AUTHOR]