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• Autotetraploidization enhanced the salt tolerance of Ziziphus jujuba Mill. var. spinosa. • Salinity stress induced differential expression of many value genes and pathways between the diploid and autotetraploid. • More diverse transcription factors and complex protein-protein interaction networks may enhance salt tolerance of the autotetraploid. • More up-regulated genes and greater fold change related to osmotic adjustment exhibited in the autotetraploid than that in diploid. Chinese jujube (Ziziphus jujuba Mill.), native to China, is an important deciduous fruit tree. This species is mainly propagated by grafting, with Z. jujuba var. spinosa widely used as the rootstock because of its resistance to adverse conditions such as saline environments. In a previous study, we found that autotetraploid jujube is phenotypically superior to the corresponding diploid, furthermore, the differences in salt tolerance between the two plant materials and the underlying molecular mechanism were still unclear. To clarify this issue, we investigated the leaf and shoot morphology and physiology of diploid and autotetraploid plants treated with NaCl for 0, 2, 6, 10, and 14 days. We also carried out transcriptome profiling after 0, 1, and 2 days of salinity treatment. Comparisons of diploid and autotetraploid plants under salinity conditions in morphology and eight physiological traits indicating that the autotetraploid has superior salt tolerance. Many differentially expressed genes related to salt stress response in diploid and autotetraploid Z. jujuba were assigned to functional categories such as detoxification, stimulus response, catalytic enzyme activity, antioxidant enzyme activity, glutathione metabolism, phenylpropanoid biosynthesis, flavonoid biosynthesis, peroxisome, plant hormone signaling, and ABC transport. These genes constituted a complex regulatory network for maintaining osmosis and intracellular ion homeostasis and resisting oxidative stress. In addition, several genes encoding MYB, AP2/ERF-ERF, WRKY, GRAS, and C2H2 as well as hub proteins, including aquaporins, heat stress transcription factors, chaperone, cytochrome P450, and kinases, were differentially expressed under salt stress. The number, function, and fold changes of these genes differentially expressed under salinity treatment differed between the diploid and its autotetraploid, with more active, diverse strategies taking place in the autotetraploid to adapt to long-term salt stress. Finally, we found that there were more up-regulated DEGs and greater fold change related to osmotic adjustment in autotetraploid than in diploid which could further explain the enhanced salt stress tolerance in the autotetraploid. Our findings contribute to an understanding of the genetic basis of salt tolerance in autotetraploid jujube, which can guide future tolerance breeding of jujube cultivars and their rootstocks. [ABSTRACT FROM AUTHOR]

Modern maize cultivars have high nitrogen responsiveness of grain yield. However, the underlying physiological mechanism is unclear. In the present study, from 17 cultivars released from 1950 s to 2010 s in China, three maize cultivars released in 1950 s (BMY), 1970 s (ZD2), and 1990 s (ZD958) were selected according to their growth responses to nitrogen supply. Nitrogen responsiveness of shoot biomass was highest in the new cultivar ZD958, and the lowest in the old cultivar BMY, with the medium cultivar ZD2 in between. Shoot biomass was closely related to leaf elongation rate. Leaf elongation was further analyzed using kinematic analysis method. Cell division rate and cell production rate were greater and more responsive to nitrogen supply in ZD958 than in the other cultivars. In agreement, there were more cells in the elongation zone of ZD958 and they were more responsive to increasing supply, resulting a longer leaf elongation zone. The interaction effect between cultivar and nitrogen supply on leaf elongation was in consistence with the change in gibberellin (GA 1 and GA 3) concentration in leaf growth zone. Accordingly, the genes encoding gibberellin biosynthesis or signal transduction was more up-regulated in ZD958, which was positively correlated to the up-regulation of genes related to cell cycle and DNA replication. On the contrary, the genes related to the inactivation of gibberellin was more down-regulated in ZD958. Exogenous application of bioactive gibberellin or its biosynthesis inhibitor eliminated the interaction effect between cultivar and nitrogen supply on leaf elongation rate. In conclusion, modern maize breeding may have increased nitrogen responsiveness in maize by enhancing the gibberellins-dependent leaf elongation response to high nitrogen supply. • Nitrogen responsiveness is partly explained by leaf elongation rate. • Nitrogen responsiveness of leaf elongation is driven by gain in cell division. • Nitrogen-dependent gibberellin biosynthesis and signal transduction promote cell division in leaf growth zone. [ABSTRACT FROM AUTHOR]

Castor (Ricinus communis L.) is an important oilseed crop worldwide, and is also considered as one of the most promising plants for alkali-affected soil amelioration in the northeast of China. Seed germination plays a vital role in seedling establishment, and is always sensitive to alkali stress. However, little is known about the dynamic changes and regulatory mechanisms of gene expression and metabolic processes of this species during germination stage under alkali stress. In the present study, physiological, metabolome and transcriptome responses in germinating seeds of castor were investigated when exposed to 0, 50, 100 and 150 mM alkalinity (NaHCO 3). The results showed that alkali stress sharply decreased germination percentage. The Na+ content increased but K+ content decreased under alkalinity. In addition, the malondialdehyde and proline contents increased with the increasing alkalinities. Meanwhile, 50, 100 and 150 mM alkalinity induced 31, 48 and 113 differential metabolites, respectively. Furthermore, transcriptome profiling result showed that there were 138, 845 and 694 differentially expressed genes in the seeds under different concentrations alkali stresses, respectively. The integrating analysis of metabolite and gene expression changes indicating that germination response of castor seeds under alkali stress was closely related to amino acid metabolism, carbohydrate metabolism, lipid metabolism and nucleotide metabolism. The adaptive strategies of castor seeds under alkaline stress were promoting amino acid metabolism and tricarboxylic acid cycle to regulate osmotic balance and ROS level; as well as providing materials and energy for secondary metabolism, although alkali stress affected the membrane fluidity due to the reduction of unsaturated fatty acid content. Moreover, castor seeds increased metabolites on nucleotide biosynthesis to ensure their germination process under alkaline salt stress. The present research provides a deeper insight into overall understanding alkali-tolerant mechanisms of oil crops during germination in a holistic level. • l Using metabolomics and transcriptomics explored physiological adaptation mechanisms of castor seeds under alkali stress. • l 31, 48 and 113 differential metabolites and 138, 845 and 694 differentially expressed genes were found under alkali stress. • l Germination of castor at alkalinity was closely related to amino acid, carbohydrate, lipid and nucleotide metabolisms. • l Seeds of castor promoted amino acid metabolism and tricarboxylic acid cycle under stress. l Seeds of castor provided materials and energy for secondary metabolism under stress. [ABSTRACT FROM AUTHOR]

In terrestrial ecosystems, the mechanisms that allow plants to adapted to low P availability are largely not understood, particularly for woody legume woody. Here, we investigated the responses of rhizobia inoculation and low phosphorus (P) availability on black locust (Robinia pseudoacacia L.) from different geographic origins of China. For this purpose, black locust seedlings from two provenances with distinct climatic and soil background, i.e., the Gansu Province (GS) of Northwest China and the Dongbei region (DB) of Northeast China, were exposed to sufficient (0.5 mM) and low P availability (0.5 µM) with and without rhizobia inoculation in a greenhouse for two months. The rhizobia strain used for inoculation was obtained from a black locust forest stand of 50-years-old in the Shandong Province of East China. CO 2 and H 2 O gas exchange parameters as well as foliar physiological traits were measured. Our results indicated significantly different provenance-specific responses to inoculation and low P availability. Compared to sufficient P supply, inoculated DB Robinia showed a 57.6% decrease in whole plant biomass and a 49.2% decrease in the number of nodules at low P supply. However, low P availability had no effects on biomass accumulation of GS Robinia and increased its nodule formation by 240%. Still, gas exchange parameters and foliar physiological traits of GS Robinia plants were more responsive to low P supply than in DB plants. When inoculated with rhizobia at low P treatment, Robinia plants seem to use P preferentially for nodule production, thus weakening photosynthesis (86%) and reducing total biomass (58%) compared to non-inoculated plants. From these results it is concluded that GS Robinia may constitute a feasible candidate provenance for future afforestation programs of vulnerable terrestrial ecosystems. However, long-term systemic studies are needed in future to elucidate the physiological mechanisms of its adaption to low P availability. • The mechanisms about how plants adapted to low P supply are largely not understood. • Rhizobia inoculation and low P supply applied to two black locust provenances. • Provenance-specific responses to inoculation and low P supply were detected. • Photosynthetic and foliar traits of GS Robinia were more responsive to low P supply. • Long-term systemic studies are needed to elucidate behind physiological mechanisms. [ABSTRACT FROM AUTHOR]

Nitrogen (N) is an essential macronutrient that limits agricultural productivity; however, excessive N fertilizers are still used, especially in China. Improving crop N use efficiency (NUE) is an effective measure to reduce environmental pollution and is a primary direction in agricultural crop improvement. Although the physiological and molecular mechanisms for uncovering differences in NUE have become increasingly important, only a few crops have been studied to date. Two proso millet (Panicum miliaceum L.) cultivars with contrasting NUE, the low–N–tolerant cultivar (T184) and the low–N–sensitive cultivar (S111), were used to explore physiological as well as comparative transcriptomic mechanisms for earning high NUE in field and hydroponic experiments. The results showed that T184 had higher N uptake and utilization efficiencies and better photosynthetic capacity than S111 in field trials, as measured by increased chlorophyll content and net photosynthetic rate. Meanwhile, improved NUE and yield of T184 were observed compared with S111 under different N regimes. In hydroponic experiments, T184 had higher photosynthetic capacities in leaves and higher N metabolism enzyme activities in leaves and roots than S111, despite the photosynthetic and physiological parameters exhibited decreasing tendency to N deficiency in both T184 and S111. Furthermore, transcriptomic analysis revealed that T184 had less differentially expressed genes (DEGs) than S111. Many genes involved in photosynthesis and N uptake and assimilation were implicated in conferring NUE. Four nitrate transporter genes and eight photosynthetic genes were higher in T184 than in S111 under low and recovery N conditions and were strongly associated with NUE. These results revealed that greater N uptake and utilization efficiencies, accelerated N assimilation and translocation, and enhanced photosynthetic activity confer higher NUE in proso millet. • The low N–tolerant proso millet had increased N uptake, N utilization efficiency (NUE), and grain yield. • Higher photosynthetic capacity and physiological metabolism of the low–N–tolerant proso millet were observed. • Identify photosynthesis candidate genes could facilitate breeding for enhanced NUE. • High N uptake and utilization efficiencies, maintained photosynthesis, and N transport resulted in a higher NUE. [ABSTRACT FROM AUTHOR]