No abstract

To investigate soybean responses to drought stress and growth through metabolism compensation after rehydration, and for the establishment of an optimal water-saving irrigation model, we used the soybean variety Suinong 14 as experimental material and adopted a weighing method for water control in potted plants. We exposed soybean plants to stress treatments at different growth stages using different stress levels and durations. We then studied the effects of drought stress and rehydration on soybean growth and development, osmoregulation, and endogenous hormonal regulations, as well as antioxidant systems. The results showed that drought stress inhibited increases in the soybean plant height and leaf area. This inhibition became more significant as the level, duration, and frequency of the drought stress increased. After rehydration, the soybean plant heights and leaf areas exhibited rapid increases and partial compensation for their decreased sizes. As the level, duration, and frequency of drought stress increased, the compensation effect decreased, but it did not return to the control level. Drought stress reduced the chlorophyll content and relative water content in the soybean leaves and increased the osmolyte contents, antioxidant potential, and peroxidation of the membrane lipids. In addition, the changes mentioned above became more dramatic as the drought stress level, duration, and frequency increased. Upon rehydration, various levels of growth compensation were observed in each physio-biochemical parameter. As the drought stress level, duration, and frequency increased, the compensation effect also increased. Overall, the compensation effect for drought stress that occurred at the early growth stages was higher than that at the later growth stages. Drought stress led to decreases in the ZR/IAA and ZR/ABA ratios in soybean leaves and an increase in the ABA/(IAA + GA + ZR) ratio; thus, the plant growth was inhibited. These hormone ratios exhibited more dramatic changes when the drought stress level became more severe and the stress duration was prolonged. After rehydration, these hormone ratios produced equal compensation effects. Therefore, the compensatory effect of rewatering after drought stress is conditional. Severe stress, especially long-term severe stress, will reduce the compensatory effect. At the same time, drought resistance treatment at seedling stage can improve the adaptability and compensatory effect of re-drought at grain filling stage.

Currently, the mechanisms underlying the effects of nitrogen on nodulation and nitrogen fixation of leguminous plants remain uncertain. To further investigate the relationship between nitrogen with nodulation and nitrogen fixation of soybean plants, a young seedling grafting technique was applied to generate soybean plants with dual root systems. The two root systems were separately cultured in sand medium, with one irrigated with nutrient solution containing NH þ 4 or NO À 3 as nitrogen sources (the N+ side) and another irrigated with nitrogen-free nutrient solution (the N− side). Various nitrogen concentrations, 0, 25, 50, 75, and 100 mg/L, were applied to the N+-side root system to determine the effects of nitrogen concentrations on nodulation and nitrogenase activity of soybean plants. The results showed that in the dual root systems constructed by seedling grafting, the number and weight of root nodules at the N+ side both exhibited a single-peak changing trend of first increasing and then decreasing with nitrogen concentrations. Root nodulation was accelerated by low concentrations of nitrogen (<50 mg/L) and significantly suppressed by high concentrations of nitrogen (>50 mg/L). In contrast, the number and weight of root nodules at the N− side showed a constant increasing trend with the increase in nitrogen concentrations. Taken together, these results indicated that high nitrogen concentration exerts a contact-dependent localized inhibitory effect on the formation (number of nodules) and growth of root nodules (weight of nodules). The nitrogenase activities in the root nodules at both the N+ and the N− sides displayed trends of first increasing and then decreasing with nitrogen concentrations, reaching a single peak when the nitrogen concentration was 50 mg/L. In addition, the promotive or inhibitory effects of nitrogen at different concentrations on nitrogenase activity in the root nodules were synchronous between the N+ and the N− sides, suggesting that the effect of nitrogen is systematically regulated via interactions between the aboveground and underground parts of the plants.

No abstract

No abstract

BackgroundThe major medicinal alkaloids isolated from Uncaria rhynchophylla (gouteng in chinese) capsules are rhynchophylline (RIN) and isorhynchophylline (IRN). Extracts containing these terpene indole alkaloids (TIAs) can inhibit the formation and destabilize preformed fibrils of amyloid β protein (a pathological marker of Alzheimer’s disease), and have been shown to improve the cognitive function of mice with Alzheimer-like symptoms. The biosynthetic pathways of RIN and IRN are largely unknown.ResultsIn this study, RNA-sequencing of pooled Uncaria capsules RNA samples taken at three developmental stages that accumulate different amount of RIN and IRN was performed. More than 50 million high-quality reads from a cDNA library were generated and de novo assembled. Sequences for all of the known enzymes involved in TIAs synthesis were identified. Additionally, 193 cytochrome P450 (CYP450), 280 methyltransferase and 144 isomerase genes were identified, that are potential candidates for enzymes involved in RIN and IRN synthesis. Digital gene expression profile (DGE) analysis was performed on the three capsule developmental stages, and based on genes possessing expression profiles consistent with RIN and IRN levels; four CYP450s, three methyltransferases and three isomerases were identified as the candidates most likely to be involved in the later steps of RIN and IRN biosynthesis.ConclusionA combination of de novo transcriptome assembly and DGE analysis was shown to be a powerful method for identifying genes encoding enzymes potentially involved in the biosynthesis of important secondary metabolites in a non-model plant. The transcriptome data from this study provides an important resource for understanding the formation of major bioactive constituents in the capsule extract from Uncaria, and provides information that may aid in metabolic engineering to increase yields of these important alkaloids.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-676) contains supplementary material, which is available to authorized users.

No abstract

Soybean is an important cash crop in the world, and drought is the main reason for the loss of soybean plants productivity, with drought stress during the most water-sensitive flowering period of soybeans. In this article, drought-tolerant variety Heinong 44 (HN44) and drought-sensitive variety Heinong 65 (HN65) were used as experimental materials. Drought treatment was carried out at the early flowering stage. The method of controlling soil moisture content was used to simulate different degrees of drought, and the physiological changes of these two varieties of soybean under different soil moisture contents were studied. The results showed that with a decrease in soil moisture content, the content of malondialdehyde (MDA) in soybean leaves increased significantly; the activities of peroxidase (POD), catalase (CAT), and ascorbic acid peroxidase (APX) increased first and then decreased; the content of proline, soluble sugar, and soluble protein increased; and the total antioxidant capacity (T-AOC) increased significantly. When the soil moisture content was 15.5%, the degree of membrane lipid peroxidation, osmotic regulatory substances, antioxidant enzyme activity, and T-AOC increased the most, and the decrease in drought-tolerant variety HN44 was significantly less than that of drought-sensitive variety HN65. Our research reveals the response law of soybean crops to physiological characteristics under water deficit and provides theoretical basis and guiding significance for drought-resistant cultivation and breeding of soybean.