Physiological and molecular responses to drought and salinity in soybean

Drought and salinity are severe environmental stresses and limit soybean growth. In this study, a comparative analysis of physiological and molecular responses of two soybean (Glycine max L.) genotypes to these stresses was carried out. Plants of drought-tolerant genotype RD (cv. FD92) and sensitive genotype SD (cv. Z1303) were exposed to 15 % (m/v) PEG 6000, which simulated drought stress, or 150 mM NaCl. The RD plants maintained larger leaf area and higher net photosynthetic rate, chlorophyll content, stomatal conductance, and relative water content compared with the SD plants. Leaf proline content increased under both stresses more in RD than in SD. The drought tolerance of RD plants was also correlated with greater antioxidant activity and lower content of hydrogen peroxide and malondialdehyde under stress conditions. Amounts of abscisic acid, jasmonic acid, and salicylic acid under stress increased to a greater extent in RD than in SD plants. At the molecular level, the effects of 20-d stress treatments were manifested by relatively higher expression of drought- or salt-related genes: GmP5CS, GmDREB1a, GmGOLS, GmBADH, and GmNCED1 in RD plants than in SD plants. These results form the basis for understanding the mechanisms of the drought- and salt-stress tolerance in soybean.     

Overaccumulation of glycine betaine enhances tolerance to drought and heat stress in wheat leaves in the protection of photosynthesis

We investigated the different responses of wheat (Triticum aestivum L.) plants to drought- (DS) and heat stress (HS), and analyzed the physiological mechanisms of glycine betaine (GB) involved in the improvement of wheat tolerance to the combination of these stresses. The transgenic wheat T6 line was generated by introducing a gene encoding betaine aldehyde dehydrogenase (BADH) into the wild-type (WT) Shi4185 line. The gene was cloned from the Garden Orache plant (Atriplex hortensis L.). Wheat seedlings were subjected to drought stress (30%, PEG-6000), heat stress (40°C), and their combination. Photosynthetic gas exchange, water status and lipid peroxidation of wheat leaves were examined under different stresses. When subjected to a combination of drought and heat, the inhibition of photosynthesis was significantly increased compared to that under DS or HS alone. The increased inhibition of photosynthesis by the combined stresses was not simply the additive stress effect of separate heat- and drought treatments; different responses in plant physiology to DS and HS were also found. HS decreased the chlorophyll (Chl) content, net photosynthetic rate (P _N), carboxylation efficiency (CE) and apparent quantum yield (AQY) more than DS but DS decreased the transpiration rate (E), stomata conductance (g _s) and intercellular CO₂ concentration (C _i) more than HS. GB over-accumulation led to increased photosynthesis not only under individual DS or HS but also under their combination. The enhancement of antioxidant activity and the improvement of water status may be the mechanisms underlying the improvement of photosynthesis by GB in wheat plants.     

Salicylhydroxamic acid (SHAM) negatively mediates tea herbivore-induced direct and indirect defense against the tea geometrid Ectropis obliqua

We investigated the effect of the SHAM treatment of tea plants on their induced defense on a tea geometrid (TG), Ectropis obliqua Prout. Treatment of tea leaves with SHAM reduced the performance of TG and TG-elicited level of the lipoxygenase gene CsiLOX1 and the putative allene oxide synthase gene CsiAOS1. The release of wound-induced green leaf volatiles (GLVs) and the expression of the hydroperoxide lyase (HPL) gene CsiHPL1 were also reduced by SHAM treatment. The negative effect of SHAM dramatically reduced the total hebivore-induced plant volatiles (HIPVs) and the attractiveness to the parasitoid wasp Apanteles sp. These results indicated that SHAM may negatively mediate tea defense response against TG by modulating the wound-induced emission of GLVs, the expression of genes involved in oxylipin pathway, and the emission of other HIPV compounds that mediate direct and indirect defenses.