Growth and physiological responses of cotton plants to salt stress

The objective of this study was to investigate the growth and physiological responses cotton plants to salt stress. At seven leaf stage, cotton plants were subjected to two treatments; 0 mM NaCl as the control and 150 mM NaCl as the salt stress treatment, respectively. The effect of salt stress on leaf gas exchange rates, leaf nitrogen concentration, chlorophyll content, leaf K+ and Na+ concentrations, plant water status, endogenous phytohormone concentrations, dry matter accumulation and partitioning in plant organs was evaluated. The results showed that salt stress significantly decreased plant growth, water consumption, leaf water relations characteristics and leaf gas exchange rates as compared to the control. Under salt, photosynthetic rate was reduced to less extend than did stomatal conductance (g(s)) and transpiration rate, resulting in greater intrinsic and instantaneous water use efficiencies compared to the control plants. g(s) decreased linearly with decreasing leaf water potential and leaf hydraulic conductance under salt. Salt-stressed plants possessed a significant higher concentration of abscisic acid ([ABA](leaf)), while a significantly lower concentrations of gibberellic acid ([GA3](leaf)) and zeatin riboside ([ZR](leaf)) in leaf than those grown under control. Negative linear relationships were found between g(s) and [ABA](leaf), ratio of [ABA](leaf) to [GA3](leaf), ratio of [ABA](leaf) to ([GA3](leaf)+[ZR](leaf)), respectively. Salt stress significantly decreased leaf K+ concentration, the ratio of K+/Na+ in leaf, shoot growth and biomass partitioning into leaf and stem, whereas increased leaf chlorophyll content, leaf nitrogen concentration and biomass partitioning into boll. Although the water use efficiency of plant biomass was unaffected, the water use efficiency of boll biomass was significantly enhanced by salt stress. Collectively, salt-induced changes in both hydraulic and chemical properties were involved in mediating the leaf gas exchange response to salt stress, and the enhanced leaf nitrogen concentration and biomass partitioning into boll may lead to a sustained yield with less water consumption in cotton plants grown under moderate salinity stress.