Physiological and biochemical responses to salt stress in the mangrove, Bruguiera gymnorrhiza

Abstract

Physiological and biochemical responses induced by salt stress were studied in laboratory-grown young plants of the mangrove, Bruguiera gymnorrhiza. The growth rates and leaf areas were highest in the culture with 125 mM NaCl. Transpiration rates showed a diel periodicity when the plants were placed in water, but the oscillatory cycles disappeared for plants placed in higher salt concentration (250–500 mM NaCl). The transfer of plants from water to any higher salinity resulted in an immediate increase in transpiration. Both the steady-state rates of transpiration and light-saturated rates of photosynthesis decreased as the salt concentration was increased. The activities of the antioxidant enzymes, superoxide dismutase (SOD) and catalase, showed an immediate increase after the plants were transferred from water to high salinity, reaching in 10 days five and eight times those of initial activities, respectively. The activities of these two enzymes were not affected by salt concentrations up to 1000 mM NaCl, twice that of seawater.