EXOGENOUS ABA AS A MODULATOR OF THE RESPONSE OF SORGHUM TO HIGH SALINITY

Treatment of Sorghum bicolor (L.) Moench, cv. 610, with abscisic acid (ABA) during the first week of salinization with 150 mol m(-3) NaCl induced enhancement of growth and accelerated adaptation to high salinity (300 mol m(-3) NaCl). Adaptation is defined as the development of the ability of the plant to survive, grow, and set seeds upon exposure to a NaCl concentration which is lethal for the unadapted plant. In the absence of ABA the saline pretreatment requires 20 d for the development of adaptation (Amzallag et al., 1990); with ABA treatment the same result is achieved within approximately one week. The exposure of the plants to non-lethal salinity (150 mol m(-3)NaCl) apparently triggers a transient sensitivity to ABA lasting for about 8 to 10 d following the beginning of salinization. This period coincides with an increase in leaf PEP carboxylase activity which seems to occur faster if the plants are treated with ABA. Exogenous ABA-induced enhancement of growth and control of shoot Na+ concentration, occur at a lower ABA concentration (almost-equal-to-10 mmol m(-3)) than the induction of adaptation to salinity which occurs at almost-equal-to-40 mmol m(-3) or above. The lowered shoot Na+ concentration which is induced by a low ABA concentration is not sufficient to induce survival of the plants in high salinity (300 mol m(-3) NaCl).