ABSTRACT
Abscisic acid (ABA) has been extensively implicated with stress tolerance of crop plants including temperature stress. Heat tolerance in the mutant was marginally less than that in the wild-type, and in contrast, ABA application significantly reduced the heat tolerance of wild-type leaves. Heat tolerance was determined by assessing 50% death rate of parenchymatous cells, after 5 minutes heating of leaf discs in water. The range of ethylene evolution rate from field grown lines and cultivars suggested the existence of considerable genetic variability; ethylene evolution rate was associated with heat tolerance as estimated by electrolyte leakage. Lu et al. concluded that the ABA-insensitive genotypes may have higher growth rates and long leaf area duration under stress and that selection for ABA-insensitivity may be an effective approach to improving heat tolerance. In both anther and leaf tissues, levels of diamine and putrescine and the polyamine spermidine were higher in heat tolerant genotypes than in heat sensitive genotypes.
