DROUGHT STRESS INCREASES THE EXPRESSION OF WHEAT LEAF RIBULOSE- 1, 5- BISPHOSPHATE CARBOXYLASE/OXYENASE PROTEIN

The effects of drought stress and exogenous abscisic acid on the expression of ribulose-1, 5- bisphosphate carboxyIase/oxygenase activase (Rubisco activase) were examined in wheat (Triticum aestivum L.). In response to water stress and abscisic acid, both the levels of endogenous abscisic acid and Rubisco activase increased in the leaves. Immunoblot analysis showed that both drought stress and abscisic acid, increased the amount of a 51KD activase form of the enzyme. In addition, our results from wheat leaves showed that Rubisco activase up regulated under drought stress by increasing the amount of endogenous abscisic acid. Therefore the level of Rubisco activase was dependent on the abscisic acid level. These results are consistent with previous findings that Rubisco activase increases under high temperature stress. These results indicate that the increased rate of activases synthesis may play a role in coping with the decline in photosynthetic capacity under drought stress. Effects of drought stress and abscisic acid and their interaction were highly significant (p < 0.01) for all variables.