Endoproteinase activities in wheat leaves upon water deficit.

In wheat leaves acclimated and non-acclimated to water deficit the azocaseinolytic activities of endoproteinases were increased about 7-fold under drought conditions. Under such conditions both the pH dependence profile and the endoproteinase pattern were also changed. The predominant contribution of serine proteinase (about 50% of total endoproteinase activity) remains unaltered in the drought stressed leaves. Cysteine proteinase was induced to the same extent in the drought-stressed leaves irrespective of the acclimation pretreatment, while the contribution of aspartic proteinase was reduced upon water deficit but in the acclimated stressed leaves was as high as in the non-stressed leaves. These changes in the pattern of endoproteinases seem to imply that the water deficiency affects endogenous proteolysis.