Effect of benzyladenine on proteolytic activity of excised watermelon cotyledons

Abstract

Excised watermelon cotyledons were grown in presence or absence of 10 −4 M benzyladenine (BA). The time course of proteolytic activity was assayed with hemoglobin and azocasein. Total protease activity shows a large peak at pH 4.4 (with hemoglobin) or 5.4 (with azocasein) and a smaller one at pH 8.5. BA does not enhance proteolytic activity. On the other hand electron microscopical data show an accelerated breakdown of protein bodies in BA-treated cotyledons. BA increases autolytic activity (release of free aminoacids without exogenous substrate) in a 17 500 × g pellet and in a band that sediments to equilibrium at 1.28–1.30 g/cm 3 on a sucrose gradient. This band is most probably formed by protein body fragments. It is likely that BA enhances the action of proteases that are sequestered inside protein bodies and are inaccessible to exogenous substrates.