Control by the embryo axis of the breakdown of storage proteins in cotyledons of germinating seeds of citrus limon

Azocaseolytic (endopeptidase) and carboxypeptidase activities in cotyledons of germinating seeds of Citrus limon (L) Burm f (cv Verna) showed a peak on the fourth day after the onset of imbibition and then decreased. A second peak of activity in both enzymes appeared 16 days after imbibition. The activities of leucine-aminopeptidase and alanine-aminopeptidase increased until 12 days after imbibition and then declined. When cotyledons were detached from seedlings 8 days after imbibition and then incubated in water, protein breakdown was accelerated and α-amino N accumulation increased. In detached and incubated cotyledons, the azocaseolytic activity decreased whereas the carboxypeptidase activity continued to increase more markedly than when the axis remained attached. The effect of the axis on azocaseolytic activity was replaceable by kinetin. On the other hand, kinetin, GA₃ and IAA showed no significant effect on the carboxypeptidase and aminopeptidase activities in detached cotyledons.