Profiles of proteolytic activities during senescence of primary leaves of mung bean (Vigna radiata (L) Wilczek)

Abstract

In the primary leaves of mungbean (Vigna radiata (L.) Wilczek) seedlings, grown in pots containing soil, changes in the contents of chlorophyll, soluble protein and reduced nitrogen were related to changes in the activities of aminopeptidase, carboxypeptidase and endopeptidases (assayed with casein as substrate at pH 5.0 and 7.3), Chlorophyll degradation commenced subsequent to protein breakdown. The decrease in soluble protein and leaf N content during senescence was not accompanied by a corresponding increase in free amino acid level. Aminopeptidase and carboxypeptidase activities were high in the young primary leaves. In senescing leaves, undergoing rapid loss of nitrogen, the aminopeptidase activity remained low while carboxypeptidase activity declined significantly. The endopeptidase activity at pH 5.0, however, increased more than 3 fold during this period. At pH 7.3, the activity was low.