Leaf Proteolytic Activities and Senescence during Grain Development of Field-grown Corn (Zea mays L.).

Plant Physiology
U FellerR H Hageman


Some proteolytic enzymes occurring in the leaves of field-grown corn (Zea mays) (B73) were identified and partially characterized. Changes in activities of several proteolytic enzymes and in concentrations of protein and chlorophyll as a function of intraleaf segments (tip to base), leaf position, and leaf senescence during grain development and maturation were followed in crude leaf extracts.The aminopeptidase (not affected by sulfhydryl or fluoride reagents) was most active at pH 7, while the carboxypeptidase(s) (sensitive to fluoride, but insensitive to sulfhydryl reagents) was most active in the acid range, pH 3 to 6. The presence of two or more endopeptidases is indicated. Endopeptidase (caseolytic) activity at pH 5.4 appeared to be stimulated by sulfhydryl groups or EDTA, while caseolytic activity at pH 7.5 was not.Visually, individual leaf senescence starts at the leaf tip and the necrotic (brown) V-shaped area enlarges progressively toward the leaf base. Canopy senescence occurs in two phases. Foliar symptoms are first observed on the bottom leaf and then in sequential order up the plant. Subsequently, senescence occurs on the top leaf and moves downward. These foliar senescence symptoms are paralleled by decreases in e...Continue Reading


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