SENESCENCE AND PROTEIN-DEGRADATION IN LEAF SEGMENTS OF YOUNG WINTER-WHEAT - INFLUENCE OF LEAD AGE

Leaf senescence in intact wheat plants can be strongly influenced by altered source/sink relations. Interactions with other plant parts are no longer possible in detached leaves and therefore differences in their senescence behaviour reflect the physiological status of the leaf before cutting. the net degradation of chlorophylls and of selected enzyme proteins (detected by SDS-PAGE and immunoblotting) was delayed in detached young leaves as compared to senescing or mature leaves excised from the same field-grown wheat plants. The physiological leaf age was therefore decisive for the velocity of artificial senescence. Net degradation rates of the enzymes investigated varied in detached leaves. The protein quantities of plastidial glutamine synthetase, phosphoribulokinase and phosphoglycolate phosphatase decreased more rapidly than those of ferredoxin-dependent glutamate synthase and nitrite reductase. Differences were also detected between two enzymes involved in the same metabolic pathway (photorespiratory carbon cycle) but located in different subcellular compartments: the plastidial enzyme phosphoglycolate phosphatase was lost more rapidly than glycolate oxidase (peroxisomal enzyme).