Regreening of senescent Nicotiana leaves I.: Reappearance of NADPH-protochlorophyllide oxidoreductase and light-harvesting chlorophyll a/b-binding protein

Decapitation of Nicotiana rustica L. plants above a single senescent leaf induced regreening, which was promoted by cytokinin treatment. Regreening required low light. The decline in leaf protein content and increase in protease activity seen during senescence were reversed on regreening, Western blotting showed that light-harvesting chlorophyll a/b-binding protein declined considerably during senescence, but on regreening it increased back to the levels seen in green leaves. NADPH-protochlorophyllide oxidoreductase (POR) was found by Western blotting at high levels in etiolated cotyledons, but at low levels in green leaves and not at all in senescent leaves. However, FOR reappeared in regreening leaves, and cytokinin accelerated its increase.