Chlorophyll metabolism in higher plants. VII. Chlorophyll degradation in senescing tobacco leaves; phenolic-dependent peroxidative degradation

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Abstract
Not only solubilized chlorophyll but also membrane (thylakoid) and protein (light-harvesting chlorophyll-protein complex) bound chlorophyll of tobacco plants [Nicotiana tabacum]was bleached by a phenolic-peroxidase-H2O2 system. The bleaching rate of thylakoid membranes in old leaves was higher than in young leaves. A similar phenomenom was observed in thylakoid membranes prepared from aged leaves. Peroxidase activity, peroxide content, and total phenolic content were high in senescent tobacco leaves. The defence mechanism against peroxide chlorophyll degradation was less active in senescent leaves than in young leaves. These results suggest that deterioration of the subcellar environment induced by senescence accelerates chlorophyll bleaching by a peroxidase-catalyzed reaction.