Changes in Chlorophyll Content and Organization During Senescence of the Primary Leaves ofPhaseolus vulgarisL. in Relation to Photosynthetic Electron Transport

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Abstract
A large decrease was observed in the chlorophyll content of the primary leaves of Phaseolus vulgaris during senescence. Chloroplasts isolated from mature and senescent leaves gave very similar light saturation curves for electron transport reactions involving either PS I or PS II, indicating that the average number of chlorophyll molecules associated with each reaction centre did not change during senescence. It is concluded that the reaction centres ceased to function at the same time as, or perhaps before, their antenna chlorophylls were lost from the thylakoid membrane, and that the percentage decrease in the number of functional reaction centres per leaf was at least as great as the percentage decrease in the leaf chlorophyll content.