Überschüssige Plastidenchinone in Blättern

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Abstract
The synthesis of plastidquinones was studied during the development through the degeneration of Ficus leaves and compared with chlorophyll and carotenoid synthesis. 1. The plastidquinone content of Ficus chloroplasts increases steadily with increasing age of leaf tissue. The augmentation of the plastidquinone level is mainly due to the synthesis of the reduced quinone forms plastoquinol 45 (Plastohydrochinon 45) and a-tocopherol, the chromanol of α-tocoquinone. In several years old leaves the concentration (moles) of plastoquinol 45 and α-tocopherol reaches or exceeds that of chlorophyll a. 2. The naphthoquinone vitamin K1 (phylloquinone) as well as the oxidized quinone forms (α-tocoquinone and plastoquinone 45) seem not to be produced in excess amounts. The levels of the latter increase, however, in older and senescent leaves, apparently by oxidation of some α-tocopherol and plastoquinol 45 respectively. 3. The production of excess plastidquinones starts very early during leaf development. The main synthesis phase begins after the end of chlorophyll and thylakoid synthesis and continues in senescent Ficus leaves during the breakdown of chlorophyll until the early yellow stage. 4. The young pale green leaves still rolled up within the buds, possess a quinone and carotenoid composition which is quite different from that of fully expanded leaves. It resembles that of shortly illuminated etiolated seedlings. 5. The carotenoid level of older fully grown Ficus leaves slowly increases, mainly by synthesis of lutein. These additional carotenoids represent excess amounts, which are deposited together with the excess plastidquinones in the plastoglobuli of the plastid stroma. 6. There is no indication for a re-incorporation of excess plastidquinones in the general chloroplast metabolism. Thus the excess plastidquinones, accumulated in the osmiophilic plastoglobuli, may be regarded as secondary plant products.

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