Abstract
1. During illumination of isolated chloroplasts (Spinacea oleracea) with red or white light in the presence of AS an immediate de-epoxidation of viol, to zea. takes place as in the case of intact cells. Inhibition of this light induced formation of zea. in isolated chloroplasts by DCMU is overcome by the addition of PMS + AS (pseudocyclic electron transport). PMS or PMS+FMN (without AS; cyclic electron transport) catalyze a conversion of viol, to zea. during illumination which is no longer inhibited by DCMU. In this case light reaction II of photo synthesis is not necessary for the xanthophyll interconversion. It can be shown that the formation of zea. takes place under conditions under which photophosphorylation takes place. A connection between these two processes seems to exist since uncouplers (CCCP, DNP, Methylamine, NH^) can completely eliminate the light dependent formation of zea. in chloroplasts (at pH 7 or higher). On the other hand, addition of ATP to chloroplasts can also trigger the con version of viol, to zea. without illumination.
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