THE KINETICS OF ZEAXANTHIN FORMATION IS RETARDED BY DICYCLOHEXYLCAUBODIIMIDE

The de-epoxidation of violaxanthin to antheraxanthin (Anth) and zeaxan thin (Zeax) in the xanthophyll cycle of higher plants and the generati on of nonphotochemical fluorescence quenching in the antenna of photos ystem II (PSII) are induced by acidification of the thylakoid lumen. D icyclohexylcarbodiimide (DCCD) has been shown (a) to bind to lumen-exp osed carboxy groups of antenna proteins and (b) to inhibit the pH-depe ndent fluorescence quenching. The possible influence of DCCD on the de -epoxidation reactions has been investigated in isolated pea (Pisum sa tivum L.) thylakoids. The Zeax formation was found to be slowed down i n the presence of DCCD. The second step (Anth --> Zeax) of the reactio n sequence seemed to be more affected than the violaxanthin --> Anth c onversion. Comparative studies with antenna-depleted thylakoids from p lants grown under intermittent light and with unstacked thylakoids wer e in agreement with the assumption that binding of DCCD to antenna pro teins is probably responsible for the retarded kinetics. Analyses of t he DCCD-induced alterations in different antenna subcomplexes showed t hat Zeax formation in the PSII antenna proteins was predominantly infl uenced by DCCD, whereas Zeax formation in photosystem I was nearly una ffected. Our data support the suggestion that DCCD binding to PSII ant enna proteins is responsible for the observed alterations in xanthophy ll conversion.