THE XANTHOPHYLL CYCLE OF HIGHER-PLANTS - INFLUENCE OF ANTENNA SIZE AND MEMBRANE ORGANIZATION

The development of the photosynthetic apparatus of intermittent light grown pea plants under continuous illumination has been investigated. We determined the formation of antenna proteins and the synthesis of p igments at different stages of greening and compared the data with the changes in the xanthophyll cycle reactions. The limited convertibilit y of violaxanthin in the de-epoxidation reactions of the cycle was fou nd to be closely related to the presence of antenna proteins and could be attributed to direct (pigment binding) and indirect (grana formati on) functions of antenna proteins. The reduced epoxidation rate in int ermittent light plants was found to be accelerated with increasing amo unts of antenna proteins. However, the changes in the epoxidation rate s were not consistent with the assignment of the epoxidase activity to LHC II, the major light harvesting complex protein of photosystem II. This interpretation was further supported by an unchanged epoxidase a ctivity in - also LHC II depleted - bundle sheath cells of the C-4 pla nt Sorghum bicolor and stroma fractions of isolated spinach thylakoids . We assume that the basic function of antenna proteins in the xanthop hyll cycle of higher plants is mainly related to the binding of the su bstrate and/or to interactions with the de-epoxidase/epoxidase. By tha t antenna proteins seem to be responsible for the limited violaxanthin convertibility as well as they are required for highest epoxidation r ates. (C) 1998 Elsevier Science B.V.