XANTHOPHYLL CYCLE AND ENERGY-DEPENDENT FLUORESCENCE QUENCHING IN LEAVES FROM PEA-PLANTS GROWN UNDER INTERMITTENT LIGHT

The possible role of zeaxanthin formation and antenna proteins in ener gy-dependent chlorophyll fluorescence quenching (qE) has been investig ated. Intermittent-light-grown pea (Pisum sativum L.) plants that lack most of the chlorophyll a/b antenna proteins exhibited a significantl y reduced qE upon illumination with respect to control plants. On the other hand, the violaxanthin content related to the number of reaction centers and to xanthophyll cycle activity, i.e. the conversion of vio laxanthin into zeaxanthin, was found to be increased in the antenna-pr otein-depleted plants. Western blot analyses indicated that, with the exception of CP 26, the content of all chlorophyll a/b-binding protein s in these plants is reduced to less than 10% of control values. The r esults indicate that chlorophyll a/b-binding antenna proteins are invo lved in the energy-dependent fluorescence quenching but that only a pa rt of qE can be attributed to quenching by chlorophyll a/b-binding pro teins. It seems very unlikely that xanthophylls are exclusively respon sible for the qE mechanism.