ENERGY-DEPENDENT FLUORESCENCE QUENCHING IN THYLAKOIDS FROM INTERMITTENT LIGHT-GROWN PEA-PLANTS - EVIDENCE FOR AN INTERACTION OF ZEAXANTHIN AND THE CHLOROPHYLL A B BINDING-PROTEIN CP26/

We investigated the possible function of zeaxanthin in the energy-depe ndent fluorescence quenching (qE) in thylakoid preparations from inter mittent light grown pea plants (IML-plants). The extent of qE in IML-p lants (which are devoid of most of the chlorophyll nib binding protein s) has been shown to be substantially reduced in comparison to control plants, although IML-plants were capable of forming high amounts of z eaxanthin. This suggested an important function of chlorophyll nib bin ding proteins in the qE-mechanism. In the present study it is shown th at inhibition of zeaxanthin formation either by addition of dithiothre itol or due to the absence of ascorbate completely suppressed the qE f ormation in IML-thylakoids. In control thylakoids, however, the extent of qE was only partially reduced. The results corroborate the existen ce of two components contributing to qE and indicate that the interact ion of zeaxanthin and CP26 (the only chlorophyll a/b binding protein p resent in IML-plants) determines the zeaxanthin-dependent qE-component .