KINETIC CORRELATION OF RECOVERY FROM PHOTOINHIBITION AND ZEAXANTHIN EPOXIDATION

The generation of non-photochemical fluorescence quenching under photo inhibitory illumination and its relaxation under subsequent low light illumination in leaves from intermittent-light-grown pea (Pisim sativu m L.) plants (IML-plants) has been investigated. In parallel, we studi ed (i) the activity of the xanthophyll cycle with emphasis on zeaxanth in formation and reconversion to violaxanthin and (ii) the degradation rate of D1 protein. In comparison to control plants grown in continuo us light, IML-plants were much more susceptible to photoinhibition as determined from the increase of slowly (half-times > 20 min) relaxing quenching (qI) of variable chlorophyll fluorescence. The relaxation (r ecovery) kinetics of qI (under weak light) in both types of plant depe nded on the photon flux density, temperature and duration of pre-illum ination. The recovery time generally increased with an increasing degr ee of qI. In IML-plants, relaxation of qI was kinetically closely rela ted to the epoxidation of zeaxanthin. At high degrees of photosystem I I inhibition the kinetics resembled those of D1 degradation. The resul ts are discussed in terms of the mechanisms of photosystem II inactiva tion in vivo.