ADAPTATION TO SALINITY AS MONITORED BY PSII OXYGEN-EVOLVING REACTIONSIN BARLEY THYLAKOIDS

The effects of NaCl salinity and Abscisic acid pretreatment on the pol ypeptide composition, photochemical activity and kinetic characteristi cs of oxygen evolving reactions in isolated thylakoids from barley (Ho rdeum vulgare L., var. Alfa) seedlings were studied. It was shown that thylakoids isolated from plants previously subjected to a prolonged N aCl treatment were more resistant to high concentration of NaCl after in vitro incubation. Pretreatment with ABA 3 clays before salinization diminished the inhibitory effect of the NaCl. Both ABA and NaCl treat ment lead to an increase in the internal ABA level in the plant leaves . ABA seems to play a specific role in this adaptive process, promotin g some structural changes in the chloroplast membranes, which in turn reflect on the oxygen evolving mechanisms. The obtained results are di scussed in terms of an effect of salinity and ABA treatment leading to an increased participation of the stroma situated photosystem PI cent ers, possessing higher resistance to damaging factors.