Photoinhibition of Photosystem II In Vivo During Greening of the Wheat Seedlings

The photoinhibition of photosystem II in vivo by analysis of diverse components -initial rate, steady state rate and lagphase-of photosynthetic O2 evolution curves on greening wheat seedlings after illumination by excess white light (320 W/m2) was investigated. A sharp reduction in the initial and steady state rates and a simultaneous intense rise in the lag phase of O2 evolution were observed under the illumination of seedlings by excess light on the lag phase of chlorophyll a biosynthesis (less than 6 h of seedling greening in comparison with the illumination of seedlings by excess light at the stage of substantial pigment synthesis ( 6 h of seedling greening). It is assumed that photosystem II proteins not completely integrated in thylakoid membranes aschlorophyll-protein complexes of reaction centres at the early stage of wheat seedling greening were more susceptible to excess light.