Photoinhibition of photosystem II in vivo during greening of the wheat seedlings

Kuwetli ışık (320 W/m2) uygulanan buğday fidelerinin yeşermesi üzerinde 02 çıkışı eğrilerinin çeşitli elemanlan-başlangıç hızı, anlık hız ve gecikme evresi-analiz edilerek Fotosistem2-nin fotoinhibisyonu araştırılmıştır. Büyük miktarda pigment sentezlenme evresinde uygulanan kuvvetli ışıklandırmaya göre, klorofil biyosentezinin gecikme evresinde kuvvetli ışık uygulamasına bağlı olarak 02 çıkışının başlangıç ve anlık hızlarında ani bir düşüş, gecikme evresinde ise ani bir yükseliş gözlenmiştir. The photoinhibition of photosystem II in vivo by analysis of diverse components -initial rate, steady state rate and lag phase-of photosynthetic 02 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 02 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 as chlorophyll-protein complexes of reaction centres at the early stage of wheat seedling greening were more susceptible to excess light.