Photosynthetic Apparatus and High Temperature: Role of Light

The rate of oxygen evolution/consumption, in vivo electron transport activity, overall photosynthetic capacity and accumulation of the chloroplast 30 kDa heat shock proteins were studied after treatment of intact barley seedlings at 40oC for 3 hours either in presence of low white light (100 μmol m–2.s–1) or in the dark. High temperature impact in the dark resulted in lowering of water-splitting capacity, photosynthetic electron transport rate, suppression of non-photochemical energy dissipation and membrane energization (qE), caused the photoinhibition of PS2 at high PFD and indicate impairment of CO2-assimilation rate in old (11 d-old) leaves. The observed data revealed a positive influence of low light in the resistance of the photosynthetic apparatus of barley leaves to high temperature including primary photosynthetic reaction and carbon metabolism. The heat-induced damaging processes increased considerably with leaf senescence whereas the young seedlings were the most adaptive and flexible to the environment. Heat shock chloroplast 30 kDa proteins were found to be accumulated after plant heating under the both conditions, light and the dark. It was suggested that light-dependent resistance of intact plants to high temperatures could depend not only on transthylakoid proton gradient but also on the leaf transpiration rate, intracellular antioxidant balance and accumulation of low molecular weight organic compounds.