Salinity and in vitro Ageing Effects on Primary Photosynthetic Processes of Thylakoids Isolated from Pisum sativum and Spinacia oleracea

The effects of in vitro ageing and salinity of the reactionmedium on the primary photochemistry of photosystem II and thepattern of energy distribution within the photochemical apparatusof thylakoids isolated from Pisum sativum and Spinacia oleraceaare described. Analyses of the low temperature induction curvesof fluorescence emission at 695 and 735 nm and of low temperatureabsorption and fluorescence emission spectra were used to examinethese processes. In vitro ageing over short periods reducedthe photochemical activity and changed the energy distributionwithin thylakoids of P. sativum, but had little effect on thylakoidsof S. oleracea. A synergistic effect of in vitro ageing andsalinity of the reaction medium was observed for P. sativumthylakoids. Ageing effects could be minimized by addition of100 mM NaCl to the resuspension medium. Changes in NaCl concentrationin the reaction medium produced large and similar changes inthe primary photochemical functioning of thylakoids from P.sativum and S. oleracea, which could be attributed mainly tothe cation species, Na^$; however, experiments using mannitolto produce osmotic stress indicated some small osmotically inducedchanges in photofunction of the thylakoids. Optimal primaryphotochemical activity of photosystem II, for both species,was observed with 200 mM NaCl. Cation-induced regulation ofexciton distribution appears to be facilitated by controllingthe degree of energy coupling between the light-harvesting chlorophylla/b complex and the two photosystems, I and II, and not by regulationof coupling between photosystems I and II.