Electron transfer and energy dependent reactions in glutaraldehyde-fixed chloroplasts

The effects of GA fixation on electron transfers in photosystemsI and II in photosynthesis and energy dependent reactions ofchloroplasts, such as changes in light scattering, H⁺ uptakeand 515-nm absorbance, were investigated. Fixation of chloroplastswith GA resulted in a lowering of the DCIP and MV photoreductions.DCIP photoreduction activity in fixed chloroplasts was not restoredin the presence of DPC, an electron donor to photosystem II,but was significantly stimulated by DPC when chloroplasts werefixed after aging. The results suggest that the inhibitory effectof GA fixation on photosystem II differs in its mechanism fromthose of treatments such as heating, Tris-washing and aging.The oxidation-reduction reaction of P700 was depressed by GAfixation. Energy dependent reactions in fixed chloroplasts were more markedlydepressed than were electron transfers. Fixed chloroplasts showeda slight conformational response in the presence of PMS. Analysis of the emission spectrum and the induction of chlorophylla fluorescence in fixed chloroplasts suggested that the twopigment systems were partially disordered and that the correspondingprimary photochemical processes were inhibited. (Received November 21, 1972; )