Аннотация:This chapter presents the retrospective overview of temperature-dependent regulation of photosynthetic electron transport processes in chloroplasts as studied by the electron paramagnetic resonance (EPR) method. The performance of photosynthetic electron transport chain was evaluated from the redox transients of P700, the primary electron donor in photosystem I. The spin labeling technique was applied to monitor structural changes in the lipid phase of thylakoid membranes. Summarizing the results of these studies, one can conclude that the physical state (fluidity) of the thylakoid membrane is one of the crucial factors that determine the regulation of photosynthetic performance of chloroplasts providing sustainable development of plants upon variations of ambient temperatur