Regulation of Electron Transport in Chloroplasts: Induction Processes in Tradescantia Leaves

The results of a comparative study of electron transport in chloroplasts in situ in the leaves of shade-tolerant and light-loving tradescantia species (T. fluminensis and T. sillamontana) grown under conditions of strong (800−1000 μmole m–2 s–1of photons) or weak (moderate) illumination (50−125 μmole m–2 s–1of photons) are described. Electron transport processes were monitored using the methods of electron paramagnetic resonance and optical spectroscopy. The photoinduced redox transformations of the primary electron donor of photosystem I (P700) and the slow induction of chlorophyll a fluorescence were studied. It has been shown that plants acclimated to high light intensity are characterized by faster processes of P700 oxidation and chlorophyll a fluorescence attenuation compared to plants grown at low light intensity. The data obtained are analyzed in the context of “short-term” mechanisms of pH-dependent regulation of electron transport in intact chloroplasts (non-photochemical quenching of excitation in photosystem II, slowing down the oxidation of plastoquinol by cytochrome b6f complex, and activation of Calvin−Benson cycle reactions).