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).