<p>The results of a comparative study of electron transport in chloroplasts in situ in the leaves of shade-tolerant and light-loving tradescantia species (<i>T. fluminensis</i> and <i>T. sillamontana</i>) 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 <i>a</i> fluorescence were studied. It has been shown that plants acclimated to high light intensity are characterized by faster processes of P₇₀₀ oxidation and chlorophyll <i>a</i> 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 <i>b</i>₆<i>f</i> complex, and activation of Calvin−Benson cycle reactions).</p>