Electron Transport in Chloroplast Membranes of Shade-Tolerant and Light Loving Tradescantia Species

The processes of electronic transport in chloroplasts of two contrasting species of Tradescantia, the shade-tolerant species Tradescantia fluminensis and the light loving species T. sillamontana, grown in moderate or strong light conditions were investigated. The parameters of fast (OJIP test) and slow induction of fluorescence (SIF) of chlorophyll a in chloroplasts in vivo and in situ were used as indicators reflecting the photochemical activity of photosystem 2 (PS2). The coefficient of nonphotochemical quenching of chlorophyll a fluorescence, which provides protection of the photosynthetic apparatus from light stress, was determined from the SIF kinetics. The functioning of photosystem 1 (PS1) was monitored by the kinetics of photoinduced changes in the redox state of P₇₀₀, the reaction center of PS1, recorded by electron paramagnetic resonance. A significant difference in the dynamics of changes in photosynthetic parameters of shade-tolerant and light loving tradescantia species under conditions of prolonged acclimation of plants (up to 5 months) to moderate (50–125 µmol photons m^–2 s^–1) or strong (850–1000 µmol photons m^–2 s^–1) illumination with photosynthetically active white light was observed. In the light loving species T. sillamontana, photosynthetic parameters of chloroplasts changed slightly during acclimation of plants to moderate and strong light. Photosynthetic characteristics of leaves of shade-tolerant species T. fluminenesis were sensitive to the conditions of illumination, which indicated a weakening of photochemical activity with an increase in light intensity during acclimation of plants. The effect of attenuation of photosynthetic parameters of the leaves was reversible, that is, the fluorescence parameters returned to the initial level after attenuation of light.