Effect of CO2 on the energization of thylakoids in leaves of higher plants

Abstract We investigated the effect of CO 2 on the flash-induced electrochromic absorbance change of chloroplasts in leaves of higher plants. In leaves depleted of CO 2 the initial electrochromic rise was followed by a fast ( t 1 2 10–20 ms) and a slow (100–200 ms) decay. These kinetic components could be correlated with a dissipative and an ATP-synthetizing current, respectively. In leaves supplied with CO 2 an additional slow electrochromic rise (5–10 ms) appeared in the absorbance change. This component could be tentatively correlated with the enhancement of the electron transport by CO 2 between the two photosystems. In leaves supplied with CO 2 the decay could be fitted with a single exponential with a t 1 2 ≈200 ms. We conclude that both energization and ATP-synthesis are strongly regulated by CO 2 in chloroplasts in situ.