AbstractWe investigated the effect of CO2 on the flash-induced electrochromic absorbance change of chloroplasts in leaves of higher plants. In leaves depleted of CO2 the initial electrochromic rise was followed by a fast (t12 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 CO2 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 CO2 between the two photosystems. In leaves supplied with CO2 the decay could be fitted with a single exponential with a t12 ≈200 ms. We conclude that both energization and ATP-synthesis are strongly regulated by CO2 in chloroplasts in situ
