Abstract
We have shown that in the C4 plant maize, CO2 assimilation does not start in the absence of O2, but after photosynthesis starts once, CO2 assimilation is able to proceed even under anaerobic conditions. In order to understand a mechanism why O2 is required to start CO2 assimilation, detailed analysis under various O2 concentrations was done.
In 2% O2, CO2 assimilation and transpiration rates at the steady state after dark-adaptation were 80% compared with those in 21% O2. ΦPS2 and ΦPS1 were 70% and 100%, respectively. In O2 lower than 2%, these parameters were further lowered. In 0% O2, CO2 assimilation rate and ΦPS1 were 15% and 40%, respectively, compared with those in 21% O2. ΦPS2 and transpiration were close to zero. These results suggest that O2 is required to start water-water cycle, and it produces essential ATP for CO2 assimilation cycle and opening of the guard cell.
