Abstract
We previously reported that WWC and/or PSI-cyclic function as a starter of photosynthesis. In this report, we tried to determine limiting steps of photosynthesis during induction phase. When the dark-treated leaves were illuminated, NPQ formation and ATP/ADP rapidly enhanced before CO2 assimilation increased. Because of a highly positive correlation between NPQ and ATP/ADP, WWC and PSI-cyclic may have formed ΔpH and produced ATP. In rice, a substantial dark inhibition against Rubisco occurred under more than 5-hour darkness, and the induction of CO2 assimilation was very slow. Since Rubisco activation requires ATP, we examined the relationship between ATP production and Rubisco activation. After illumination, ATP/ADP reached a maximum rapidly and then Rubisco was activated. However, these responses were not correlated with CO2 assimilation. On the other hand, RuBP pool increased slowly and highly correlated with CO2 assimilation. Thus, we considered that RuBP regeneration is a limiting step of photosynthetic induction.
