Leaves in the natural plant canopies experience a highly variable light environment over the course of a day due to changes in leaf angle, cloud cover, and overshadowing canopy cover. When the light intensity on a leaf is increased suddenly after a prolonged period of low light or darkness, the rate of photosynthesis rises gradually over several minutes and approaches a new steady state. This phenomenon has been termed “photosynthetic induction”. However, the biochemical and the underlying molecular mechanism of the photosynthetic induction have remained unclarified. A better understanding of the metabolic and diffusional limitations of photosynthesis in fluctuating irradiance would lead to an identification of targets for improving crop yields in a natural environment.
  We used various mutants and transgenics in Arabidopsis and rice plants to characterize the importance of Rubisco activase and stomatal conductance on photosynthesis in fluctuating irradiance. Leaf gas exchange and chlorophyll fluorescence were measured in leaves exposed to stepwise increases and decreases in irradiance. Our comprehensive analysis showed that the light activation of Rubisco by Rubisco activase and gas diffusion conductance including stomatal conductance and mesophyll conductance would be limiting for the photosynthetic induction process.