Abstract
In C3 plants, photosynthesis is classically considered to be limited by the slower rate of two processes: (1) Rubisco activity, or (2) RuBP regeneration (Farquhar et al. 1980). RuBP regeneration rate has been believed to be determined by chloroplast electron transport rate, but it is possible that chloroplast ATPase and some enzymes of the Calvin cycle, other than Rubisco, could also be involved. In order to clarify what steps in RuBP regeneration are limiting, gas exchange and chlorophyll fluorescence was examined in antisense tobacco with either reduced contents of cytochrome b6/f complex for determination of electron transport rate or reduced contents of ATPase relative to wild-type plants. Reductions in cytochrome b6/f complex or ATPase contents were accompanied with decreases in the RuBP regeneration rate estimated from the C3 photosynthesis model and the light saturated photosynthetic rate at ambient CO2 concentration over a broad temperature range. This study clearly showed that both cytochrome b6/f complex and ATPase potentially co-limit the RuBP regeneration rate and the light saturated photosynthetic rate over a broad temperature range.
