Photosynthetic induction in C4 leaves : An investigation using infra-red gas analysis and chlorophyll a fluorescence.

Simultaneous measurements of CO2 uptake, transpiration rate, and chlorophyll a fluorescence in leaf strips of C4 plants during the induction phase of photosynthesis are described. The timecourse of CO2 fixation is biphasic with the initial phase occurring within the first 1 to 5 min and the secondary phase consisting of a slow rise to the steady-state rate of photosynthesis. Transpiration rate follows the CO2-fixation timecourse closely but the intercellular CO2 concentration never falls below saturation for C4 plants. Chlorophyll a fluorescence quenching occurs exclusively during the initial fast phase of the CO2-fixation timecourse. The effect of duration of dark pretreatment of leaves on these parameters and the effects of light intensity and CO2 concentration are examined. These results are discussed with respect to the C4 cycle and photochemical and non-photochemical chlorophyll fluorescence quenching.