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Partitioning of photosynthetic electron flow between CO 2 and O 2 reduction in a C 3 leaf ( Phaseolus vulgaris L.) at different CO 2 concentrations and during drought stress

Partitioning of photosynthetic electron flow between CO 2 and O 2 reduction in a C 3 leaf ( Phaseolus vulgaris L.) at different CO 2 concentrations an

Partitioning of photosynthetic electron flow between CO 2 and O 2 reduction in a C 3 leaf ( Phaseolus vulgaris L.) at different CO 2 concentrations and during drought stress   (Citations: 105)
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Photosystem II chlorophyll fluorescence and leaf net gas exchanges (CO2 and H2O) were measured simultaneously on bean leaves (Phaseolus vulgaris L.) submitted either to different ambient CO2 concentrations or to a drought stress. When leaves are under photorespiratory conditions, a simple fluorescence parameter ?F/ Fm (B. Genty et al. 1989, Biochem. Biophys. Acta 990, 87–92; ?F = difference between maximum, Fm, and steady-state fluorescence emissions) allows the calculation of the total rate of photosynthetic electron-transport and the rate of electron transport to O2. These rates are in agreement with the measurements of leaf O2 absorption using 18O2 and the kinetic properties of ribulose-1,5bisphosphate carboxylase/oxygenase. The fluorescence parameter, ?F/Fm, showed that the allocation of photosynthetic electrons to O2 was increased during the desiccation of a leaf. Decreasing leaf net CO2 uptake, either by decreasing the ambient CO2 concentration or by dehydrating a leaf, had the same effect on the partitioning of photosynthetic electrons between CO2 and O2 reduction. It is concluded that the decline of net CO2 uptake of a leaf under drought stress is only due, at least for a mild reversible stress (causing at most a leaf water deficit of 35%), to stomatal closure which leads to a decrease in leaf internal CO2 concentration. Since, during the dehydration of a leaf, the calculated internal CO2 concentration remained constant or even increased we conclude that this calculation is misleading under such conditions.
Journal: Planta , vol. 183, no. 2, pp. 178-184, 1991
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