Partitioning of photosynthetic electron flow between CO2and O2reduction in a C3leaf (Phaseolus vulgarisL.) at different CO2concentrations and during drought stress
✍ Scribed by Gabriel Cornic; Jean-Marie Briantais
- Publisher
- Springer-Verlag
- Year
- 1991
- Tongue
- English
- Weight
- 732 KB
- Volume
- 183
- Category
- Article
- ISSN
- 0032-0935
No coin nor oath required. For personal study only.
✦ Synopsis
Photosystem II chlorophyll fluorescence and leaf net gas exchanges (CO2 and H20) 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 AF/ F m (B. Genty et al. 1989, Biochem. Biophys. Acta 990, 87 92; AF = difference between maximum, F~ and steady-state fluorescence emissions) allows the calculation of the total rate of photosynthetic electron-transport and the rate of electron transport to 02. These rates are in agreement with the measurements of leaf 02 absorption using 1802 and the kinetic properties of ribulose-1,5bisphosphate carboxylase/oxygenase. The fluorescence parameter, AF/Fm, showed that the allocation of photosynthetic electrons to 02 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 02 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.