Does photorespiration protect the photosynthetic apparatus in French bean leaves from photoinhibition during drought stress?
1995
Brestic, M. | Cornic, G. | Fryer, M.J. | Baker, N.R.
Ten days after withholding water from bean (Phaseolus vulgaris L. cv. Contender) plants net photosynthetic CO2 uptake by leaves declined and no net CO2 uptake occurred after 15d. A similar decline in stomatal conductance also occurred over this 15-d period. Leaf relative water content and tugor pressure remained very similar to that measured on control plants during most of the experimental period. The decline of net CO2 uptake by leaves during dehydration is attributed to stomatal closure since CO2-dependent O2 evolution measured on the same leaves at saturating light and CO2 concentration always remained identical to that of control plants. Dehydration of the leaves had no effect on the quantum yield of CO2-dependent O2 evolution during the experimental period. Leaves from dehydrating plants maintained in normal (21% O2 + 350 1lmol mol-1 CO2) air exhibited a substantial rate of photosynthetic activity (about 38% of that measured at saturation light and CO2 concentration) associated with O2 reduction. Decreasing the oxygen content of the air from 21% to 2% in order to inhibit photorespiration produced a decrease in the linear electron transport rate by cat 65% However, inhibiting photosynthetic O2 reduction during high-light treatment did not increase the extent of photoinhibition of photosystem II photochemistry and did not change the amount of violaxanthin converted to zeaxanthin. It is concluded that photorespiration does not protect the photosynthetic apparatus against high-light damage during drought conditions. Thermal deactivation of energy in the photosystem II antennae appears to be the main protective mechanism against deleterious effects of high light.
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