Oxygen Exchange in Relation to Carbon Assimilation in Water-stressed Leaves During Photosynthesis |
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Authors: | HAUPT-HERTING, SILKE FOCK, HEINRICH P. |
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Affiliation: | 1Department of Biology, University of Kaiserslautern, PO Box 3049, D-67653 Kaiserslautern, Germany |
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Abstract: | In a study on metabolic consumption of photosynthetic electronsand dissipation of excess light energy under water stress, O2and CO2 gas exchange was measured by mass spectrometry in tomatoplants using 18O2 and 13CO2. Under water stress, gross O2 evolution(EO), gross O2 uptake (UO), net CO2 uptake (PN), gross CO2 uptake(TPS), and gross CO2 evolution (EC) declined. The ratio PN/EOfell during stress, while the ratios UO/EO and EC/TPS rose.Mitochondrial respiration in the light, which can be measureddirectly by 12CO2 evolution during 13CO2 uptake at 3000 µll1 13CO2, is small in relation to gross CO2 evolutionand CO2 release from the glycolate pathway. It is concludedthat PSII, the Calvin cycle and mitochondrial respiration aredown-regulated under water stress. The percentages of photosyntheticelectrons dissipated by CO2 assimilation, photorespiration andthe Mehler reaction were calculated: in control leaves morethan 50 % of the electrons were consumed in CO2 assimilation,23 % in photorespiration and 13 % in the Mehler reaction. Undersevere stress the percentages of electrons dissipated by CO2assimilation and the Mehler reaction declined while the percentageof electrons used in photorespiration doubled. The consumptionof electrons in photorespiration may reduce the likelihood ofdamage during water deficit. |
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Keywords: | Lycopersicon esculentum tomato high-pigment mutant water stress oxygen exchange CO2 assimilation photorespiration mitochondrial respiration in the light Mehler reaction mass spectrometry. |
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