Igamberdiev AU, Mikkelsen TN, Ambus P, Bauwe H, Lea PJ, Gardestrom P
Photorespiration contributes to stomatal regulation and carbon isotope fractionation: a study with barley, potato and Arabidopsis plants deficient in glycine decarboxylase
Photosynthesis Research: 2004 81:139-152
The rates of respiration in light and darkness, C-i/C-a and carbon isotope fractionation were investigated in glycine decarboxylase-deficient plants of barley, potato and Arabidopsis thaliana grown in climate chambers with controlled light intensity, temperature, humidity, irradiation and different CO2 concentrations (360, 700 and 1400 mul l(-1)) and compared to the wild-type plants. All photorespiration-impaired plants exhibited higher C-i/C-a and corresponding lower apparent water-use efficiencies, which were more expressed under high irradiance and elevated temperature. The mutants were depleted in C-13 as compared to the wild-type plants, with a difference of up to 6parts per thousand following growth in 360 mul l(-1) CO2. We determined the carbon isotope content at different CO2 concentrations to calculate the contribution of both C-i/C-a and photorespiration for C-13/C-12 fractionation. The direct effect of photorespiration was in the range of 0.7 - 1.0parts per thousand, from which we calculated the value of fractionation at the site of glycine decarboxylation as being 10 - 13parts per thousand, which is in agreement with the previously reported carbon isotope discrimination exerted by the glycine decarboxylase. Respiratory rates, particularly in the light, were increased in the glycine decarboxylase mutants. The necessity of the maintenance of a high CO2 concentration near the site of carboxylation in chloroplasts in plants deficient in photorespiratory enzymes, requires an increased opening of the stomata with a corresponding decrease in water-use efficiency. It is concluded that photorespiration participates in the regulation of C-i/C-a and contributes to carbon isotope fractionation, both via effects on stomata and via discrimination of C-13 in the glycine decarboxylase reaction.
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