Effect of CO2 Concentration on Glycine and Serine Formation during Photorespiration 1

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Amount and products of photosynthesis during 10 minutes were measured at different 14CO2 concentrations in air. With tobacco (Nicotiana tabacum L. cv. Maryland Mammoth) leaves the percentage of 14C in glycine plus serine was highest (42%) at 0.005% CO2, and decreased with increasing CO2 concentration to 7% of the total at 1% CO2 in air. However, above 0.03% CO2 the total amount of 14C incorporated into the glycine and serine pool was about constant. At 0.005% or 0.03% CO2 the percentage and amount of 14C in sucrose was small but increased greatly at higher CO2 levels as sucrose accumulated as an end product. Relatively similar data were obtained with sugar beet (Beta vulgaris L. cv. US H20) leaves. The results suggest that photorespiration at high CO2 concentration is not inhibited but that CO2 loss from it becomes less significant.

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