Effect of CO2 Concentration on Glycine and Serine Formation during Photorespiration

Amount and products of photosynthesis during 10 minutes were measured at different (14)CO(2) concentrations in air. With tobacco (Nicotiana tabacum L. cv. Maryland Mammoth) leaves the percentage of (14)C in glycine plus serine was highest (42%) at 0.005% CO(2), and decreased with increasing CO(2) concentration to 7% of the total at 1% CO(2) in air. However, above 0.03% CO(2) the total amount of (14)C incorporated into the glycine and serine pool was about constant. At 0.005% or 0.03% CO(2) the percentage and amount of (14)C in sucrose was small but increased greatly at higher CO(2) 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 CO(2) concentration is not inhibited but that CO(2) loss from it becomes less significant.