The Effect of CO2-Concentration on the Occurrence of a Number of Acids from the Citric Acid Cycle in Tomato Leaves

Examination of the effect of CO₂-concentration and time of day on the content of malic acid, citric acid, aconitic acid, isocitric acid, succinic acid and fumaric acid in tomato leaves, revealed that the total content of these acids will rise with the CO₂-concentration up to 0.10 vol% CO₂. In the morning up to 0.22 vol% CO₂ was needed for optimal effect. Samples of leaves picked at 1 a.m. showed the lowest content of these acids. At 9 a.m. the content had increased, and at 4 p.m. the increase was considerable. The content of malic and citric acid constituted 36 and 34% of the total acid content. In the afternoon and the night the aconitic acid represented 14% and in the morning 20% of the total acid content. Isocitric acid, fumaric acid and succinic acid occurred only in relatively small concentrations.