Conversion of photosynthetic products in the light in CO2-free O 2 and N 2 in leaves of Zea mays L. and Phaseolus vulgaris L.

After 10 min illumination of segments of bean (Phaseolus vulgaris L.) or maize (Zea mays L.) leaves in air with (14)CO2, the atmosphere was changed to CO2-free O2 or N2 and conversion of photosynthetic products in the light was investigated. The experiments have shown that after the (14)CO2 assimilation period the bean leaves contain the pool of weakly fixed (14)C (WF-(14)C) which is converted into stable products during the subsequent period of illumination in CO2-free N2. In O2 atmosphere the WF-(14)C pool is initially the main source of CO2 evolved. The marked decrease in radioactivity of sucrose and starch during illumination of bean leaves in O2 atmosphere indicates that these compounds were also the source of CO2 evolved in the light. The total amount of previously fixed (14)C remained almost on the same level during illumination of maize leaves in N2 as well as in O2. However, oxygen changed the distribution of (14)C in photosynthetic products, which is suggested to be the consequence of the photorespiration process in maize.