Conversion of photosynthetic products in the light in CO2-free O2 and N2 in leaves of Zea mays L. and Phaseolus vulgaris L.

Summary After 10 min illumination of segments of bean (Phaseolus vulgaris L.) or maize (Zea mays L.) leaves in air with ¹⁴CO₂, 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 ¹⁴CO₂ assimilation period the bean leaves contain the pool of weakly fixed ¹⁴C (WF-¹⁴C) which is converted into stable products during the subsequent period of illumination in CO₂-free N₂. In O₂ atmosphere the WF-¹⁴C 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 ¹⁴C remained almost on the same level during illumination of maize leaves in N₂ as well as in O₂. However, oxygen changed the distribution of ¹⁴C in photosynthetic products, which is suggested to be the consequence of the photorespiration process in maize.Abbreviation WF-¹⁴C weakly fixed ¹⁴C