14CO2 Uptake and Photosynthetic Products of Bean Leaves after 0.5 or 10 Hours Pretreatment of Plants with 100 % O2 in Light

Abstract

Summary The effects of either 0.5 or 10 hours of pretreatment of bean leaves with 100 % O2 and illumination on 14CO2 uptake and on photosynthetic 14C-products after 2 minutes of fixation were examined. For comparative purposes these measurements were carried out after illumination of the leaves for 0.5 hours in 21 % O2. It was found that the 14CO2 uptake of leaves having been exposed to 100 % O2 for 0.5 or 10 hours was inhibited by 76.2 and 96.5 % respectively compared to that after pretreatment in air. The chlorophyll a and b contents in the leaves of plants pretreated with 100 % O2 for 10 hours was about 2.5 times lower than that of plants pretreated with air or with 100 % O2 for 0.5 hours. High O2 concentration treatments of plants caused a decrease in the incorporation of 14C into the labelling of the amino acid fraction. In the amino acids the bulk of the radioactivity was found in glycine and serine. The incorporation of radioactivity into these compounds was enhanced by pretreatment with 100 % O2. At the same time, the labelling of alanine and of glutamic and aspartic acids was lower compared to that after pretreatment in air. In the organic acid fraction the greatest part of the radioactivity was found in malate and was found in greater amounts after exposure to an atmosphere of 100 % O2. Glycolic acid was found after exposure to air and was absent after pretreatment 100 % O2. Among the sugars, sucrose was a major radioactive product either in air or in 100 % O2. A high O2 concentration and a treatment of the leaves in this atmosphere for 10 hours enhanced the incorporation of 14C into this compound. It is suggested that high O2 concentrations enhanced the glycolic acid pathway and inhibited the biosynthesis the amino acids derived from PGA. A high O2 may also stimulate the production of sucrose in this manner.