Replacement of oxidation by light as the energy source for glucose metabolism in tobacco leaf.

Abstract

Tobacco-leaf disks synthesized starch and sucrose when infiltrated with 5 % solutions of glucose-1- 14 C or glucose-6- 14 C and kept in light under the anaerobic conditions produced by a reduced air pressure of 2 cm mercury (vacuum). In the dark, glucose was absorbed into the leaf cells but there was no synthesis, CO 2 output was low and there was no evidence for fermentation of glucose. Respiration on transfer to air after 24 h of vacuum treatment showed that in the light the respiratory mechanism had been maintained intact but in darkness it was irreversibly damaged. In the sucrose and starch synthesized, an average of 73% of the total 14 C was in the position (1 or 6) originally labelled, 15% appeared in the other terminal carbon atom , and the remaining 14 C was unevenly distributed between carbons 2 to 5. With this type of distribution, the products could not have been formed by photo synthesis but must be attributed predominantly to polymerization of hexose or triose. It is concluded that the phosphorylation of glucose, essential to such syntheses, was lightinduced by reactions which proceeded anaerobically.In similar experiments in air, starch and sucrose again derived mainly from the glucose substrates. There was evidence both for some reassimilation of respired 14 CO 2 and photo phosphorylation of glucose.