Effect of Light and Dark on the Intracellular Fate of Photosynthetic Products

Abstract

In attempts to distinguish the various pools of metabolic products that may be chemically or physically separated in photosynthesizing cells, C14 labeled compounds have been fed to cells in a number of kinetic studies (2, 3, 7, 10). From these studies it is evident that the photosynthetic intermediates, presumably within the chloroplasts, rapidly acquire the same specific activity as the substrate CO2 and that C'4 enters other (nonplastid) pools more slowly, presumably in the hyaloplasm or vacuoles. Smith, Bassham, and Kirk (10) showed that the active pool of alanine becomes saturated with C'4 within 30 minutes of photosynthesis by Chlorella in C1402. In contrast, the specific activity curve of glutamic acid passes through an inflection after 20 minutes and continues to increase slowly. This was interpreted as evidence for a secondary slowly labeled pool (presumably outside of the plastid). The active pools of several amino acids were found to represent 20 to 25 % of the total pools. It has become possible with the development of the nonaqueous method of isolating chloroplasts to study the intracellular distribution and movement of some of the early products of photosynthesis (4, 13). Leaching of water soluble components during chloroplast isolation in buffered sucrose or saline solutions renders the current aqueous methods of little use in such studies. It has been shown that there is a rapid movement of certain carbon compounds from the chloroplast into its cytoplasmic environment while other carbon compounds particularly those directly concerned with the carbon cycle of photosynthesis (4) are unable to pass readily out of the plastid. It should be possible by using the nonaqueous method of isolating chloroplasts to determine the actual sizes of the chloroplast pools of various compounds and to compare these pools with those found outside of the plastids. The present study involved the use of the nonaqueous method of isolation of plasticls to follow the influence of light and dark onl the fate of some of the early products of photosynthesis.