Abstract

Cause and effect relationships between chloroplast photochemical reactions, CO2 assimilation and oxygen photosynthetic metabolism, transport of sugars in the phloem, apoplastic invertase and leaf stomata activity have been established. Regulation of photosynthesis at the level of an assimilate donor leaf with the change of illumination or export of products of photosynthesis is effectuated as follows. In case of deficiency of products of chloroplast photochemical reactions there occurs incomplete regeneration of resulting primary CO2 fixation products and rapid accumulation of oxygenated substances in cells, vacuoles and the apoplast of the leaf. Apoplastic fluid pH decrease activates the invertase and intensifies the sucrose splitting in the apoplast, which increases the osmolality of extracellular environment that is increased approaching the guard cells, where the main evaporation of water takes place. The osmolality of extracellular environment decreases the turgor of the guard cells and increases the resistance of СО2 diffusion into the leaf.