The Participation of Apoplast Invertase in the Regulation of Photosynthesis by Stomatal Mechanism

A multi-year research on the influence of donor-acceptor relations between photosynthetic and assimilate-consuming organs on regulation of plant photosynthesis has been summarized. Cause and effect relationships between chloroplast photochemical reactions, CO 2 assimilation and oxygen photosynthetic metabolism, transport of sugars in the phloem, apoplastic invertase and leaf stomata activity have been established. A concept, according to which the 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, has been introduced. In case of deficiency of products of chloroplast photochemical reactions there occurs incomplete regeneration of resulting primary CO 2 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 СО 2 diffusion into the leaf, which leads to photosynthesis decrease. Increased illumination or assimilate consumption activity leads to the opposite outcome. Thus, the intensity of light and dark reactions in photosynthesis is coordinated and chloroplasts are protected against photodamage.