Photorespiration and Its Role in the Regulation of Photosynthesis and Plant Productivity

Abstract

The results of long-term studies of photorespiration are summarized and the unsuccessful attempts to increase productivity by suppressing this process are shown. It has been shown that photorespiration and glycolate metabolism are involved in the regulation of the relationship between light processes in chloroplasts and the dark reactions of carbon dioxide assimilation. The studies were conducted on plants in vivo and were associated with the activity of the apoplastic invertase enzyme, affecting assimilate transport. In violation of donor-acceptor relations between photosynthetic and plant-assimilating organs (removal of part of organs-consumers of assimilates or leaves, increase in nitrate nutrition), the kinetics of inclusion of 14 C in glycolate was changed. This is due to the strengthening of the role of the transketolase mechanism of its formation. The study of genetically transformed plants, in which either an additional apoplastic invertase gene was introduced, or the existing gene was blocked and did not act, showed a different change in the ratio of 14 C-labeled sucrose/hexose and the transpiration response to reduced light. In this connection, the concept of the mechanism of photorespiration interaction with apoplastic invertase and stomatal apparatus of the leaf is proposed when the ratio of light and dark reactions of photosynthesis or assimilate transport is changed. The essence of the concept is that when the ratio of light and dark processes is disturbed, the concentration of organic acids changes first in mesophilic cells (mainly by photorespiration), and then in the extracellular space. It changes the activity of apoplastic invertase, which hydrolyzes sucrose and prevents it from being exported from the leaf. Hydrolysis of sucrose increases the osmoticity of the aquatic environment of the apoplast, which increases with movement to the stomata. The changed osmoticity of the environment around the stomatal guard cells changes the resistance of CO 2 diffusion into the leaf. This normalizes the ratio of light and dark processes in the sheet. Therefore, when illumination decreases, nitrate nutrition increases or difficulties arise with the use of photosynthesis products in acceptor organs, the ratio of 14 C-labeled sucrose/hexose decreases, and the stomata close. With increasing illumination, reverse events occur.

Elevated CO2 induces rapid dephosphorylation of plasma membrane H+‐ATPase in guard cells

“…To examine the interrelationships among the photosynthetic rate, C i and stomatal movement during the light–dark transition, we performed time‐resolved gas‐exchange analyses. As in previous studies (Engineer et al ., 2016 ; Chikov & Akhtyamova, 2019 ), the photosynthetic rate decreased immediately and reached its minimum value within 1 min after the light–dark transition (Fig. 2 ).…”

“…When the plants are transferred to dark conditions, photosynthesis ceases and CO 2 is emitted by respiration, and transiently by photorespiration (post‐illumination CO 2 burst) in the leaves; therefore, dark‐induced stomatal closure may be partly mediated by CO 2 (Engineer et al ., 2016 ; Zhang et al ., 2018 ; Chikov & Akhtyamova, 2019 ). Previous studies on CO 2 ‐induced stomatal closure focused on the activation of PM anion channels in guard cells.…”

Ecological Significance of the Interaction of Photosynthesis Light and Dark Processes

“…What is the reason for these differences in the 14 C inclusion in glycolate? In fruit-free plants, sugar export from leaves almost stopped, photosynthesis is reduced [2], since the removal of such a number of assimilate acceptor organs causes an extraordinary excess of photosynthetic products in the leaf. That means that the use of "restorative power" in chloroplasts (the conditions: clear day, temperature above +35˚C) is difficult.…”

“…Therefore, the main task of humanity is to learn self-regulation of this process in changing conditions and what can be done to preserve life on Earth. It has long been shown [1] that not only oxygen release takes place in plant leaves exposed to light, but also the so-called photorespiration (light-stimulated absorption of oxygen by plant leaves), which reduces total leaf photosynthesis, for many years this process was considered a parasitic process [2]. The investigators searched plant species with low photorespiration and conditions affecting its intensity without much success.…”

“…If oxygen enters the active centre of RBPC/O, then as a result of (oxygenation reaction) one glycolate molecule and one phosphoglyceric acid (PGA) are formed. And if CO 2 gets to the active centre of RBPC/O, then (in carboxylation reaction) two PGA molecules are formed [2].…”