TITLE:
Photorespiration and Its Role in the Regulation of Photosynthesis and Plant Productivity
AUTHORS:
V. I. Chikov, G. A. Akhtyamova
KEYWORDS:
Assimilate Transport, Apoplast, Stomata, Invertase, Chloroplast
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.10 No.12,
December
12,
2019
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 14C 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 14C-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 CO2 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 14C-labeled sucrose/hexose decreases,
and the stomata close. With increasing illumination, reverse events occur.