A Functional Photorespiratory Cycle Is Essential for Light-Dependent Stomata Opening in Epidermal Peels of Arabidopsis thaliana.

Traditionally viewed as a wasteful pathway, photorespiration plays essential roles in cellular metabolism and stress responses. While its role in leaf mesophyll cells is well characterized, its functioning in leaf epidermal guard cells and its involvement in stomatal opening remain poorly understood. Using data mining, all photorespiratory genes were expressed, and their respective proteins were present in Arabidopsis thaliana guard cells, thus indicating the presence of a complete photorespiratory cycle. The inhibition of glycolate oxidase (GOX) by hydroxy-pyridyl-methane-sulfonic acid (HPMS) or the glycine decarboxylase complex (GDC) by amino-aceto-nitrile (AAN) reduced light-induced stomatal opening in Arabidopsis thaliana leaf epidermal peels. The exogenous supply of serine, 3-phosphoglycerate, or malate alleviated this inhibition. It is proposed that guard cell photorespiratory metabolism contributes to light-induced stomatal opening by supporting metabolite fluxes crucial for the regulation of guard cell turgor. These findings highlight the importance of a functional guard cell photorespiratory cycle in stomatal dynamics that could play a role in plant responses to environmental stimuli.