Guard Cell Metabolism

Abstract

Guard cells are found in leaf epidermis as a pair of cells surrounding the stomatal pore. Stomatal aperture is regulated by the metabolism of guard cells according to the prevailing environmental condition. Guard cell metabolism is thus adapted to support stomatal movement, which demands a high control of osmolytes content within the cell as well as the need to balance the exchange of ions and metabolites between the cytoplasm and the apoplastic space. Guard cells have several characteristics of sink cells. This is probably an alternative given the low photosynthetic rate and the few number of chloroplasts found in these cells. The glycolysis, the tricarboxylic acid cycle and the degradation of starch and lipids seem to be activated in the light to support stomatal opening. This indicates that guard cell metabolism is differentially regulated compared to mesophyll cells. The particularities of guard cell metabolism are reviewed here. Key Concepts Stomatal aperture controls water use efficiency by modulating CO 2 and H 2 O exchanges between the leaf and the atmosphere. Changes in osmolyte concentration within guard cells regulate stomatal aperture. Signals from mesophyll cells are known to alter stomatal movements. Malate imported from mesophyll cells or produced within guard cells is involved on stomatal movement regulation. Guard cells have several characteristics of sink cells. It seems likely that photosynthesis in guard cell chloroplasts is mainly related to provide ATP and NADPH required for turgor control rather than producing carbohydrates. Lipids, starch and sucrose are degraded during light‐induced stomatal opening. Mitochondria metabolism is important to maintain guard cell energetic demands.