Calvin Benson Cycle Enzymes in Guard-cell Protoplasts and Their Role in Stomatal Movement

Calvin-Benson cycle enzymes were found in Vicia guard-cell protoplasts. On the basis of enzyme activities and rates of photosynthetic O2 evolution in guard-cell and mesophyll protoplasts, we conclude that guard-cell chloroplasts utilize largely the phosphoglycerate (PGA)/dihydroxyacetone phosphate (DHAP) shuttle for the transfer of ATP and reducing equivalents from chloroplasts to the cytosol. In guard cells, PGA formation by photosynthetic CO2 fixation may act as a starter of the PGA/DHAP shuttle across the chloroplast envelope in synchronization with the photophosphorylation, thereby driving the stomatal opening.