Guard cell starch concentration quantitatively related to stomatal aperture [Broadbeans]

Using quantitative histochemical techniques, the carbohydrate levels of guard cells from open and closed stomatal apparatus of Vicia faba L. were compared. To minimize experimental error, all comparisons were between leaflets of the same pair. Stomata on one leaflet were caused to open by light and reduced CO2. The other leaflet, which was in darkness, had closed stomata. In one experiment, data were also collected on palisade parenchyma, spongy parenchyma, and epidermal cells. Guard cell starch concentration was higher in the leaflets with closed stomata than in open stomata by 72 ± 16 millimoles per kilogram dry weight (anhydroglucosyl equivalents) (N = 117, P < 0.02). Variation in guard cell starch concentration from one part of a leaflet to another was small. The data are consistent with the hypothesis that starch degradation provides the carbon skeletons for anion synthesis in guard cells during stomatal opening. Sucrose concentration was higher in guard cells when stomata were open than when they were closed in all three experiments (average difference = 45 ± 7 millimoles per kilogram dry weight [N = 59, P < 0.01]). The variability of sucrose concentration within test leaflets prevented an unequivocal interpretation of these results. When all data are considered, it appears that soluble sugars increase in guard cells when stomata of Vicia faba open.