Effects of potassium and calcium deficiencies on stomatal functioning in intact leaves of Vicia faba

The effects of potassium or calcium deficiency on stomatal functioning were investigated in Vicia faba L. plants grown hydroponically. In the leaves of plants grown with 1 mM K+, stomatal opening occurred in light with either normal or CO2-free air; K+ and C1− accumulations in guard cells were similar to those of the control plants grown with 5 mM K+. With the zero K+ treatment, stomatal apertures were not affected, while K+ and Cl− guard cell concentrations fell to 30% of the control values. These results may indicate that other solutes contribute to the lowering of osmotic potential during opening. Stomata of calcium-deficient plants remained fully open in darkness, whereas abscisic acid (ABA) supply induced a partial stomatal closing movement. Therefore, calcium deficiency inhibited the process(es) linked with the perception of darkness and stomatal closure. On the other hand, stomatal sensitivity to ABA was only partially affected. Key words: stomatal aperture, potassium, calcium, X-ray microanalysis.