Blue light-promoted stomatal opening in abaxial epidermis of Commelina benghalensis is maximal at low calcium

Abstract

The requirement for calcium in blue light-promoted stomatal opening, in comparison with that in red light, was studied in epidermal strips of Commelina benghalensis L. Blue light promoted stomatal opening in the presence of a low level of calcium, whereas in red light opening was relatively tolerant to calcium. Stomatal opening under blue light was restricted by external calcium (above 5 μM) or abscisic acid. When present in the incubation medium, EGTA increased the extent of stomatal opening under blue light. Verapamil (a calcium-channel blocker) and trifluoperazine (TFP, a calmodulin antagonist) reduced the stimulation of stomatal opening by blue light. Lanthanum, an external calcium-channel antagonist, had no significant effect on stomatal opening under either blue or red light. These observations indicate that blue light-promoted stomatal opening preferentially occurs at low levels of calcium, and modulation by calmodulin is strongly suggested. We conclude that a fine-tuning of the calcium level within guard cells is essential during the transduction of the blue light signal.