XVI International Botanical Congess

The pattern of stomatal opening in epidermal strips of Commelina benghalensis was examined under red or blue light in relation to calcium availability. Blue light promoted stomatal opening in the presence of low levels of calcium, while in red light opening was relatively tolerant to calcium. Calcium (above 5 mM) or abscisic acid restricted stomatal opening under blue light. Stomatal opening under blue light was enhanced by EGTA, while being decreased by verapamil (calcium-channel blocker) and trifluoperazine (TFP, calmodulin antagonist). Thus, blue light-promoted stomatal opening occurs under conditions of low calcium, and is modulated by calmodulin. A fine-tuning of the calcium within guard cells is essential during the transduction of blue light signal.