Effect of pH and metabolic inhibitors on stomatal opening in Crassula argentea

In the CAM plant Crassula argentea, a transient increase in leaf acidity was observed just prior to the beginning of darkness, whereas the stomata remained closed. Stomata opened most rapidly after they had been in darkness for 30-120 min; during this time, leaf acidity was relatively low but then began to increase again after 2-3 h of darkness. Epidermal strips of C. argentea floated in 10 mM KCl at pH 3.5-4.0 showed partial opening, while those incubated at greater than pH 5 remained closed. This acid-induced opening was associated with K+uptake into guard cells. Both K+uptake and stomatal opening were completely inhibited by ABA and DCCD.