Figure 2. (A) Treatment with 10 μM ABA induces stomatal closure in the light, as did 150 μM ATPγS and 1.5 mM ATP. (B) Treatment with 10 μM ABA induces stomatal closure in the light, but in combination with 8 units of potato apyrase closure is blocked. (C) Treatment with either 0.1 μM ABA or 1.5 μg/mL apyrase inhibitor #13 alone does not change stomatal apertures, but in combination induce stomatal closure in the light. (D) Combining 10 μM ABA with 8 units of boiled apyrase has no effect on ABA-induced closure. Treatment with either 0.1 μM ABA or 75 μM ATPγS alone does not change stomatal apertures, but in combination induce stomatal closure in the light. (E) Treatment with 10 μM ABA induces stomatal closure in both Col-0 and the gpa1–3 mutant in the light, however treatment with 250 μM ATPγS in the light only induces stomatal closure in Col-0. Apertures measured in epidermal peels as width/length after 2 h treatment of whole leaves. Different letters above bars = mean values that are significantly different from one another as determined by Student’s t-test (p < 0.05; n > 50).