GPA1 modulates NO synthesis in ExtCaM guard cell signaling. A and B, Guard cells preloaded with 10 μm DAF2-DA in the wild type (WT/WS), gpa1 mutants, and the cGα line were incubated in MES buffer (control) or 10−8 m CaM for 30 min in darkness. Fluorescence images and intensities in guard cells were recorded and are shown in A and B, respectively. Bar = 10 μm. C, Open stomata in the wild type, gpa1-1, and gpa1-2 were incubated in MES buffer (control) or 60 μm SNP. Stomatal apertures were measured 2 h after treatment. WS, Ecotype Ws.