Two plasma membrane H+-ATPase genes expressed in guard cells of Vicia faba are also expressed throughout the plant. Plant Cell Physioi

Guard cells modulate stomatal apertures in response to hormones, metabolic demands and environmental stimuli. The guard cell PM H+-ATPases play a critical role in this process by generating the electrochemical gradient to drive solute transport and concomitant water flux. The PM H+-ATPase activity is specifically regulated by red and blue light, fungal toxins and auxin. To determine if the unique responsiveness of the guard cell PM H+-ATPase is due to the expression of a cell-specific isoform, we amplified by PCR, and cloned portions of PM H+-ATPase genes VHA1 and VHA2, which are expressed in guard cell protoplasts (GCP). In situ hybridization to leaf tissue sec-tions indicated that VHA1 and VHA2 genes were expressed in guard cells and mesophyll cells but not in epidermal cells or vascular tissues. Furthermore, a gene-specific quantita