Regulation of the Arabidopsis thaliana aquaporin gene AthH2 (PIP1b).

Arabidopsis thaliana was transformed with constructs composed of the aquaporin AthH2 promoter and the coding sequence of beta-glucuronidase (GUS) as reporter gene. The transgenic plants obtained were treated with different light qualities or phytohormones and the activity of the AthH2 promoter was determined in situ using a specific GUS assay. With blue light (400-550 nm) and white light, significant activation of the promoter was observed. The same was true for the application of gibberellic acid (GA) and abscisic acid (ABA). In contrast, red light and indole-3-acetic acid (IAA) had only minor effects on the promoter activity. The significance of sequence elements with relation to GA or ABA was confirmed by deletion analyses of the AthH2 promoter. Likewise, a promoter segment with importance for hydathoid specific expression was identified.