Abstract
Water transport in plants is regulated by light. Gene expression of many plant aquaporins is also regulated by light and diurnal changes in water permeability of the root are well synchronized with diurnal changes of aquaporin transcripts. In Arabidopsis roots, the transcripts of several aquaporin genes increase during dark adaptation. One of the dark-inducible aquaporin genes, TIP2;2 seems to be regulated by light via phytochrome A, but the detailed mechanism of light regulation and its function remain unknown. To investigate the mechanism of light regulation of TIP2;2 and its function, we generated Arabidopsis transgenic plants expressing a TIP2;2-GFP fusion protein driven by its own promoter. First, we observed localization of TIP2;2-GFP using confocal laser scanning microscopy. TIP2;2-GFP localized in the endodermis, the cortex and the epidermis in the developed region of the root. There was no TIP2;2-GFP signal in the root apical meristem and lateral root primordium. The TIP2;2-GFP signals in the dark-grown plants were extremely brighter than in the light-grown plants, suggesting that the amount of a TIP2;2 protein increases during dark adaptation like its transcript does.
