Desiccation and osmotic stress increase the abundance of mRNA of the tonoplast aquaporin BobTIP26-1 in cauliflower cells

Changes in vacuolar structure and the expression at the RNA level of a tono plast aquaporin (BobTIP26-1) were examined in cauliflower (Brassica olerace a L. var. botrytis) under water-stress conditions. Gradual drying out of sl ices of cauliflower floret tissue caused its collapse, with a shrinkage in tissue and cell volumes and an apparent vesiculation of the central vacuole , whereas osmotic stress resulted in plasmolysis with a collapse of the cyt oplasm and the central vacuole within. Osmotic stress caused a rapid and su bstantial increase in BobTIP26 mRNA in slices of floret tissue. Exposure of tissue slices to a regime of desiccation showed a slower but equally large rise in BobTIP26 mRNA followed by a rapid decline upon rehydration. In sit u hybridization showed that BobTIP26-2 mRNA is expressed most highly in mer istematic and expanding cells of the cauliflower florets and that desiccati on strongly increased the expression in those cells and in differentiated c ells near the xylem vessels. These data indicate that under water-deficit c onditions, expression of the tonoplast aquaporin gene in cauliflower is sub ject to a precise regulation that can be correlated with important cytologi cal changes in the cells.