Tonoplast vesicles of Beta vulgaris storage roots shows funtional aquaporins regulated by protons

MOIRA SUTKA; KARINA ALLEVA; MARIO PARISI; GABRIELA AMODEO

BIOLOGY OF THE CELL

Portland Press

Lugar: London; Año: 2005 vol. 97 p. 837 - 846

0248-4900

Water is crucial for plant development and growth and its transport pathways inside a plant are a permanent topic for study. Plants express a large number of membrane intrinsic proteins (MIP) whose role is now being re-evaluated concerning not only the control of the overall plant water balance but also in adaptation to environmental challenges that may affect its physiology. In particular we focused our work in water movements across the root cell tonoplast, the delimiting membrane of the vacuole. This major organelle plays a central role in osmoregulation. An enriched fraction of tonoplast vesicles from Beta vulgaris (red beet) storage roots obtained following a conventional protocol was used to characterize its water permeability properties by means of the stopped flow technique. The preparation showed a high water permeability (485 m m.s-1), consistent with values reported in the literature. The water permeability was strongly blocked by HgCl2 (reduced to 16%) and its energy activation was low. These observations allow us to postulate the presence of functional water channels in this preparation. Moreover, western blot analysis demonstrated the presence of a tonoplast intrinsic protein. With the purpose of studying the regulation of the water channels, tonoplast vesicles were exposed to different acidic pH media. When the pH of medium was low (pH 5.6), the water permeability exhibited a 42% inhibition. Our findings prove that while almost all water channels present in the tonoplast vesicles of Beta vulgaris root are sensitive to mercuric chloride not all are inhibited by pH. This interesting selectivity to medium acidification could play a role in adapting the water balance in the cell-to-cell pathway.