Tonoplast vesicles of Beta vulgaris storage root show funtional aquaporins regulated by protons

M SUTKA, K ALLEVA, M PARISI, G AMODEO

BIOLOGY OF THE CELL

Pórtland press Ltd

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

0248-4900

Background information. Water is crucial for plant development and growth, and its transport pathways inside a plant are an ongoing topic for study. Plants express a large number ofmembrane intrinsic proteins whose role is now being re-evaluated by considering not only the control of the overall plant water balance but also in adaptation to environmental challenges that may affect their physiology. In particular, we focused our work on water movements across the root cell TP (tonoplast), the delimiting membrane of the vacuole. This major organelle plays a central role in osmoregulation. Results. An enriched fraction of TP vesicles from Beta vulgaris (red beet) storage roots obtained by a conventional method was used to characterize its water permeability properties by means of the stopped-flow technique. The preparation showed high water permeability (485 ìm·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,Westernblot analysis demonstrated the presence of a tonoplast intrinsic protein. With the purpose of studying the regulation of water channels, TP vesicles were exposed to different acidic pH media. When the pH of a medium was low (pH 5.6), the water permeability exhibited a 42% inhibition. Conclusions. Our findings prove that although almost all water channels present in the TP vesicles of B. Vulgaris root are sensitive to HgCl2, not all are inhibited by pH. This interesting selectivity to acidification of the medium could play a role in adapting the water balance in the cell-to-cell pathway.