Root plasma membrane and tonoplast aquaporins show different properties and regulatory mechanisms

K. ALLEVA, M. SUTKA, M. PARISI AND G. AMODEO

Chateau du Lac, Genval, Bélgica

Congreso; International Conference on Aquaporins; 2005

Comite organizador ad hoc

In plants, most aquaporins are distributed in two membranes that play a critical role in osmoregulation: PIPs in the plasma membrane and TIPs, localized in the tonoplast -the vacuolar membrane-. Recent findings suggest that both types of aquaporins have different behaviour patterns. Moreover, the role (synchronized or not) that plays each type and their regulatory mechanisms involved in controlling their pattern expression or modulating their activity are yet not well understood. This understanding is key to clarify the contribution of cellular pathway to the overall water transport process. Therefore, the here presented research work will attempt to complete a comparative study and characterization of water transport in both plasma membrane and tonoplast and also to elucidate the involved regulatory mechanisms responsible in the protein gating process. In previous works we demonstrated the presence of a transcellular water pathway sensible to mercurial compounds in Beta vulgaris storage roots and functional evidences of the existence of aquaporins in plasma membrane (PIPs) and tonoplast (TIPs) of these root cells. To further investigate the contribution of the water permeability of these two main membranes in water transport, we perform different approaches: molecular detection of aquaporins (western blot) and experiments to discriminate differential regulation of the two subfamilies of water channel (volume changes of vesicles under osmotic shock followed by light scattering). The obtained results showed: 1) high water permeability values in both membrane fractions; 2) the presence of PIP1 and PIP2 in PM fractions and TIP in TP fraction, 3) different inhibitory effects by HgCI2 and 4) a complete blockage by acidic pH of PIPs contrasting with only a partial blockage of TIPs. We postulate that this different behaviour of aquaporins in both membranes allow a fine tuning of water redistribution in the cell to cell pathway.