Inhibition of Water Channels by HgCl₂ in Intact Wheat Root Cells¹

Wen-Hao Zhang^* and Stephen D. Tyerman

School of Biological Sciences, The Flinders University of South Australia, G.P.O. Box 2100, Adelaide 5001, Australia

To assess the extent of water flow through channels in the membranes of intact higher plant cells, the effects of HgCl₂ on hydraulic conductivity (L_P) of wheat (Triticum aestivum L.) root cells were investigated using a pressure probe. The L_P of root cells was reduced by 75% in the presence of 100 µM HgCl₂. The K⁺-channel blocker tetraethylammonium had no effect on the L_P at concentrations that normally block K⁺ channels. HgCl₂ rapidly depolarized the membrane potential (V_m) of the root cells. The dose-response relationship of inhibition of L_P and depolarization of V_m were not significantly different, with half-maximal inhibition occurring at 4.6 and 7.8 µM, respectively. The inhibition of L_P and the depolarization of V_m caused by HgCl₂ were partially reversed by -mercaptoethanol. The inhibition of L_P by HgCl₂ was similar in magnitude to that caused by hypoxia, and the addition of HgCl₂ to hypoxia-treated cells did not result in further inhibition. We compared the L_P of intact cells with that predicted from a model of cortical cells incorporating water flow across both the plasma membrane and the tonoplast using measured values of water permeability from isolated membranes, and found that HgCl₂ has other effects in addition to the direct inhibition of water channels.

Plant Physiol. (1999) 120: 849-858
Copyright Clearance Center:   0032-0889/99/120//10
© 1999 American Society of Plant Physiologists

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