Inhibition of water channels by HgCl2 in intact wheat root cells

To assess the extent of water flow through channels in the membranes of int act higher plant cells, the effects of HgCl2 on hydraulic conductivity (L-P ) of wheat (Triticum aestivum L.) root cells were investigated using a pres sure probe. The L-P of root cells was reduced by 75% in the presence of 100 mu M HgCl2. The K+-channel blocker tetraethylammonium had no effect on the L-P at concentrations that normally block K+ channels. HgCl2 rapidly depol arized the membrane potential (V-m) of the root cells. The dose-response re lationship of inhibition of L-P and depolarization of V-m were not signific antly different, with half-maximal inhibition occurring at 4.6 and 7.8 mu M , respectively. The inhibition of L-P and the depolarization of V-m caused by HgCl2 were partially reversed by beta-mercaptoethanol. The inhibition of L-P by HBCl2 was similar in magnitude to that caused by hypoxia, and the a ddition of HgCl2 to hypoxia-treated cells did not result in further inhibit ion. We compared the L-P of intact cells with that predicted from a model o f cortical cells incorporating water flow across both the plasma membrane a nd 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.