Reversible closure of water channels in parenchymatic cells of sunflower hypocotyl depends on turgor status of the cells

Segments of the inner tissue (IT, i.e. mostly ground-tissue parenchyma) from hypocotyls of sunflower extended rapidly in water and this extension could be reversed in a hypertonic osmoticum. The rates of water uptake or loss that caused the extension or shrinkage were sensitive to submillimolar concentrations of HgCl2. The hydraulic conductance of the IT was lowered two- to five-fold by 10 min treatment with 50 mu M HgCl2. This inhibition could be fully reversed by treatment with 5 mM 2-mercaptoethanol. However, such reversibility only occurred when the IT was in a turgorless state during the HgCl2 and mercaptoethanol treatments, and provided that in between the treatments it was not allowed to regain even a low turgor. These results indicate that turgor changes the state of water channels affected by HgCl2 so that the mercury-sensitive sites are not accessible to mercaptoethanol.