Loss of responsiveness to osmotic stress in maize root: The effect of water channel blocker HgCl₂

In order to investigate the effect of water channel blocker HgCl₂ on the hydraulic resistance in roots of maize seedlings, a xylem pressure probe was used to monitor the changes in root xylem pressure in response to NaCl- or mannitol-induced osmotic stresses before and after the application of HgCl₂. When the maize roots were subjected to 500 μmol L^-1 HgCl₂ in root bathing solution, not only a considerable decline in xylem pressure (increase in xylem tension) was observed, but the loss of responsiveness of the plant to both salt- and mannitol-induced osmotic stresses in terms of xylem pressure change was seen as well when the transpiration rate of the plant was not significantly changed. The results are similar but different from the reversed osmosis by the Fenton reaction in the internodes of Chara coralline, showing that the mechanisms of water transport across cell membrane in plant roots are far more complicated than expected.