title: Rapid accumulation of hydrogen peroxide in cucumber roots due to exposure to low temperature appears to mediate decreases in water transport.
abstract: Water transport across root systems of young cucumber (Cucumis sativus L.) seedlings was measured following exposure to low temperature (LT, 8-13 degrees C) for varying periods of time. In addition, the amount of water transported through the stems was evaluated using a heat-balance sap-flow gauge. Following LT treatment, hydrogen peroxide was localized cytochemically in root tissue by the oxidation of cerium (III) chloride. The effects of hydrogen peroxide on the hydraulic conductivity of single cells (Lp) in root tissues, and on the H+-ATPase activity of isolated root plasma membrane, have been worked out. Cytochemical evidence suggested that exposure of roots to LT stress caused a release of hydrogen peroxide in the millimolar range in the vicinity of plasma membranes. In response to a low root temperature (8 degrees C), the hydraulic conductivity of the root (Lp(r)) decreased by a factor of 4, and the half-times of water exchange increased by a factor of 5-6. Decreasing root temperatures from 25-13 degrees C increased the half-times of water exchange in a cell by a factor of 6-9. The measurement of axial water transport with a heat-balance sap-flow gauge showed that only a small amount of water was transported when 8 degrees C was imposed on cucumber roots. Lp and the H+-ATPase activity of the isolated root plasma membrane were very sensitive to externally applied hydrogen peroxide at a concentration of 1-16 mM. These observations suggest that the accumulation of hydrogen peroxide appears to mediate decreases in water transport in cucumber roots under low temperature.
authors.affiliation: Agricultural Plant Stress Research Center (APSRC), Division of Applied Plant Science, College of Agriculture, Chonnam National University, Gwangju 500-757, South Korea.
authors.forename: Seong Hee
authors.initials: SH
authors.lastname: Lee
authors.forename: Adya P
authors.initials: AP
authors.lastname: Singh
authors.forename: Gap Chae
authors.initials: GC
authors.lastname: Chung
mesh_terms: D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D003080:Cold Temperature; D018553:Cucumis sativus / Q000737:chemistry / Q000378:metabolism*; D006861:Hydrogen Peroxide / Q000378:metabolism*; D009997:Osmotic Pressure; D018517:Plant Roots / Q000737:chemistry / Q000378:metabolism*; D006180:Proton-Translocating ATPases / Q000378:metabolism; D014867:Water / Q000378:metabolism*
chemical_list: D014867:Water; D006861:Hydrogen Peroxide; D006180:Proton-Translocating ATPases