Water Potential and Mechanical Properties of the Cell Wall of Hypocotyls of Dark-Grown Squash (Cucurbita maximaDuch.) under Water-Stress Conditions

摘要

Hypocotyl growth of seedlings of dark-grown squash (Cucurbita maximaDuch.) was greatly reduced by the addition of 60mMpolyethylene glycol (PEG) to hydroponic solution (water stress).Apoplastic solution (A) and cell sap (C) were separately collected from the hypocotyl segments by a centrifugation method. The osmotic potentials of A (πA) and C (πc), andΔπ(=πc–πA) of stressed hypocotyls were always lower than those of unstressed hypocotyls.Suction force was measured by immersing the segments into solutions of different concentrations of mannitol. Suction force was significantly correlated withπC(r=–0.99).The mechanical properties of the cell wall of hypocotyl segments were measured by stressrelaxation technique. Minimum stress relaxation time (To), relaxation rate (R) and residual stress of unstressed hypocotyls were low during the growth period and increased when the growth ceased. Toand R of stressed hypocotyls decreased one day after the stress treatment, but the residual stress was not decreased by the water stress throughout the experiment.These results suggest that the suppressed growth of dark-grown squash hypocotyls under water stress was due neither to the reduction of the osmotic potential difference between inner and outer space of the cell, nor to the decrease in suction force, but was partly due to the unchanged mechanical properties of the cell wall, as represented by one stress-relaxation parameter, resid