PLASMA-MEMBRANE FLUIDITY AND HYDRAULIC CONDUCTANCE IN WHEAT ROOTS - INTERACTIONS BETWEEN ROOT TEMPERATURE AND NITRATE OR PHOSPHATE DEPRIVATION

The hypothesis was tested that the negative effect of mineral nutrient deprivation (-N and -P) on the hydraulic conductance (L(o)) of wheat roots may be relieved by increasing the fluidity of plasma membrane (P M) lipids through elevated temperature, An increase in root temperatur e from 20 to 30 degrees C increased the sap flow, J(V), from the excis ed roots of nutrient-deprived plants for 4 h, with a corresponding Inc rease in L(o). In the same period, there was a decline in the flux of osmotically active solutes (J(S)) to the xylem. As the duration of the period at 30 degrees C increased, it was clear that the differential in L(o) between control and nutrient-deprived roots was maintained, ev en though L(o) was significantly greater than the initial (20 degrees C) value after 48 h. The lipid order parameter, determined by fluoresc ence polarization of 1,6 diphenyl- 1,3,5-hexatriene (DPH), decreased m arkedly in two-phase purified PMs in the first 4 h of treatment at 30 degrees C, but thereafter remained steady. Tile differential between c ontrol and nutrient deprived roots was maintained throughout the 48 h period, The correlation between lowered L(o) in nutrient-deprived root s and increased PM lipid ordering remained unchanged in conditions whe re the overall membrane fluidity was increased by elevated temperature .