Abstract
The influx of K+(86Rb+) into intact roots of rye (Secale cereale L. cv. Rheidal) exposed to a differential temperature (DT) between the root (8° C) and shoot (20° C) is initially reduced compared with warm-grown (WG) controls with both shoot and root maintained at 20° C. Over a period of 3 d, however, K+-influx rates into DT plants are restored to levels similar to or greater than those of the WG controls, the absolute rates of K+ influx being strongly dependent upon the shoot/root ratio. Acclimation in DT plants results in a reduction of K+ influx into the apical (0—2 cm) region of the seminal root which is associated with a compensatory increase in K+ influx into the more mature, basal regions of the root. Values of Vmax and apparent Km for K+ influx into DT plants were similar to those for WG plants at assay temperatures of 8° C and 20° C except for an increase in the apparent Km at 8° C. The influx of K+ from solutions containing 0.6 mol·m-3 K+ into both WG and DT plants was found to be linearly related to assay temperature over the range 2—27° C, and the temperature sensitivity of K+ influx to be dependent upon shoot/root ratio. At high shoot/root ratios, the ratio of K+ influx at 20° C:K+ influx at 8° C for WG plants approached a minimum value of 1.9 whereas that for DT plants approached unity indicating that K+ influx into DT plants has a large temperature-insensitive component. Additionally, when plants were grown in solutions of low potassium concentration, K+ influx into DT plants was consistently greater than that into WG plants, in spite of having a greater root potassium concentration ([K+]int). This result indicates some change in the regulation of K+ influx by [K+]int in plants exposed to low root temperatures. We suggest that K+ influx into rye seedlings exposed to low root temperatures is regulated by the increased demand placed on the root system by a proportionally larger shoot and that the acclimation of K+ influx to low temperatures may be the result of an increased hydraulic conductivity of the root system.