Acclimation of potassium influx in rye (Secale cereale) to low root temperatures

The influx of K(+)((86)Rb(+)) 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 V max and apparent K m 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 K m 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.