Compensatory Changes in Ion Fluxes into Barley (Hordeum vulgareL. cv. Betzes) Seedlings in Response to Differential Root/Shoot Growth Temperature

The effect of growth temperature on the short term influx of ⁸⁶Rb⁺/K⁺, ³⁶Cl⁻/Cl⁻, $C36lO3-/NO3-$, ⁴⁵Ca²⁺/Ca²⁺ and $S35O42-/SO42-$ into barley plants (Hordeum vulgare L. cv. Betzes) has been examined. When barley plants were grown with a differential root: shoot temperature (15 °C/25 °C) there was a marked stimulation of influx of all ions except Ca²⁺. Q₁₀ measurements were close to 2.0 for all ions except Ca²⁺, where Q₁₀ ∼ 1.0 was found. Kinetics of ion influx showed that there had been almost complete compensation for the lower growing temperature over a range of concentrations. The regulation of $NO3-$ uptake was affected by growth temperature. On exposure to 15°C $NO3-$ efflux/influx fell initially but was restored after 5 d. Sensitivity of net $NO3-$ uptake to $NO4+$ was increased by growth at a lower temperature. The importance of these observations in relation to application to field experiments and the proposed mechanism for $NO3-$ uptake is discussed.