The Effect of Increased Internal Ion Concentration upon the Ion Uptake Isotherms of Excised Maize Root Segments

Abstract

The influence of salt status of root tissue of Zea mays on influx of ⁸⁴Rb and ²²Na and net accumulation of K⁺ and Na⁺ was studied. Low-salt roots were grown in 0.5 mM CaCl₂, and high-salt roots in 2.5 mM KC1 + 7.5 mM NaCl + 0.5 mM CaCl₂. High-salt status greatly reduced (approx. 90 per cent inhibition) both ²²Na and ⁸⁶Rb influxes in the low concentration range isotherm (i.e. at external concentrations below 1 mM). A less marked inhibition was observed in the higher concentration range isotherm (1–30 mM), indicating that the uptake in this range is less affected by the salt status of the tissue. During transition from low- to high-salt status there was a net accumulation of K⁺ but not of Na⁺ despite the presence of a measurable ²²Na⁺ influx at all times. The presence of a continuous ²²Na influx but no net accumulation implies an Na⁺ efflux from maize root tissue. The results differ significantly from those previously published for barley and a possible explanation of these differences is discussed.