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

The influence of salt status of root tissue of Zea mays on influxof 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 rootsin 2.5 mM KC1 + 7.5 mM NaCl + 0.5 mM CaCl₂. High-salt statusgreatly reduced (approx. 90 per cent inhibition) both ²²Na and⁸⁶Rb influxes in the low concentration range isotherm (i.e.at external concentrations below 1 mM). A less marked inhibitionwas observed in the higher concentration range isotherm (1–30mM), indicating that the uptake in this range is less affectedby the salt status of the tissue. During transition from low- to high-salt status there was anet accumulation of K⁺ but not of Na⁺ despite the presence ofa measurable ²²Na⁺ influx at all times. The presence of a continuous²²Na influx but no net accumulation implies an Na⁺ efflux frommaize root tissue. The results differ significantly from thosepreviously published for barley and a possible explanation ofthese differences is discussed.