Ion Transport to the Xylem in Aerenchymatous Roots ofZea maysL.

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Abstract
Aerenchyma was induced in the developing nodal (adventitious) roots of maize (Zea mays L. cv. LG11) in solution culture by treatment with an atmosphere of 5% (v/v) oxygen (oxygen partial pressure 5.0 k Pa). Ion uptake by aerenchymatous and ordinary (non-aerenchymatous) roots was then compared to determine the effect of degeneration of much of the cortex in aerenchymatous roots on radial ion movement to the xylem. Rates of uptake and transport of phosphate, potassium and chloride were followed by labelling 4–12mm length segments of intact roots using radioactive tracers. In some experiments, enhanced rates of phosphate transport were induced by means of a divided root system and nutrient deprivation. For all three nutrient ions, and over a range of concentration for phosphate (10–100 mmol m−3 and potassium (0·25–5·0 mol m−3 and with enhanced rates of transport, aerenchymatous roots were at least as effective as ordinary roots (per mm3 of root) and sometimes more effective (per mm root length). These findings are discussed in relation to hypotheses concerning the pathways for radial ion movement across the cortex in ordinary and aerenchymatous roots. Correspondence to: Long Ashton Research Station, Long Ashton, Bristol BS18 9AF, U.K.