Changes in the Root System of Wheat Seedlings Following Root Anaerobiosis: III. Oxygen Concentration in the Roots

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Abstract
The oxygen status in roots of wheat seedlings (Triticum aestivum) was determined by a volumetric micro-absorption method. Plants grew in nutrient solution (aerated or nitrogen-flushed) or on flooded sand up to the 10th day. The roots were then exposed to aerated or hypoxic conditions for several hours before gas was extracted by reducing the pressure within a concentrated salt solution or by physical crushing. The oxygen content of the extracted gas bubbles was measured with pyrogallol. Comparative experiments with the helophytes Phalaris arundinacea and Carex acutiformis yielded similar oxygen concentrations to those already described in literature. The concentrations of oxygen (13–16%) in young wheat roots were surprisingly high when exposed to nutrient solution flushed with nitrogen gas. Removal of the shoots decreased the oxygen concentration in the roots, indicating some internal oxygen transport from shoots to roots. Detached, submerged roots of wheat still contained 6% oxygen following 20 h of submergence in nitrogen-flushed solution. A linear relationship was found between the oxygen concentration in roots of Triticum aestivum, Zea mays and the two helophytes and the volume of extractable gas per volume of root. This ratio corresponded to the extent of aerenchyma formation. Hence, a certain amount of oxygen may have been adsorbed onto the inner surfaces of the lacunae of the roots. However, the large amount of oxygen in the roots of intact wheat plants suggest that some parts of the root system are unlikely to suffer from the oxygen shortage imposed by oxygen-deficient external conditions such as flooded soil.