Longitudinal Movement and Loss of Nutrients, Pesticides, and Water in Barley Roots

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Abstract
Segments of the roots of young, intact barley plants were treated in solution culture with labelled nutrients, pesticides, and tritiated water (THO). Some of the labelled substances taken up were lost to the unlabelled solutions surrounding the remainder of the root system. The magnitude of this longitudinal movement and subsequent loss has been compared for phosphate, calcium, and nitrate, for the pesticides simazine and ethirimol, and for THO. Losses of phosphate and calcium at a distance of 5 mm from the treated segments were very small by comparison with the amounts translocated to the shoots and did not appear to be greater towards the basal than towards the apical portion of the root system when the labelled solutions were applied to the middlle segments. There was a larger loss of nitrate and there was some suggestion that this loss was polar, being greater in a basipetal direction than towards the root tip. Losses of the two pesticides and in particular of THO were strongly polar and sufficiently great that over a peried of 24 h only small amounts of these substances which had been taken up by the apical zones of the roots were translocated to the shoots. The polarity of longitudinal movement and loss of THO was still very marked even when transpiration was eliminated by removing the shoots. Some consideration is given to the possibility of the existence of contrasting pathways of movement for the different substances.