Relation between Anion Transport and Water Flow in Tomato Plants

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Abstract
Lowering the water potential of culture solutions from −0.4 to −5.4 atm reduced both phosphorus and bromide transport to the shoot, hut the content in the roots was not affected. Reductions in phosphorus transport to the shoot were measured during the first four hours of treatment and were related to concurrent decreases in water flow and not to an impairment of active phosphorus transport. The effect of low water potential on phosphorus transport to shoots was similar at external phosphorus concentrations between 0.6 and 15 mg/l.Phosphorus transport was greater in the dark at −0.4 atm than in the light at −5.4 atm even when these treatments gave the same overall rates of water flow; this is attributed to a different pattern of water flow through the various root zones. The results suggest that the main effect of water flow on anion transport to shoots occurred after the ions had been actively adsorbed by the roots and was not due to mass flow increasing ion delivery to sites of active uptake.