PLANT PHYSIOLOGY , Vol 110, Issue 4 1293-1299, Copyright © 1996 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Chlorate as a Transport Analog for Nitrate Absorption by Roots of Tomato
K. R. Kosola and A. J. Bloom
Vegetable Crops Department, University of California, Davis, Davis, California 95616-8746
Several studies have indicated that chlorate (ClO3-) and nitrate (NO3-) may
share a common transport system in higher plants. Here, we compared the
interactions between ClO3- and NO3-uptake by roots of intact tomato
(Lycopersicon esculentum cv T5) plants. Exposure to ClO3- for more than 2 h
inhibited both net ClO3- and K+ uptake, presumably because of ClO3-
toxicity; consequently, subsequent measurements were conducted after short
exposures to ClO3-. The apparent affinity and apparent maximum rate of
absorption for net ClO3- and NO3- uptake were very similar. Interactions
between ClO3- and NO3- transport were complex; 50 [mu]M NO3- acted as a
mixed inhibitor of net ClO3- uptake, but 50 [mu]M ClO3- had no significant
effect on net NO3- uptake, and 500 [mu]M ClO3- had no significant effect on
15NO3- influx. If the two ions share a single common high-affinity
transport system, it is much more selective for NO3- than would be
suggested by the similarity of net NO3- and ClO3- uptake kinetics. Our
results indicate that, although NO3- may interfere with root ClO3- uptake,
ClO3- is not a useful analog for the root high-affinity NO3- transport
system.
