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Journal of Experimental Botany, Vol 49, 95-100, Copyright © 1998 by Oxford University Press

ARTICLES

Investigations of ion absorption during NH4+ exposure I. Relationship between H+ efflux and NO3- absorption

D Smart and A Bloom
Department of Vegetable Crops, University of California, Davis, CA 95616, USA; Corresponding author e-mail: drsmart@vegmail.ucdavis.edu

Root NO3- absorption was examined under steady-state conditions in the presence and absence of NH4+ using intact tomato plants (Lycopersicon esculentum cv. T-5). Plants grown under a low-salt regime showed much higher rates of NO3- absorption than plants grown under a high-salt regime, but the presence of NH4+ at concentrations less than 200 M increased the capacity for net NO3- uptake for both the low- and high-salt conditions. Simultaneous changes in net NO3-, K+, and H+ exchanges were continuously monitored for 3 h prior to and up to 7 h following exposure to NH4+. Upon first exposure to 50 or 100 M NH4+, NO3- absorption remained constant; but during the subsequent 6 to 7 h, NO3- absorption continually increased. Net K+ absorption decreased immediately following its first exposure to NH4+, but gradually recovered during the 7 h following first exposure. Changes in K+ absorption were not correlated with changes in NO3- absorption. Proton efflux gradually increased under NH4+ exposure and was significantly correlated with the observed increase in NO3- absorption. When roots absorbing NO3- were exposed to 5000 M NH4-, NO3- absorption declined throughout the entire observation period.Key words: Ammonium, nitrate, proton, absorption, tomato
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A. J. BLOOM, J. FRENSCH, and A. R. TAYLOR
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