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Ammonium, nitrate, and proton fluxes along the maize root
Author(s) -
Taylor A. R.,
Bloom A. J.
Publication year - 1998
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1046/j.1365-3040.1998.00357.x
Subject(s) - nitrogen , ammonium , extrusion , nitrate , chemistry , apex (geometry) , nutrient , zoology , botany , biology , materials science , organic chemistry , metallurgy
Ion‐selective microelectrodes were used to measure NH 4 + , NO 3 – and H + fluxes along the primary root of maize seedlings. Plants were exposed to nutrient solutions containing NH 4 + , NO 3 – or both ions. Nitrogen fluxes along the root varied substantially among the different treatments. Net NH 4 + and NO 3 – uptake and H + extrusion were low at the very apex of the root and generally increased in the more basal regions. In the absence of nitrogen or in the presence of NO 3 – alone, net H + uptake (and root surface alkalinization) occurred at the root tip (0–1 mm), whereas net H + extrusion occurred in all other regions. In the presence of NH 4 + alone, a dramatic increase in net H + extrusion was detected in all regions except for the region 6–11 mm from the apex. In contrast, when NO 3 – alone was supplied, net H + extrusion was depressed at all locations except for the tip (0–1 mm). When both NH 4 + and NO 3 – were supplied, NO 3 – uptake was suppressed at all locations while net H + extrusion was increased relative to NO 3 – alone. The capacities to absorb NH 4 + and NO 3 – at the tip were similar, as indicated by flux rates when NH 4 + or NO 3 – were supplied as sole sources, but when supplied together, net NO 3 – uptake was half that of net NH 4 + uptake, indicating that NH 4 + may satisfy the nitrogen requirements of the poorly vascularized apical tissue in the most energy‐efficient way. The high spatial resolution of the measurements enabled us to establish that acidification in the root expansion zone is maintained regardless of nitrogen source.