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Induction of ammonium assimilation: leguminous roots compared with nodules using a split root system
Author(s) -
Reynolds Paul H. S.,
Boland Michael J.,
McNaughton Graeme S.,
More Raymond D.,
Jones William T.
Publication year - 1990
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1990.tb06754.x
Subject(s) - ammonium , xylem , root nodule , asparagine , nitrogen , nitrogen fixation , botany , biology , assimilation (phonology) , amino acid , root system , glycine , horticulture , chemistry , biochemistry , linguistics , philosophy , organic chemistry
A split root system for nitrogen uptake, in which one part of the root system was exposed to nitrogen‐free nutrient and the other to circulated buffered ammonium, was used to investigate the effects of ammonium per se on the enzyme pathway for its assimilation in nodules and roots of leguminous plants. Plants of Trifolium repens L. cv. Grasslands Huia grown in the system showed similar growth and similar free amino acid content in the NH + 4 ‐fed roots and in nodulated plants. Studies of ammonium assimilation using [ 13 N]‐NH + 4 , applied to Glycine max [L.] Merr. cv. Amsoy plants, showed the label to be assimilated into amino acids in the NH + 4 ‐fed roots and to be transported to the tops before subsequently appearing in the minus‐N side of the split root system. Analysis of the xylem sap showed [ 13 N]‐asparagine to be the principal labelled amino acid component. In these plants, levels of both allantoate and the nodule‐specific isoenzyme aspartate aminotransferase‐P 2 were at least 10 times higher in the NH + 4 ‐fed roots than in the minus‐N side of the split root system. These studies strongly suggest that a nodule‐type of ammonium assimilation was occurring in the NH + 4 ‐fed side of the split root, and that this part of the root was transporting assimilatory products to the tops of the plants in a fashion analogous to that of a nitrogen‐fixing nodule. These data implicate the involvement of NH + 4 in the induction of its own assimilatory pathway.