PLANT PHYSIOLOGY , Vol 111, Issue 4 1109-1117, Copyright © 1996 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
The Effect of Nitrogen Nutrition on the Cellular Localization of Glutamine Synthetase Isoforms in Barley Roots
L. J. Peat and A. K. Tobin
Plant Sciences Laboratory, Sir Harold Mitchell Building, School of Biological and Medical Sciences, University of St. Andrews, St. Andrews, United Kingdom KY16 9TH
Glutamine synthetase (GS) was detected by immunogold localization in the
cytosol and plastids of roots of 7-d-old barley (Hordeum vulgare L. cv
Klaxon) seedlings grown in the presence or absence of NO3- (15 mM) or NH4+
(30 mM). The number of GS polypeptides changed during root development, and
this was affected by N nutrition. There was no evidence of a NO3--inducible
root plastid GS.In apical 5- to 10-mm regions of the root the concentration
of immunogold labeling of cytosolic GS was higher in the cortical
parenchyma than in the vascular cells of the stele, irrespective of N
nutrition. This labeling was at least 50% higher in both cell types in
N-free compared with N-grown (either NO3- or NH4+) seedlings. In contrast,
GS specific activity was highest in roots of NO3--grown seedlings. It is
suggested that this indicates the presence of inactive GS in roots grown
without N. This study has identified both cell- and development-specific
responses of GS to N nutrition.
