title: The Effect of Nitrogen Nutrition on the Cellular Localization of Glutamine Synthetase Isoforms in Barley Roots.
abstract: 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.
authors.affiliation: Plant Sciences Laboratory, Sir Harold Mitchell Building, School of Biological and Medical Sciences, University of St. Andrews, St. Andrews, United Kingdom KY16 9TH.
authors.forename: L. J.
authors.initials: LJ
authors.lastname: Peat
authors.forename: A. K.
authors.initials: AK
authors.lastname: Tobin