The effect of nitrogen nutrition on the cellular localization of glutamine synthetase isoforms in barley roots
1996
Peat, L.J. | Tobin, A.K.
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 plastic GS. In apical 5- to 10-mm regions of the root the concentration of immunogoid 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.
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