Activity of glutamine synthetase and glutamate dehydrogenase in Trifolium subterraneum L. and Allium cepa L: effects of mycorrhizal infection and phosphate nutrition

• Published in: The New phytologist 1985-01, Vol.99 (2), p.211-227
• Main Authors: Smith, S.E, St.John, B.J, Smith, F.A, Nicholas, D.J.D
• Format: Article
• Language: English
• Subjects: Agricultural soils; Agronomy. Soil science and plant productions; Allium cepa; ammonium nutrition; Biological and medical sciences; Crop harvesting; Economic plant physiology; enzyme activity; Fundamental and applied biological sciences. Psychology; Fungi; Glomus mosseae; glutamate dehydrogenase; glutamate dehydrogenase (NADP super(+)); glutamate synthetase; glutamate-ammonia ligase; glutamine synthetase; Infections; mycorrhizal fungi; mycorrhizas; Nutrition; Parasitism and symbiosis; phosphate; Phosphates; phosphorus; plant nutrition; Plant physiology and development; Plant roots; Plants; Quaternary ammonium compounds; Soil fungi; Symbiosis (nodules, symbiotic nitrogen fixation, mycorrhiza...); Trifolium subterraneum; VA mycorrhiza
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/j.1469-8137.1985.tb03651.x

Activities of glutamate dehydrogenase and glutamine synthetase were determined using crude extracts of roots and shoots of mycorrhizal and non-mycorrhizal plants of Trifolium subterraneum L. and Allium cepa L., grown at different levels of fertilizer phosphate. Glutamate dehydrogenase activity was low in all tissues [0.1 to 1.6 μ mol NAD(P)H oxidized min-1gFW-1tissue] and there was no consistent effect of mycorrhizal infection or phosphate nutrition on this activity. Glutamine synthetase (GS) activity (assayed by the transferase method) was in the range 1 to 40 μ mol γ-glutamyl hydroxamate produced min-1gFW-1. In general, activity of this enzyme was low in phosphate-deficient plants and was increased both by mycorrhizal infection and by improved phosphate supply. In T. subterraneum routine assays of GS were done on roots only. The effects of mycorrhizal infection in increasing enzyme activity in roots were similar whether natural soil inoculum (containing a mixture of several mycorrhizal fungi) or inoculum of Glomus mosseae Nichol. & Gerd. was used. Both increased phosphate supply and mycorrhizal infection increased nodulation of clover plants as well as GS activity, so that it was difficult to relate changes in GS activity to the interacting effects of mycorrhizal infection and phosphate nutrition. Onions had low GS activity in uninfected roots, compared with shoots. Again improved phosphate supply resulted in increased enzyme activity in both roots and shoots. However, the patterns of interaction between phosphate supply, P concentration in tissues, mycorrhizal infection and enzyme activity were different in the two tissues. In shoots, as expected, the effects were consistent with an indirect effect of mycorrhizal infection on enzyme activity, via improved P nutrition. In roots there appeared to be a 'fungal effect' superimposed on the 'phosphate effect'. This was investigated by manipulating the amount of fungal tissue in mycorrhizal roots via differences in propagule density of G. mosseae in soil. Results were again consistent with the hypothesis that the mycorrhizal fungi contributed GS activity to the symbiotic root system. Fungal structures were separated from roots following digestion in cellulase and pectinase. GS activity was high in fungal tissue from young roots (29 to 31 d), but low in older infections (55 d). The high activity could not have been caused by contamination of fungal tissue by root cells. The digestion technique reduced GS activi