Báo cáo lâm nghiệp: "Changing electrophoretic patterns of glutamate dehydrogenases and aspartate aminotransferases in a few tree species under the influence of ectomycorrhization"

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Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp Original article đề tài: Changing electrophoretic patterns of glutamate dehydrogenases and aspartate aminotransferases in a few tree species under the influence of ectomycorrhization...

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Nội dung Text: Báo cáo lâm nghiệp: "Changing electrophoretic patterns of glutamate dehydrogenases and aspartate aminotransferases in a few tree species under the influence of ectomycorrhization"

Changing electrophoretic patterns of glutamate dehydro- genases and aspartate aminotransferases in a few tree species under the influence of ectomycorrhization B. Dell 2 M. Chalot 1 B. Botton 1 Universit6 de Nancy I, Facult6 des Sciences, Laboratoire de Physiologie V6g6tale et Forestiere, BP 239, 54506 Vandceuvre-les-Nancy Cedex, France, and 2 Murdoch University, School of Biological and Environmental Sciences, Murdoch, Western Austra- lia, 6150 Australia Introduction tate aminotransferase (AAT), an enzyme which converts glutamate into aspartate. Numerous studies have demonstrated the widespread existence oftwo systems for Materials and Methods nitrogen assimilation in plants and microorganisms: the glutamate dehydro- genase (GDH) pathway and the glutamine Norway spruce (Picea excelsa) roots and Hebeloma sp. ectomycorrhizas were obtained synthetase (GS)/glutamate synthase from 4 yr old plants grown under nursery condi- (GOGAT) cycle. While the GS/GOGAT tions. Douglas fir (Pseudotsuga douglasii ) roots pathway is operative in higher plants (Lea either non-mycorrhizal or ectomycorrhizal with and Miflin, 1974), ammonia assimilation Laccaria laccata (strain S 238) were collected from 1 yr old seedlings grown under nursery in fungi generally occurs via the GDH conditions. Beech (Fagus sylvatica) roots and pathway (Pateman and Kinghorn, 1975), Paxillus involutus (Naudet strain) ectomycorrhi- although some non-mycorrhizal fungi well Hebeloma crustuliniforme ecto- zas as as seem capable of utilizing the alternative mycorrhizas were collected from 4-6 mo old glutamine synthetase/glutamate synthase seedlings grown in a pasteurized peat mix under nursery conditions. The fungi were culti- route (Kusnan et al., 1987). In mycorrhizal vated in pure culture in Pachlewski’s medium. associations, preliminary data have shown Enzyme activities and protein concentration that the fungal pathways of nitrogen as- were determined according to methods de- similation in beech-mycorrhizas are modi- scribed elsewhere (Khalid et al., 1988; Dell et fied by the establishment of the symbiosis al., 1989). Electrophoresis was carried out on 6% polyacrylamide slab gels. The bands of and that glutamate dehydrogenase plays NADP-GDH and NAD-GDH activities were lo- a minor role in this process (Martin et al., cated by using a tetrazolium assay system (Blu- 1986). Taking these observations into menthal and Smith, 1973) and AAT activity was account, we studied a few ectomycorrhizal revealed with Fast violet blue (Khalid et aL, associations, focusing on GDH and aspar- 1988).
Results level of NADP-GDH activity in the fungus (one major band and one minor band). Both GDHs were detected in spruce ecto- In the free-living fungus Hebeloma sp. a mycorrhizas (Fig. 1 A). In the Beech-H. high level of NADP-GDH activity was crustuliniforme association, the single found, whereas only NAD-GDH activity band of NADP-GDH activity found in the was detected in non-mycorrhizal roots. In fungus was represented as traces in the the association spruce-Hebefoma, both mycorrhiza, which exhibited a high level of activities were present (Table I). A similar NAD-GDH activity as did the non-mycor- distribution of enzyme activities was rhizal roots (Fig. 1 B). observed in the Douglas fir-L. laccata As for aspartate aminotransferase, the association (not shown). distinct isoforms found in mycorrhizas, These results contrast with those ob- always corresponded to the host root iso- tained with Beech ectomycorrhizas where forms, whereas the fungal form found in NADP-specific activity was very low (Table the fungus cultivated in pure culture was I). Identical data were also obtained with not detected. Dissection of the mycorrhizal the associations beech-P. involutus and tissues in spruce confirmed these results: Beech-H. crustuliniforme (not shown). the vascular cylinder free of fungus and In the the cortical region including host cells and Spruce-Hebeloma sp. associa- fungal hyphae revealed identical isoforms, tion, gel electrophoresis confirmed the while no activity was found in the peri- presence of NAD-GDH in the host cells (one band) and the presence of a high pheral mycelial layer (Table II).
Dell B., Botton B., Martin F. & Le Tacon F. Conclusion (1989) Glutama dehydrogenases in ectomy- le 1 corrhizas of spruce (Picea excelsa L.) and beech (Fagus sylvatica L.). New Phytol. 111, In all the associations investigated, fungal 683-692 AAT was strongly repressed, whereas fun- Khalid A., Boukroute A., Botton B. & Martin F. gal NADP-GDH was only repressed in (1988) The aspartate aminotransferase of the ectomycorrhizal fungus Cenococcum geophi- beech!ctomycorrhizas. These results lum: purification and molecular properties. suggest that the repression may come Plant Physiol. Biochem. 26, 17-28 from the host plant, since the same fungus Kusnan M.B., Berger M.G. & Fock H.P. (1987) gives rise to two kinds of responses de- The involvement of glutamine synthetase/gluta- pending upon the plants. However, to mate synthase in ammonia assimilation by date, the mechanism of repression Aspergillus nidulans. J. Gen. Microbiol. 123, 1235-1242 remains unknown. Lea P.J. & Miflin B.B. (1974) An alternative route for nitrogen assimilation in higher plants. Nature 251, 614-616 6 Martin F., Stewart G.R., Genetet 1. & Le Tacon References F. (1986) Assimilation of 15 by beech + 4 NH (Fagus sylvatica L.) ectomycorrhizas. New Phytol. 102, 85-94 Pateman J.A. & Kinghorn J.R. (1975) Nitrogen Blumenthal K.H. & Smith E.L. (1973) Nicotina- metabolism. In: The Filamentous Fungi. Vol. 2, mide adenine dinucleotide phosphate-specific (Smith J.E. & Berry D.R., eds.). Edward Arnold, glutamate dehydrogenase of Neurospora. J. London, pp. 159-237 Biol. Chem. 248, 6002-6008