plant surface microbiology.pdf

Contents XVII
6 Carbohydrates as Signal, Regulating Fungal
Gene Expression in Ectomycorrhizas . . . . . . . . . . . . . 377
7 Nitrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 380
8 Utilization of Inorganic Nitrogen . . . . . . . . . . . . . . . 381
9 Utilization of Organic Nitrogen . . . . . . . . . . . . . . . . 382
10 Proteolytic Activities of Ectomycorrhizal Fungi . . . . . . . 383
11 Uptake of Amino Acids . . . . . . . . . . . . . . . . . . . . . 383
12 Regulation of Fungal Nitrogen Export in Mycorrhizas
by the Nitrogen-Status of Hyphae . . . . . . . . . . . . . . . 385
13 Carbohydrate and Nitrogen-Dependent Regulation
of Fungal Gene Expression . . . . . . . . . . . . . . . . . . . 385
14 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . 385
References and Selected Reading . . . . . . . . . . . . . . . . . . . . . 386
22 Nitrogen Transport and Metabolism
in Mycorrhizal Fungi and Mycorrhizas . . . . . . . . . . . . 393
Arnaud Javelle, Michel Chalot, Annick Brun
and Bernard Botton
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 393
1.1 Ecological Significance of Ectomycorrhizas . . . . . . . . . 393
1.2 Nitrogen Uptake and Translocation by Ectomycorrhizas . . 394
2 Nitrate and Nitrite Transport . . . . . . . . . . . . . . . . . . 395
2.1 Uptake Kinetics . . . . . . . . . . . . . . . . . . . . . . . . . 395
2.2 Characterization of Nitrate and Nitrite Transporters . . . . 395
3 Ammonium Transport . . . . . . . . . . . . . . . . . . . . . 398
3.1 Physico-Chemical Properties of Ammonium:
Active Uptake Versus Diffusion . . . . . . . . . . . . . . . . 398
3.2 Physiology of Ammonium Transport in Ectomycorrhizas . . 399
3.3 Isolation of Ammonium Transporter Genes . . . . . . . . . 400
3.4 Regulation of the Ammonium Transporters . . . . . . . . . 400
3.5 Other Putative Functions of Ammonium Transporters . . . 402
4 Amino Acid Transport . . . . . . . . . . . . . . . . . . . . . 403
4.1 Utilization of Amino Acids by Ectomycorrhizal Partners . . 403
4.2 Molecular Regulation of Amino Acid Transport . . . . . . . 404
5 Reduction of Nitrate to Nitrite and Ammonium . . . . . . . 405
5.1 Reduction of Nitrate to Nitrite . . . . . . . . . . . . . . . . . 405
5.2 Reduction of Nitrite to Ammonium . . . . . . . . . . . . . . 406
5.3 Molecular Characterization of Nitrate Reductase
and Nitrite Reductase . . . . . . . . . . . . . . . . . . . . . . 406
6 Assimilation of Ammonium . . . . . . . . . . . . . . . . . . 409
6.1 Role and Properties of Glutamate Dehydrogenase . . . . . . 410