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Untersuchungen zur molekularbiologischen Charakterisierung der Nitratassimilation in der Symbiose zwischen dem arbuskulären Mykorrhizapilz Glomus und Tomate
| Content Provider | Semantic Scholar |
|---|---|
| Author | Hildebrandt, Ulrich |
| Copyright Year | 2000 |
| Abstract | The role of the arbuscular mycorrhizal (AM) fungus Glomus intraradices in assisting its host plant tomato in nitrate assimilation was studied. Parts of the genes coding for putative lowand high-affinity nitrate transporters (NTR), nitrate and nitrite reductases were specifically amplified from tomato root cDNA (or DNA) by PCR, subsequently cloned and sequenced. Some characteristics of nitrate transporter genes were investigated: The low-affinity nitrate transporter gene Tomate-lo1 (LeNRT 1;1) and the putative high-affinity nitrate transporter genes Tomate-hi2 (LeNRT2;2) and Tomate-hi3 were expressed in nitrate-grown tomato roots, as demonstrated by Northern-analysis. In addition, the expression of tomato NTR-, nitrate and nitrite reductase genes was influenced by different external N-sources. Tomate-hi2 and Tomate-hi3 differ in their transcript levels when glutamine was the sole Nsource in the nutrient solution. In situ-hybridization experiments showed a tissue-specific localization of Tomate-lo1 and Tomate-hi3 transcripts in tomato roots. The results of RT-PCR-experiments indicate that the expression of tomato high-affinity nitrate transporter genes is not restricted to roots. Northern-analyses show that the mRNA level of the putative high-affinity nitrate transporter gene Tomate-hi3 is significantly increased in mycorrhizal plants, whereas transcript levels of Tomate-hi2 and Tomate-lo1 remain more or less unaltered in mycorrhizal plants in comparison to non-colonized controls. The expression of Tomate-hi3 is expanded into cortical cells of mycorrhizal roots, in contrast to the situation in noncolonized roots, as shown by in situ-hybridization experiments. A specific expression in cells containing arbuscules was not observed. Transcript levels of the tomato nitrate reductase gene were only weakly increased in leaves of mycorrhizal plants, whereas a significant increase in tomato nitrite reductase transcript levels in leaves of mycorrhizal tomato was observed. The specific nitrate reductase activity of mycorrhizal plants was slightly increased in all experiments. Glomus nitrate reductase mRNA was detected in mycorrhizal tomato roots by Northernanalysis. RT-PCR-experiments and activity measurements indicate that the fungal nitrate reductase is expressed in the extraradical mycelium of Glomus intraradices. The data-set obtained is discussed with respect to the role of AM-fungi in nitrateassimilation in the arbuscular mycorrhizal symbiosis. Data on AM-fungal biomass do not necessarily represent the fungal rRNA content in mycorrhizal roots. Therefore RNA-Dot-Blot experiments were performed using the internal transcribed spacer-5.8S ribosomal DNA as a molecular probe to assess the proportion of fungal rRNA in mycorrhizal roots. The obtained data suggest that the AMfungal rRNA might represent up to 50% of total mycorrhizal root RNA. Insufficiently surface-disinfected spores of Glomus intraradices allowed the isolation of an AM-associated bacterium (Paenibacillus sp.). The co-culture of germinating spores of Glomus intraradices Sy167 with Paenibacillus sp. was monitored. Presence of Paenibacillus sp. led to an improved growth of Glomus-hyphae and to morphological alterations of the formed mycelium. A more intense branching, the formation of arbusculelike structures and spores was observed. The morphology of Glomus intraradices germinated with Paenibacillus sp. differed in comparison to structures observed in an AMculture system with Ri T-DNA transformed carrot-roots. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://kups.ub.uni-koeln.de/516/1/11v4094.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
