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| Hauptseite > Publikationsdatenbank > Systemic effects of mycorrhization on root and shoot physiology of $\textit{Lycopersicon esculentum}$ |
| Hauptseite > Publikationsdatenbank > Systemic effects of mycorrhization on root and shoot physiology of $\textit{Lycopersicon esculentum}$ |
| Dissertation / PhD Thesis/Book | PreJuSER-46951 |
2006
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
ISBN: 3-89336-463-3, 978-3-89336-463-3
Please use a persistent id in citations: http://hdl.handle.net/2128/2483
Abstract: In a splitroot system, the influence of mycorrhization of tomato plants with the vesiculararbuscular mycorrhizal fungus $\textit{Glomus intraradices}$ on physiology and shikimate pathway transcription was investigated to distinguish between local effects in the mycorrhizal roots and systemic effects in the shoot and in the non-mycorrhizal part of a half-mycorrhizal root. Mycorrhization caused a growth depression and reduced concentrations of elemental carbon and carbohydrates in mycorrhizal and half mycorrhizal roots compared to controls. The two parts of the half mycorrhizal root showed the same low carbon concentration, indicating a systemic effect on carbon availability in the root and the great sink strength of the fungus. Despite, in a developed symbiosis the elevated nitrogen concentration in shoots and roots of mycorrhizal plants, with higher concentrations in the mycorrhizal part of the half mycorrhizal roots, indicated a better supply of mycorrhizal roots and shoots with nutrients, on the cost of nitrogen supply of the non-mycorrhizal part of the root. Although increased nitrogen levels could lead to increased amino acid synthesis, the biosynthesis pathway for the three aromatic amino acids, the shikimate pathway, was not regulated in this later stage of the symbiosis. However, elevated shikimate pathway transcripts in mycorrhizal roots in the early stage of the symbiosis were demonstrated for the first time. This indicates an involvement of the shikimate pathway in early defence responses against the fungus and an influence of changes in carbon status and sugar metabolism on the pathway. A more detailed look to the entry enzyme of the shikimate pathway in plants revealed that one of its two isoforms (DAHPS2) was upregulated by mycorrhization. This one was also induced by short-term ozone exposure, whereas the other was unaffected under the investigated conditions. Furthermore, an influence of mycorrhization on the shoot reaction to ozone was found. Dependent on the mycorrhization rate, an additional treatment with ozone caused additive DAHPS induction of the second isoform in shoots. VOC emissions and glutathione concentrations were only elevated in shoots of non-mycorrhizal plants after ozone exposure, indicating changes in root-shoot interactions involving signalling cascades. Neither early jasmonic acid or hexenal induction nor later methyl-salicylate emissions seem to be relevant in the regulation of DAHPS in response to ozone. Moreover, ozone alone did not only induce the shikimate pathway in shoots, but there was also an isoform specific induction of DAHPS transcripts in roots after ozone treatment, what would require a fast transduction of a shoot signal to the roots. Whether the signalling from shoot to root after ozone exposure is mediated by the same compounds as the root to shoot signalling in the mycorrhizal symbiosis still remains unclear. Furthermore, the different affected pathways and substances may be influenced by different signalling cascades, reflecting the various re-programming in plant metabolism during interactions with belowground symbionts and aboveground environmental parameters.
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