We analysed immediate-early local and systemic responses to the perception of Pi in Pi-deplete plants or suspension cells. In Pi-deplete plants or cells, RNA abundance of Pi starvation-induced (PSI) genes is very rapidly downregulated in response to Pi or phosphonate, a non-metabolic analogue of Pi. This indicates that Pi perception, not its metabolism is the crucial event in Pi-signalling. We proposed a model for local Pi signalling in which the perception of Pi controls the stability of negative regulators of downstream responses. Systemic signalling was examined in a split-root system. Pi perception also initiates systemic Pi signalling. The slow systemic translocation of Pi demonstrates that Pi itself is not the systemic signal. To access on the relationship between different nutrient metabolic and signalling pathways, the effects of varying carbon (C) and nitrogen (N) availability on phosphate (Pi) starvation responses and on plant growth were examined. Increased levels of C enhance PSI gene expression responses in roots and shoots, while elevated nitrogen or cytokinin (CK) treatments suppress these responses strongly in roots only. Elevated nitrogen or CK availability shifts shoot-root mass ratios in favour of shoots and alters cellular Pi concentration in both tissues, while increased carbon specifically promotes root growth. Our data indicate that the carbon-nitrogen balance informs growth control networks controlling shoot-root mass ratios. Altered allocation of growth potential by these two nutrients is not dependent on Pi nutritional status and is dominant over Pi starvation-induced growth responses. To identify genes involved in Pi signalling, a genetic screen with Pi starvation responsive reporter (luciferase) line was also performed. A candidate mutant was identified and initial analysis showed it is likely to be a signalling mutant.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:653609 |
| Date | January 2006 |
| Creators | Lai, Fan |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/15185 |
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