Plant phosphate starvation responses are initiated to reduce Pi demand, conserve Pi reserves and to increase Pi availability. Responses to Pi depravation range from alterations in growth and metabolism to the induction of Pi-inducible genes. Signalling pathways governing starvation responses are unknown, although individual responses have been found to be under the control of local phosphate availability, whilst other responses have been shown to be controlled by shoot-derived systemic signals. A comparison of the kinetics of different phosphate starvation responses, representing growth, physiology and gene expression, suggesting that changes in gene expression and physiology occurred prior to growth responses. The magnitude of all responses was found to be dependent on the duration of starvation and on previous Pi growth conditions, suggesting that internal Pi levels regulate the initiation of responses. Kinetic studies investigating gene expression after Pi re-supply found that down-regulation of expression is rapid and therefore possibly under local control. Enhanced Pi starvation responses were observed under increased sucrose availability, illustrating the importance of a balanced internal C:P ratio for plants. Split-root experiments revealed the systemic down-regulated of Pi-inducible genes and confirmed the existence of long-range signals governed by shoot Pi status in <i>Arabidopsis</i>. Experiments to determine the kinetics of down-regulation in split root plants discovered that the extent of down-regulation was dependent on internal Pi status and on the duration of split-root treatment. Complete down-regulation occurred only after several days. Split-root experiments were conducted with various mutants to further dissect signalling. Wild-type down-regulation was observed in the phosphate response mutant, <i>phr1-1</i>, the cytokinin receptor mutant, <i>cre1</i>and in <i>Arabidopsis</i> plants containing the Pi-inducible At4 gene under the control of the CaMV 35S promoter. Reduced systemic down-regulation was observed in the phosphate translocation mutant, <i>pho1</i>, confirming low shoot Pi status of this mutant.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:663741 |
| Date | January 2004 |
| Creators | Whyte, Jennifer |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/11568 |
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