Senescence is the last stage of leaf development. During leaf senescence essential nutrients are remobilised to the growing parts of the plant. This highly regulated process involves the expression of senescence-associated genes and a decrease in photosynthesis accompanied by chloroplast protein degradation. The following studies were performed in order to characterise the functions of the papain-like cysteine proteases and the WHIRLY1 protein in the regulation of senescence. Transgenic Arabidopsis lines expressing the rice cystatin, oryzacystatin-I (OCI) in either the chloroplasts or cytosol were characterized. These lines had a slow growth phenotype relative to the wild type. Furthermore, ectopic OCI expression in Arabidopsis increased leaf numbers and enhanced shoot and root branching at flowering. Transgenic barley lines with decreased levels of WHIRLY1 transcripts were grown under optimal and low nitrogen stress conditions. Under optimal conditions, the WHIRLY1 transgenic lines had similar CO2 assimilation rates to those of the wild type but they had significantly more chlorophyll and less sucrose. Moreover, these lines produced fewer tillers and seeds than the wild type. The WHIRLY1 transgenic plants grew better than the wild type under nitrogen deficiency, maintaining higher photosynthetic capacity and chlorophyll content. The WHIRLY1 protein influenced the expression of specific subsets of transcripts encoding chloroplast proteins including thylakoid NADH and cytochrome b6/f complexes. Additionally, the transcript profile revealed new target proteins for WHIRLY1, supporting the involvement of this protein in chloroplast signalling and stress responses. Finally, this study allowed the successful production of barley plants expressing SAG21 and wheat plants expressing the OCI gene in the cytosol, which have the potential to improve stress tolerance and increase seed yield.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:666582 |
| Date | January 2015 |
| Creators | Comadira, Gloria |
| Contributors | Foyer, Christine |
| Publisher | University of Leeds |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://etheses.whiterose.ac.uk/9575/ |
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