The Role of Nitrate in Breaking Dormancy
Proteomics as a tool in the indentification of genes that are differentially expressed
This project is one of a series in the theme of 'Diagnosis of Viability and Germination'.
Seed germination of species in the Brassicaceae family is known to be affected by primary dormancy. These seeds are fully viable but fail to germinate under optimum conditions: they require a dormancy-breaking treatment to enter the germination phase. Nitrate has been described to break this physiological dormancy of seeds of several Brassicaceae species, amongst which Arabidopsis thaliana ecotype Cvi and Sisymbrium officinale, and a current study has identified a third member of the family that responds to nitrate. Dormancy in this species can be broken by a string of factors, yet the dormancy is very deep. In contrast, another member of the same family has deep primary dormancy that cannot be broken by nitrate. This raises the possibility that different dormancy-breaking mechanisms exist, one being nitrate-mediated and another nitrate-independent.
Although nitrate breaks primary dormancy in three mentioned species, it does not break secondary dormancy. When primary dormancy is broken, non-dormant seeds are rendered that require no nitrate to germinate. Keeping these seeds in the dark results in secondary dormancy. This form of dormancy can be distinguished from primary dormancy by gene profiling (Toorop et al., 2005, see project 'A genomic approach to understanding seed dormancy'). Differences in nitrate response have been observed, both for species and types of dormancy, and this may well have an ecological significance.
The question that arises is: which genes are induced in relation to nitrate metabolism, and which genes are induced by nitrate in relation to dormancy? Two systems can be used to investigate this: 1) comparison of a nitrate-responsive species to an irresponsive species; 2) comparison of primary dormancy to secondary dormancy. Proteomics allows identification of proteins that are specifically present or absent in particular conditions. This technique will be used to identify expression of nitrate-induced proteins in association with dormancy and germination. In order to verify expression real-time Polymerase Chain Reaction (PCR) will be used, which should rule out whether these genes are nitrate-induced but not related to dormancy or truly associated with breaking of dormancy. In addition, results from the project “genomic approach to dormancy” can be used to investigate nitrate responsiveness.
The objective of this project is to explain the difference between nitrate-responsive and -irresponsive dormancy in terms of gene expression. The purpose is to generate a better understanding of dormancy, which can be used to understand the behaviour of banked seeds. The project may lead to the development of a diagnostics test to assess dormancy and germination capacity in any accession of the MSB. The project links with the Defra-funded project “genomic approach to dormancy”.
Duration: to commence ±2007
Outputs: peer-reviewed publications
Project Team
Project Leader: Toorop, Peter
Seed Conservation Department
Peter Toorop
Funders
UK
MSB project
Annex Material
Annex 1: Information outputs (Word document)