Conclusions

It has been shown that priming of seeds can confer cross-tolerance. These effects exceed the normal enhancement of the seeds under non-stress conditions. This can be seen not only during germination under oxidative and temperature stress (Figs 14.1 and 14.2), but also during germination under high osmotic stress (data not shown). Furthermore, the cross-tolerance phenomenon can be observed after treatment of the seeds with different priming methods as observed after treatment of the seeds in the SC.

With the help of microarray hybridizations, we have been able to identify a set of genes that are differentially regulated during priming and germination. Future research will focus on the genes that show a priming-specific differential expression, since these are the best candidates to be responsible for the observed cross-tolerance phenotype. The upregulated genes that are annotated as cell defence genes are particularly interesting in this respect. However, the transcription-related genes are also significant, since they may be the key regulators of the observed differential expression. These genes will be further analysed for their exact role in cross-tolerance by studying their expression patterns under different conditions and in different seed batches and especially by the generation and phenotypical characterization of overexpression and gene-silencing mutants.

DownreguIated genes

Unknown

Protein folding

Protein catabolism

Cellular organization

Unknown

Protein folding

Protein catabolism

Cellular organization

Signal transduction

Transcription

Metabolism

Energy

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Transport

Signal transduction

Transcription

Metabolism

Energy

Cell growth

UpreguIated genes

Signal transduction

Transcription

Unknown

Protein folding

Protein catabolism

Transcription

Unknown

Protein folding

Protein catabolism

Metabolism Cell growth

Energy Transport

Cellular organization

Cell defence

Fig. 14.7. Categorization of priming-specific genes that are either (a) downregulated or (b) upregulated. Annotations of the genes were made using the Munich Information Centre for Protein Sequence (MIPS) classification (Mewes et al., 2004).

In addition to a better understanding of the processes that lead to the positive effect of seed priming, the practical implications of this research will be the identification of possible marker genes that are specific for stress resistance which can be used to control and optimize the priming process, accurately predict the vigour of seedlings and aid in breeding programmes.

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