Nucleic acid integrity and synthesis in relation to seed vigour in sugar beet

Redfearn, Melanie (1996). Nucleic acid integrity and synthesis in relation to seed vigour in sugar beet. PhD thesis The Open University.



This research has been directed to understanding the nature of vigour in seeds of sugar beet and to methods for predicting germination success. The ratio of extractable RNA to DNA correlated significantly (p<0.05) with vigour assessments made using a range of germination tests and field trials when the seedlots fi-om several cultivars were analysed together. However, comparisons of selected seedlots all of similar high quality produced few significant correlations between the laboratory assessments (RNA/DNA ratios and germination test measurements) and field performance.

Triploid cultivars yielded more extractable nucleic acids than diploid cultivars although overall the ratio of RNA to DNA was not affected by ploidy level. The amount of extractable RNA and DNA and the RNA/DNA ratio increased with fruit size although within the smaller size range used commercially, fruit size did not affect the RNA/DNA ratio.

A primed advancement treatment which improved field performance and produced faster germination at 9°C, had higher RNA/DNA ratios in comparison with thiram-steeped seedlots. The root tips from the embryos of advanced seeds also showed a higher percentage of nuclei with 4°C DNA contents compared to those of untreated seeds but without cell division occurring indicating that the advancement treatment facilitated RNA synthesis and DNA replication. The RNA/DNA ratios of artificially aged seeds did not reflect the loss in germination seen in the standard germination test. Artificially ageing seeds produced a slightly lower percentage of root tip nuclei with a 4°C DNA content although this decrease was more pronounced for advanced then artificially aged seeds.

At 24°C, seedlots differing in vigour showed equal capabilities for the repair of single strandDNA breaks following y-irradiation, but had different capabilities for repair at 9°C. Limited repair occurred in the seedlot with poor performance under sub-optimal germination conditions, suggesting that the ability to repair DNA under stress could be a useful indicator of overall seed vigour.

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