It has been suggested that lipid peroxidation is involved in the loss of seed vigour, although many attempts to examine the relationships between lipid peroxidation and seed vigour have proved equivocal. Studies were undertaken on seed lots of cabbage and soya bean to find evidence for peroxidation by the analysis of i) total and polar fatty acid levels; ii) lipid hydroperoxides; iii) volatile products produced on heating dry seeds; and iv) volatile products produced on imbibition. The loss of polyunsaturated fatty acids (PUFAs) detected in the dry seeds was clearly related to germinability in both soya bean and cabbage seeds. Furthermore, an increase in hydroperoxides was observed in both seed types. Although the relationship of the level of hydroperoxides to germinability was less clear than for the decline in the level of PUFAs, these results suggested that the loss of PUFAs was possibly due to evidence the peroxidation of the seed obtained from the heating lipid, indirect of the seeds suggesting that hydroperoxide breakdown may be necessary in order that the changes in PUFAs become apparent. In contrast to the poor relationship observed between germinability and hydroperoxide level, a marked relationship between hydroperoxide level and seed moisture content was observed in the cabbage seeds. This may be significant with regard to the observed relationship between storability and seed moisture content, although no such relationship was seen in the soya beans. Certain volatile compounds derived from dry heated seeds were related to seed vigour in both seed types and evidence suggests that the lipid hydroperoxides were the source of these compounds. Although the total volatiles counts evolved from imbibing cabbage seeds showed no quantitative relationship to seed vigour, one peak was noted which was clearly associated with the vigour of these seeds. The variability in the volatiles evolved from soya beans on imbibition, however, precluded the detection of any possible relationship between these and seed vigour. In both seed types, results suggest that the volatiles derived on imbibition were of a different source to those derived on heating. A marked increase in the level of hydroperoxides was observed in whole cabbage seeds and soya bean axes of low vigour over the first hour of imbibition. This may suggest that an exacerbation of damage on imbibition was associated with low vigour seeds. In contrast to this, in the seeds of high vigour, the increase in hydroperoxide levels was markedly less or rapidly reduced, suggesting the possible activity of repair mechanisms. Ferrous ions were shown to invigorate both seed types, particularly cabbage seeds. It is suggested that the invigorating effect of these compounds was due to the facilitation of repair, including hydroperoxide breakdown and the quenching of any free radicals.

Thesis (M.Sc.)-University of Natal, Durban, 1986.