The impact of freezing during maturation on storage products in canola seeds.

Mature canoia (Brassica napus cv. Westar) seeds contain large quantities of the storage proteins cruciferin and napin and storage lipids rich in C18:1 and C18:2 fatty acids. Both the quantity and quality of these products are altered by freezing during development. Further, the response to freezing changes during seed development. The effects include decreased fatty acid chain elongation, altered fatty acid unsaturation, higher lipid levels and lower protein levels. In addition, seeds in the pivotal moisture range (55%) may be predisposed to precocious germination, which is then inhibited by a lack of adequate seed moisture. The results indicate that freezing imparts its effect in two ways. Initially, there is a freezing (low temperature) component and this is followed by rapid desiccation of the seeds. Although most responses probably result from a combination of the stresses, it appears that inhibition of fatty acid chain elongation is caused by the freezing component and the gradual inhibition of storage protein accumulation is a result of accelerated seed desiccation. [ABSTRACT FROM AUTHOR]