LIPID AND MORPHOLOGICAL CHANGES IN DEVELOPING RAPESEED, BRASSICA NAPUS

Abstract

Self-pollinated seed from normal and erucic acid free plants of summer rapeseed (Brassica napus L.) was harvested at weekly intervals from pollination to maturity. Oven-dried whole seeds and their component parts were weighed and analyzed for oil content and fatty acid composition. Oil and dry matter accumulation followed sigmoidal patterns, most of the deposition occurring between 14 and 35 days after pollination (DAP). The relative contribution of the testa, endosperm and embryo to dry weight and oil content of whole seeds changed significantly during seed development. Oil content of the developing embryo varied from 22 to 44%, and the testa from 1.6 to 13%, although at maturity only 6 to 8% oil was found in the testa and adhering aleurone. The nucleate endosperm oil content was estimated to be low and in the order of 2 to 2.5%. In 7- to 14-day-old seeds the dry weight, oil content and fatty acid composition were largely determined by the testa and endosperm. From 14 to 21 DAP the testa and embryo were dominant and after 21 DAP the embryo was the controlling influence on the seed characteristics studied.Oils of the testa, nucleate endosperm and embryo differed in fatty acid composition. In seeds free of erucic acid, the ratios of the 18 carbon fatty acids of the embryo and testa remained nearly constant from 21 DAP to maturity. This suggested that the variation in fatty acid composition as well as oil content during seed development in this material was due to disproportionate changes in the contribution of the testa, nucleate endosperm and embryo. However, in developing seeds capable of producing erucic acid a change in the ratio of fatty acid synthesis occurred in both the testa and embryo.