Changes in Lipid Composition during Callus Differentiation in Cultures of Oilseed Rape (Brassica napus L.)

Abstract

The lipid composition of different callus cultures of Brassica napus varied according to their state of differentiation. Photomixotrophic callus was characterized by the ability to synthesize relatively high levels of triacylglycerol (TAG) which was rich in oleate. Glycosyldiacylglycerols were also detected. In contrast, heterotrophic callus was found to possess high proportions of membraneous phospholipids which were rich in palmitate, linoleate, and linolenate. Moreover, the lipid content was considerably less than that of photomixotrophic callus. Caulogenesis was achieved in both types of callus strains and the lipid composition of the regenerated leaves contained a much higher proportion of chloroplast glycosyldiacylglycerols and thus resembled more those of the parent plant. Some calli entered a senescent phase whereby there was considerable degradation of the constituent membrane lipids. Senescent callus also exhibited a high proportion of polyploid nuclei. In this study we have been able to cause large changes in the morphology of callus cultures. These morphological changes were accompanied by significant alterations in the quality and quantity of acyl lipids. In photomixotrophic cells the lipid changes resembled those seen for developing seed tissues where high rates of TAG deposition are accompanied by an altered fatty acid pattern. Thus, the selection of different callus types should be of use for investigations of the regulation of lipid biosynthesis under controlled culture conditions.