Inheritance and characterization of EMS-induced fatty acid mutations in McGregor flax
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Genetic studies were carried out under controlled phytotron conditions, on McGregor (a Canadian flax cultivar) and four EMS-induced fatty acid mutant lines of McGregor. The objective of this study was to determine the inheritance of the mutated genes in the mutants (which, prior to this study, were described as: E67 - high in palmitic acid; E1747 -low in linolenic acid; E1929 -elevated oleic acid; and E1536 -high in both oleic and linoleic acids). Crosses among these five flax lines were made in all possible combinations. Fatty acid analysis of the seed oil from F1, F2 and backcross populations indicated the control of the characteristic fatty acids in the mutant lines to be under simple Mendelian inheritance. The high palmitic acid character in E67 and the moderately low linolenic-high oleic acid character of E1929 were each controlled by a single partially dominant gene, whereas the very low linolenic-high linoleic character of E1747 was controlled by two partially dominant genes at independent loci. The E1929 gene apparently is allelic to one of the two genes in E1747. A partial maternal effect was observed for the control of the palmitic acid trait in E67. E1536 is a true mutant. However, its mutated character could not be detected, due to its "chameleon-like" behaviour. A moderately low linolenic-elevated oleic and linoleic acid phenotype was vaguely inferred. The flax mutants showed varying degrees of interaction when they were crossed with each other; this interaction(s) being inversely proportional to the closeness of the characteristic fatty acid phenotypes of the mutants (involved in a cross), in the fatty acid synthesis pathway. Since the inheritance of these mutant characters are controlled by one or two genes, breeding for these characteristics should be relatively simple. Two ¹⁴C radio-labelled investigations were conducted to determine enzymes in the fatty acid biosynthesis pathway that may have been affected to produce these mutant phenotypes: i) ¹⁴C acetate (in vivo) assays and ii) in vitro target enzyme assays using ¹⁴C-labelled precursors. Gas chromatography was used for the analysis of fatty acid composition, whereas a scintillation counter and high performance liquid chromatography were used for assaying radioactive fatty acids. ¹H-NMR analyses were also conducted on intact seeds to determine oil contents of the flax lines. The ¹⁴C-sodium acetate experiments could not help in the identification of the fatty acid synthesis enzymes which were affected in producing these mutant lines. Based on the in vitro enzyme assays, none of the following ,enzymes appeared to be responsible for the high palmitic acid character in E67: 16:0-ACP thioesterase, 18:1-ACP thioesterase and β-ketoacyl-ACP synthetase II. ¹H-NMR data on oil content showed that whereas the mutations in E67 and E1929 had no effect on oil content (relative to McGregor), the mutation in E1536 resulted in a drastic 47% reduction in oil content. A relative 30% increment in oil content was shown by E1747. This higher oil content character, coupled with the very low linolenic-high linoleic acid trait of E1747, should boost the edible oil candidacy of this mutant flax line.