Polymorphism and inheritance of methionine-rich 2S albumins in sunflower

2S albumin fractions were isolated by a modified acetone precipitation method (Kortt and Caldwell 1990) from seeds of 103 sunflower (Helianthus annuus L.) accessions and analysed by SDS-PAGE, IEF and RP-HPLC. Two methionine-rich albumins SFA7 and SFA8 showed no differences in mobility on SDS-PAGE gels but were readily separated by RP-HPLC. Their levels also varied widely between different genotypes, in relation to each other and as proportions of the total albumin fraction. A variant form of SFA8 was identified which differed from the normal SFA8 in its pI (6.5 compared to 6,0) and mobility on SDS-PAGE. N-terminal sequences of both the variant form of SFA8 and the major form of SFA7 were identical to that reported previously for the normal form of SFA8 from the cultivar Hysun (Kortt et al., 1991) indicating their structural relatedness. Analysis of segregation in the F₂ of the cross between lines VIR130 (variant SFA8) and VIR104 (normal SFA8) showed that the normal and variant forms of SFA8 are encoded by alleles at a single Mendelian locus. The levels of SFA7 and SFA8 in the seeds of parental lines, F₁ hybrids and individual F₂ seeds classified from SDS-PAGE and IEF as homozygous for normal SFA8 (VIR104 type), homozygous for variant SFA8 (VIR130 type) and heterozygous (F₁ type) were determined by RP-HPLC. Seeds of the parental line VIR130 contained 3.7% SFA7 and 19.0% SFA8 whereas seeds of VIR104 contained 9.9% SFA7 and 12.8% SFA8. The F₁ hybrid seeds contained a higher total amount of SFA7+8 proteins (32% comparing to 22% in each parent) which was largely accounted for by a high proportion of SFA7. The mean combined proportions of SFA7+8 in each of the three phenotypic classes of F₂ seeds were about 18-19% of the total. However, the combined proportions of SFA7+8 varied in the range 10-20% among the individual seeds. The ratio of SFA7 to SFA8 was highest in the VIR104-type and heterozygous seeds, with the amount of SFA7 exceeding that of SFA8 in six heterozygous seeds. The proportions of SFA7 and SFA8 were inversely correlated among individual F₂ seeds. The results suggest that the amounts and proportions of SFA7 and SFA8 are determined by genetic factors in addition to availability of sulphur.