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

Abstract

2S albumin fractions were isolated by a modified acetone precipitationmethod (Kortt and Caldwell 1990) from seeds of 103 sunflower (Helianthus annuus L.) accessions and analysed by SDS-PAGE, IEF andRP-HPLC. Two methionine-rich albumins SFA7 and SFA8 showed nodifferences in mobility on SDS-PAGE gels but were readily separated byRP-HPLC. Their levels also varied widely between different genotypes, inrelation to each other and as proportions of the total albumin fraction. Avariant form of SFA8 was identified which differed from the normal SFA8in 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 majorform of SFA7 were identical to that reported previously for the normalform of SFA8 from the cultivar Hysun (Kortt et al., 1991) indicating theirstructural relatedness. Analysis of segregation in the F₂ of the crossbetween lines VIR130 (variant SFA8) and VIR104 (normal SFA8) showedthat the normal and variant forms of SFA8 are encoded by alleles at asingle Mendelian locus. The levels of SFA7 and SFA8 in the seeds ofparental lines, F₁ hybrids and individual F₂ seeds classifiedfrom SDS-PAGE and IEF as homozygous for normal SFA8 (VIR104 type),homozygous for variant SFA8 (VIR130 type) and heterozygous (F₁type) were determined by RP-HPLC. Seeds of the parental line VIR130contained 3.7% SFA7 and 19.0% SFA8 whereas seeds of VIR104contained 9.9% SFA7 and 12.8% SFA8. The F₁ hybrid seedscontained a higher total amount of SFA7+8 proteins (32% comparingto 22% in each parent) which was largely accounted for by a highproportion of SFA7. The mean combined proportions of SFA7+8 in eachof the three phenotypic classes of F₂ seeds were about 18–19% ofthe total. However, the combined proportions of SFA7+8 varied in therange 10–20% among the individual seeds. The ratio of SFA7 to SFA8was highest in the VIR104-type and heterozygous seeds, with the amountof SFA7 exceeding that of SFA8 in six heterozygous seeds. Theproportions of SFA7 and SFA8 were inversely correlated among individualF₂ seeds. The results suggest that the amounts and proportions ofSFA7 and SFA8 are determined by genetic factors in addition toavailability of sulphur.