Contrôle génétique de l'hydroxylation en 5' des anthocyanes dans les fleurs d'Hedysarum coronarium L et H capitatum Desf, Asch et Gr

Résumé - L'analyse génétique et chromatographique de la pigmentation florale chez H coronarium et H capitatum montre que l'introduction du groupement hydroxyle en position 5' de la molécule anthocyanique est déterminée par deux gènes indépendants V et R. Les allèles dominants de ces gènes contrôlent la synthèse de la malvidine. Cependant, l'action du gène R est moins prononcée, de sorte que : - dans les lignées VVRR (ou VVrr), l'hydroxylation quasi totale en 5' des anthocyanidines détermine l'accumulation de la malvidine et l'expression du phénotype violet; - dans les lignées vvRR, l'hydroxylation partielle en 5' des anthocyanidines entraîne l'accumulation simultanée de la malvidine et de la paeonidine, déterminant le phénotype rouge-violacé; - dans les lignées homozygotes récessives (wrr), l'hydroxylation en 5' des anthocyanidines n'a pas lieu et la paeonidine est synthétisée en abondance dans les fleurs rouges.

Abstract - The genetic control of anthocyanin 5' hydroxylation in flowers of Hedysarum coronarium L and H capitatum Desf, Asch et Gr. The results of chemogenetic studies on flower pigmentation in Hedysarum coronarium and H capitatum are reported. Using thin-layer chromatography for the identification of anthocyanidins in parental strains with different flower colorations, 3 phenotypes were clearly defined (table II) : - The red phenotype is determined by the accumulation of paeonidin, a pigment derived from cyanidin (3'hydroxylated: fig 1). - The purple flowers accumulate malvidin derived from delphinidin (3', 5'-dihydroxylated : fig 1). - The purplish-red phenotype results from the simultaneous accumulation of malvidin and paeonidin. The chromatographic study of pigments in different colored strains was confirmed by semi-quantitative determination of anthocyanidins in defined phenotypes (table III). We concluded that the flower color type in Hedysarum was correlated with flavonoid 5'-hydroxylation activity. Segregation analysis of flower colors in F₂ (table VI), showed that the introduction of the 5'-hydroxyl group of the anthocyanidin molecule was determined by 2 particular genes, V and R (table VII). Dominant alleles of these genes control the synthesis of malvidin. However, the action of the gene R is less pronounced, so that : - In lines VVRR (or VVrr), the quasi-total anthocyanidin 5'-hydroxylation determines the accumulation of malvidin and the expression of purple phenotype. - In lines vvRR, the partial anthocyanidin 5'-hydroxylation is correlated with the simultaneous accumulation of malvidin and paeonidin, determining the purplish-red phenotype. - In homozygous recessive lines (vvrr), anthocyanidin 5'-hydroxylation does not occur and paeonidin is abundantly synthesized in red flowers.