Biochemical genetics of pigmentation in pisum

The biochemical genetics of flavonoid pigmentation has been investigated for many species and genera over a long period. In the case of the genus Pisum, a great many genetical studies have been carried out, but very little biochemistry has been undertaken. The present investigation was designed to use the large amount of genetical material available as a basis for an investigation of the biochemistry of pigmentation in Pisum. Six loci were known to affect flower colour in Pisum, these being A, Am, Ar, B, Ce and Cr, and a pair of complementary loci, PUr and Pu had been shown to be responsible for the anthocyanin colouration of pod tissue. No specific information was available as to the mode of action of these loci in the biosynthesis of flavonoids in Pisum, and also there were no reports of the interaction of the flower colour loci with the loci responsible for the flavonoid pigmentation in vegetative tissues. The results presented in this thesis outline the mode of action of the six loci, A, Am, Ar, B, Ce and Cr, in the production of the range of flower colours found in the genus Pisum. Three of these loci, A, B and GP, have a direct qualitative effect on the nature of the floral anthocyanins, A being responsible for the production of all classes of flavonoid in the flowers and for the production of anthocyanins in pod and leaf axil tissue; the B gene is responsible for the 5 1 -hydroxylation of anthocyanins in the flowers, pods and leaf axils, while the Cr gene was found to be responsible for the 3' - and 5' -methylation of floral anthocyanins and for the determination of rhamnose as the glycosyl substituent at position 3 of such anthocyanins. Further investigations showed that the biochemical effect of the Cr gene is confined to floral tissues, and is not evident in the vegetative tissues such as pods and axils. The other three loci which were known to affect flower colour in Pisum, Am, Ar and Ce, were shown to have quantitative effects on floral anthocyanins, the precise complement being determined by the genotypic constitution with respect to the previously mentioned loci, A, B and Cr, The three quantitative flower colour loci have varying effects in vegetative tissue, which is described in the text. No definite conclusions as to the mode of action of the quantitative loci were reached, but the results obtained suggested that the loci, Ar and Ce, may have their effects by modifying the action of one of the qualitative loci, Cr. During the investigation, a new gene, Cgf, was described, C-glycosyl flavones being present in the standard petals of Pisum in the presence of the dominant allele. Several new combinations of this gene with the previously described flower colour genes were obtained from the crossing programme undertaken, and the chemical screening of these new genotypes showed the dominant Cgf gene to be hypostatic to the recessive a gene. The structure of the standard petal flavones was found to be the same for all genotypes investigated, and the qualitative flower colour loci do not affect the chemical structure of the floral flavones.