THE GENETICS AND CHEMISTRY OF FLOWER COLOUR VARIATION

Abstract
Summary: 1. The principal flower colouring matters are the anthocyanins, anthoxanthins and carotinoids. Variation in colour depends upon the presence or absence of one or more of these substances, upon structural alterations in their molecules, changes in thep pH of the cell sap, or quantitative changes affecting the amounts of pigment produced.2. Pigment production is genetically controlled, and in a number of cases complementary genes are involved.3. Variation in the amount of any pigment is also gene controlled. Such quantitative differences can be interpreted in terms of the velocity of the reactions involved in pigment production.4. Modifications of the chemical structure of anthocyanins, including the state of oxidation, glycosidal type and probably the degree of methylation are each determined by simple gene relationships. In certain cases reactions are incomplete, giving rise to mixtures of anthocyanins.5. The synthesis of anthocyanins in the plant is correlated with that of anthoxanthins. Some workers consider that the anthocyanins are formed from flavones or flavonols, but the most comprehensive theory, put forward by Robinson, postulates parallel formation of anthocyanin and anthoxanthin from the same intermediate. On this theory cyanidin and quercetin are synthetically the simplest members of their classes, others requiring additional stages of oxidation or reduction. The above view is supported by statistical analysis of the distribution of anthocyanins in flowers, fruits and leaves.6. Heritable chemical differences result in the first place from gene action. They may be accentuated or minimized by gene interaction, which can modify dominance relationships and is sometimes the causal factor of epistasy. A study of gene interaction can also help in the determination of the sequence of gene action.

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