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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Basics of blue flower colouration | 2/3 | https://en.wikipedia.org/wiki/Basics_of_blue_flower_colouration | reference | science, encyclopedia | 2026-05-05T13:56:13.307018+00:00 | kb-cron |
Vacuolar pH influence on flower colour: pH theory was the first concept, that tried to explain the mystery of blue colour formation in flower petals. First observation showed that cyanine extracted from blue cornflower changes the colour in aqueous solution in different pH. In the acidic range pigment was red but in alkaline solution was blue. It leads to conclusion that increase of pH in cell vacuole should cause increase of blue coloration. This phenomenon we can observe in the morning glory (Ipomoea tricolor) and Japanese blue morning glory (Ipomoea nil) petals. During the flower development we can observe change of the flower colour form purple to blue. Morning glory has just one delphinidin type anthocyanin and the composition of it does not change during the flower development, but change of the colour is caused by increase of pH in vacuole of coloured cells from 6.6 in buds to 7.7 in fully matured flowers. During the early stage of development acidic pH is maintained by proton pumps, on the latter stage K+/H+ exchanger is responsible for vacuole alkalization.
== Molecular basis == The anthocyanin biosynthesis pathway is now well known and most of the enzymes are characterized. In the formation of blue pigments a few enzymes have particularly important roles, in particular flavonoid 3'5'-hydroxylase (F3'5'H) and dihydroflavonol 4-reductase (DFR). The flavonoid 3'5'H-hydroxylase is responsible for the introduction of the second and third hydroxyl group in the B-ring of dihydrokaempferol (DHK) or naringenin which are regarded as the main substrates of the reaction. Product of the reaction with DHK is dihydromyricetin (DHM), precursor for synthesis of all delphinidin type anthocyanin. Enzyme is a member of cytochrome P450 protein family (P450s). It is a very diverse group of heme-containing oxidases, which catalyze NADPH- or NADH-dependent oxidation. F3'5'H was classified into CYP75A subfamily. This enzyme appears to be the primary route for blue pigment formation in many plants. Furthermore, interference with F3'5'H expression in plants that natively produce it results in a shift in flower color from purple/blue to red/orange hues Dihydroflavonol 4-reductase is the oxidoreductase that catalyzes in the presence of NADPH the stereospecific reduction of the keto group in position 4 of dihydroflavonols producing colourless leucoanthocyanidins as a precursor for anthocyanin formation. Enzyme can show substrate specificity with respect to the B-ring hydroxylation pattern of the dihydroflavonol and can therefore have an influence on the type of formed anthocyanin. For the blue pigment formation, necessary is enzyme, which accept dihydromyricetin (DHM) as a substrate. Product of DFR reaction with DHM in the following steps of the pathway is converted to delphinidin type blue pigments.
== Cultivation == In some very economically important flowers like roses, carnations and chrysanthemums despite a lot of efforts was not possible to breed the flowers with blue petals coloration. The lack of F3'5'H enzyme and hence delphinidin type anthocyanin is the reason why blue flower colour was not possible to obtain.
=== Blue carnations ===
Delphinidin accumulating carnations (Dianthus caryophyllus) were obtained by overexpression of petunia F3'5'H and DFR in the cultivars, without endogenous DFR activity. As a result, a few cultivars with different purple hue of the flowers were generated. Blue Chrysanthemums Strategies built on using genetic engineering to introduce F3'5'H and therefore blue pigments into chrysanthemums have also led to notable results, with recent work in transgenic chrysanthemums resulting in what may be the first transgenic "true blue" flower development in plants that are F3'5'H-negative. Work in chrysanthemums has shown that not all F3'5'H genes and promoters have the same capacity for delphinidin production when provided through genetic engineering. Overexpression of Campanula F3'5'H however, results in dramatic production of delphinidin in chrysanthemum, resulting in a novel purple phenotype similar to what had been seen in chrysanthemum and roses. True blue flower presentation in chrysanthemums has been genetically engineered through the introduction of the butterfly pea UDP-glucose:anthocyanin 3',5'-O-glucosyltransferase (UA3'5'GT) gene, which allows for production of blue-appearing ternatins from F3'5'H-produced delphinidins. This is C5 ternatin, the simplest ternatin, which is further modified to form other ternatin derivatives. Modifications made to delphinidin in the derivation of ternatins allow for stacking, contributing to a more stable blue color.
=== Blue roses ===