5.7 KiB
| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Basics of blue flower colouration | 1/3 | https://en.wikipedia.org/wiki/Basics_of_blue_flower_colouration | reference | science, encyclopedia | 2026-05-05T13:56:13.307018+00:00 | kb-cron |
Blue flowers are rare in nature, and despite many attempts, blue roses, carnations and chrysanthemums in particular cannot not be produced by conventional breeding techniques. Blue colour in flower petals is caused by delphinidin, a type of anthocyanin, which are a class of flavonoids. The presence of delphinidin is not enough to produce blue color on its own; it must be in a alkaline environment, form a complex with flavones and metal ions, or some other mechanism. Blue color has also been produced through breeding with the anthocynanin rosacyanin. Among gardeners and florists, there exists a colloqial concept known as "true blue", which pertains to flowers that display a pure blue hue and not a black, deep purple, or lavender that could be mistaken for blue.
== Mechanisms ==
Self-association is correlated with the anthocyanin concentration. When concentration is higher we can observe change in the absorbance maximum and increase of colour intensity. Molecules of anthocyanins associate together what results in stronger and darker colour. Co-pigmentation stabilizes and gives protection to anthocyanins in the complexes. Co-pigments are colourless or have slightly yellow colour. Co-pigments usually are flavonoids (flavones, flavonols, flavanones, flavanols), other polyphenols, alkaloids, amino acids or organic acids. The most efficient co-pigments are flavonols like rutin or quercetin and phenolic acids like sinapic acid or ferulic acid. Association of co-pigment with anthocyanin causes bathochromic effect, shift in absorption maximum to higher wavelength, in result we can observe change of the colour from red to blue. This phenomenon is also called bluing effect. We can diversify two types of co-pigmentation, intermolecular and intramolecular. In the first type co-pigment is bound to anthocyanin by non-covalent bond (hydrogen bond, hydrophobic interaction, ionic interaction). In the second type, we can observe covalent acylation of the glycosyl moiety of anthocyanin. Intramolecular co-pigmentation has stronger effect on the colour. This type of protective stacking is called also a sandwich type stacking and is a very common mechanism in the formation of blue flower colour. Ternatin present in Clitoria ternatea (butterfly pea) and phacelianin present in Phacelia campanularia are examples of pigments with intramolecular co-pigmentation.
Metal complexation: Often blue flower colour is correlated with presence of anthocyanins in the complexes with metals ions. Metalloanthocyanins are composed from anthocyanins, flavones and metal ions in the stochiometric amounts of 6:6:2, respectively. Typical metals found in anthocyanin complexes are iron (Fe), Magnesium (Mg), aluminium (Al), copper (Cu), potassium (K) and tin (Sn). The only anthocyanins that can form complexes with metal ions are only cyanidin or delphinidin type, because at least two free hydroxyl groups in the B-ring are necessary to be present. Some flowers such as certain species of Tulipa display blue color only in some petal sections, such as the perianth. In the case of the "Murasakizuisho" variety of Tulipa gesneriana, the blue colored perianths originate from accumulation of iron ions. These iron atoms are likely absorbed early in the plants development. Iron ions may be transported into the vacuole of perianth cells by T. genseriana vacoular iron transporter (TgVit1) activity and complexed for storage in ferritin proteins.
Examples of metalloanthocyanins: Commelinin isolated from Commelina communis contains malonylawobanin (delphinidin type), flavocommelin (as a co-pigment) and magnesium ions in stochiometric ratio 6:6:2.
Nemophilin, isolated from Baby Blue Eyes (Nemophila menziesii), is very structurally similar to commelinin, but its anthocyanin is replaced by a petunidin glycoside. Interestingly, the petal color of Nemophila menziesii changes depending on the metal cation complexed with nemophilin. Complexes with primarily magnesium seem to result in a purple-blue hue in comparison to a mixture of magnesium and iron, which results in a blue color.
Protocyanin is a blue pigment of cornflower (Centaurea cyanus). It is composed from succinylcyanin (anthocyanin), malonylflavone (co-pigment), iron and magnesium anions, and two calcium ions to stabilize the complex. Interestingly, when not in complex with metal ions, it is the same anthocyanin present in red rose petals . Fuzzy metal complex pigments: In the blue coloured flowers, much often instead than metalloanthocyanins we can find non – stoichiometric metal – complex pigments stabilized by co-pigmentation. Those pigments show blue colour only in aqueous solution and are less stable than metalloanthocyanins. Example of this kind of pigment is present in hydrangea sepals. Main anthocyanin here is delphinidin-3-glucoside what should result in the blue flower formation, but cultivars with red and pink flowers are also present. It is known that acidification of soil can cause change of the hydrangea flower colour from red/pink to blue/violet. Explanation of this phenomenon we can find in the molar ratio of co-pigment (acylquninic acid) to anthocyanin, which is much higher in the blue cells, also the level of Al3+ ions is higher in the blue flowers. Additionally, the pH of blue cell is around 4,1 and red is lower around 3,3. This supramolecule is relatively unstable and easily can fall apart in result of change of component concentration or pH conditions, so this can explain why blue colour in hydrangea sepals has low stability.