Colors of flowers

Not all carotenoids are hydrocarbons Oxygen containing carotenes called xantho phylls which are often the pigments responsible for the yellow color of flowers are espe cially abundant... 

The bright colors of flowers and the varied hues of autumn leaves have always been a cause for delight, but it was nor until the twentieth century that chemists understood how these colors arise from the presence of organic compounds with common structural features. They discovered how small differences in the structures of the molecules of these compounds can enhance photosynthesis, produce important vitamins, and attract pollinating bees. They now know how the shapes of molecules and the orbitals occupied by their electrons explain the properties of these compounds and even the processes taking place in our eyes that allow us to see them. 

The colors of flowering plants such as hydrangeas are highly sensitive to soil acidity. At pH > 6.5, these showy flowers are deep pink, but at pH < 5, the blossoms are vivid blue. The chemistry of these changes involves complexation of aluminum by pigments that have acidic groups, as the structures show. 

The flavonoids universally occur in vascular plants, in which they are often responsible for the colors of flowers and fruits, although they are also present (often less apparently) in roots, stems, and leaves [10]. The number of possible sources from which these compoimds can be isolated is very large and much useful information on this can be obtained in reviews [10-12]. 

The invention relates to genes encoding proteins having aurone synthase activity involved in the yellow color of flowers. Jerusalem artichoke flower color is due to the aurone compound sulfetin. 

The involvement of metal ions in the color of anthocyanins and flavonoids was discovered almost a century ago, whereby the different colors of flowers originated from the same molecules under different conditions . The crystal structure of the pigment complex affords better understanding of the color and the role of metal ions , where Fe(III) and Mg(II) bind anthocyanins via the catechol moiety and Ca(II) binds flavone glycosides through a vicinal diol on the glycone. 

Fig. 2.5 Malcolmia maritima, the color of flower unaltered by metal exposition. Concerning isolated anthocyanes (probably oenin) from grape (Vitis vinifera), the red pigment does not apparently react with Fe(III) in either water or ethanol but turns dark-purple with Cu(II) and yields a blue precipitate with Pb(ll) acetate (Anderson 1924). It also behaves as a pH indicator. The yellowish-green colour observed in live plants thus can be due to superposition of some chlorosis and formation of blue to blue-red (i.e. purple) complexes possibly some third ligand such as an amino acid also contributes...

Raman left Calcutta in 1933 to become the director of the Indian Institute of Science, in Bangalore, where he remained until 1948. He continued his research on optical and electromechanical phenomena but also worked on a wide range of problems that reflected his fascination with the natural world—diamonds, seashells, and the coloration of flowers and feathers. In 1948 he established the Raman Research Institute in Bangalore, where he continued to carry out research until almost the end of his life. He died on November 21, 1970. see also Spectroscopy. 

The benzopyrylium ion structure is widespread in nature. It is frequently found substituted with a 2-phenyl group, and such structures (3.59) are known as flavylium ions. Various hydroxylated forms, the anthocyanidins, are usually responsible for the beautiful colors of flowers and fruits. An example of such a structure is the reddish-brown pelargonidin chloride (3.60). 

Flower pigments. Term for a subgroup of plant pigments responsible for the manifold colors of flowers. The most important F. p. are the anthocyanins, flav-onoids, carotinoids, and betalains. Yellow colors are caused by flavonoids, carotenoids, and betaxanthins while anthocyans and betacyans (see betalains) are responsible for red, violet, and blue colors. The many color tones result on the one hand from the simultaneous presence of flavonoids and anthocyans (intermo-lecular copigmentation) and on the other hand from intramolecular copigmentation and the formation of chelates between metal salts and anthocyans. 

O. 1 % of dried plant materials). They serve as color filters for photosynthesis in the leaves of plants, giving rise to the yellow and red color of the leaves during fell because they are more slowly degraded than the green chlorophyll. Many Suits such as paprika Capsicum annuum, Solanaceae Table 8) contain various carotenoids. As colors of flowers, carotenoids play a minor role when compared with anthocyanidines and flavonoids nevertheless, they contribute to yellow and red shades in the blossoms and Suits of Rosaceae and Liliaceae. 

Anthocyanins, glycosides of anthocyanidins, such as (1-3), are primarily responsible for the red, blue, and violet colors of flowers and fruits. More than 260 naturally occurring anthocyanins have been described (Harbome, 1991) the techniques for isolation, purification, and characterization of these compounds have been reviewed (Harbome and Grayer, 1988 Strack and Wray, 1989). 

Delphinidin (2) and its derivatives are found frequently in bee-pollinated plants and are typical of families such as the Boraginaceae, Hydrophyllaceae, Polemoniaceae, and Scrophulariaceae. Sometimes the color of flowers of a species apparently varies in response to the type of pollinator present. As an example, one species of Penstemon, a blue, carpenter bee-pollinated species, hybridizes naturally with a red, hummingbird-pollinated species to produce a purple-flowered hybrid. Although normally this hybrid would fall outside the limits that the pollinators of the parental species would pollinate, this purple flowered hybrid is, fortuitously, pollinated by a wasp (Harbome, 1988c). 

The yellow coloration of flowers may be produced by a number of substances, but carotenoids frequently are important among them (Fig. 26.14). Almost all yellow and lemon-yellow flowers contain xanthophylls, such as zeaxanthin (15)... 

It s found [9] that in selection for seed productivity it s possible to receive positive results, using phenotypic selection on following traits coloration of flowers, number of generative shoots, size of flowering heads and inflorescences. Seed production depends heavily upon content of starch in the root crown in the period of flowering (correlation coefficient r = 0.63), content of sugar in nectar (r = 0.78) and presence of pollinators (r = 0.95). 

Heterocycies form the largest class of organic compounds. In fact, many natural products and most drugs contain heterocyclic rings. The colors of flowers and plants, antibiotics known to all as penicillins, compounds that transport the oxygen we breathe to our vital organs, and the components of DNA responsible for the genetic code are all heterocyclic compounds. 

Besides the more restricted occurrences of the red carotenoids and the red to purple betalains and anthraquinones, anthocyanins are largely responsible for the scarlet through purple to blue colors of flowers, fruits, roots and leaves of higher plants, fruit juices, red wines, etc. They are accumulating in the vacuoles of epidermal or subepidermal cells, but may also be confined to the leaf mesophyll. Around 300 different naturally occurring anthocyanins have been reported (27). 

Anthocyanins, which are responsible for the colors of flowers and fruits of higher plants, are the most important group of water-soluble plant pigments. The anthocyanin... 

The carotenoids represent one of the most important and widespread groups of pigments in nature. The structures of some 500 of them are known, and they are responsible for many of the yellow and red colors of flowers, fruits, birds, insects, and other animals. " Carotenoids are synthesized de novo in all organisms except for animals, where the pigments are of dietary origin." Their universal presence in photosynthetic tissues is only noticeable at the onset of leaf senescence, when the chlorophylls disappear. The dramatic changes in color of ripening fruits also reflect the disappearance of chlorophyll and the concomitant, massive increase in carotenoids. 

During the last decade the photochromism of flavylium derivatives has been the object of some attention. [5] This family of compounds comprises anthocyanins, the ubiquitous colorants of flowers and fruits. In spate of the fact that anthocyanins by themselves do not show significant photochromism, many synthetic[5] and also natural[6] flavylium derivatives exhibit a versatile photochemistry. 

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