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Biosynthesis of plant pigments: anthocyanins, betalains and ..

Flavonoids include red or blue anthocyanins and white or pale yellow compounds such asrutin, quercitin, and kaempferol (;). Flavonoids in flowers and fruit providevisual cues for animal pollinators and seed dispersers to locate their target. They alsooccur in most other plant parts and in most genera. Flavonoids are located in thecytoplasm and plastids. Like carotenoids and flavonoids in flowers and fruit, betalainsalso are likely to play an important role in attracting animals (). These red-violet (betacyanin) andyellow (betaxanthin) pigments, which are located in the cytoplasm of plant tissue, onlyoccur in about 10 plant families (and always independent of anthocyanins).

Biosynthesis of betalains: Yellow and violet plant pigments

AB - Anthocyanins, betalains, and carotenoids provide nongreen coloration in plants. In addition to adding aesthetic value to ornamental species, plant pigments play important roles in pollination, light harvesting, plant defense, protection against unfavorable environmental conditions, and human health. In leaves, anthocyanins are responsible for most red, burgundy, and purple coloration. In a small number of families, betalains provide red coloration instead of anthocyanins and the occurrence of these two pigment classes is mutually exclusive. Cyanidin glycosides are the most common anthocyanins in vegetative organs. The biosynthesis and regulation of anthocyanins, factors (biotic and abiotic) influencing their accumulation, their putative functions in leaves, and their impact on leaf photosynthesis will be addressed in this chapter. Environmental factors attributed with anthocyanin accumulation include irradiance (both light quality and quantity), UVB radiation, temperature, nutrient deficiency, drought, and high salinity. The major physiological roles attributed to anthocyanins include herbivory defense, photoprotection, free radical scavenging as antioxidants, and regulation of cell osmotic potential (osmoregulation). Red leaves may have lower, equivalent, or higher photosynthetic rates than comparable green leaves, depending upon species and environmental conditions. Foliar anthocyanins localize in epidermal and/or mesophyll cells, and their location may determine their primary function and impact on leaf photosynthetic rate.

Biosynthesis of betalains: yellow and violet plant pigments

In contrast to anthocyanins and carotenoids, the biosynthetic pathway of betalains is only partially understood.

In maize, , , , , and are transcriptionally regulated by three regulatory protein families known as MYB, bHLH, and WD40 (). In particular, in maize seeds, mutations of or have been shown to cause a colorless phenotype, and a mutation in was associated with reduced pigmentation (; ). Similarly, a recent report on showed that white coloration in the petals of resulted from the loss of anthocyanin-specific MYB transcripts, which subsequently caused the loss of expression (). From this, we suggest that the simultaneous reductions of gene expression of the five genes observed in L mutants was likely due to a mutation(s) in one of the regulatory genes in anthocyanin biosynthesis. Furthermore, a novel gene identified in maize (referred to as ) was shown to function as an inhibitor in anthocyanin biosynthesis, and mutants exhibited very intense pigmentation (). This may coincide with our observations and we suggest that the increase of color intensity in the flowers of D mutants might be because of a mutation in one of the inhibitors.

Despite its white flowers, the expression profiles of the eight genes in the RW hybrid were similar and even higher for , , and than those in the SC hybrid. Two notable features were that the expression level of was about 5-fold higher than those from the other hybrids and there was likely to be an interplay between the expression of and . On the basis of our results, the production of white flowers in the RW hybrid could possibly be explained by either or both of the following causes. First, 6 amino acid alterations in the conserved regions of F3H of the RW hybrid compared with those of the SE hybrid suggest a high potential for F3H functional alteration. This could result in the blockage of subsequent anthocyanin biosynthesis and the loss of color pigments (). Second, FLS catalyzes the production of colorless flavonols and competes with DFR in terms of anthocyanin production. Previous studies in white-flowered petunia containing high levels of flavonols demonstrated that the flower color could change from white to pink when either was down-regulated or was overexpressed (). Giving that the CHI2 function was disrupted by premature termination and expression was very low at early floral developmental stages, the level of the catalytic product of CHI could be very low in RW floral tissues. Thus, the white flowers of the RW hybrid could be the result of low expression levels of and high expression levels of , which cause the conversion of color flavonoid intermediates into colorless flavonols. To rule out these possibilities, further study of anthocyanin and flavonol compositions in RW flowers is required. If the RW hybrid exhibited white flowers because of CHI and/or F3H deficiencies, the accumulation of both anthocyanins and flavonols should be greatly reduced, whereas if this white flower phenotype is caused by the up-regulation of , the accumulation of flavonols should be increased and that of anthocyanins should be reduced.

and betalains--characteristics, biosynthesis, ..

- Biosynthesis of plant pigments: anthocyanins, betalains and carotenoids

N2 - Anthocyanins, betalains, and carotenoids provide nongreen coloration in plants. In addition to adding aesthetic value to ornamental species, plant pigments play important roles in pollination, light harvesting, plant defense, protection against unfavorable environmental conditions, and human health. In leaves, anthocyanins are responsible for most red, burgundy, and purple coloration. In a small number of families, betalains provide red coloration instead of anthocyanins and the occurrence of these two pigment classes is mutually exclusive. Cyanidin glycosides are the most common anthocyanins in vegetative organs. The biosynthesis and regulation of anthocyanins, factors (biotic and abiotic) influencing their accumulation, their putative functions in leaves, and their impact on leaf photosynthesis will be addressed in this chapter. Environmental factors attributed with anthocyanin accumulation include irradiance (both light quality and quantity), UVB radiation, temperature, nutrient deficiency, drought, and high salinity. The major physiological roles attributed to anthocyanins include herbivory defense, photoprotection, free radical scavenging as antioxidants, and regulation of cell osmotic potential (osmoregulation). Red leaves may have lower, equivalent, or higher photosynthetic rates than comparable green leaves, depending upon species and environmental conditions. Foliar anthocyanins localize in epidermal and/or mesophyll cells, and their location may determine their primary function and impact on leaf photosynthetic rate.

Anthocyanins, betalains, and carotenoids provide nongreen coloration in plants. In addition to adding aesthetic value to ornamental species, plant pigments play important roles in pollination, light harvesting, plant defense, protection against unfavorable environmental conditions, and human health. In leaves, anthocyanins are responsible for most red, burgundy, and purple coloration. In a small number of families, betalains provide red coloration instead of anthocyanins and the occurrence of these two pigment classes is mutually exclusive. Cyanidin glycosides are the most common anthocyanins in vegetative organs. The biosynthesis and regulation of anthocyanins, factors (biotic and abiotic) influencing their accumulation, their putative functions in leaves, and their impact on leaf photosynthesis will be addressed in this chapter. Environmental factors attributed with anthocyanin accumulation include irradiance (both light quality and quantity), UVB radiation, temperature, nutrient deficiency, drought, and high salinity. The major physiological roles attributed to anthocyanins include herbivory defense, photoprotection, free radical scavenging as antioxidants, and regulation of cell osmotic potential (osmoregulation). Red leaves may have lower, equivalent, or higher photosynthetic rates than comparable green leaves, depending upon species and environmental conditions. Foliar anthocyanins localize in epidermal and/or mesophyll cells, and their location may determine their primary function and impact on leaf photosynthetic rate.

| Betalains are the yellow and violet pigments that substitute anthocyanins in plants belonging to the order Caryophyllales
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Foliar-applied ethephon enhances the ..

Anthocyanins are a group of flavonoid glycosides constituting the major color pigments in flowers and fruit. Anthocyanins are synthesized along with flavonoid biosynthesis through a series of enzymatic reactions that convert chalcone into three major anthocyanidin types: cyanidin (red to magenta), pelargonidin (brick red to scarlet) and delphinidin (purple to violet) (see , for reviews). Structural and regulatory genes are the key controls for the biosynthesis process. Spatial and temporal expression of the structural genes regulated through regulatory proteins dictates the production of anthocyanins in plants ().

BMC Plant Biology BMC series ..

Anthocyanin biosynthesis requires at least six enzymes including chalcone synthase (CHS), chalcone isomerase (CHI), flavanone 3-β-hydroxylase (F3H), dihydroflavonol-4-reductase (DFR), anthocyanidin synthase (ANS) and flavonoid glycosyltransferase. Depending on the plant species, the product of F3H, dihydroflavonol, could be further substituted with hydroxyl groups by flavonoid 3'-hydroxylase (F3'H) and/or flavonoid 3',5'-β-hydroxylase (F3'5'H), generating three dihydroflavonol derivatives as intermediates for three branches of subsequent biosynthesis cascades. This leads to variations in pigment production via the three dihydroflavonols, namely, dihydroquercetin, dihydrokaempferol, and dihydromyricetin, which are then catalyzed by DFR and subsequently ANS, producing cyanidins, pelargonidins and delphinidins, respectively (). Additionally, along with anthocyanin biosynthesis, flavone and flavonol are synthesized through the activity of flavone synthase (FNS) and flavonol synthase (FLS), respectively (; ).

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Many studies have demonstrated the effects of mutations in anthocyanin structural or regulatory genes on anthocyanin pigmentation. Loss-of-function mutations in , , , , and normally cause a block in the biosynthesis, and plants harboring these mutations often produce white flowers or are colorless in tissues that usually contain color pigments (; ; ; ; ). Studies of several yellow-flowered varieties of ornamental plants including and showed that recessive mutations in caused the accumulation of naringenin chalcone, resulting in yellow flowers (; ). However, in some cases, mutations did not result in complete disruption of anthocyanin production because some portion of the CHI substrate, naringenin chalcone, could be spontaneously catalyzed and proceed into the pathway (; ). Mutations in either or in many cases caused color alterations. Studies in roses, and demonstrated that the lack of blue-purple in these plants was due to the loss of , which encodes the key enzyme responsible for delphinidin synthesis (). F3'H switches anthocyanin biosynthesis to red-colored cyanidins and, in some varieties of in which is mutated, anthocyanin biosynthesis proceeds towards pelargonidin production resulting in orange flowers (). Furthermore, certain types of mutation in led to alterations in enzyme specificity towards its substrates. For example, while DFRs from many species such as and have broad specificity to the three types of dihydroflavonol, DFRs from petunia and cannot reduce dihydrokaempferol efficiently and, therefore, cannot produce pelargonidin-based color pigments (; ; ; ).

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