Synthesis of hydroxycinnamic acid esters of betacyanins via 1-O-acylglucosides of hydroxycinnamic acids by protein preparations from cell suspension cultures of Chenopodium rubrum and petals of Lampranthus sociorum

Tecticornia sp. (Samphire)-A Promising Underutilized Australian Indigenous Edible Halophyte

Salinization is gradually increasing over cropping soils and is challenging Governments in many countries, including Australia. There has been a high demand for utilizing arid and semi-arid land for sustainable food production. Currently, the main crops and forage plants are salt sensitive, while halophytes can tolerate a wide range of salinities. Samphire is an Australian indigenous edible halophyte and belongs to the genus Tecticornia. It is an underutilized, succulent plant growing on arid or semi-arid land. Most samphire species have a long history of use as food, but also as non-food (fodder and medicine), among indigenous communities in Australia, while scientific information is limited on their nutritional composition and potential bioactivity. The present study reports, for the first time, the nutritional composition, bioactive compounds (phytochemicals) and antioxidant capacity of six Australian grown samphire from different locations. The results showed that celosianin II and isocelosianin II could be identified as the predominant betalains (phytochemicals) in pigmented samphire species. Proximates and fiber varied significantly (p < 0.05) between the samphire species with a highest value of fiber of 46.8 g/100 g dry weight (DW). Furthermore, samphire could be identified as a valuable source of essential minerals and trace elements, such as iron (41.5 mg/100 g DW), magnesium (1.2 g/100 g DW) and sodium (16.7 g/100 g DW). The fatty acid profile, mainly palmitic, stearic, oleic, linoleic and α-linolenic acid, was similar among the studied species. Total phenolic content and DPPH-radical scavenging capacity were different (p < 0.05) between the six samphire samples. These initial results are very promising and indicate that Australian grown samphire may have the potential to be utilized as a functional food ingredient.

Transcriptomics-based identification and characterization of glucosyltransferases involved in betalain biosynthesis in Hylocereus megalanthus

Pitaya (Hylocereus spp.) is the only commercial cultivation of fruit containing abundant betalains for consumer. Betalains are water-soluble nitrogen-containing pigments with high nutritional value and bioactivities. In this study, contents of betaxanthins and betacyanins were compared between 'Guanhuabai' (H. undatus) and 'Huanglong' (H. megalanthus) pitayas and key genes involved in betalain biosynthesis were screened from 'Huanglong' pitaya by RNA-Seq technology. Twenty-nine candidate genes related to betalain biosynthesis were obtained from the transcriptome data. Based on expression characteristics and sequence analyses, HmB5GT1 and HmHCGT2 were further analyzed. HmB5GT1 and HmHCGT2 were both conserved in 'PSPG-box' and localized in nucleus. Silencing of HmB5GT1 and HmHCGT2 resulted in a significant reduction in betacyanin and betaxanthin contents. Those results suggested that HmB5GT1 and HmHCGT2 are possibly involved in betalain biosynthesis in H. megalanthus. The present work provides new information on betalain biosynthesis in Hylocereus at the transcriptional level.

"La Vie en Rose": Biosynthesis, Sources, and Applications of Betalain Pigments

Betalains are tyrosine-derived red-violet and yellow pigments found exclusively in plants of the Caryophyllales order, which have drawn both scientific and economic interest. Nevertheless, research into betalain chemistry, biochemistry, and function has been limited as comparison with other major classes of plant pigments such as anthocyanins and carotenoids. The core biosynthetic pathway of this pigment class has only been fully elucidated in the past few years, opening up the possibility for betalain pigment engineering in plants and microbes. In this review, we discuss betalain metabolism in light of recent advances in the field, with a current survey of characterized genes and enzymes that take part in betalain biosynthesis, catabolism, and transcriptional regulation, and an outlook of what is yet to be discovered. A broad view of currently used and potential new sources for betalains, including utilization of natural sources or metabolic engineering, is provided together with a summary of potential applications of betalains in research and commercial use.

Transcriptome and Metabolic Profiling Provides Insights into Betalain Biosynthesis and Evolution in Mirabilis jalapa

Betalains are tyrosine-derived pigments that occur solely in one plant order, the Caryophyllales, where they largely replace the anthocyanins in a mutually exclusive manner. In this study, we conducted multi-species transcriptome and metabolic profiling in Mirabilis jalapa and additional betalain-producing species to identify candidate genes possibly involved in betalain biosynthesis. Among the candidates identified, betalain-related cytochrome P450 and glucosyltransferase-type genes, which catalyze tyrosine hydroxylation or (hydroxy)cinnamoyl-glucose formation, respectively, were further functionally characterized. We detected the expression of genes in the flavonoid/anthocyanin biosynthetic pathways as well as their metabolite intermediates in betalain-accumulating M. jalapa flowers, and found that the anthocyanin-related gene ANTHOCYANIDIN SYNTHASE (MjANS) is highly expressed in the betalain-accumulating petals. However, it appears that MjANS contains a significant deletion in a region spanning the corresponding enzyme active site. These findings provide novel insights into betalain biosynthesis and a possible explanation for how anthocyanins have been lost in this plant species. Our study also implies a complex, non-uniform history for the loss of anthocyanin production across betalain producers, previously assumed to be strictly due to diminished expression of anthocyanin-related genes.

The role of acyl-glucose in anthocyanin modifications

Higher plants can produce a wide variety of anthocyanin molecules through modification of the six common anthocyanin aglycons that they present. Thus, hydrophilic anthocyanin molecules can be formed and stabilized by glycosylation and acylation. Two types of glycosyltransferase (GT) and acyltransferase (AT) have been identified, namely cytoplasmic GT and AT and vacuolar GT and AT. Cytoplasmic GT and AT utilize UDP-sugar and acyl-CoA as donor molecules, respectively, whereas both vacuolar GT and AT use acyl-glucoses as donor molecules. In carnation plants, vacuolar GT uses aromatic acyl-glucoses as the glucose donor in vivo; independently, vacuolar AT uses malylglucose, an aliphatic acyl-glucose, as the acyl-donor. In delphinium and Arabidopsis, p-hydroxybenzoylglucose and sinapoylglucose are used in vivo as bi-functional donor molecules by vacuolar GT and AT, respectively. The evolution of these enzymes has allowed delphinium and Arabidopsis to utilize unique donor molecules for production of highly modified anthocyanins.

Sinapate esters in brassicaceous plants: biochemistry, molecular biology, evolution and metabolic engineering

Brassicaceous plants are characterized by a pronounced metabolic flux toward sinapate, produced by the shikimate/phenylpropanoid pathway, which is converted into a broad spectrum of O-ester conjugates. The abundant sinapate esters in Brassica napus and Arabidopsis thaliana reflect a well-known metabolic network, including UDP-glucose:sinapate glucosyltransferase (SGT), sinapoylglucose:choline sinapoyltransferase (SCT), sinapoylglucose:L-malate sinapoyltransferase (SMT) and sinapoylcholine (sinapine) esterase (SCE). 1-O-Sinapoylglucose, produced by SGT during seed development, is converted to sinapine by SCT and hydrolyzed by SCE in germinating seeds. The released sinapate feeds via sinapoylglucose into the biosynthesis of sinapoylmalate in the seedlings catalyzed by SMT. Sinapoylmalate is involved in protecting the leaves against the deleterious effects of UV-B radiation. Sinapine might function as storage vehicle for ready supply of choline for phosphatidylcholine biosynthesis in young seedlings. The antinutritive character of sinapine and related sinapate esters hamper the use of the valuable seed protein of the oilseed crop B. napus for animal feed and human nutrition. Due to limited variation in seed sinapine content within the assortment of B. napus cultivars, low sinapine lines cannot be generated by conventional breeding giving rise to genetic engineering of sinapate ester metabolism as a promising means. In this article we review the progress made throughout the last decade in identification of genes involved in sinapate ester metabolism and characterization of the encoded enzymes. Based on gene structures and enzyme recruitment, evolution of sinapate ester metabolism is discussed. Strategies of targeted metabolic engineering, designed to generate low-sinapate ester lines of B. napus, are evaluated.

Biosynthesis of plant pigments: anthocyanins, betalains and carotenoids

Plant compounds that are perceived by humans to have color are generally referred to as 'pigments'. Their varied structures and colors have long fascinated chemists and biologists, who have examined their chemical and physical properties, their mode of synthesis, and their physiological and ecological roles. Plant pigments also have a long history of use by humans. The major classes of plant pigments, with the exception of the chlorophylls, are reviewed here. Anthocyanins, a class of flavonoids derived ultimately from phenylalanine, are water-soluble, synthesized in the cytosol, and localized in vacuoles. They provide a wide range of colors ranging from orange/red to violet/blue. In addition to various modifications to their structures, their specific color also depends on co-pigments, metal ions and pH. They are widely distributed in the plant kingdom. The lipid-soluble, yellow-to-red carotenoids, a subclass of terpenoids, are also distributed ubiquitously in plants. They are synthesized in chloroplasts and are essential to the integrity of the photosynthetic apparatus. Betalains, also conferring yellow-to-red colors, are nitrogen-containing water-soluble compounds derived from tyrosine that are found only in a limited number of plant lineages. In contrast to anthocyanins and carotenoids, the biosynthetic pathway of betalains is only partially understood. All three classes of pigments act as visible signals to attract insects, birds and animals for pollination and seed dispersal. They also protect plants from damage caused by UV and visible light.

Parameters for cellular viability and membrane function in chenopodium cells show a specific response of extracellular pH to heat shock with extreme Q10

The effect of brief heat shock on Chenopodium cells was investigated by measuring biochemical parameters for cellular vitality, membrane function and integrity: extracellular pH, release of osmotic compounds, phosphatase, protein and betalain, and cellular reduction of DCPIP and MTT. A threshold temperature was found at 45 degrees C, where release of osmotic compounds, protein and betalain, and reduction of DCPIP and MTT indicate loss of vitality. Extracellular pH and an alkaline phosphatase responded 10-20 degrees C below this threshold, suggesting that extracellular alkalinization, and probably the release of a phosphatase, are part of a specific cellular response to abiotic stress induced by heat shock. The extracellular proton concentration did not increase above 45 degrees C: this may indicate equilibration of gradients driving this process or an inactivation of cellular mechanisms responsible for extracellular alkalinization. The response of extracellular pH to heat shock in Chenopodium cell suspensions was fast, i.e., up to +1 pH in 5 min. Addition of the K+/H+ antiporter nigericin to Chenopodium cells caused an extracellular alkalinization similar to heat shock. The heat shock-induced extracellular alkalinization was characterized by Q10 values for distinct ranges of temperature (Q10 of 56 for 24-31 degrees C, 2.3 for 31-42 degrees C, and 1.0 for 42-50 degrees C). To the author's knowledge, the Q10 of 56 is the highest found up to now. These results suggest that extracellular protons are involved in temperature sensing and signalling in plant cells, probably via a channel-mediated pathway.

Amaranthin in feather cockscombs is synthesized via glucuronylation at the cyclo-DOPA glucoside step in the betacyanin biosynthetic pathway

Uridine 5'-diphosphate (UDP)-glucuronic acid: cyclo-DOPA 5-glucoside glucuronosyltransferase activity was detected in a crude extract prepared from the purple flowers of feather cockscombs. This suggests that the glucuronic acid moiety of amaranthin and its derivatives may be introduced at the cyclo-DOPA glucoside step, but not at the betanidin glucoside step.

Identification of betalains from petioles of differently colored Swiss chard (Beta vulgaris L. ssp. cicla [L.] Alef. Cv. Bright Lights) by high-performance liquid chromatography-electrospray ionization mass spectrometry

The betalain pattern of differently colored Swiss chard (Beta vulgaris L. ssp. cicla [L.] Alef. cv. Bright Lights) was investigated for the first time. Nineteen betaxanthins and nine betacyanins were identified by RP-HPLC and positive ion electrospray mass spectrometry, co-injection experiments with semisynthetic reference compounds, and standards derived from authentic plant material, respectively. Histamine-betaxanthin and alanine-betaxanthin were found to be novel betaxanthins, which to the best of our knowledge have not been reported as natural compounds until now. Furthermore, tyramine-betaxanthin (miraxanthin III) and 3-methoxytyramine-betaxanthin, which to date were known only from families other than the Chenopodiaceae, were detected for the first time in colored Swiss chard. The betacyanin pattern of purple petioles was composed of betanin, isobetanin, betanidin, and isobetanidin. Although phyllocactin was present in only trace amounts, further acylated structures such as betanidin-monoferuloyl-5-O-beta-diglucoside and lampranthin II, accompanied by their corresponding C(15)-epimers, were identified. In addition, quantification of betalains and CIE LCh degrees measurements were performed with the colored extracts to correlate the visual appearance with the respective pigment patterns. Besides the novel phytochemical findings, the present study is useful for the evaluation of betalainic Swiss chard as a potential coloring foodstuff.

Betalains of Celosia argentea

The betalains of yellow, orange and red inflorescences of common cockscomb (Celosia argentea var. cristata) were compared and proved to be qualitatively identical to those of feathered amaranth (Celosia argentea var. plumosa). In addition to the known compounds amaranthin and betalamic acid, the structures of three yellow pigments were elucidated to be immonium conjugates of betalamic acid with dopamine, 3-methoxytyramine and (S)-tryptophan by various spectroscopic techniques and comparison to synthesized reference compounds; the latter two are new to plants. Among the betacyanins occurring in yellow inflorescences in trace amounts, the presence of 2-descarboxy-betanidin, a dopamine-derived betacyanin, has been ascertained. The detection of high dopamine concentration may be of toxicological relevance in use of yellow inflorescences as a vegetable and in traditional Chinese medicine, common uses for the red inflorescences of common cockscomb.

Identification and distribution of simple and acylated betacyanins in the Amaranthaceae

Red-colored plants in the family Amaranthaceae are recognized as a rich source of diverse and unique betacyanins. The distribution of betacyanins in 37 species of 8 genera in the Amaranthaceae was investigated. A total of 16 kinds of betacyanins were isolated and characterized by HPLC, spectral analyses, and MS. They consisted of 6 simple (nonacylated) betacyanins and 10 acylated betacyanins, including 8 amaranthine-type pigments, 6 gomphrenin-type pigments, and 2 betanin-type pigments. Acylated betacyanins were identified as betanidin 5-O-beta-glucuronosylglucoside or betanidin 6-O-beta-glucoside acylated with ferulic, p-coumaric, or 3-hydroxy-3-methylglutaric acids. Total betacyanin content in the 37 species ranged from 0.08 to 1.36 mg/g of fresh weight. Simple betacyanins (such as amaranthine, which averaged 91.5% of total peak area) were widespread among all species of 8 genera. Acylated betacyanins were distributed among 11 species of 6 genera, with the highest proportion occurring in Iresine herbstii (79.6%) and Gomphrena globosa (68.4%). Some cultivated species contained many more acylated betacyanins than wild species, representing a potential new source of these pigments as natural colorants.

Production of food related colorants by culture of plant cells. The case of betalains

Betalains are vacuole pigments produced solely by Caryophyllales plants and few superior fungi. For many years, betalains have been used as food colorants. The aim of the present chapter is to present relevant aspects related to betalains characteristics and feasibility of their industrial production in bioreactors.

Betanidin formation from dihydroxyphenylalanine in a model assay system

Formation of betanidin, the aglycone of the red-violet betacyanins, has been demonstrated by a two-step model assay system. In the first step, dihydroxyphenylalanine (Dopa) was incubated with a Dopa dioxygenase preparation from Amanita muscaria, resulting in the formation of 4,5-seco-Dopa that spontaneously recyclized to betalamic acid. In the second step, a tyrosinase preparation from Portulaca grandiflora was added to the Dopa dioxygenase assay, resulting in Dopa oxidation followed by a spontaneous formation of cyclo-Dopa that, in turn, reacted spontaneously with betalamic acid to form betanidin. Thus, two enzymatic reactions, Dopa extradiol ring cleavage by the fungal enzyme and Dopa oxidation by the plant enzyme, initiate three spontaneous steps: the formation of cyclo-Dopa and betalamic acid and finally the condensation of these compounds to betanidin.

Accumulation of phenolic acid conjugates and betacyanins, and changes in the activities of enzymes involved in feruloylglucose metabolism in cell-suspension cultures of Chenopodium rubrum L

Cell-suspension cultures of Chenopodium rubrum accumulate various soluble secondary phenolic metabolites such as the hydroxybenzoic acid glycosides 4-hydroxybenzoic acid-β-glucoside, vanillic acid-β-glucoside, the hydroxycinnamic acid acylglycosides 1-O-(4-coumaroyl)-β-glucose, 1-O-feruloyl-β-glucose, 1-O-sinapoyl-β-glucose and 1-O-feruloyl-(β-1,2-glucuronosyl)-β-glucose, the hydroxycinnamic acid amide N-feruloylaspartate, and the betacyanins betanin, amaranthin and celosianin II. In addition, accumulation of the insoluble cell wall-bound hydroxycinnamic acids with ferulic acid as the major component occurs parallel to culture growth. The changes of three pivotal enzymatic activities, all O-transferases which are involved in the formation of the dominant ferulic acid conjugates, were determined. These are (i) uridine 5'-diphosphate(UDP)glucose-hydroxycinnamic acid O-glucosyltransferase (EC 2.4.1), (ii) UDP-glucuronic acid:1-O-hydroxycin-namoyl-β-glucose O-glucuronosyltransferase (EC 2.4.1) and (iii) 1-O-hydroxycinnamoyl-β-glucose:amaranthin O-hydroxycinnamoyltransferase (EC 2.3.1). The patterns of metabolite accumulation associated with these enzyme activities show that the hydroxycinnamic acid-glucose esters play a central role as metabolically active intermediates in the secondary metabolism of Ch. rubrum. Two cell lines of this culture (CH, CHN), differing in their betacyanin content, were compared with respect to this metabolism. A markedly higher total betacyanin content in the CHN line might possibly be the consequence of an increased supply of the key precursor for betalain biosynthesis, i.e. 3,4-dihydroxyphenylalanine (DOPA). In addition, the enhanced accumulation of celosianin II in the CHN line correlates well with a higher activity of the enzyme catalyzing the transfer of ferulic acid from 1-O-feruloyl-β-glucose to amaranthin.