Biosynthesis of floral scent 2-phenylethanol in rose flowers

Plants emit chemically diverse volatile compounds for attracting pollinators or putting up a chemical defense against herbivores. 2-Phenylethanol (2PE) is one of the abundantly emitted scent compounds in rose flowers. Feeding experiments with l-[²H₈]phenylalanine into rose flowers and subsequent analysis using gas chromatography–mass spectrometry analysis revealed the hypothetical biosynthetic intermediates to [²H₈]-2PE, and the biochemical and genetic analyses elucidated the principal pathway to [²H₈]-2PE. We recently found season-specific 2PE pathway producing [²H₇]-2PE from l-[²H₈]phenylalanine. This is a unique example where the dominant pathway to a specific compound changes with the seasons. This review focuses on the biosynthesis of floral volatiles and their regulation to adapt to the changes in the environment.     

Cloning and characterization of a novel chalcone synthase gene from Phalaenopsis hybrida orchid flowers

Chalcone synthase (CHS, EC 2.3.1.74) is the key enzyme involved in flavonoid and anthocyanin biosynthesis. A complete DNA sequence of chalcone synthase gene designated Pchs1 was isolated by means of usual and then inverse polymerase chain reactions from genomic DNA of an orchid, Phalaenopsis hybrida, cv. Formosa rose. Nucleotide sequence analysis based on alignment with published Phalaenopsis chs cDNA revealed that Pchs1 contained an intact open reading frame of 1173-bp with one 109-bp intron at the conserved site. The deduced polypeptide (PCHS1) from Pchs1 comprised 390 amino acids with a predicted mol wt of 42.5 kD. PCHS1 showed 61–65% identities with CHS from other plants and retained most of the conserved residues. Some putative cis-regulatory elements were present at the 5′ and 3′ flanking regions of Pchs1. Southern blot analysis predicted at least four chs-like genes, thus indicating the presence of a small multigene chs family in P. hybrida. Relative quantitative RT-PCR showed that Pchs1 is expressed in petals at early flower development as well as in lip tissue when the flower has just opened. Published in Russian in Fiziologiya Rastenii, 2006, Vol. 53, No. 2, pp. 250–258. The text was submitted by the authors in English.     

Evolution of floral scent in Clarkia: novel patterns of S-linalool synthase gene expression in the C. breweri flower.

Flowers of Clarkia breweri, an annual plant from the coastal range of California, emit a strong sweet scent of which S-linalool, an acyclic monoterpene, is a major component. Chromosomal, chemical, and morphological data, and the species' geographic distribution, suggest that C. breweri evolved from an extant nonscented species, C. concinna. A cDNA of Lis, the gene encoding S-linalool synthase, was isolated from C. breweri. We show that in C. breweri, Lis is highly expressed in cells of the transmitting tract of the stigma and style and in the epidermal cells of petals, as well as in stamens, whereas in the nonscented C. concinna, Lis is expressed only in the stigma and at a relatively low level. In both species, changes in protein levels parallel changes in mRNA levels, and changes in enzyme activity levels parallel changes in protein levels. The results indicate that in C. breweri, the expression of Lis has been upregulated and its range enlarged to include cells not expressing this gene in C. concinna. These results show how scent can evolve in a relatively simple way without the evolution of highly specialized "scent glands" and other specialized structures. Lis encodes a protein that is structurally related to the family of proteins termed terpene synthases. The protein encoded by Lis is the first member of this family found to catalyze the formation of an acyclic monoterpene.     

花颜色和花气味的量化研究方法

花颜色和花气味是花部构成的重要内容。在已开展的传粉生态学研究中对二者的报道主要是描述性的,而其量化研究可以为揭示传粉机制提供有力的实验证据。本文主要介绍了花颜色的测量和标定方法,包括比色卡、分光色差仪和便携式光谱仪等;花气味的采集方法,包括动态顶空套袋-吸附采集法、吸附-溶剂洗脱法和固相微萃取法等;花气味的检测和分析方法,包括气相色谱-质谱联用仪分析和电子鼻型超速气相色谱仪分析等;以及昆虫行为学实验方法,包括气相色谱-昆虫触角电位联用技术、Y型嗅觉仪和飞行箱实验等。科研人员可以根据实验材料的特点和实验目的选择适合的量化研究方法。     

Diversity and distribution of floral scent

A list of 1719 chemical compounds identified from headspace samples of floral scent is presented. The list has been compiled from some 270 published papers, including analyses of 991 species of flowering plants and a few gymnosperms, a sample including seed plants from 90 families and 38 orders. The compounds belong to seven major compound classes, of which the aliphatics, the benzenoids and phenylpropanoids, and, among the terpenes, the mono- and sesquiterpenes, occur in most orders of seeds plants. C5-branched compounds, irregular terpenes, nitrogen-containing compounds, and a class of miscellaneous cyclic compounds have been recorded in about two-thirds of the orders. Sulfur-containing compounds occur in a third of the orders, whereas diterpenes have been reported from three orders only. The most common single compounds in floral scent are the monoterpenes limonene, (E)-β-ocimene, myrcene, linalool, α- and β-pinene, and the benzenoids benzaldehyde, methyl 2-hydroxybenzoate (methyl salicylate), benzyl alcohol, and 2-phenyl ethanol, which occur in 54–71% of the families investigated so far. The sesquiterpene caryophyllene and the irregular terpene 6-methyl-5-hepten-2-one are also common and occur in more than 50% of the families. Orchidaceae are by far the best investigated family, followed by several families known to have many species with strongly scented flowers, such as Araceae, Arecaceae, Magnoliaceae, and Rosaceae. However, the majority of angiosperm families are still poorly investigated. Relationships between floral scent and pollination, chemistry, evolution, and phylogeny are briefly discussed. It is concluded that floral scent chemistry is of little use for phylogenetic estimates above the genus level, whereas the distribution and combinations of floral scent compounds at species and subspecific levels is a promising field of investigation for the understanding of adaptations and evolutionary processes in angiosperms.     

Abscission of flowers and floral parts

The abscission of inflorescences, flowers, petals, sepals, styles,and stamens is discussed, with emphasis on the anatomy and ultrastructureof the abscission zones, and the role of cell wall degradingenzymes and hormonal control. Shedding of these parts is usuallydue to cell wall dissolution, but abscission of petals, stamens,and styles in some species occurs due to the forces generatedby the growing fruit. Flower abscission is clearly regulatedby ethylene, whilst auxins apparently decrease the sensitivityto ethylene. Petal, style and stamen abscission also seems tobe controlled by endogenous ethylene. Auxin is apparently involvedin abscission of styles and stamens, but in petals its roleis at yet unclear. The ultrastructural data indicate high proteinsynthesis and high secretory activity of material toward cellwalls of abscission zone cells. The physiological evidence indicatesa role of both polygalacturonase and cellulase in cell walldissolution, whilst the role of other cell wall degrading enzymesis still unknown. The physiological processes occurring in thewalls of the separating cells should be distinguished from thoserelating to defence against microbial intrusion, such as depositionof lignin and suberin and tylose formation. Experimentationusing mutants and transgenic plants may aid in separating theseprocesses. Sequencing of the isoenzymes specific for the abscissionzone and a search for abscission zone-specific promoters seemsa requirement for the successful evaluation of the enzymes involvedin cell wall degradation. Key words: Abscission, anatomy, abscission zone, hormonal control, cell wall degrading enzymes, inflorescences     

Anthocyanins from red flowers of Camellia cultivar 'Dalicha'

Five anthocyanins, cyanidin 3-O-(2-O-β-xylopyranosyl-6-O-(Z)-p-coumaroyl)-β-galactopyranoside (2), cyanidin 3-O-(2-O-β-xylopyranosyl-6-O-(E)-p-coumaroyl)-β-galactopyranoside (3), cyanidin 3-O-(2-O-β-xylopyranosyl-6-O-(E)-caffeoyl)-β-galactopyranoside (4), cyanidin 3-O-(2-O-β-xylopyranosyl-6-O-acetyl)-β-galactopyranoside (5), and cyanidin 3-O-(2-O-β-xylopyranosyl-6-O-acetyl)-β-glucopyranoside (6), together with the known cyanidin 3-O-(2-O-β-xylopyranosyl)-β-galactopyranoside (1), were isolated from red flowers of Camellia cultivar ‘Dalicha’ (Camellia reticulata) by chromatography using open columns. Their structures were subsequently determined on the basis of spectroscopic analyses, i.e., ¹H NMR, ¹³C NMR, HMQC, HMBC, HR ESI-MS and UV-vis.     

Anthocyanins from red flowers of Camellia reticulata LINDL

Ten anthocyanins, cyanidin 3-sambubioside, 3-glucoside and their acylated derivatives, cyanidin 3-lathyroside and cyanidin 3-galactoside, were isolated from red flowers of Camellia reticulata. Their structures were determined on the basis of spectroscopic analyses, and the chemotaxonomic distribution of the accumulated anthocyanins in the petals of wild Camellia reticulata and C. pitardii var. yunnanica is discussed.     

A novel ethylene receptor homolog gene isolated from ethylene-insensitive flowers of gladiolus (Gladiolus grandiflora hort.)

Gladiolus is an ethylene insensitive flower whose exogenous ethylene and ethylene inhibitors have no effect on the petal senescence process. To study which processes in gladiolus are associated with changes in ethylene perception, two types of gladiolus genes, named GgERS1a and GgERS1b, respectively, homologous to the Arabidopsis ethylene receptor gene ERS1 were isolated. GgERS1a is conserved in terms of exon numbers and intron positions, whereas GgERS1b is almost same with GgERS1a except lacking 636 nucleotide encoding first and second histidine kinase (HisKA) motifs. The sequence data on full length genomic DNA indicated that both GgERS1a and b were spliced from different genomic DNA. As the result of mRNA expression study, in spite of lacking the two significant motifs, the expression of GgERS1b dramatically changed with advance in petal senescence, whereas the level of GgERS1a expressed highly and constitutively. The result suggests that both the genes possess a significant role for the subfunctionalization process to provide ethylene insensitivity in gladiolus flowers.     

(E)-beta-ocimene and myrcene synthase genes of floral scent biosynthesis in snapdragon: function and expression of three terpene synthase genes of a new terpene synthase subfamily

Snapdragon flowers emit two monoterpene olefins, myrcene and (E)-beta-ocimene, derived from geranyl diphosphate, in addition to a major phenylpropanoid floral scent component, methylbenzoate. Emission of these monoterpenes is regulated developmentally and follows diurnal rhythms controlled by a circadian clock. Using a functional genomics approach, we have isolated and characterized three closely related cDNAs from a snapdragon petal-specific library that encode two myrcene synthases (ama1e20 and ama0c15) and an (E)-beta-ocimene synthase (ama0a23). Although the two myrcene synthases are almost identical (98%), except for the N-terminal 13 amino acids, and are catalytically active, yielding a single monoterpene product, myrcene, only ama0c15 is expressed at a high level in flowers and contributes to floral myrcene emission. (E)-beta-Ocimene synthase is highly similar to snapdragon myrcene synthases (92% amino acid identity) and produces predominantly (E)-beta-ocimene (97% of total monoterpene olefin product) with small amounts of (Z)-beta-ocimene and myrcene. These newly isolated snapdragon monoterpene synthases, together with Arabidopsis AtTPS14 (At1g61680), define a new subfamily of the terpene synthase (TPS) family designated the Tps-g group. Members of this new Tps-g group lack the RRx(8)W motif, which is a characteristic feature of the Tps-d and Tps-b monoterpene synthases, suggesting that the reaction mechanism of Tps-g monoterpene synthase product formation does not proceed via an RR-dependent isomerization of geranyl diphosphate to 3S-linalyl diphosphate, as shown previously for limonene cyclase. Analyses of tissue-specific, developmental, and rhythmic expression of these monoterpene synthase genes in snapdragon flowers revealed coordinated regulation of phenylpropanoid and isoprenoid scent production.     

金花茶花化学成分的研究

采用反复硅胶柱色谱法、Sephadex LH-20柱色谱法、ODS柱色谱法、反复重结晶等方法对金花茶花的化学成分进行分离纯化,并通过理化常数测定和波谱分析等方法进行结构鉴定.从金花茶花的乙醇提取物中分离得到13个化合物,分别鉴定为:槲皮素(1)、槲皮素-7-O-β-D-葡萄糖苷(2)、槲皮素-3-O-β-D-葡萄糖苷(...     

Geographic variation of floral scent in a highly specialized pollination mutualism

Floral scents are important signals for communication between plants and pollinators. Several studies have focused on interspecific variation of these signals, but little is known about intraspecific variation in flower scent, particularly for species with wide geographic distributions. In the highly specific mutualism between Ficus species and their pollinating wasps, chemical mediation is crucial for partner encounter. Several studies show that scents, i.e. blends of volatiles, are species-specific, but no studies address interpopulation variation of scents in fig pollination mutualisms, which often have broad geographic distributions. In this study, using absorption/desorption headspace techniques, we analyzed variation in floral scent composition among three populations of each of two widely distributed Asian Ficus species. We identified more than 100 different volatile organic compounds, predominantly terpenes. In both species, significant differences were found between scent bouquets of East Asian and Indian populations. These differences are discussed in relation to geographical barriers that could disrupt gene exchange between these two areas, thereby isolating Indian populations from those of Eastern Asia.     

Molecular cloning and expression of a novel trehalose synthase gene from Enterobacter hormaechei

Background  

Trehalose synthase (TreS) which converts maltose to trehalose is considered to be a potential biocatalyst for trehalose production. This enzymatic process has the advantage of simple reaction and employs an inexpensive substrate. Therefore, new TreS producing bacteria with suitable enzyme properties are expected to be isolated from extreme environment.     

On the roles of colour and scent in a specialized floral mimicry system

Background and Aims

Sexually deceptive orchids achieve cross-pollination by mimicking the mating signals of female insects, generally hymenopterans. This pollination mechanism is often highly specific as it is based primarily on the mimicry of mating signals, especially the female sex pheromones of the targeted pollinator. Like many deceptive orchids, the Mediterranean species Ophrys arachnitiformis shows high levels of floral trait variation, especially in the colour of the perianth, which is either green or white/pinkinsh within populations. The adaptive significance of perianth colour polymorphism and its influence on pollinator visitation rates in sexually deceptive orchids remain obscure.

Methods

The relative importance of floral scent versus perianth colour in pollinator attraction in this orchid pollinator mimicry system was evaluated by performing floral scent analyses by gas chromatography-mass spectrometry (GC-MS) and behavioural bioassays with the pollinators under natural conditions were performed.

Key Results

The relative and absolute amounts of behaviourally active compounds are identical in the two colour morphs of O. arachnitiformis. Neither presence/absence nor the colour of the perianth (green versus white) influence attractiveness of the flowers to Colletes cunicularius males, the main pollinator of O. arachnitiformis.

Conclusion

Chemical signals alone can mediate the interactions in highly specialized mimicry systems. Floral colour polymorphism in O. arachnitiformis is not subjected to selection imposed by C. cunicularius males, and an interplay between different non-adaptive processes may be responsible for the maintenance of floral colour polymorphism both within and among populations.