Flowers regulate the growth and vascular development of the inflorescence rachis in Vitis vinifera L.

The rachis, the structural framework of the grapevine (Vitis vinifera L.) inflorescence (and subsequent bunch), consists of a main axis and one or more orders of lateral branches with the flower-bearing pedicels at their fine tips. The rachis is crucial both for support, and transport from the shoot. Earlier suggestions that the flowers per se affect normal rachis development are investigated further in this study. Different percentages (0, 25, 50, 75 or 100) of flowers were removed manually one week before anthesis on field-grown vines. Treatment effects on subsequent rachis development (curvature, vitality, anatomy, starch deposit) were assessed. Sections, both fixed and embedded, and fresh hand-cut were observed by fluorescence and bright-field optics after appropriate staining. Emphasis was on measurement of changes in cross-sectional area of secondary xylem and phloem, and on maturation of fibres and periderm. Specific defects in rachis development were dependent on the percent and location of flower removal one week prior to anthesis. The rachises curved inwards where most of the flowers were removed. When fully de-flowered, they became progressively necrotic from the laterals back to the primary axes and from the distal to the proximal end of those axes, with a concurrent disorganisation of their anatomy. A few remaining groups of flowers prevented desiccation and abscission of the rachis axes proximal to the group, but not distally. Flower removal (50%) reduced rachis elongation, while 75% removal reduced xylem and phloem area and delayed phloem fibre and periderm development. 75% flower removal did not affect starch present in the rachis during berry development. Developing flowers affect the growth and vitality of the rachis and the development of its vascular and support structures. The extent of these effects depends on the cultivar and the number and position of flowers remaining after some are removed one week before anthesis.

Pollen transfer efficiency and its effect on inflorescence size in deceptive pollination strategies.

Pollination systems differ in pollen transfer efficiency, a variable that may influence the evolution of flower number. Here we apply a comparative approach to examine the link between pollen transfer efficiency and the evolution of inflorescence size in food and sexually deceptive orchids. We examined pollination performance in nine food-deceptive, and eight sexually deceptive orchids by recording pollen removal and deposition in the field. We calculated correlations between reproductive success and flower number (as a proxy for resources allocated during reproductive process), and directional selection differentials were estimated on flower number for four species. Results indicate that sexually deceptive species experience decreased pollen loss compared to food-deceptive species. Despite producing fewer flowers, sexually deceptive species attained levels of overall pollination success (through male and female function) similar to food-deceptive species. Furthermore, a positive correlation between flower number and pollination success was observed in food-deceptive species, but this correlation was not detected in sexually deceptive species. Directional selection differentials for flower number were significantly higher in food compared to sexually deceptive species. We suggest that pollination systems with more efficient pollen transfer and no correlation between pollination success and number of flowers produced, such as sexual deception, may allow the production of inflorescences with fewer flowers that permit the plant to allocate fewer resources to floral displays and, at the same time, limit transpiration. This strategy can be particularly important for ecological success in Mediterranean water-deprived habitats, and might explain the high frequency of sexually deceptive species in these specialised ecosystems.

Self-pollination rate and floral-display size in Asclepias syriaca (Common Milkweed) with regard to floral-visitor taxa.

BACKGROUND: Animals fertilize thousands of angiosperm species whose floral-display sizes can significantly influence pollinator behavior and plant reproductive success. Many studies have measured the interactions among pollinator behavior, floral-display size, and plant reproductive success, but few studies have been able to separate the effects of pollinator behavior and post-pollination processes on angiosperm sexual reproduction. In this study, we utilized the highly self-incompatible pollinium-pollination system of Asclepias syriaca (Common Milkweed) to quantify how insect visitors influenced male reproductive success measured as pollen removal, female reproductive success measured as pollen deposition, and self-pollination rate. We also determined how floral-display size impacts both visitor behavior and self-pollination rate. RESULTS: Four insect taxonomic orders visited A. syriaca: Coleoptera, Diptera, Hymenoptera, and Lepidoptera. We focused on three groups of visitor taxa within two orders (Hymenoptera and Lepidoptera) with sample sizes large enough for quantitative analysis: Apis mellifera (Western Honey Bee), Bombus spp. (bumble bees) and lepidopterans (butterflies and moths). Qualitatively, lepidopterans had the highest pollinator importance values, but the large variability in the lepidopteran data precluded meaningful interpretation of much of their behavior. The introduced A. mellifera was the most effective and most important diurnal pollinator with regard to both pollen removal and pollen deposition. However, when considering the self-incompatibility of A. syriaca, A. mellifera was not the most important pollinator because of its high self-pollination rate as compared to Bombus spp. Additionally, the rate of self-pollination increased more rapidly with the number of flowers per inflorescence in A. mellifera than in the native Bombus spp. CONCLUSIONS: Apis mellifera's high rate of self-pollination may have significant negative effects on both male and female reproductive successes in A. syriaca, causing different selection on floral-display size than native pollinators.

Flower morphology and floral sequence in Artemisia annua (Asteraceae)1.

UNLABELLED: • PREMISE OF THE STUDY: Artemisia annua produces phytochemicals possessing antimalarial, antitumor, anti-inflammatory, and anthelmintic activities. The main active ingredient, artemisinin, is extremely effective against malaria. Breeding to develop cultivars producing high levels of artemisinin can help meet worldwide demand for artemisinin and its derivatives. However, fundamental reproductive processes, such as the sequence of flowering and fertility, are not well understood and impair breeding and seed propagation programs.• METHODS: Capitulum structure and floral sequence were studied using light and scanning electron microscopy to describe inflorescence architecture, floret opening, and seed set.• KEY RESULTS: Florets are minute and born in capitula containing pistillate ray florets and hermaphroditic disk florets. Ray florets have elongated stigmatic arms that extend prior to disk floret opening. Disk florets exhibit protandry. During the staminate phase, pollen is released within a staminate tube and actively presented with projections at the tip of stigmas as the pistil elongates. During the pistillate phase, stigmatic arms bifurcate and reflex. Stigmas are of the dry type and stain positively for polysaccharides, lipids, and an intact cuticle. Floret numbers vary with genotype, and capitula are predominantly composed of disk florets. Both ray and disk florets produce filled seed.• CONCLUSIONS: Gynomonoecy, early opening of ray florets, and dichogamy of disk florets promote outcrossing in A. annua For breeding and seed development, flowering in genotypes can be synchronized under short days according to the floral developmental stages defined. Floret number and percentage seed fill vary with genotype and may be a beneficial selection criterion.

The evolution of sex ratio differences and inflorescence architectures in Begonia (Begoniaceae).

PREMISE OF THE STUDY: A major benefit conferred by monoecy is the ability to alter floral sex ratio in response to selection. In monoecious species that produce flowers of a given sex at set positions on the inflorescence, floral sex ratio may be related to inflorescence architecture. We studied the loci underlying differences in inflorescence architecture between two monoecious Begonia species and related this to floral sex ratios. METHODS: We performed trait comparisons and quantitative trait locus (QTL) mapping in a segregating backcross population between Central American Begonia plebeja and B. conchifolia. We focused on traits related to inflorescence architecture, sex ratios, and other reproductive traits. KEY RESULTS: The inflorescence branching pattern of B. conchifolia was more asymmetric than B. plebeja, which in turn affects the floral sex ratio. Colocalizing QTLs of moderate effect influenced both the number of male flowers and the fate decisions of axillary meristems, demonstrating the close link between inflorescence architecture and sex ratio. Additional QTLs were found for stamen number (30% variance explained, VE) and pollen sterility (12.3% VE). CONCLUSIONS: One way in which Begonia species develop different floral sex ratios is through modifications of their inflorescence architecture. The potential pleiotropic action of QTL on inflorescence branching and floral sex ratios may have major implications for trait evolution and responses to selection. The presence of a single QTL of large effect on stamen number may allow rapid divergence for this key floral trait. We propose candidate loci for stamen number and inflorescence branching for future characterization.

Can floral display size compensate for Allee effects caused by low population abundance and density in Synthyris bullii (Plantaginaceae), a rare species?

PREMISE OF THE STUDY: Conservation seeks to address the issues of small population size, and the reproductive limitations confronting these populations. Sparse, small plant populations often suffer Allee effects such as pollinator limitation. However, some studies show that plants in sparse populations experience reduced resource competition. As a result, these plants may produce larger floral displays, which are also predicted to attract pollinators. The negative impacts from reduced floral quantity may thus be offset by improved floral quality. METHODS: In a 2-yr field study, population abundance and density were quantified for 24 populations of Synthyris bullii (Plantaginaceae), a rare prairie endemic. In each population, data were collected on inflorescence size, fruit/seed set, and seed germination. KEY RESULTS: Inflorescence size had a positive relationship with population inflorescence abundance and density. Fruit set and germination responded positively to floral quality (i.e., flower density). In comparison, seed set showed a positive relationship with only floral quantity (i.e., population abundance). CONCLUSIONS: Contrary to our predictions, inflorescence size and population size were not inversely related. While attractive floral displays in sparse populations potentially compensate in terms of fruit set, population abundance nevertheless plays an important role in seed set. Because floral quality and quantity differ in their ability to explain reproductive outcomes, studies should examine reproduction at several stages, otherwise the impacts of population size may be overlooked. Allee effects manifesting at a critical stage of reproduction, such as seed production, may act as a bottleneck impeding successful recruitment.

Pollination and floral ecology of Arundina graminifolia (Orchidaceae) at the northern border of the species' natural distribution.

Arundina graminifolia is an early successional plant on Iriomote Island, the Ryukyus, Japan, where it is endangered. Populations flower for more than half a year, and many inflorescences bloom for one to several months. The nectarless gullet flowers, which open for up to six days, are self-compatible but cannot self-pollinate spontaneously; thus they rely on pollinating agents for capsule production. Field observations at two habitats identified at least six species of bees and wasps, primarily mate-seeking males of Megachile yaeyamaensis and Thyreus takaonis, as legitimate pollinators. Thus, this orchid is a pollinator generalist, probably owing to its long blooming period and simple flower morphology. Carpenter bees, which were previously reported to pollinate this orchid, frequently visited flowers but were too large to crawl into the labellum chamber and never pollinated the flowers. Extrafloral nectaries on inflorescences attracted approximately 40 insect taxa but were not involved with pollination. Fruit-set ratios at the population level varied spatiotemporally but were generally low (5.2-12.4 %), presumably owing to infrequent flower visits by mate-seeking pollinators and the lack of food rewards to pollinators.

Inflorescence dimorphism, heterodichogamy and thrips pollination in Platycarya strobilacea (Juglandaceae).

BACKGROUND AND AIMS: Unlike other taxa in Juglandaceae or in closely related families, which are anemophilous, Platycarya strobilacea has been suggested to be entomophilous. In Juglandaceae, Juglans and Carya show heterodichogamy, a reproductive strategy in which two morphs coexist in a population and undergo synchronous reciprocal sex changes. However, there has been no study focusing on heterodichogamy in the other six or seven genera, including Platycarya. METHODS: Inflorescence architecture, sexual expression and pollination biology were examined in a P. strobilacea population in Japan. Flowering phenology was monitored daily for 24 trees in 2008 and 27 in 2009. Flower visitors and inhabitants were recorded or collected from different sexes and stages. KEY RESULTS: The population of P. strobilacea showed heterodichogamous phenology with protogynous and duodichogamous-protandrous morphs. This dimorphism in dichogamy was associated with distinct inflorescence morphologies. Thrips pollination was suggested by the frequent presence of thrips with attached pollen grains, the scarcity of other insect visitors, the synchronicity of thrips number in male spikes with the maturation of female flowers, and morphological characters shared with previously reported thrips-pollinated plants. Male spikes went through two consecutive stages: bright yellow and strong-scented M1 stage, and brownish and little-scented M2 stage. The latter contained more thrips, synchronized better with the receptive stage of female flowers of the reciprocal morph and is probably the main period of pollen export. CONCLUSIONS: Platycarya strobilacea is heterodichogamous and thrips-pollinated, both of which are relatively rare conditions in angiosperms. In male spikes of P. strobilacea, there is probably a temporal decoupling of pollinator attraction and pollen export.

Modified leaves with disk-shaped nectaries of Macaranga sinensis (Euphorbiaceae) provide reward for pollinators.

PREMISE OF THE STUDY: Nectar is the most common reward provided by animal-pollinated flowers. Diversity in position and structure of floral nectaries suggests that floral nectar production evolved repeatedly, but the evolutionary origins are not well known. Flowers of the genus Macaranga (Euphorbiaceae) are apetalous and lack floral nectar. Nevertheless, many Macaranga species possess disk-shaped nectaries on their leaves, sought by ants that defend plants from herbivory. In some Macaranga species, similar glands also occur on the bracteoles-modified leaves subtending the flowers. We investigated whether these glands on the bracteoles of M. sinensis are involved in pollination. • METHODS: Flower visitors were captured, and body pollen was examined. The behavior of flower visitors on inflorescences was also observed. Sugar composition of the nectar from bracteoles and leaves was collected and analyzed using high-performance liquid chromatography. • KEY RESULTS: Various bees and flies with body pollen visited both male and female inflorescences, feeding on nectar from the bracteoles and touching anthers and stigmas in the process. Sugar composition of nectar from the bracteoles and the leaves did not differ. • CONCLUSIONS: Macaranga sinensis was pollinated by insects foraging on the disk-shaped nectaries on bracteoles. The similar appearance, position, and sugar composition of nectar suggest that disk-shaped nectaries on bracteoles and leaves are homologous and that nectaries on leaves were recruited to inflorescences to serve floral function in M. sinensis. Having protective mutualism with ants has likely opened an unusual route for the evolution of floral nectar in otherwise non-nectar-producing flowers of M. sinensis.

Adding perches for cross-pollination ensures the reproduction of a self-incompatible orchid.

BACKGROUND: Outcrossing is known to carry genetic advantages in comparison with inbreeding. In many cases, flowering plants develop a self-incompatibility mechanism, along with a floral component adaptation mechanism, to avoid self-pollination and to promote outbreeding. Orchids commonly have a lip in their flower that functions as the a visiting plate for insect pollinators. Aside from the lip, however, many species (including Coelogyne rigida) have sheaths around the axis of inflorescence. The function of these sheaths remains unknown, and has long been a puzzle to researchers. METHODOLOGY/PRINCIPAL FINDINGS: We investigated the function of these sheaths in relation to the lip and the pollinators, as well as their role in the modes of pollination and reproduction of Coelogyne rigida in 30 flowering populations of orchids in the limestone area of Southeast Yunnan, China. We found that self-incompatible C. rigida developed specialized bird perches around the basal axis of inflorescence to attract sunbirds and to complement their behavioral tendency to change foraging locations frequently. This self-incompatibility mechanism operates separately from the floral component adaptation mechanism. This mechanism thus prevents bees from repeatedly visiting the floral lip of the same plant which, in turn, results in autogamy. In this way, instead of preventing autogamy, C. rigida responds to these negative effects through a highly efficient cross-pollination method that successfully transfers pollen to different plants. CONCLUSIONS: The proposed method ensures reproductive success, while offsetting the infertile self-pollination by insects, thereby reducing mating costs and addressing the lack of cross-pollination. The adaptation provides a novel and striking example of structural adaptation that promotes cross-pollination in angiosperms.

[Study on inflorescences microscopic characteristics of five wild medicinal plants from Chrysanthemum genus in Anhui].

OBJECTIVE: To probe into the disparities in the microscopic characteristics of each part of inflorescences of five wild medicinal plants from Chrysanthemum genus in Anhui Province, and explore the correlation between the distribution of plants and ecological environment. METHODS: The transverse sections of peduncles of the five Chrysanthemum species were observed; The surface piles of the involucre, ray flower, and tubular flower were compared; The ultra-morphology of pollen was observed. RESULTS: There were evident differences, which were associated with ecological environment, among the structures of peduncles of the five species. The morphology of non-glandular hairs on the external involucre presented significant differences, but the morphology of non-glandular hairs tended to be similar gradually from the external to the internal layer of the involucre, and the morphology of surface piles of each part of the inflorescences also tended to converge from the external to the internal. The disparities of glandular hairs among different species were their sizes; As for each species, the size of glandular hairs grew bigger from the involucre to ray flower, and to tubular flower, the density of glandular hairs decreased from the external to the internal layer of the involucre, while it increased on ray flower and tubular flower. The ultra-morphology of pollen of C. zawadskii was distinctly different from that of other species, and disparities of pollen morphology also existed between C. nankingense and C. indicum. CONCLUSION: The structure of peduncles and the disparities in morphology of non-glandular hairs on the surface of external involucre can serve as significant basis for differentiating the inflorescences of Chrysanthemum plants. The categorizing of designating C. nankingense as an separate species is supported.

Male gametogenesis and sterility in garlic (Allium sativum L.): barriers on the way to fertilization and seed production.

Commercial cultivars of garlic (Allium sativum) do not produce flowers and seed; hence, information on microgametogenesis and genetic knowledge of this important crop is unavailable. Recently, physiological studies enabled flowering and fertility restoration in garlic bolting genotypes by environmental manipulations, thus broadening of the genetic variation and facilitating genetic studies. The present report provides first detailed description of the development of male gametophytes in 11 garlic genotypes varying in their fertility traits. Morphological and anatomical studies revealed completely fertile genotypes, as well as variation in anther and pollen development and disruption of the male organs and gametes at different developmental stages. Three types of plant sterility were observed, including complete sterility, male sterility and environmentally induced male sterility. The ITS1 and ITS2 regions of rRNA of the studied genotypes proved to be strongly conservative and thus did not correspond with the phenotypic expression of fertility or sterility in garlic. On the other hand, two-dimensional protein separation maps revealed significant differences between fertile and sterile genotypes, as well as between developmental stages of microsporogenesis. Further research is needed to investigate the internal mechanisms and environmental component of garlic sterility, as well as the possible molecular markers of these traits.

Homologies of the flower and inflorescence in the early-divergent grass Anomochloa (Poaceae).

PREMISE OF THE STUDY: The grass subfamily Anomochlooideae is phylogenetically significant as the sister group to all other grasses. Thus, comparison of their structure with that of other grasses could provide clues to the evolutionary origin of these characters. METHODS: We describe the structure, embryology, and development of the flower and partial inflorescence of the monotypic Brazilian grass Anomochloa marantoidea. We compare these features with those of other early-divergent grasses such as Pharus and Streptochaeta and closely related Poales such as Ecdeiocolea. KEY RESULTS: Anomochloa possesses several features that are characteristic of Poaceae, notably a scutellum, a solid style, reduced stamen number, and an ovary with a single ovule that develops into a single indehiscent fruit. Interpretation of floral patterning in Anomochloa is problematic because the ramification pattern of the florets places the bracts and axes in unusual positions relative to the primary inflorescence axis. Our study indicates that there is a single abaxial carpel in Anomochloa, probably due to a cryptic type of pseudomonomery in Anomochloa that resembles the pseudomonomery of other grasses. On the other hand, the Anomochloa flower differs from the "typical" grass flower in lacking lodicules and possessing four stamens, in contrast with the tristaminate condition that characterizes many other grasses. CONCLUSIONS: Using the median part of the innermost bract as a locator, we tentatively homologize the inner bract of the Anomochloa partial inflorescence with the palea of other grasses. In this interpretation, the pattern of monosymmetry due to stamen suppression differs from that of Ecdeiocolea.

Inflorescence architecture affects pollinator behaviour and mating success in Spiranthes sinensis (Orchidaceae).

• Despite the wide inflorescence diversity among angiosperms, the effects of inflorescence architecture (three-dimensional flower arrangement) on pollinator behaviour and mating success have not been sufficiently studied in natural plant populations. • Here, we investigated how inflorescence architecture affected inter- and intra-plant pollinator movements and consequent mating success in a field population of Spiranthes sinensis var. amoena (S. sinensis). In this species, the flowers are helically arranged around the stem, and the degree of twisting varies greatly among individuals. The large variation in inflorescence architecture in S. sinensis results from variation in a single structural parameter, the helical angle (the angular distance between neighbour-flower directions). • The numbers of visits per inflorescence and successive probes per visit by leaf-cutting bees decreased with helical angle, indicating that individual flowers of tightly twisted inflorescences received less visitations. As expected from pollinator behaviour, pollinia removal and fruit set of individual flowers decreased with helical angle. Meanwhile, geitonogamy decreased in tightly twisted inflorescences. • Our novel findings demonstrate that natural variation in inflorescence architecture significantly affects pollinator behaviour and reproductive success, suggesting that inflorescence architecture can evolve under pollinator-mediated natural selection in plant populations. We also discuss how diverse inflorescence architectures may have been maintained in S. sinensis populations.

Floral dimorphism in plant populations with combined versus separate sexes.

BACKGROUND AND AIMS: Dimorphism among floral traits can evolve through variation in selection intensity between female and male performance, especially when sex functions are separated between flowers on a plant (monoecy), or between individuals (dioecy). In animal-pollinated species, male floral traits are predicted to be larger because competition for pollinators should favour larger displays. Floral dimorphism may be greater in dioecious than monoecious populations because of trade-offs between female and male function and opportunities for selfing in hermaphrodites. METHODS: These predictions were tested by surveying flower size, total flowers per inflorescence and daily display size in the insect-pollinated Sagittaria latifolia (Alismataceae). This species is useful for comparative analysis because populations are mostly either monoecious or dioecious. We examined floral dimorphism in 13 monoecious and 16 dioecious populations in eastern North America. KEY RESULTS: Male flowers were significantly larger than female flowers in monoecious and dioecious populations, but there was no evidence for greater flower size dimorphism in dioecious populations despite their larger flower sizes overall. Although inflorescences in both dioecious and monoecious populations produced more male flowers, daily floral displays were significantly larger for female than male function due to more synchronous female flower opening. Daily floral display dimorphism was significantly greater in dioecious populations, due to greater female daily floral displays. There was a positive relationship between mean flower size and total flowers per inflorescence for both sexes in dioecious populations, but no relationship for either sex function in monoecious populations. Flower size dimorphism was positively correlated with the frequencies of females in dioecious populations. CONCLUSIONS: The increased size and number of male flowers and protracted male floral displays in S. latifolia are probably shaped by sexual selection for more effective pollen dispersal.

Influence of inflorescence size on sexual expression and female reproductive success in a monoecious species.

Sex allocation theory forecasts that larger plant size may modify the balance in fitness gain in both genders, leading to uneven optimal male and female allocation. This reasoning can be applied to flowers and inflorescences, because the increase in flower or inflorescence size can differentially benefit different gender functions, and thus favour preferential allocation to specific floral structures. We investigated how inflorescence size influenced sexual expression and female reproductive success in the monoecious Tussilago farfara, by measuring patterns of biomass, and N and P allocation. Inflorescences of T. farfara showed broad variation in sex expression and, according to expectations, allocation to different sexual structures showed an allometric pattern. Unexpectedly, two studied populations had a contrasting pattern of sex allocation with an increase in inflorescence size. In a shaded site, larger inflorescences were female-biased and had disproportionately more allocation to attraction structures; while in an open site, larger inflorescences were male-biased. Female reproductive success was higher in larger, showier inflorescences. Surprisingly, male flowers positively influenced female reproductive success. These allometric patterns were not easily interpretable as a result of pollen limitation when naïvely assuming an unequivocal relationship between structure and function for the inflorescence structures. In this and other Asteraceae, where inflorescences are the pollination unit, both male and female flowers can play a role in pollinator attraction.

Phylogeny of Pyroleae (Ericaceae): implications for character evolution.

Pyroleae (Ericaceae) consist of four genera, all of which are distributed widely in temperate coniferous or sometimes deciduous forests of the Northern Hemisphere. To investigate the phylogenetic relationships among these genera and to explore the evolution of the characteristics of the subfamily, we conducted maximum parsimony and Bayesian analyses with nrDNA ITS and three cpDNA intergenic spacers (atpB-rbcL, trnS-trnG and trnL-trnF). The results from cpDNA and combined cpDNA + ITS data sets strongly support the monophyly of Pyroleae as well as a sister relationship between Pyrola and Moneses-Chimaphila, with Orthilia as the basal lineage. The sister-group relationship between Moneses and Chimaphila is supported by a set of synapomorphies, e.g., single flower, colpate pollen, five bundles in the style, straight fruiting pedicel orientation, complete capsule dehiscence, and the basic chromosome number, x = 13. The Moneses-Chimaphila-Pyrola clade is supported by at least one homologous character of pollen in tetrads. Conflicts associated with the phylogenetic position of Orthilia may imply a hybrid origin for it, and therefore further study is needed.

Morfología, anatomía, ontogenia y composición química de metabolitos secundarios en inflorescencias de Lippia alba (Verbenaceae)

Morphology, anatomy, ontogeny and chemical composition of inflorescences volatile secondary metabolites of Lippia alba (Verbenaceae) at three stages of development. There is an increased interest to know and scientifically validate traditional knowledge of medicinal plants. Lippia alba belongs to Verbenaceae family and has been of interest, not only because of its worldwide extensive distribution, but also for its variable use as antiviral, bactericide, citostatic, analgesic and sedative. To study this, the morphology and ontogeny of Lippia alba inflorescences and the chemical composition of its volatile secondary metabolites were analyzed during three different stages of development. Plants were collected at the experimental crop field in CENIVAM, Bucaramanga, Colombia. The inflorescence’s morphology and ontogeny, and the chemical composition of volatile secondary metabolites were analyzed using a stereoscopic microscope and chromatographic and spectroscopic techniques. Fresh material corresponding to each stage was fixed in F.A.A (formol, acetic acid and alcohol), included in paraffin and cutted in transversal and longitudinal sections. Sections were stained with safranine-fastgreen, photographed and decribed. The chemical composition of volatile secondary metabolites at each ontogenic stage, was extracted by solid phase micro-extraction in the headspace mode and analyzed by gas chromatography coupled to mass spectrometry. Stage I showed a meristematic mass of cells in vegetative apex and bracts, with an outline of floral whorls. In Stage III, the stamens were adnate, epipetals and didynamous, bicarpelar and syncarpic gynoecium, with superior ovary and decurrent stigma. The main secondary metabolites detected were the bicyclosesquiphellandrene followed by carvone, limonene and trans-β-farnesene, that constituted the 78% of the total relative amounts of compounds. Other metabolites such as β-copaene, γ-amorphene and cis-β-guaiene, were reported for the first time in this study. When compared to other studies, morphological differences reported in this study are possibly related to adaptation to environmental conditions or pollinators, which let us suggest that there is no specific ontogenic pattern. Similarly, the qualitative and quantitative variations in the detected compounds could be explained because one or more of them are used as precursors of others. Rev. Biol. Trop. 58 (4): 1533-1548. Epub 2010 December 01.

La especie Lippia alba (Verbenaceae) llama la atención de los investigadores por su amplia distribución en todo el mundo y sus diversas propiedades. Se establecieron tres etapas durante el desarrollo de sus inflorescencias, fueron recolectadas en Bucaramanga, Colombia para analizar los cambios morfoanatómicos. Para ello, las muestras se trataron mediante la técnica safraninafastgreen y se observaron utilizando microscopio óptico convencional. Se realizó el aislamiento de los metabolitos secundarios volátiles usando la técnica de microextracción en fase sólida en el modo headspace (HS-SPME) y su posterior análisis de componentes, mediante cromatografía de gases acoplada a espectrometría de masas (GC-MS). En la Etapa I se observó una masa de células meristemáticas en el ápice vegetativo. En la Etapa II la acción de procesos morfogenéticos dan paso a la formación de los verticilos florales del perianto. En la Etapa III se establecen todos los verticilos florales. Los principales metabolitos secundarios constituyen el 78% de la cantidad relativa total. Ellos son el biciclosesquifelandreno, la carvona, el limoneno y el trans-β-farneseno. Los metabolitos β-copaeno, γ-amorfeno y cis-β-guaieno, no estαn registrados en la bibliografνa revisada. Estos compuestos activos pueden variar de acuerdo con el estado de desarrollo de la planta, la parte empleada para la extracciσn y el mιtodo implementado para ello.

[Morphology, anatomy, ontogeny and chemical composition of inflorescences volatile secondary metabolites of Lippia alba (Verbenaceae) at three stages of development]. / Morfología, anatomía, ontogenia y composición química de metabolitos secundarios en inflorescencias de Lippia alba (Verbenaceae).

There is an increased interest to know and scientifically validate traditional knowledge of medicinal plants. Lippia alba belongs to Verbenaceae family and has been of interest, not only because of its worldwide extensive distribution, but also for its variable use as antiviral, bactericide, citostatic, analgesic and sedative. To study this, the morphology and ontogeny of Lippia alba inflorescences and the chemical composition of its volatile secondary metabolites were analyzed during three different stages of development. Plants were collected at the experimental crop field in CENIVAM, Bucaramanga, Colombia. The inflorescence's morphology and ontogeny, and the chemical composition of volatile secondary metabolites were analyzed using a stereoscopic microscope and chromatographic and spectroscopic techniques. Fresh material corresponding to each stage was fixed in F.A.A (formol, acetic acid and alcohol), included in paraffin and cutted in transversal and longitudinal sections. Sections were stained with safranine-fastgreen, photographed and decribed. The chemical composition of volatile secondary metabolites at each ontogenic stage, was extracted by solid phase micro-extraction in the headspace mode and analyzed by gas chromatography coupled to mass spectrometry. Stage I showed a meristematic mass of cells in vegetative apex and bracts, with an outline of floral whorls. In Stage III. the stamens were adnate, epipetals and didynamous, bicarpelar and syncarpic gynoecium, with superior ovary and decurrent stigma. The main secondary metabolites detected were the bicyclosesquiphellandrene followed by carvone, limonene and trans-beta-farnesene, that constituted the 78% of the total relative amounts of compounds. Other metabolites such as beta-copaene, gamma-amorphene and cis-beta-guaiene, were reported for the first time in this study. When compared to other studies, morphological differences reported in this study are possibly related to adaptation to environmental conditions or pollinators, which let us suggest that there is no specific ontogenic pattern. Similarly, the qualitative and quantitative variations in the detected compounds could be explained because one or more of them are used as precursors of others.