Complementary roles of hummingbirds and bees: Pollen pickup, pollen deposition, and fruit production in the distylous Palicourea rigida.

PREMISE: Distyly is a condition in which individual plants in a population express two floral morphs, L- and S-morph, characterized by reciprocal placements of anthers and stigmas between morphs. The function of distyly requires that pollinators collect pollen from L- and S-morphs on different parts along their bodies to then deposit it on the stigmas of the opposite morph, known as legitimate pollination. However, different pollinator groups might differ in the ability to transfer pollen legitimately. METHODS: We investigated patterns of pollen pickup along the body of different functional groups (hummingbirds and bees) using preserved specimens to analyze their role in the reproductive success of Palicourea rigida. We measured pollen deposition on the body of pollinators, on stigmas, and fruit production after a single visit. RESULTS: Pollen from L- and S-flowers appeared segregated on different body parts of the hummingbird and bee used in the study. S-pollen was deposited primarily on the proximal regions (near the head), and L-pollen was placed in the distal regions (tip of the proboscis and bill). Hummingbirds were more efficient at legitimate pollination than bees, particularly to S-stigmas. However, fruit formation after single visits by both pollinators was similar. CONCLUSIONS: The morphology of distylous flowers allows the segregated placement of L-and S-pollen on different body parts of the animal specimens used, facilitating the promotion of legitimate pollen transfer, an observation consistent between the two functional pollinator groups. Also, the results show that full fruit set requires more than one visit.

Incomplete partitioning of pollinators by Linum suffruticosum and its coflowering congeners.

PREMISE: Linum suffruticosum shows variations in pollinator fit, pollen pickup, and local pollinators that predict pollen deposition rates. The species often coflowers with other Linum species using the same pollinators. We investigated whether L. suffruticosum trait variation could be explained by local patterns of pollinator sharing and associated evolution to reduce interspecific pollen transfer. METHODS: Pollinator observations were made in different localities (single species, coflowering with other congeners). Floral traits were measured to detect differences across populations and from coflowering species. Reproductive costs were quantified using interspecific hand pollinations and measures of pollen-tube formation, combined with observations of pollen arrival on stigmas and pollen-tube formation after natural pollination in allopatric and sympatric localities. RESULTS: The size and identity of the most important pollinator of L. suffruticosum and whether there was pollinator sharing with coflowering species appeared to explain floral trait variation related to pollinator fit. The morphological overlap of the flowers of L. suffruticosum with those of coflowering species varied, depending on coflowering species identity. A post-pollination incompatibility system maintains reproductive isolation, but conspecific pollen-tube formation was lower after heterospecific pollination. Under natural pollination at sites of coflowering with congeners, conspecific pollen-tube formation was lower than at single-species localities. CONCLUSIONS: Trait variation in L. suffruticosum appears to respond to the most important local pollinator. Locally, incomplete pollinator partitioning might cause interspecific pollination, imposing reproductive costs. These reproductive costs may generate selection on floral traits for reduced morphological overlap with coflowering congeners, leading to the evolution of pollination ecotypes.

Sexual dimorphism in a dioecious species with complex, specialist-pollinated flowers.

PREMISE: Pollinators with flower constancy and long nectar-feeding organs should favor less or no sexual dimorphism in the individual flowers of dioecious plants. This hypothesis is deduced because such pollinators can discriminate between intersexual flower size differences, and morphological differences between male and female flowers often diminish pollen transfer. METHODS: We compared floral traits and pollinator behavior between male and female flowers in the hawkmoth-pollinated species, Trichosanthes cucumeroides. In field studies, we removed petal fringes on both sexes and observed pollinators to assess the role of elaborate petal fringes in pollinator attraction and pollination success for each flower sex. RESULTS: Female flowers had a similar front flower size and fringe extension as male flowers, supporting our hypothesis. In contrast, females allocated fewer resources to floral biomass. Additionally, they had smaller and narrower petal lobes, lower fringe density, shorter tubes with inferior nectar rewards, and lower display size than males, which is inconsistent with the hypothesis. Nocturnal hawkmoths prefer flowers with long fringe extensions. Fringe removal significantly decreased hawkmoth visitations to both female and male flowers but reduced success only in females. A literature survey indicated that female flowers of specialist-pollinated species are similar in size or larger than the males and thus tend to attract more pollinators compared with female flowers of generalist-pollinated species. CONCLUSIONS: Female flowers have evolved fringe extensions that are similar to those of male flowers, likely increasing pollinator attraction even slightly, and had less biomass in other floral parts and produced less nectar compared with male flowers. Our findings imply that female-biased resource limitation and flower-size sensitivity of pollinators together exert sex-specific selection of floral traits in T. cucumeroides.

Are the floral morphology and anatomy of Galphimia australis, an atypical neotropical Malpighiaceae, associated to a new pollination syndrome?

The flowers of the species of Malpighiaceae in the Neotropical Region are relatively uniform in their morphology due to their dependence on oil-collecting bees as their main pollinators. However, many species of the genus Galphimia seem to have acquired a different floral syndrome, lacking markedly zygomorphic flowers and developed elaiophores in the calyx. Likewise, these species present anthers with great development, probably in response to the selection of pollinators that collect pollen. Galphimia australis incorporated some of these traits but also retained some residual characteristics typical of species pollinated by oil bees. This leads to many questions on how these flowers ensure their pollination. Inquiring about the reduction or modification of these characteristics allows us to understand how G. australis achieves a different pollination syndrome. In this research, we carry out a detailed morphological and anatomical study of the flowers and pollen grain devolvement of G. australis and floral visitors were observed and captured. Results were analyzed in order to determine how this species changed from the oil-floral syndrome, typical of neotropical Malpighiaceae, to one syndrome with pollen as the main reward.

Intraspecific variation in morphology of spiny pollen grains along an altitudinal gradient in an insect-pollinated shrub.

Intraspecific variations in pollen morphological traits are poorly studied. Interspecific variations are often associated with pollination systems and pollinator types. Altitudinal environmental changes, which can influence local pollinator assemblages, provide opportunities to explore differentiation in pollen traits of a single species over short distances. The aim of this study is to examine intraspecific variations in pollen traits of an insect-pollinated shrub, Weigela hortensis (Caprifoliaceae), along an altitudinal gradient. Pollen spine phenotypes (length, number and density), pollen diameter, lipid mass (pollenkitt) around pollen grains, pollen production per flower and pollinator assemblages were compared at four sites at different altitudes. Spine length and the spine length/diameter ratio of pollen grains were greater at higher altitudes but not correlated with flower or plant size. Spine number and density increased as flower size increased, and pollen lipid mass decreased as plant size increased. Bees were the predominant pollinators at low-altitude sites whereas flies, specifically Oligoneura spp. (Acroceridae), increased in relative abundance with increasing altitude. The results of this study suggest that the increase in spine length with altitude was the result of selection favouring longer spines at higher-altitude sites and/or shorter spines at lower-altitude sites. The altitudinal variation in selection pressure on spine length could reflect changes in local pollinator assemblages with altitude.

Sex-specific flower resource use in hummingbird communities.

Research Highlight: Maglianesi, M. A., Maruyama, P. K., Temeles, E. J., Schleuning, M., Zanata, T. B., Sazima, M., Gutiérrez-Zamora, A., Marín-Gómez, O. H., Rosero-Lasprilla, L., Ramírez-Burbano, M. B., Ruffini, A. E., Salamanca-Reyes, J. R., Sazima, I., Nuñez-Rosas, L. E., Arizmendi, M. C., Rahbek, C., & Dalsgaard, B. (2022). Behavioural and morphological traits influence sex-specific floral resource use by hummingbirds across the Americas. Journal of Animal Ecology, 00: 00-00. https://doi.org/10.1111/1365-2656.13746. In their paper on intersexual differences in niche breadth and niche overlap in floral resource use in hummingbird communities, Maglianesi et al. compiled data of plant-hummingbird interactions based on pollen loads, and territoriality and morphological traits for 31 hummingbird species, and investigated whether patterns of resource use by females and males were related to sexual dimorphism and foraging behaviour. While accounting for evolutionary relatedness among species, the authors found a high level of resource partitioning between sexes (broader and more dissimilar floral niche breadth in females) and the sex-specific resource use by hummingbird species was related to territoriality and morphological traits; niche overlap between sexes was greater for territorial than non-territorial species, and lower for species with greater sexual dimorphism in bill curvature. This paper addresses two very timely issues, on the one hand on resource partitioning by sex to reduce intersexual competition in hummingbirds, and on the other hand highlight the much needed information on foraging ecology of female hummingbirds for better understanding of intersexual variation in shaping coexistence and species diversity in hummingbird communities and the interactions between plants and their hummingbird pollinators.

Investigación Destacada: Maglianesi, M. A., Maruyama, P. K., Temeles, E. J., Schleuning, M., Zanata, T. B., Sazima, M., Gutiérrez-Zamora, A., Marín-Gómez, O. H., Rosero-Lasprilla, L., Ramírez-Burbano, M. B., Ruffini, A. E., Salamanca-Reyes, J. R., Sazima, I., Nuñez-Rosas, L. E., Arizmendi, M. C., Rahbek, C., & Dalsgaard, B. (2022). Behavioural and morphological traits influence sex-specific floral resource use by hummingbirds across the Americas. Journal of Animal Ecology, 00: 00-00. https://doi.org/10.1111/1365-2656.13746. En su artículo sobre las diferencias intersexuales en la amplitud de nicho y la superposición de nicho en el uso de recursos florales en las comunidades de colibríes, Maglianesi et al. recopilaron datos de interacciones planta-colibrí basados en cargas de polen, y de territorialidad y rasgos morfológicos para 31 especies de colibríes, e investigaron si los patrones de uso de recursos por parte de hembras y machos estaban relacionados con el dimorfismo sexual y la conducta de forrajeo. Al tener en cuenta la relación evolutiva entre las especies, los autores encontraron un alto nivel de partición de recursos entre sexos (amplitud de nicho floral más amplio y diferente en las hembras) y el uso de recursos específico del sexo por parte de las especies de colibríes estaba relacionado con la territorialidad y los rasgos morfológicos; la superposición de nicho entre sexos fue mayor para las especies territoriales que para las no territoriales, y menor para las especies con mayor dimorfismo sexual en la curvatura del pico. Este artículo aborda dos temas muy oportunos, por un lado, la partición de recursos por sexo para reducir la competencia intersexual en los colibríes y, por otro lado, destaca la necesidad de información sobre la ecología de alimentación de las hembras de los colibríes para una mejor comprensión de la variación intersexual en la conformación de la coexistencia y diversidad de especies en las comunidades de colibríes y las interacciones entre las plantas y sus colibríes polinizadores.

Structural anther mimics improve reproductive success through dishonest signaling that enhances both attraction and the morphological fit of pollinators with flowers.

Numerous studies have identified traits associated with anther mimicry; however, the processes underlying floral deception remain poorly documented for these structures. We studied the importance of pollinator attraction and mechanical fit of anther mimics in Tritonia laxifolia (Iridaceae) and their relative contributions to reproductive success. To determine anther mimics role in attraction, we offered bees' binary choices to flowers painted with UV-absorbent and UV-reflecting paints. We also conducted preference experiments between flowers with excised anther mimics and unmanipulated controls, from which mechanical fit was assessed by allowing single visits. Anther mimics' effects on female reproductive success were determined using similar treatments, but on rooted plants. Bees preferred UV-absorbent over UV-reflecting anther mimics. Bees did not discriminate between flowers with and without three-dimensional anther mimics. Single visits resulted in more pollen deposition on unmanipulated controls over flowers with their anther mimics excised, which was directly linked to pollen-collecting behavior. Controls with unmanipulated anther mimics had higher seed set than those with their anther mimics excised. This study provides insights into pollinator-mediated selection on deceptive floral signals and shows that three-dimensional anther mimics increases reproductive success through both attraction and pollen-collecting behaviors.

Behavioural and morphological traits influence sex-specific floral resource use by hummingbirds.

Research on resource partitioning in plant-pollinator mutualistic systems is mainly concentrated at the levels of species and communities, whereas differences between males and females are typically ignored. Nevertheless, pollinators often show large sexual differences in behaviour and morphology, which may lead to sex-specific patterns of resource use with the potential to differentially affect plant reproduction and diversification. We investigated variation in behavioural and morphological traits between sexes of hummingbird species as potential mechanisms underlying sex-specific flower resource use in ecological communities. To do so, we compiled a dataset of plant-hummingbird interactions based on pollen loads for 31 hummingbird species from 13 localities across the Americas, complemented by data on territorial behaviour (territorial or non-territorial) and morphological traits (bill length, bill curvature, wing length and body mass). We assessed the extent of intersexual differences in niche breadth and niche overlap in floral resource use across hummingbird species. Then, we tested whether floral niche breadth and overlap between sexes are associated with sexual dimorphism in behavioural or morphological traits of hummingbird species while accounting for evolutionary relatedness among the species. We found striking differences in patterns of floral resource use between sex. Females had a broader floral niche breadth and were more dissimilar in the plant species visited with respect to males of the same species, resulting in a high level of resource partitioning between sexes. We found that both territoriality and morphological traits were related to sex-specific resource use by hummingbird species. Notably, niche overlap between sexes was greater for territorial than non-territorial species, and moreover, niche overlap was negatively associated with sexual dimorphism in bill curvature across hummingbird species. These results reveal the importance of behavioural and morphological traits of hummingbird species in sex-specific resource use and that resource partitioning by sex is likely to be an important mechanism to reduce intersexual competition in hummingbirds. These findings highlight the need for better understanding the putative role of intersexual variation in shaping patterns of interactions and plant reproduction in ecological communities.

La investigación sobre la partición de recursos en los sistemas mutualistas planta-polinizador se concentra principalmente en los niveles de especies y comunidades, mientras que las diferencias entre machos y hembras suelen ser ignoradas. Sin embargo, los polinizadores suelen mostrar grandes diferencias sexuales en su comportamiento y morfología, lo que puede dar lugar a patrones específicos de uso de recursos para cada sexo con el potencial de afectar de forma diferencial la reproducción y la diversificación de las plantas. Se estudió la variación en los rasgos de comportamiento y morfológicos entre sexos de las especies de colibríes como posibles mecanismos que explican el uso de recursos florales específicos para cada sexo en las comunidades ecológicas. Para ello, se recopiló un conjunto de datos de interacciones planta-colibrí con base en las cargas de polen de 31 especies de colibríes de 13 localidades en las Américas, además de datos sobre su comportamiento territorial (territorial o no territorial) y rasgos morfológicos (longitud y curvatura del pico, longitud del ala y masa corporal). Se evaluaron las diferencias intersexuales en la amplitud y el solapamiento del nicho en el uso de los recursos florales para las distintas especies de colibríes. Posteriormente, se comprobó si la amplitud del nicho floral y el solapamiento entre sexos están asociados con el dimorfismo sexual en los rasgos de comportamiento o morfológicos de las especies de colibríes, teniendo en cuenta el parentesco evolutivo entre las especies. Se encontraron diferencias notables en los patrones de uso de los recursos florales entre sexos. Las hembras presentaron una mayor amplitud de nicho floral y fueron más disímiles en las especies de plantas visitadas con respecto a los machos de la misma especie, lo que resultó en un alto nivel de partición de recursos entre los sexos. Se encontró que tanto la territorialidad como los rasgos morfológicos están relacionados con el uso de recursos específicos por sexo en las especies de colibríes. En particular, el solapamiento de nicho entre sexos fue mayor para las especies territoriales que para las no territoriales y, además, el solapamiento de nicho se asoció negativamente con el dimorfismo sexual en la curvatura del pico en las especies de colibríes. Estos resultados revelan la importancia de los rasgos conductuales y morfológicos de las especies de colibríes en el uso de recursos según el sexo y que la partición de recursos entre sexos es probablemente un mecanismo importante para reducir la competencia intersexual en los colibríes. Estos resultados ponen de manifiesto la necesidad de comprender mejor el rol que tiene la variación intersexual en los patrones de interacción y en la reproducción de las plantas en las comunidades ecológicas.

Reproductive biology of an endangered lithophytic shrub and implications for its conservation.

BACKGROUND: Plants in cliff habitats may evolve specific reproductive strategies to cope with harsh environments, and unraveling these reproductive characteristics can improve our understanding of survival strategies and lithophyte evolution. This understanding is especially important for efforts to protect rare and endemic plants. Here, we investigated the reproductive biology of Lonicera oblata, an endangered lithophytic shrub that is scattered in highly fragmented and isolated cliff habitats of the Taihang and Yan mountains in North China. RESULTS: Flowers of L. oblata are herkogamous and protandrous, characteristics that can prevent autogamy at the single-flower level, and insects are necessary for pollination. The outcrossing index, pollen/ovule ratio, and the results of hand pollination were measured and all revealed a mixed mating system for L. oblata, that combines cross-fertilization and partial self-fertilization. The floral traits of L. oblata of zygomorphic and brightly yellowish corolla, heavy fragrance, and rich nectar, suggest an entomophilous pollination system. Sweat bees were observed as the most effective pollinators but their visiting frequencies were not high. Pollen limitation may limit the reproductive success of L. oblata. CONCLUSIONS: We determined the reproductive characteristics of L. oblata, a critically endangered species endemic to cliffs in North China, providing insight into its endangerment and suggesting conservation strategies. L. oblata has highly pollinator-dependent self-fertilization as part of a mixed mating system. Floral features such as low-flowering synchrony, asynchronous anthers dehiscence, and high duration of stigma receptivity, improve pollination efficiency in the case of low pollinator service. Our work provides reference information to understand the survival strategies and conservation of L. oblata and other lithophytes.

Flower morphology and plant-bee pollinator interactions are related to stamen dimorphism in Melastomataceae.

Approximately 20,000 species of flowering plant offer mainly pollen to their pollinators, generally bees. Stamen dimorphism, a floral trait commonly present in some pollen flowers, is thought to be associated with exclusive pollen provision for highly effective bee pollinators. Notwithstanding, little is known about how stamen dimorphism is related to other floral morphological traits and, consequently, plant-pollinator interactions at the community scale. Here we investigated the relationship between stamen dimorphism and other floral morphological traits, as well as the interactions with pollinators in plants of Melastomataceae. We characterized each plant species as stamen dimorphic or stamen isomorphic according to differences in size and shape between stamen sets. Data on interactions between the plants and their bee pollinators were analysed as quantitative bipartite networks. We found that petal and style size and shape were correlated to stamen dimorphism. Stamen dimorphic species present larger flowers and less variable style shapes than stamen isomorphic species. Furthermore, stamen dimorphism is associated with higher richness of visiting bees, i.e. higher ecological generalization. During the evolutionary history of Melastomataceae, the dependence on pollinators for fruit set has possibly favoured the evolution of larger flowers with dimorphic stamens, which in turn are able to make use of a larger spectrum of pollen-collecting bees, leading to ecological generalization.

Floral anatomy, embryology, seed, and fruit development in Cephalanthus (Naucleeae-Rubiaceae), with emphasis on C. glabratus.

Information on the reproductive anatomy in genera of the tribe Naucleeae, particularly Cephalanthus, is scarce and fragmented. Of the six species in the genus, only the mature megagamethophyte of Cephalanthus occidentalis has been described. This study aims to provide information on embryological aspects in flowers of C. glabratus and to analyze the morphology and anatomy of the flowers, fruit, and seed in the six species of the genus. Cephalanthus glabratus have imperfect flowers: pistillate (PF) and staminate (SF). In the PF, the ovules are functional, while in the SF, they atrophy during the formation of the embryo sac. The mature ovule has a single integument, corresponds to the Phyllis type and the embryo sac is a Polygonum type, forming only in the PF. The presence of pollenkitt and secondary presentation of pollen were observed in the SF, as well as in the pollen formation previously described, whereas in the PF, they are absent, due to the collapse of the pollen grains inside the indehiscent anthers. The analysis of the ontogeny of the ovular excrescence in C. glabratus determined its funicular origin, calling it an aril. Its development is a pre-anthesis event, initiated during megasporogenesis. In seeds, the aril is a fleshy, white appendage which almost completely envelops the seeds of Cephalanthus, except for Cephalanthus natalensis where it is noticeably more reduced. Studies of the fruit in Cephalanthus species indicate that the infructescence is a dry schizocarp which separates into uni-seminated mericarps, except in C. natalensis that has fleshy indehiscent fruit.

Female self-incompatibility type in heterostylous Primula is determined by the brassinosteroid-inactivating cytochrome P450 CYP734A50.

Most flowering plants are hermaphrodites, with flowers having both male and female reproductive organs. One widespread adaptation to limit self-fertilization is self-incompatibility (SI), where self-pollen fails to fertilize ovules.1,2 In homomorphic SI, many morphologically indistinguishable mating types are found, although in heteromorphic SI, the two or three mating types are associated with different floral morphologies.3-6 In heterostylous Primula, a hemizygous supergene determines a short-styled S-morph and a long-styled L-morph, corresponding to two different mating types, and full seed set only results from intermorph crosses.7-9 Style length is controlled by the brassinosteroid (BR)-inactivating cytochrome P450 CYP734A50,10 yet it remains unclear what defines the male and female incompatibility types. Here, we show that CYP734A50 also determines the female incompatibility type. Inactivating CYP734A50 converts short S-morph styles into long styles with the same incompatibility behavior as L-morph styles, and this effect can be mimicked by exogenous BR treatment. In vitro responses of S- and L-morph pollen grains and pollen tubes to increasing BR levels could only partly explain their different in vivo behavior, suggesting both direct and indirect effects of the different BR levels in S- versus L-morph stigmas and styles in controlling pollen performance. This BR-mediated SI provides a novel mechanism for preventing self-fertilization. The joint control of morphology and SI by CYP734A50 has important implications for the evolutionary buildup of the heterostylous syndrome and provides a straightforward explanation for why essentially all of the derived self-compatible homostylous Primula species are long homostyles.11.

A Comprehensive Study of the Genus Sanguisorba (Rosaceae) Based on the Floral Micromorphology, Palynology, and Plastome Analysis.

Sanguisorba, commonly known as burnet, is a genus in the family Rosaceae native to the temperate regions of the Northern hemisphere. Five of its thirty species are distributed in Korea: Sanguisorba officinalis, S. stipulata, S. hakusanensis, S. longifolia, and S. tenuifolia. S. officinalis has been designated as a medicinal remedy in the Chinese and Korean Herbal Pharmacopeias. Despite being a valuable medicinal resource, the morphological and genomic information, as well as the genetic characteristics of Sanguisorba, are still elusive. Therefore, we carried out the first comprehensive study on the floral micromorphology, palynology, and complete chloroplast (cp) genome of the Sanguisorba species. The outer sepal waxes and hypanthium characters showed diagnostic value, despite a similar floral micromorphology across different species. All the studied Sanguisorba pollen were small to medium, oblate to prolate-spheroidal, and their exine ornamentation was microechinate. The orbicules, which are possibly synapomorphic, were consistently absent in this genus. Additionally, the cp genomes of S. officinalis, S. stipulata, and S. hakusanensis have been completely sequenced. The comparative analysis of the reported Sanguisorba cp genomes revealed local divergence regions. The nucleotide diversity of trnH-psbA and rps2-rpoC2, referred to as hotspot regions, revealed the highest pi values in six Sanguisorba. The ndhG indicated positive selection pressures as a species-specific variation in S. filiformis. The S. stipulata and S. tenuifolia species had psbK genes at the selected pressures. We developed new DNA barcodes that distinguish the typical S. officinalis and S. officinalis var. longifolia, important herbal medicinal plants, from other similar Sanguisorba species with species-specific distinctive markers. The phylogenetic trees showed the positions of the reported Sanguisorba species; S. officinalis, S. tenuifolia, and S. stipulata showed the nearest genetic distance. The results of our comprehensive study on micromorphology, pollen chemistry, cp genome analysis, and the development of species identification markers can provide valuable information for future studies on S. officinalis, including those highlighting it as an important medicinal resource.

Pistil Mating Type and Morphology Are Mediated by the Brassinosteroid Inactivating Activity of the S-Locus Gene BAHD in Heterostylous Turnera Species.

Heterostyly is a breeding system that promotes outbreeding through a combination of morphological and physiological floral traits. In Turnera these traits are governed by a single, hemizygous S-locus containing just three genes. We report that the S-locus gene, BAHD, is mutated and encodes a severely truncated protein in a self-compatible long homostyle species. Further, a self-compatible long homostyle mutant possesses a T. krapovickasii BAHD allele with a point mutation in a highly conserved domain of BAHD acyl transferases. Wild type and mutant TkBAHD alleles were expressed in Arabidopsis to assay for brassinosteroid (BR) inactivating activity. The wild type but not mutant allele caused dwarfism, consistent with the wild type possessing, but the mutant allele having lost, BR inactivating activity. To investigate whether BRs act directly in self-incompatibility, BRs were added to in vitro pollen cultures of the two mating types. A small morph specific stimulatory effect on pollen tube growth was found with 5 µM brassinolide, but no genotype specific inhibition was observed. These results suggest that BAHD acts pleiotropically to mediate pistil length and physiological mating type through BR inactivation, and that in regard to self-incompatibility, BR acts by differentially regulating gene expression in pistils, rather than directly on pollen.

Pollinators contribute to the maintenance of flowering plant diversity.

Mechanisms that favour rare species are key to the maintenance of diverse communities1-3. One of the most critical tasks for conservation of flowering plant biodiversity is to understand how plant-pollinator interactions contribute to the maintenance of rare species4-7. Here we show that niche partitioning in pollinator use and asymmetric facilitation confer fitness advantage of rarer species in a biodiversity hotspot using phylogenetic structural equation modelling that integrates plant-pollinator and interspecific pollen transfer networks with floral functional traits. Co-flowering species filtered pollinators via floral traits, and rarer species showed greater pollinator specialization leading to higher pollination-mediated male and female fitness than more abundant species. When plants shared pollinator resources, asymmetric facilitation via pollen transport dynamics benefitted the rarer species at the cost of more abundant species, serving as an alternative diversity-promoting mechanism. Our results emphasize the importance of community-wide plant-pollinator interactions that affect reproduction for biodiversity maintenance.

Morpho-Physiological and Transcriptome Changes in Tomato Anthers of Different Developmental Stages under Drought Stress.

Drought limits the growth and productivity of plants. Reproductive development is sensitive to drought but the underlying physiological and molecular mechanisms remain unclear in tomatoes. Here, we investigated the effect of drought on tomato floral development using morpho-physiological and transcriptome analyses. Drought-induced male sterility through abnormal anther development includes pollen abortion, inadequate pollen starch accumulation and anther indehiscence which caused floral bud and opened flower abortions and reduced fruit set/yield. Under drought stress (DS), pollen mother cell to meiotic (PMC-MEI) anthers survived whereas tetrad to vacuolated uninucleate microspore (TED-VUM) anthers aborted. PMC-MEI anthers had lower ABA increase, reduced IAA and elevated sugar contents under DS relative to well-watered tomato plants. However, TED-VUM anthers had higher ABA increase and IAA levels, and lower accumulation of soluble sugars, indicating abnormal carbohydrate and hormone metabolisms when exposed to drought-stress conditions. Moreover, RNA-Seq analysis identified altogether >15,000 differentially expressed genes that were assigned to multiple pathways, suggesting that tomato anthers utilize complicated mechanisms to cope with drought. In particular, we found that tapetum development and ABA homeostasis genes were drought-induced while sugar utilization and IAA metabolic genes were drought-repressed in PMC-MEI anthers. Our results suggest an important role of phytohormones metabolisms in anther development under DS and provide novel insight into the molecular mechanism underlying drought resistance in tomatoes.

Comparative metabolomics analysis of different sesame (Sesamum indicum L.) tissues reveals a tissue-specific accumulation of metabolites.

BACKGROUND: Sesame (Sesamum indicum L.) leaves, flowers, especially seeds are used in traditional medicine to prevent or cure various diseases. Its seed's market is expanding. However, the other tissues are still underexploited due to the lack of information related to metabolites distribution and variability in the plant. Herein, the metabolite profiles of five sesame tissues (leaves, fresh seeds, white and purple flowers, and fresh carpels) have been investigated using ultra-high-performance liquid chromatography-mass spectrometry (UPLC-MS/MS)-based widely targeted metabolomics analysis platform. RESULTS: In total, 776 metabolites belonging to diverse classes were qualitatively and quantitatively identified. The different tissues exhibited obvious differences in metabolites composition. The majority of flavonoids predominantly accumulated in flowers. Amino acids and derivatives, and lipids were identified predominantly in fresh seeds followed by flowers. Many metabolites, including quinones, coumarins, tannins, vitamins, terpenoids and some bioactive phenolic acids (acteoside, isoacteoside, verbascoside, plantamajoside, etc.) accumulated mostly in leaves. Lignans were principally detected in seeds. 238 key significantly differential metabolites were filtered out. KEGG annotation and enrichment analyses of the differential metabolites revealed that flavonoid biosynthesis, amino acids biosynthesis, and phenylpropanoid biosynthesis were the main differently regulated pathways. In addition to the tissue-specific accumulation of metabolites, we noticed a cooperative relationship between leaves, fresh carpels, and developing seeds in terms of metabolites transfer. Delphinidin-3-O-(6"-O-p-coumaroyl)glucoside and most of the flavonols were up-regulated in the purple flowers indicating they might be responsible for the purple coloration. CONCLUSION: This study revealed that the metabolic processes in the sesame tissues are differently regulated. It offers valuable resources for investigating gene-metabolites interactions in sesame tissues and examining metabolic transports during seed development in sesame. Furthermore, our findings provide crucial knowledge that will facilitate sesame biomass valorization.

Heteranthery.

The stamens within a flower are usually very similar in appearance, although some species possess two or more structurally distinct types that often differ in reproductive function - a feature referred to as heteranthery. In this Quick guide, Spencer Barrett discusses the origins and functions of heteranthery.

A combination of pollen mosaics on pollinators and floral handedness facilitates the increase of outcross pollen movement.

Darwin devoted an entire book to style and stamen polymorphisms, exemplifying the importance of pollen movement efficiency as a selective agent on floral form.1 However, after its publication, his interest was piqued by a description of floral handedness2 or enantiostyly.3 Todd2 described how left- and right-handed Solanum rostratum flowers have styles deflected to the left and right, respectively. Darwin4 wrote to Todd for seeds so that he could "…have the pleasure of seeing the flowers and experimenting on them," but he died just days later on 19 April 1882. More than a century elapsed before the first experiments demonstrated that handedness leads to high rates of outcrossing.5,6 By attaching quantum dots to pollen grains, we tracked pollen movement in Wachendorfia paniculata, which has one stamen on the same side of the style and two deflected in the opposite direction. We found that handedness leads to outcrossing because left- and right-handed morphs place most of their pollen on different sides of the pollinators. However, the partial separation of stamens and style also results in two-dimensional pollen quality mosaics on each side of carpenter bee pollinators, generating hotspots and coldspots of outcrossed pollen. Similar mosaics were not found on honeybee pollinators. Outcrossed pollen receipt was much higher than expected because stigmatic positions are fine-tuned to match the outcross pollen hotspots on carpenter bees. Exploitation of these pollen mosaics enables plants to increase the probability of between-morph (i.e., disassortative), outcross pollen movement beyond the expectations of enantiostyly.

Bene"fit" Assessment in Pollination Coevolution: Mechanistic Perspectives on Hummingbird Bill-Flower Matching.

One of the reasons why flowering plants became the most diverse group of land plants is their association with animals to reproduce. The earliest examples of this mutualism involved insects foraging for food from plants and, in the process, pollinating them. Vertebrates are latecomers to these mutualisms, but birds, in particular, present a wide variety of nectar-feeding clades that have adapted to solve similar challenges. Such challenges include surviving on small caloric rewards widely scattered across the landscape, matching their foraging strategy to nectar replenishment rate, and efficiently collecting this liquid food from well-protected chambers deep inside flowers. One particular set of convergent traits among plants and their bird pollinators has been especially well studied: the match between the shape and size of bird bills and ornithophilous flowers. Focusing on a highly specialized group, hummingbirds, we examine the expected benefits from bill-flower matching, with a strong focus on the benefits to the hummingbird and how to quantify them. Explanations for the coevolution of bill-flower matching include (1) that the evolution of traits by bird-pollinated plants, such as long and thin corollas, prevents less efficient pollinators (e.g., insects) from accessing the nectar and (2) that increased matching, as a result of reciprocal adaptation, benefits both the bird (nectar extraction efficiency) and the plant (pollen transfer). In addition to nectar-feeding, we discuss how interference and exploitative competition also play a significant role in the evolution and maintenance of trait matching. We present hummingbird-plant interactions as a model system to understand how trait matching evolves and how pollinator behavior can modify expectations based solely on morphological matching, and discuss the implications of this behavioral modulation for the maintenance of specialization. While this perspective piece directly concerns hummingbird-plant interactions, the implications are much broader. Functional trait matching is likely common in coevolutionary interactions (e.g., in predator-prey interactions), yet the physical mechanisms underlying trait matching are understudied and rarely quantified. We summarize existing methods and present novel approaches that can be used to quantify key benefits to interacting partners in a variety of ecological systems.