The relationship between cell division and elongation during development of the nectar-yielding petal spur in Centranthus ruber (Valerianaceae)

Background and Aims Floral spurs are hollow, tubular outgrowths that typically conceal nectar. By their involvement in specialized pollinator interactions, spurs have ecological and evolutionary significance, often leading to speciation. Despite their importance and diversity in shape and size among angiosperm taxa, detailed investigations of the mechanism of spur development have been conducted only recently.Methods Initiation and growth of the nectar-yielding petal spur of Centranthus ruber ‘Snowcloud’ was investigated throughout seven stages, based on bud size and developmental events. The determination of the frequency of cell division, quantified for the first time in spurs, was conducted by confocal microscopy following 4'',6-diamidino-2-phenylindole (DAPI) staining of mitotic figures. Moreover, using scanning electron microscospy of the outer petal spur surface unobstructed by trichomes, morphometry of epidermal cells was determined throughout development in order to understand the ontogeny of this elongate, hollow tube.Key Results Spur growth from the corolla base initially included diffuse cell divisions identified among epidermal cells as the spur progressed through its early stages. However, cell divisions clearly diminished before a petal spur attained 30 % of its final length of 4·5 mm. Thereafter until anthesis, elongation of individual cells was primarily responsible for the spur’s own extension. Consequently, a prolonged period of anisotropy, wherein epidermal cells elongated almost uniformly in all regions along the petal spur’s longitudinal axis, contributed principally to the spur’s mature length.Conclusions This research demonstrates that anisotropic growth of epidermal cells – in the same orientation as spur elongation – chiefly explains petal spur extension in C. ruber. Representing the inaugural investigation of the cellular basis for spur ontogeny within the Euasterids II clade, this study complements the patterns in Aquilegia species (order Ranunculales, Eudicots) and Linaria vulgaris (order Lamiales, Euasterids I), thereby suggesting the existence of a common underlying mechanism for petal spur ontogeny in disparate dicot lineages.     

Are Petals Sterile Stamens or Bracts? The Origin and Evolution of Petals in the Core Eudicots

BACKGROUND: The aim of this paper is to discuss the controversial origins of petals from tepals or stamens and the links between the morphological expression of petals and floral organ identity genes in the core eudicots. SCOPE: I challenge the widely held classical view that petals are morphologically derived from stamens in the core eudicots, and sepals from tepals or bracts. Morphological data suggest that tepal-derived petals have evolved independently in the major lineages of the core eudicots (i.e. asterids, Santalales and rosids) from Berberidopsis-like prototypes, and that staminodial petals have arisen only in few isolated cases where petals had been previously lost (Caryophyllales, Rosales). The clear correlation between continuous changes in petal morphology, and a scenario that indicates numerous duplications to have taken place in genes controlling floral organ development, can only be fully understood within a phylogenetic context. B-gene expression plays a fundamental role in the evolution of the petals by controlling petaloidy, but it does not clarify petal homology. CONCLUSIONS: An increased synorganization of the flower in the core eudicots linked with the establishment of floral whorls restricts the petaloid gene expression to the second whorl, reducing the similarities of petals with tepals from which they were originally derived. An increased flower size linked with secondary polyandry or polycarpelly may lead to a breakdown of the restricted gene expression and a reversal to ancestral characteristics of perianth development. An altered 'sliding boundary' hypothesis is proposed for the core eudicots to explain shifts in petaloidy of the perianth and the event of staminodial petals. The repetitive changes of function in the perianth of the core eudicots are linked with shifts in petaloidy to the outer perianth whorl, or losses of petal or sepal whorls that can be secondarily compensated for by the inclusion of bracts in the flower. The origin and evolution of petals appears to be as complex on a molecular basis as it is from a morphological point of view.     

The evolution of floral nectaries in Disa (Orchidaceae: Disinae): recapitulation or diversifying innovation?

Background and Aims

The Orchidaceae have a history of recurring convergent evolution in floral function as nectar production has evolved repeatedly from an ancestral nectarless state. However, orchids exhibit considerable diversity in nectary type, position and morphology, indicating that this convergence arose from alternative adaptive solutions. Using the genus Disa, this study asks whether repeated evolution of floral nectaries involved recapitulation of the same nectary type or diversifying innovation. Epidermis morphology of closely related nectar-producing and nectarless species is also compared in order to identify histological changes that accompanied the gain or loss of nectar production.

Methods

The micromorphology of nectaries and positionally equivalent tissues in nectarless species was examined with light and scanning electron microscopy. This information was subjected to phylogenetic analyses to reconstruct nectary evolution and compare characteristics of nectar-producing and nectarless species.

Key Results

Two nectary types evolved in Disa. Nectar exudation by modified stomata in floral spurs evolved twice, whereas exudation by a secretory epidermis evolved six times in different perianth segments. The spur epidermis of nectarless species exhibited considerable micromorphological variation, including strongly textured surfaces and non-secreting stomata in some species. Epidermis morphology of nectar-producing species did not differ consistently from that of rewardless species at the magnifications used in this study, suggesting that transitions from rewardlessness to nectar production are not necessarily accompanied by visible morphological changes but only require sub-cellular modification.

Conclusions

Independent nectary evolution in Disa involved both repeated recapitulation of secretory epidermis, which is present in the sister genus Brownleea, and innovation of stomatal nectaries. These contrasting nectary types and positional diversity within types imply weak genetic, developmental or physiological constraints in ancestral, nectarless Disa. Such functional convergence generated by morphologically diverse solutions probably also underlies the extensive diversity of nectary types and positions in the Orchidaceae.     

Evolution of petal epidermal micromorphology in Leguminosae and its use as a marker of petal identity

Background and Aims

The legume flower is highly variable in symmetry and differentiation of petal types. Most papilionoid flowers are zygomorphic with three types of petals: one dorsal, two lateral and two ventral petals. Mimosoids have radial flowers with reduced petals while caesalpinioids display a range from strongly zygomorphic to nearly radial symmetry. The aims are to characterize the petal micromorphology relative to flower morphology and evolution within the family and assess its use as a marker of petal identity (whether dorsal, lateral or ventral) as determined by the expression of developmental genes.

Methods

Petals were analysed using the scanning electron microscope and light microscope. A total of 175 species were studied representing 26 tribes and 89 genera in all three subfamilies of the Leguminosae.

Key Results

The papilionoids have the highest degree of variation of epidermal types along the dorsiventral axis within the flower. In Loteae and genistoids, in particular, it is common for each petal type to have a different major epidermal micromorphology. Papillose conical cells are mainly found on dorsal and lateral petals. Tabular rugose cells are mainly found on lateral petals and tabular flat cells are found only in ventral petals. Caesalpinioids lack strong micromorphological variation along this axis and usually have only a single major epidermal type within a flower, although the type maybe either tabular rugose cells, papillose conical cells or papillose knobby rugose cells, depending on the species.

Conclusions

Strong micromorphological variation between different petals in the flower is exclusive to the subfamily Papilionoideae. Both major and minor epidermal types can be used as micromorphological markers of petal identity, at least in papilionoids, and they are important characters of flower evolution in the whole family. The molecular developmental pathway between specific epidermal micromorphology and the expression of petal identity genes has yet to be established.Key words: Epidermis, Fabaceae, Papilionoideae, Caesalpinioideae, Mimosoideae, petal surface, scanning electron microscopy, papillose conical cells, tabular rugose cells, tabular flat cells, organ identity     

Novel aspects of the flowers and floral pigmentation of two Cleome species (Cleomaceae), C. hassleriana and C. serrulata

Palely pigmented inflorescences of cultivated Cleome hassleriana Chodat (spider flower) have a unique two-toned appearance shown in the present study to be due to a loss of petal pigmentation within 24 h of anthesis, accompanied by an equally unique loss of petal mass. A similar loss occurs in deeply pigmented petals but is less evident to the eye because of the high initial content due to the presence, in the petal mesophyll, of globular anthocyanic vacuolar inclusions (AVIs). Inflorescences of the wild species, Cleome serrulata Pursh. (Rocky Mountain bee flower) are also two-toned because of the deeper pink colour of the unopened bud. No AVIs were seen. The pink colour of the bee flower petals is due to the same five acylated cyanidin glycosides as those previously isolated from mauve petals of spider flower. The structural pattern of the spider flower anthocyanins is shared with at least three genera of the Brassicaceae.     

Intraspecific independent evolution of floral spur length in response to local flower visitor size in Japanese Aquilegia in different mountain regions

Geographic differences in floral traits may reflect geographic differences in effective pollinator assemblages. Independent local adaptation to pollinator assemblages in multiple regions would be expected to cause parallel floral trait evolution, although sufficient evidence for this is still lacking. Knowing the intraspecific evolutionary history of floral traits will reveal events that occur in the early stages of trait diversification. In this study, we investigated the relationship between flower spur length and pollinator size in 16 populations of Aquilegia buergeriana var. buergeriana distributed in four mountain regions in the Japanese Alps. We also examined the genetic relationship between yellow‐ and red‐flowered individuals, to see if color differences caused genetic differentiation by pollinator isolation. Genetic relationships among 16 populations were analyzed based on genome‐wide single‐nucleotide polymorphisms. Even among populations within the same mountain region, pollinator size varied widely, and the average spur length of A. buergeriana var. buergeriana in each population was strongly related to the average visitor size of that population. Genetic relatedness between populations was not related to the similarity of spur length between populations; rather, it was related to the geographic proximity of populations in each mountain region. Our results indicate that spur length in each population evolved independently of the population genetic structure but in parallel in response to local flower visitor size in different mountain regions. Further, yellow‐ and red‐flowered individuals of A. buergeriana var. buergeriana were not genetically differentiated. Unlike other Aquilegia species in Europe and America visited by hummingbirds and hawkmoths, the Japanese Aquilegia species is consistently visited by bumblebees. As a result, genetic isolation by flower color may not have occurred.     

Expression of floral MADS-box genes in Sinofranchetia chinensis (Lardizabalaceae): implications for the nature of the nectar leaves

Background and Aims

The perianths of the Lardizabalaceae are diverse. The second-whorl floral organs of Sinofranchetia chinensis (Lardizabalaceae) are nectar leaves. The aim of this study was to explore the nature of this type of floral organ, and to determine its relationship to nectar leaves in other Ranunculales species, and to other floral organs in Sinofranchetia chinensis.

Methods

Approaches of evolutionary developmental biology were used, including 3′ RACE (rapid amplification of cDNA ends) for isolating floral MADS-box genes, phylogenetic analysis for reconstructing gene evolutionary history, in situ hybridization and tissue-specific RT-PCR for identifying gene expression patterns and SEM (scanning electron microscopy) for observing the epidermal cell morphology of floral organs.

Key Results

Fourteen new floral MADS-box genes were isolated from Sinofranchetia chinensis and from two other species of Lardizabalaceae, Holboellia grandiflora and Decaisnea insignis. The phylogenetic analysis of AP3-like genes in Ranunculales showed that three AP3 paralogues from Sinofranchetia chinensis belong to the AP3-I, -II and -III lineages. In situ hybridization results showed that SIchAP3-3 is significantly expressed only in nectar leaves at the late stages of floral development, and SIchAG, a C-class MADS-box gene, is expressed not only in stamens and carpels, but also in nectar leaves. SEM observation revealed that the adaxial surface of nectar leaves is covered with conical epidermal cells, a hallmark of petaloidy.

Conclusions

The gene expression data imply that the nectar leaves in S. chinensis might share a similar genetic regulatory code with other nectar leaves in Ranunculales species. Based on gene expression and morphological evidence, it is considered that the nectar leaves in S. chinensis could be referred to as petals. Furthermore, the study supports the hypothesis that the nectar leaves in some Ranunculales species might be derived from stamens.     

Why do so many petals have conical epidermal cells?

Background

The conical epidermal cells found on the petals of most Angiosperm species are so widespread that they have been used as markers of petal identity, but their function has only been analysed in recent years. This review brings together diverse data on the role of these cells in pollination biology.

Scope

The published effects of conical cells on petal colour, petal reflexing, scent production, petal wettability and pollinator grip on the flower surface are considered. Of these factors, pollinator grip has been shown to be of most significance in the well-studied Antirrhinum majus/bumble-bee system. Published data on the relationship between epidermal cell morphology and floral temperature were limited, so an analysis of the effects of cell shape on floral temperature in Antirrhinum is presented here. Statistically significant warming by conical cells was not detected, although insignificant trends towards faster warming at dawn were found, and it was also found that flat-celled flowers could be warmer on warm days. The warming observed is less significant than that achieved by varying pigment content. However, the possibility that the effect of conical cells on temperature might be biologically significant in certain specific instances such as marginal habitats or weather conditions cannot be ruled out.

Conclusions

Conical epidermal cells can influence a diverse set of petal properties. The fitness benefits they provide to plants are likely to vary with pollinator and habitat, and models are now required to understand how these different factors interact.     

Within and between Whorls: Comparative Transcriptional Profiling of Aquilegia and Arabidopsis

Background

The genus Aquilegia is an emerging model system in plant evolutionary biology predominantly because of its wide variation in floral traits and associated floral ecology. The anatomy of the Aquilegia flower is also very distinct. There are two whorls of petaloid organs, the outer whorl of sepals and the second whorl of petals that form nectar spurs, as well as a recently evolved fifth whorl of staminodia inserted between stamens and carpels.

Methodology/Principal Findings

We designed an oligonucleotide microarray based on EST sequences from a mixed tissue, normalized cDNA library of an A. formosa x A. pubescens F2 population representing 17,246 unigenes. We then used this array to analyze floral gene expression in late pre-anthesis stage floral organs from a natural A. formosa population. In particular, we tested for gene expression patterns specific to each floral whorl and to combinations of whorls that correspond to traditional and modified ABC model groupings. Similar analyses were performed on gene expression data of Arabidopsis thaliana whorls previously obtained using the Ath1 gene chips (data available through The Arabidopsis Information Resource).

Conclusions/Significance

Our comparative gene expression analyses suggest that 1) petaloid sepals and petals of A. formosa share gene expression patterns more than either have organ-specific patterns, 2) petals of A. formosa and A. thaliana may be independently derived, 3) staminodia express B and C genes similar to stamens but the staminodium genetic program has also converged on aspects of the carpel program and 4) staminodia have unique up-regulation of regulatory genes and genes that have been implicated with defense against microbial infection and herbivory. Our study also highlights the value of comparative gene expression profiling and the Aquilegia microarray in particular for the study of floral evolution and ecology.     

Identification of major quantitative trait loci underlying floral pollination syndrome divergence in Penstemon

Distinct floral pollination syndromes have emerged multiple times during the diversification of flowering plants. For example, in western North America, a hummingbird pollination syndrome has evolved more than 100 times, generally from within insect-pollinated lineages. The hummingbird syndrome is characterized by a suite of floral traits that attracts and facilitates pollen movement by hummingbirds, while at the same time discourages bee visitation. These floral traits generally include large nectar volume, red flower colour, elongated and narrow corolla tubes and reproductive organs that are exerted from the corolla. A handful of studies have examined the genetic architecture of hummingbird pollination syndrome evolution. These studies find that mutations of relatively large effect often explain increased nectar volume and transition to red flower colour. In addition, they suggest that adaptive suites of floral traits may often exhibit a high degree of genetic linkage, which could facilitate their fixation during pollination syndrome evolution. Here, we explore these emerging generalities by investigating the genetic basis of floral pollination syndrome divergence between two related Penstemon species with different pollination syndromes—bee-pollinated P. neomexicanus and closely related hummingbird-pollinated P. barbatus. In an F₂ mapping population derived from a cross between these two species, we characterized the effect size of genetic loci underlying floral trait divergence associated with the transition to bird pollination, as well as correlation structure of floral trait variation. We find the effect sizes of quantitative trait loci for adaptive floral traits are in line with patterns observed in previous studies, and find strong evidence that suites of floral traits are genetically linked. This linkage may be due to genetic proximity or pleiotropic effects of single causative loci. Interestingly, our data suggest that the evolution of floral traits critical for hummingbird pollination was not constrained by negative pleiotropy at loci that show co-localization for multiple traits.     

The floral organogenesis of <Emphasis Type="Italic">Koelreuteria bipinnata</Emphasis> and its variety <Emphasis Type="Italic">K. bipinnata</Emphasis> var. <Emphasis Type="Italic">integrifolia</Emphasis> (Sapindaceae): evidence of floral constraints on the evolution of monosymmetry

The floral organogenesis and anatomy of Koelreuteria bipinnata and its variety K. bipinnata var. integrifolia (Sapindaceae) has been investigated to clarify the identity of the two taxa in relation to other species of Koelreuteria, and to understand the shift to monosymmetry in the genus. Although the floral development is highly similar, we found a number of striking differences. Flowers arise in thyrses, with lateral branches forming cincinni of 5–9 flowers. Sepals initiate in a spiral sequence. Five petals arise unidirectionally alternating to the sepals. The last formed petal and one stamen between sepals 3 and 5 are strongly delayed, appearing as a common primordium, while this petal is completely suppressed in var. integrifoliola. Eight stamens initiate sequentially, differ in size and partly precede the development of petals. The gynoecium develops as a triangular primordium on which three carpellary lobes become demarcated simultaneously. Placentation is axile. Septal slits occurring within the style are interpreted as a deep-reaching non-nectariferous extension of the stigma. The massive, oblique disk with crenate apex develops in an extrastaminal position, but is interrupted on the radius of the lost petal. Floral developmental evidence supports variety K. bipinnata var. integrifolia rather than being synonym of K. bipinnata. Floral development is compared with K. paniculata and is discussed in the context of floral evolution of Sapindaceae. Our study demonstrates the importance of developmental shifts on floral evolution. The triangular gynoecium has a strong spatial impact in obliquely reorganizing the symmetry of the flower. It is demonstrated that spatial constraints of calyx and ovary are responsible for the reduction in one of the petals, two stamens and a shift in symmetry of the flower.     

The diversity of elaborate petals in Isopyreae (Ranunculaceae): a special focus on nectary structure

Elaborate petals are highly diverse in morphology, structure, and epidermal differentiation and play a key role in attracting pollinators. There have been few studies on the elaborate structure of petals in the tribe Isopyreae (Ranunculaceae). Seven genera in Isopyreae (Aquilegia, Semiaquilegia, Urophysa, Isopyrum, Paraquilegia, Dichocarpum, and Leptopyrum) have petals that vary in morphology, and two genera (Enemion and Thalictrum) have no petals. The petals of nine species belonged to 7 genera in the tribe were studied to reveal their nectary structure, epidermal micromorphology and ancestral traits. The petal nectaries of Isopyreae examined in this study were located at the tip of spurs (Aquilegia yabeana and A. rockii), or the bottom of shallow sacs (Semiaquilegia adoxoides, Urophysa henryi, Isopyrum manshuricum, and Paraquilegia microphylla), a cup-shaped structure (Dichocarpum fargesii) and a bilabiate structure (Leptopyrum fumarioides). The petal nectary of eight species in Isopyreae (except A. ecalcarata) was composed of secretory epidermis, nectary parenchyma, and vascular tissues, and some sieve tubes reached the secretory parenchyma cells. Among the eight species with nectaries examined in the present study, A. yabeana had the most developed nectaries, with 10–15 layers of secretory parenchyma cells. The epidermal cells of mature petals of the nine species were divided into 11 types. Among these 11 types, there were two types of secretory cells and two types of trichomes. Aquilegia yabeana and A. rockii had the highest number of cell types (eight types), and I. manshuricum and L. fumarioides had the lowest number of cell types (three types). Aquilegia ecalcarata had no secretory cells, and the papillose conical polygonal secretory cells of D. fargesii were different from those of the other seven species with nectaries. Trichomes were found only in Aquilegia, Semiaquilegia, Urophysa, and Paraquilegia. The ancestral mode of nectar presentation in Isopyreae was petals with hidden nectar (70.58%). The different modes of nectar presentation in petals may reflect adaptations to different pollinators in Isopyreae.

     

Over-expression of the Gerbera hybrida At-SOC1-like1 gene Gh-SOC1 leads to floral organ identity deterioration

Background and Aims

The family of MADS box genes is involved in a number of processes besides controlling floral development. In addition to supplying homeotic functions defined by the ABC model, they influence flowering time and transformation of vegetative meristem into inflorescence meristem, and have functions in roots and leaves. Three Gerbera hybrida At-SOC1-like genes (Gh-SOC1–Gh-SOC3) were identified among gerbera expressed sequence tags.

Methods

Evolutionary relationships between SOC1-like genes from gerbera and other plants were studied by phylogenetic analysis. The function of the gerbera gene Gh-SOC1 in gerbera floral development was studied using expression analysis, protein–protein interaction assays and reverse genetics. Transgenic gerbera lines over-expressing or downregulated for Gh-SOC1 were obtained using Agrobacterium transformation and investigated for their floral phenotype.

Key Results

Phylogenetic analysis revealed that the closest paralogues of At-SOC1 are Gh-SOC2 and Gh-SOC3. Gh-SOC1 is a more distantly related paralogue, grouping together with a number of other At-SOC1 paralogues from arabidopsis and other plant species. Gh-SOC1 is inflorescence abundant and no expression was seen in vegetative parts of the plant. Ectopic expression of Gh-SOC1 did not promote flowering, but disturbed the development of floral organs. The epidermal cells of ray flower petals appeared shorter and their shape was altered. The colour of ray flower petals differed from that of the wild-type petals by being darker red on the adaxial side and greenish on the abaxial surface. Several protein–protein interactions with other gerbera MADS domain proteins were identified.

Conclusions

The At-SOC1 paralogue in gerbera shows a floral abundant expression pattern. A late petal expression might indicate a role in the final stages of flower development. Over-expression of Gh-SOC1 led to partial loss of floral identity, but did not affect flowering time. Lines where Gh-SOC1 was downregulated did not show a phenotype. Several gerbera MADS domain proteins interacted with Gh-SOC1.     

Trends in flower symmetry evolution revealed through phylogenetic and developmental genetic advances

A striking aspect of flowering plant (angiosperm) diversity is variation in flower symmetry. From an ancestral form of radial symmetry (polysymmetry, actinomorphy), multiple evolutionary transitions have contributed to instances of non-radial forms, including bilateral symmetry (monosymmetry, zygomorphy) and asymmetry. Advances in flowering plant molecular phylogenetic research and studies of character evolution as well as detailed flower developmental genetic studies in a few model species (e.g. Antirrhinum majus, snapdragon) have provided a foundation for deep insights into flower symmetry evolution. From phylogenetic studies, we have a better understanding of where during flowering plant diversification transitions from radial to bilateral flower symmetry (and back to radial symmetry) have occurred. From developmental studies, we know that a genetic programme largely dependent on the functional action of the CYCLOIDEA gene is necessary for differentiation along the snapdragon dorsoventral flower axis. Bringing these two lines of inquiry together has provided surprising insights into both the parallel recruitment of a CYC-dependent developmental programme during independent transitions to bilateral flower symmetry, and the modifications to this programme in transitions back to radial flower symmetry, during flowering plant evolution.     

Spatial genetic structure of Aquilegia taxa endemic to the island of Sardinia

Background and Aims

The Mediterranean Basin is one of the most important regions for the Earth''s plant biodiversity; however, the scarcity of studies on fine scale patterns of genetic variation in this region is striking. Here, an assessment is made of the spatial genetic structure of all known locations of the three Sardinian endemic species of Aquilegia in order to determine the relative roles of gene flow and genetic drift as underlying evolutionary forces canalizing the divergence of Sardinian Aquilegia taxa, and to see if the spatial genetic structure found fits the current taxonomic differentiation of these taxa.

Methods

DNA from 89 individuals from all known locations of Aquilegia across Sardinia was analysed by means of amplified fragment length polymorphism (AFLP) markers. Both principal co-ordinates analysis (PCoA) and Bayesian clustering analyses were used to determine the spatial genetic structure irrespective of any taxonomic affiliation. Historical effects of gene flow and genetic drift were assessed by checking for the existence of isolation-by-distance patterns.

Key Results

STRUCTURE and PCoA analyses revealed a pattern of genetic variation geographically structured into four spatial genetic groups. No migration–drift equilibrium was detected for Aquilegia in Sardinia, when analysed either as a whole or in individual groups. The scenario approached a Case III pattern sensu Hutchinson and Templeton, which is associated with extreme isolation conditions where genetic drift has historically played a dominant role over gene flow.

Conclusions

The pattern of genetic variation of Sardinian taxa of Aquilegia indicates that genetic drift has been historically more influential than gene flow on population structure of Sardinian species of Aquilegia. Limited seed dispersal and divergent selection imposed by habitat conditions have been probably the main causes reinforcing post-Pleistocene geographical isolation of Aquilegia populations. The spatial genetic structure found here is not fully compatible with current taxonomic affiliations of Sardinian Aquilegia taxa. This is probably a consequence of the uncoupling between morphological and genetic patterns of differentiation frequently found in recently radiated taxa.     

长角凤仙花（凤仙花科）的花器官发生和发育

以不同发育时期的长角凤仙花Impatiens longicornuta Y.L.Chen（凤仙花科Balsaminaceae）为材料,利用扫描电镜技术观察了其花器官的分化及其发育过程。长角凤仙花为两侧对称花,具2枚侧生萼片,唇瓣囊状,旗瓣具鸡冠状突起,雄蕊5枚,子房上位,5心皮5室。其花器官分化顺序为向心式,萼片—花瓣—雄蕊—雌蕊原基。2枚侧生萼片先发生,然后近轴萼片（即唇瓣）原基和2枚前外侧萼片原基近同时发生;但是这3枚萼片原基的发育不同步,远轴的2枚前外侧萼片原基的发育渐渐滞后,然后停止发育,最后渐渐为周围组织所吸收,直至消失不见。花瓣原基中,旗瓣原基最先发生,4个侧生花瓣原基相继成对发生,且之后在基部成对愈合形成翼瓣;5枚雄蕊原基几乎同时发生,5个心皮原基轮状同时发生。本文结果支持凤仙花属植物为5基数的花,并进一步证实了唇瓣的萼片来源;此外,研究结果表明花器官早期发育资料对植物系统与进化研究具有重要参考价值。     

Temporal,but not spatial,changes in expression patterns of petal identity genes are associated with loss of papillate conical cells and the shift to bird pollination in Macaronesian Lotus (Leguminosae)

• In the generally bee‐pollinated genus Lotus a group of four species have evolved bird‐pollinated flowers. The floral changes in these species include altered petal orientation, shape and texture. In Lotus these characters are associated with dorsiventral petal identity, suggesting that shifts in the expression of dorsal identity genes may be involved in the evolution of bird pollination. Of particular interest is Lotus japonicus CYCLOIDEA 2 (LjCYC2), known to determine the presence of papillate conical cells on the dorsal petal in L. japonicus. Bird‐pollinated species are unusual in not having papillate conical cells on the dorsal petal.
• Using RT‐PCR at various stages of flower development, we determined the timing of expression in all petal types for the three putative petal identity genes (CYC‐like genes) in different species with contrasting floral morphology and pollination syndromes.
• In bird‐pollinated species the dorsal identity gene, LjCYC2, is not expressed at the floral stage when papillate conical cells are normally differentiating in bee‐pollinated species. In contrast, in bee‐pollinated species, LjCYC2 is expressed during conical cell development.
• Changes in the timing of expression of the above two genes are associated with modifications in petal growth and lateralisation of the dorsal and ventral petals in the bird‐pollinated species. This study indicates that changes in the timing, rather than spatial distribution, of expression likely contribute to the modifications of petal micromorphology and petal size during the transition from bee to bird pollination in Macaronesian Lotus species.