灌木铁线莲（毛茛科）花器官的发生与发育

用扫描电子显微镜（SEM）对铁线莲属（Clematis L.）植物灌木铁线莲(C. fruticosa Turcz.)花的形态发生和发育过程进行了观察。灌木铁线莲花原基形成后,4枚萼片以交互对生的方式首先发生,呈轮状排列。最早的4枚雄蕊原基在4枚萼片交接的位置上近螺旋状发生,此后,随着雄蕊原基的向心发生和数目不断增多,其发生的螺旋状序列逐渐明显。雄蕊原基发生后,在花原基顶端,心皮原基沿着雄蕊原基的发生序列呈螺旋状发生。本文结果支持在原始被子植物花中螺旋状排列和轮状排列同时存在的观点。此外,本文也进一步证实了花萼与苞片的同源性。     

Inflorescence and floral development in <Emphasis Type="Italic">Trochodendron aralioides</Emphasis> (Trochodendraceae)

In the early development of Trochodendron aralioides (Trochodendraceae) inflorescences lateral flowers are initiated after the appearance of the floral pherophylls (subtending bracts). The terminal flower is preceded by metaxyphylls and is initiated earlier than the uppermost lateral flowers of the botryoid inflorescence. Small scales (interpreted as rudimentary perianth organs) precede the stamens. These scales are more distinct in the terminal flower than in the lateral flowers. In the radially symmetrical terminal flower, small scales (or metaxyphylls) and stamens are initiated in a spiral during early development. At anthesis, stamen phyllotaxis appears irregular or approximately whorled as a result of the rapid elongation and irregular slight curvature of the stamen filaments which distorts the originally regular pattern. Finally, the numerous carpels arise simultaneously in a single whorl. It takes about 9 months for flowers to develop and the 2-year reproductive cycle of T. aralioides is typical of many trees. The floral development of T. aralioides is compared with that of other basal eudicots. The bottle-shaped, unicellular stigmatic papillae and long, decurrent stigma of basally united carpels are similar to those of the Buxales¸ suggesting a close relationship.     

A Dynamical Phyllotaxis Model to Determine Floral Organ Number

How organisms determine particular organ numbers is a fundamental key to the development of precise body structures; however, the developmental mechanisms underlying organ-number determination are unclear. In many eudicot plants, the primordia of sepals and petals (the floral organs) first arise sequentially at the edge of a circular, undifferentiated region called the floral meristem, and later transition into a concentric arrangement called a whorl, which includes four or five organs. The properties controlling the transition to whorls comprising particular numbers of organs is little explored. We propose a development-based model of floral organ-number determination, improving upon earlier models of plant phyllotaxis that assumed two developmental processes: the sequential initiation of primordia in the least crowded space around the meristem and the constant growth of the tip of the stem. By introducing mutual repulsion among primordia into the growth process, we numerically and analytically show that the whorled arrangement emerges spontaneously from the sequential initiation of primordia. Moreover, by allowing the strength of the inhibition exerted by each primordium to decrease as the primordium ages, we show that pentamerous whorls, in which the angular and radial positions of the primordia are consistent with those observed in sepal and petal primordia in Silene coeli-rosa, Caryophyllaceae, become the dominant arrangement. The organ number within the outmost whorl, corresponding to the sepals, takes a value of four or five in a much wider parameter space than that in which it takes a value of six or seven. These results suggest that mutual repulsion among primordia during growth and a temporal decrease in the strength of the inhibition during initiation are required for the development of the tetramerous and pentamerous whorls common in eudicots.     

Evolutionary correlation between floral monosymmetry and corolla pigmentation patterns in <Emphasis Type="Italic">Rhododendron</Emphasis>

Floral symmetry and pigmentation are features of flowers that are believed to be associated due to their shared influence on pollinator behaviour. However, the evolution of such associations has so far not been examined. We analysed variation in Rhododendron flowers, in a phylogenetic context, to test whether the evolution of floral symmetry types and pigment patterns are correlated. Variation in floral symmetry due to variation in corolla form, stamen flexion, stamen arrangement, pistil flexion, as well as corolla pigment patterns was documented in 98 species of Rhododendron. Phylogenetic relations among these species were estimated using maximum likelihood (ML) and Bayesian methods, building on a published molecular dataset of sequences of RNA Polymerase II subunit (RPB2-I). Evolution of the floral traits was studied using phylogenetic correlation tests and ancestral state reconstructions (maximum parsimony, MP and ML methods). Significant correlations were found between corolla pigment pattern and type of floral symmetry at the level of corolla form, stamen flexion or arrangement, and pistil flexion. As expected from their similar roles in enhancing attractability to pollinator, monosymmetric corollas and presence of pigment pattern are correlated; in addition, monosymmetry involving other whorls too shows such a relationship with pigment patterns, and with each other. Multiple evolutionary shifts were detected between monosymmetry and polysymmetry of floral traits in Rhododendron. The relationship between floral monosymmetry attributes and presence of corolla pigment patterns, and additionally, frequent evolutionary shifts in these traits suggest pollinator-mediated selective pressures in Rhododendron.     

floricaula: a homeotic gene required for flower development in antirrhinum majus.

Plants carrying the floricaula (flo) mutation cannot make the transition from inflorescence to floral meristems and have indeterminate shoots in place of flowers. The flo-613 allele carries a Tam3 transposon insertion, which allowed the isolation of the flo locus. The flo gene encodes a putative protein (FLO) containing a proline-rich N-terminus and a highly acidic region. In situ hybridization shows that the flo gene is transiently expressed in the very early stages of flower development. The earliest expression seen is in bract primordia, followed by sepal, petal, and carpel primordia, but no expression is detected in stamen primordia. This pattern of expression has implications for how flo affects phyllotaxis, organ identity, and determinacy. We propose that flo interacts in a sequential manner with other homeotic genes affecting floral organ identity.     

Floral phyllotaxis in basal angiosperms: development and evolution

To date, molecular developmental studies have focused on vegetative rather than floral phyllotaxis because vegetative shoot apices are technically more tractable than floral apices in model plants. In contrast to evolutionary changes in the phyllotaxis of vegetative shoots, however, changes in floral phyllotaxis appear to have played a major role in angiosperm evolution. Consolidation of a whorled floral phyllotaxis in derived groups allowed synorganization of floral organs and further adaptive radiations. In basal angiosperms, floral phyllotaxis is more flexible. To study these phenomena, we need clarification of the complex relations of both spiral and whorled phyllotaxis with divergence angles, plastochrons, spiral versus simultaneous initiation of organs, parastichies, orthostichies, organ series, and whorls. Improved resolution of phylogenetic relationships and increased knowledge of the diversity of floral phyllotaxis will allow us to trace evolutionary changes in floral phyllotaxis in ever more detail. Already, such surveys have confirmed that floral phyllotaxis was unusually labile early in angiosperm evolution. Whether the original floral phyllotaxis in angiosperms was spiral or whorled is equivocal, but it appears that spiral floral phyllotaxis in Magnoliales and Laurales is derived rather than primitive.     

Chaotic Floral Phyllotaxis and Reduced Perianth in Achlys (Berberidaceae)

Among the 16 genera of the Berberidaceae Achlys is the only one with a reduced perianth, an irregular floral phyllotaxis, and variable stamen number. Early floral stages show an unstable (chaotic) arrangement of the organ primordia. Only the single carpel of the gynoecium has a more fixed position in that the placenta is formed in the adaxial half of the flower. The irregularities in the androecium may be caused by the lack of influence of a perianth on floral symmetry. On the other hand, the regular orientation of the carpel is perhaps due to the early polarity of the flower, whereby the abaxial half of the flower is larger (with further developed stamen primordia) at the time when carpel polarity is established.     

Isolation and characterization of the C-class MADS-box gene from the distylous pseudo-cereal <Emphasis Type="Italic">Fagopyrum esculentum</Emphasis>

In the model species Arabidopsis thaliana, the floral homeotic C-class gene AGAMOUS (AG) specifies reproductive organ (stamen and carpels) identity and floral meristem determinacy. Gene function analyses in other core eudicots species reveal functional conservation, subfunctionalization and function switch of the C-lineage in this clade. To identify the possible roles of AG-like genes in regulating floral development in distylous species with dimorphic flowers (pin and thrum) and the C function evolution, we isolated and identified an AG ortholog from Fagopyrum esculentum (buckwheat, Family Polygonaceae), an early diverging species of core eudicots preceding the rosids-asterids split. Protein sequence alignment and phylogenetic analysis grouped FaesAG into the euAG lineage. Expression analysis suggested that FaesAG expressed exclusively in developing stamens and gynoecium of pin and thrum flowers. Moreover, FaesAG expression reached a high level in both pin and thrum flowers at the time when the stamens were undergoing rapidly increased in size and microspore mother cells were in meiosis. FaesAG was able to substitute for the endogenous AG gene in specifying stamen and carpel identity and in an Arabidopsis ag-1 mutant. Ectopic expression of FaesAG led to very early flowering, and produced a misshapen inflorescence and abnormal flowers in which sepals had converted into carpels and petals were converted to stamens. Our results confirmed establishment of the complete C-function of the AG orthologous gene preceding the rosids-asterids split, despite the distinct floral traits present in early- and late-diverging lineages of core eudicot angiosperms.     

Small reductions in corolla size and pollen: ovule ratio,but no changes in flower shape in selfing populations of the North American <Emphasis Type="Italic">Arabidopsis lyrata</Emphasis>

The shift from outcrossing to selfing is often accompanied by striking changes in floral morphology towards a “selfing syndrome”, which is characterized by flowers with reduction in size, pollen: ovule (P/O) ratio, and herkogamy. This study aims to test whether such changes have occurred in the North American Arabidopsis lyrata, which is of particular interest because of the relatively recent transitions to selfing in this system. Flower size, flower shape, herkogamy levels, P/O ratio, and floral integration of six self-incompatible (outcrossing) and six self-compatible (selfing) populations of A. lyrata were measured in a common environment using conventional and geometric morphometrics methods. Although selfers had on average 9.2% smaller corollas, 8.4% longer pistils, and 21.5% lower P/O ratios than outcrossers, there were no differences in shape, floral integration, and herkogamy between outcrossing and selfing populations. Moreover, most variation in floral traits was explained by population genetic background rather than by mating system. We conclude that selfing populations in A. lyrata have not evolved a selfing syndrome.     

Floral meristem size and organ number correlation in <Emphasis Type="Italic">Eucryphia</Emphasis> (Cunoniaceae)

We present a comparative flower ontogenetic study in five species of the genus Eucryphia with the aim of testing whether differences in the organ number observed can be explained by changes in the meristematic size of floral meristem and floral organs. Species native to Oceania, viz. E. milliganii, E. lucida and E. moorei, have the smallest gynoecia with ca. 6 carpels, while the Chilean E. glutinosa and E. cordifolia present more than ten carpels. E. milliganii has the smallest flower with the lowest stamen number (ca. 50), while the other species produce around 200 stamens and more. Standardized measurements of meristematic sectors were taken in 49 developing flowers that were classified into three well-defined ontogenetic stages. Sizes of meristems varied significantly among species within each developmental stage as revealed by ANOVA analyses. Significant regressions between organ number and corresponding meristem size were consistent with the premise that a larger meristem size prior to organ initiation could be determining for a higher organ number. Flower organogenesis in Eucryphia also involves relevant meristem expansion while the organs are initiated, which results in a particular androecium patterning with a chaotic stamen arrangement. Meristem expansion also appears to be slower but more extensive in species with larger initial meristematic size, suggesting that flower phenotype can be determined in ontogeny by this heterochronic interplay of space and time.     

Morphogenesis and Gene Mapping of <Emphasis Type="Italic">deformed interior floral organ 1</Emphasis> (<Emphasis Type="Italic">difo1</Emphasis>), a Novel Mutant Associated with Floral Organ Development in Rice

Floral organ identity and specific number directly affect anthesis habits, fertilization and grain yield. Here, we identified a deformed interior floral organ 1 (difo1) mutant from selfing progenies of indica cv. Zhonghui8015 (Zh8015) after ⁶⁰Co γ-ray treatment. Compared with the Zh8015 spikelet, the interior floral organs of the difo1 mutant present various numbers of stamens and stigmas, with no typical filament and no mature pollen grains. Most difo1 flowers exhibited an increased number of stigmas that were attached to the stamens and an intumescent ovule-like cell mass in addition to the ovary. Transverse sections of spikelets and scanning electron microscopy analysis revealed an indeterminate number of interior floral organs and abnormal early spikelet development for the difo1 mutant. Instead of the linear-shaped surface of wild-type stamens, difo1 displayed a glossy stamen surface resulting in immature stamens and complete sterility. In addition, the difo1 mutant exhibited delayed anthesis, rapid anthesis and non-extended stamens compared with wild type. Genetic analysis and gene mapping revealed that difo1 was controlled by a single recessive gene, which was fine-mapped to a 54-kb interval on the short arm of chromosome 4 between markers S22 and RM16439 harboring nine ORFs. Sequence analysis revealed that the mutant carried a single nucleotide deletion in its promoter region, which likely corresponded to the phenotype, in a C₂H₂-type zinc finger protein gene (LOC_Os04g08600). Moreover, qRT-PCR analysis showed a significantly down-regulated expression pattern for DIFO1 and many floral organ identity genes in the interior floral organs of difo1. DIFO1 is therefore an important floral organ development gene in rice, particularly with regard to interior organ meristem identity and floret primordium differentiation.     

Ontogeny of Staminate and Carpellate Flowers of Schisandra sphenanthera(Schisandraceae)

The ontogenetic process of the staminate and carpellate flowers of Schisandra sphenanthera Rehd. et Wils., an endemic species to China, was observed for the first time under the scanning electron microscope (SEM). In the staminate flowers, the perianth units and stamens were initiated acropetally in a continuous fasion with 2/5 spiral phyllotaxis, while no female structures were formed. Anthers were differentiated prior to the filaments formation. Throughout all the stages were the stamens arranged spirally on a columniform receptacle. In the carpellate flowers, the initiation sequence of the perianth units and carpels were similar to that of the staminate flowers. In contrast, no male structures were formed. Shortly after initiation, the carpel primordia began their marginal growth besides the apical growth and then appresses were formed on the adaxial surfaces of the primordia. However the lower margins of these appresses were inconspicuous, resulting in conduplicate carpels. Two ovules were developed on the inner surface near either lateral margins of the carpel, shaping laminar placentae. Compared with S. glabra (Brickell) Rehd., a related American species, the evolutionary trend of phyllotaxis of androecia is considered that stamens may change from spiral to approximately whorled arrangement, accompanying with the change of receptacle from a column to a flattened shield. It was also suggested that the stamens being numerous and uncertain in number become certain and decrease in number to 5 (4－7). Sterile stamens are observed and the unisexual nature of the flowers is discussed. Two types of carpel primordia are categorized, corresponding to two types of carpels, namely, ascidiate and conduplicate carpels, respectively.     

Effect of the auxin polar transport inhibitor on the morphogenesis of leaves and generative structures during fasciation in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> (L.) Heynh.

An increase in the proliferative activity of a shoot apical meristem (SAM) and the further accumulation of a pool of undifferentiated cells (fasciation) results in phyllotaxis changes. In the case of Arabidopsis thaliana, a typical spiral leaf arrangement is replaced by an opposite or verticillate one (depending on the level of a fasciation manifestation). Pistil development in mutant plants is accompanied by the appearance of a group of undifferentiated meristematic cells in its central part. The addition of N-1-naphthylphthalamic acid (NPA) causes an increase in the meristem volume and number of stipules in both mutant and control plants. The NPA effect on the floral morphogenesis results in a significant growth of meristemic cell pool. The interaction of different mechanisms of a meristem volume control is discussed.     

Do Fibonacci numbers reveal the involvement of geometrical imperatives or biological interactions in phyllotaxis?

Complex biological patterns are often governed by simple mathematical rules. A favourite botanical example is the apparent relationship between phyllotaxis (i.e. the arrangements of leaf homologues such as foliage leaves and floral organs on shoot axes) and the intriguing Fibonacci number sequence (1, 2, 3, 5, 8, 13 . . .). It is frequently alleged that leaf primordia adopt Fibonacci-related patterns in response to a universal geometrical imperative for optimal packing that is supposedly inherent in most animate and inanimate structures. This paper reviews the fundamental properties of number sequences, and discusses the under-appreciated limitations of the Fibonacci sequence for describing phyllotactic patterns. The evidence presented here shows that phyllotactic whorls of leaf homologues are not positioned in Fibonacci patterns. Insofar as developmental transitions in spiral phyllotaxis follow discernible Fibonacci formulae, phyllotactic spirals are therefore interpreted as being arranged in genuine Fibonacci patterns. Nonetheless, a simple modelling exercise argues that the most common spiral phyllotaxes do not exhibit optimal packing. Instead, the consensus starting to emerge from different subdisciplines in the phyllotaxis literature supports the alternative perspective that phyllotactic patterns arise from local inhibitory interactions among the existing primordia already positioned at the shoot apex, as opposed to the imposition of a global imperative of optimal packing.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 150 , 3–24.     

Floral development of <Emphasis Type="Italic">Gonocaryum</Emphasis> with emphasis on the gynoecium

We investigated the floral development of Gonocaryum, a genus of Cardiopteridaceae that was segregated from Icacinaceae s.l., using scanning electron microscopy to clarify its gynoecial structure and facilitate morphological comparisons of Cardiopteridaceae. The key floral developmental characters include sepal initiation that follows a quincuncial spiral sequence; petals that are valvate with inflexed tips and are postgenitally fused at the base; a petal and stamen initiation sequence that is almost simultaneous; a globular protuberance on top of the connective; a gynoecium that is tricarpellate and pseudomonomerous, with the stigma produced by one abaxial lateral carpel; and two ovules that are unitegmic and anatropous with an obturator on the funicle. The floral developmental characters of Gonocaryum are discussed relative to Cardiopteris, which has been well studied and whose gynoecial vasculature is reinterpreted here, and are briefly compared to other members of Aquifoliales and Icacinaceae s.l. The imbricate sepals, initiated in a quincuncial spiral sequence, and the tricarpellate, pseudomonomerous gynoecium are common characters of Cardiopteridaceae. Unisexual flowers are an autapomorphy of Gonocaryum in Cardiopteridaceae.     

CAPITULUM PHYLLOTAXIS AND NUMERICAL CANALIZATION IN MICROSERIS PYGMAEA (ASTERACEAE: LACTUCEAE)

The positions at which floret primordia arise in developing capitulum buds of Microseris pygmaea D. Don have been mapped by computer-assisted light microscopy. The primordia can be assigned positions along a basic phyllotactic spiral with a divergence angle of about 137.5°. In addition, there are regular deviations from a spiral arrangement. Typically, the first 26 primordia in phyllotactic sequence are arranged in two concentric circles of 13 primordia with considerable deviations in the divergence angle and in the distances between primordia along a parastichy at positions 13 and 26. This arrangement can be simulated by geometric models that include nearest neighbor packing, together with spiral phyllotaxis. The circular arrangement of peripheral primordia at nearly equal radial distances from the center of the developing capitulum helps to explain the numerical constancy (canalization) of peripheral structures, especially the constant number of 13 inner phyllaries on heads with very different numbers of florets.     

Dancing on the platform: Lability of floral organs of Beilschmiedia appendiculata (Lauraceae)

Floral characters are important for the systematics of the Lauraceae. However, structure and development of the flowers remain poorly known in the family. In this study, we observed the variation and early development of flowers of Beilschmiedia appendiculata, which belongs to the Cryptocarya clade of the family. The results indicate that the shoot apical meristems (SAMs) of the floral buds are enlarged and become a platform for the programmed initiation of the floral organs; floral organs develop basically in an acropetal pattern; phyllotaxis is whorled, initiation of floral primordia within a whorl is asynchronous; floral merosity is extremely variable, for example, dimerous, trimerous, tetramerous, dimerous plus trimerous, and trimerous plus tetramerous. In addition, this species has lost the innermost staminal whorl and glands are not closely associated with stamens of the third staminal whorl, which is unusual in the family Lauraceae. Our new observations broaden our knowledge of the variation of floral structure in Beilschmiedia and pose a fundamental question regarding the ecology underlying the lability of floral organs in B. appendiculata.