Basic principles of terminal flower formation

Studies of efflorescences of the mutants bractea and terminal flower1 and double mutant bra tfl1 of Arabidoipsis thaliana (L.) Heynh. have shown that the presence of a developed leaf in the node preceding the terminal flower is a necessary condition for the formation of the terminal flower perianth. This means that perianth cannot develop in an abracteose efflorescence of terminal flower. The second necessary condition for the terminal flower formation is a sufficient level of expression of the genes responsible for floral morphogenesis. Combination of these two conditions suffices for the development of a terminal flower with perianth. Since the general principles of organization are close for most flower plants, it can be stated that if the abracteose efflorescence is terminated by a flower with perianth, this is a consequence of forcing the lateral flower into the terminal position.     

Organographic and ontogenetic studies on the inflorescence ofLespedeza cuneata (Dum.-Cours.) G. Don (Leguminosae)

Structure of inflorescence and its variation were organographically and ontogenetically studied inLespedeza cuneata (Dum.-Cours.) G. Don. An axillary inflorescence of the species forms a compound inflorescence which is composed of three or four component inflorescences. Each component inflorescence bears four (rarely six), three, two, or one flowers. Based on the arrangement of inflorescence phyllomes, the component inflorescence with four flowers is interpreted as a pseudoraceme bearing two shortened lateral shoots (partial inflorescences) each of which has two flowers. The component inflorescence with one flower appears to be terminated by the flower and to compose the cyme. Organographic observations revealed that the terminally located flower is not truly terminal, but axillary in origin. Ontogenetic observations showed that the apices of component inflorescence and partial inflorescence exist in early developmental stages in spite of variation in the form of component inflorescence. The terminally located flower in the cyme-like inflorescence was thus demonstrated to be laterally borne on the partial inflorescence axis. The component inflorescence composing the cyme-like one inL. cuneata is a reduced form in the number of partial inflorescences and of flowers from the pseudoraceme. The cyme-like inflorescence inL. cuneata resembles the inflorescence ofKummerowia.     

寒兰花器官发生及花发育过程的研究

为了揭示寒兰的成花机理,利用石蜡切片和花芽实体解剖记录了濒危植物寒兰花芽分化和发育的过程,并着重观察唇瓣和合蕊柱早期及中期的发育(在合蕊柱伸长之前)。结果表明:寒兰花芽分化沿着花序轴从下往上可分为4个阶段:花序原基分化,花原基分化,花被片分化和合蕊柱形成。唇瓣分化分为3个阶段:褶片分化,侧裂片分化和色块形成。唇瓣侧裂片和褶片产生较晚,与退化雄蕊可能没有关系。在合蕊柱形成过程中,首先分化出花药,随后分化产生中心皮顶部,侧心皮顶部,并形成花柱道,最终分化出蕊喙和黏盘。     

Inflorescence and floral ontogeny in Crocus sativus L. (Iridaceae)

Inflorescence and floral ontogeny of the perennial, herbaceous crop Crocus sativus L. were studied using epi-illumination light microscopy. After production of leaves with helical arrangement a determinate inflorescence forms which becomes completely transformed into a single terminal flower. In some cases, bifurcation of the inflorescence meristem yields two or three floral meristems. The order of floral organs initiation is outer tepals – stamens – inner tepals – carpels. Stamens and outer tepals are produced from the lateral bifurcation of three common stamen-tepal primordia. Within each whorl, organs start developing unidirectionally from the adaxial side, except for the stamens which begin to grow from the abaxial side. Specialized features during organ development include interprimordial growth between tepals forming a perianth tube, fusion at the base of stamen filaments, and formation of an inferior ovary with unfused styles.     

<Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> plants overexpressing <Emphasis Type="Italic">Ramosa1</Emphasis> maize gene show an increase in organ size due to cell expansion

The structure of the plant inflorescence and flower is an important agronomic and ornamental trait studied for its potential economic applications. In particular, the capacity to modify flower size has always been a breeder’s goal. Genetic and molecular studies have shown that the Zea mays gene Ramosa1 (Ra1) is involved in inflorescence branching regulation. In fact the ra1 loss of function mutation causes extra branching of the inflorescence. In this work we suggest a possible utilization of the Ramosa1 maize gene as a tool to modify inflorescence architecture and flower size in transgenic plants. In fact overexpression of this gene in Arabidopsis plants promotes an increase in reproductive organ size. Pollen, seeds, cotyledons, leaves and roots are also larger than those of the wild type. Analysis of organs from transformants showed that cell expansion was increased without apparently affecting cell division. These results suggest that the RA1 protein is able to up-regulate cell expansion in all organs of Arabidopsis plants.     

Activities of auxin polar transport in inflorescence axes of flower mutants ofArabidopsis thaliana: Relevance to flower formation and growth

Relationships between the activity of auxin polar transport and flower formation were studied using several flower mutants ofArabidopsis thaliana. The activity of auxin polar transport in the upper portion of inflorescence axis of wildtype plants ofArabidopsis thaliana was significantly lower than that of the basal part. The activities of auxin polar transport in the upper portion of inflorescence axes ofap1 andclv1 mutants were significantly higher than that of wild-type plant. However, those of other flower mutants tested,ap3-1, ag, pi, Fl-40, Fl-54, Fl-89 andpin-formed, were extremely low as compared with that of wild one. We got some evidence that the reduction of the activity of auxin polar transport is concerned with the growth and development of plants. We could mimic it by the removal of all flowers and pods including mature or immature seeds. Moreover, artificial pollination inap3-1 andpi mutants, in which no seeds are found naturally, resulted in the partial recovery of the activity of auxin polar transport in inflorescence axis. Considering these results in this study together with the fact that inhibitors of auxin polar transport generated almost same disruptions ofpin-formed orpinoid mutants which normally had no flowers in inflorescence axis (Okadaet al. 1991, Uedaet al. 1992, Bennettet al. 1995), the systern of auxin polar transport and its activity in inflorescence axis seems to be essential for the development of flower bud in early stage ofArabidopsis thaliana, and the activity of auxin polar transport is also regulated by the formation of flowers and seeds in inflorescence axis.     

Intra‐individual variation of flowers in Gunnera subgenus Panke (Gunneraceae) and proposed apomorphies for Gunnerales

A study of inflorescence and flower development in 12 species from four of the six subgenera of Gunnera (Gunneraceae) was carried out. In the species of subgenus Panke, initiation of floral apices along the partial inflorescences is acropetal but ends up in the late formation of a terminal flower, forming a cyme at maturity. The terminal flower is the largest and the most complete in terms of merosity and number of whorls and thus it is the most diagnostic in terms of species‐level taxonomy. The lateral flowers undergo a basipetal gradient of organ reduction along the inflorescence, ranging from bisexual flowers (towards the distal region) to functionally (i.e. with staminodia) and structurally female flowers (towards the proximal region). Our results show that the terminal structure in Gunnera is a flower rather than a pseudanthium. The terminal flower is disymmetric, dimerous and bisexual, representing the common bauplan for Gunnera flowers. It has a differentiated perianth with two sepals and two alternate petals, the latter opposite the stamens and carpels. Comparisons with other members of the core eudicots with labile floral construction are addressed. We propose vegetative and floral putative synapomorphies for the sister‐group relationship between Gunneraceae and Myrothamnaceae. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 160 , 262–283.     

Characterization of oil palm MADS box genes in relation to the mantled flower abnormality

In vitro propagation of oil palm (Elaeis guineensis Jacq.) frequently induces a somaclonal variant called ‘mantled’ abnormality, in which the stamens of both male and female flowers are transformed into carpels. This leads to a reduced yield or complete loss of the harvest of palm oil. The high frequency of the abnormality in independent lines and the high reversal rate suggest that it is due to an epigenetic change. The type of morphological changes suggest that it involves homeotic MADS box genes that regulate the identity of the flower whorls. We have isolated a number of MADS box genes from oil palm inflorescences by a MADS box-directed mRNA display approach. The isolated partial cDNAs included genes that were likely to function at the initial stages of flowering as well as genes that may function in determination of the inflorescence and the identity of the flower whorls. For four genes that were homologous to genes known to affect the reproductive parts of the flower, full length cDNAs were isolated. These were a B-type MADS box gene which may function in the determination of stamen formation, a C-type gene expected to be involved in stamen and carpel formation, and two putative SEP genes which act in concert with the A-, B- and C-type MADS box gene in determining flower whorl formation. The B-type gene EgMADS16 was functionally characterized as a PISTILLATA orthologue; it was able to complement an Arabidopsis thaliana pi mutant. Whether EgMADS16, or any of the other EgMADS genes, are functionally involved in the mantled condition remains to be established.     

DFL, a FLORICAULA/LEAFY homologue gene from Dendranthema lavandulifolium is expressed both in the vegetative and reproductive tissues

FLO/LFY homologue genes were initially characterized as floral meristem identity genes and play a key role in flower development among diverse species. The inflorescence organization of chrysanthemum differs from typical dicotyledons such as Arabidopsis and Antirrhinum as clear sepals are absent, and instead, a pappus, a rudimentary sepal, is formed. To understand the mechanism of reproduction of chrysanthemum at the molecular level, DFL, a FLORICAULA/LEAFY homologous gene, was cloned from Dendranthema lavandulifolium, which is one of the original species of chrysanthemum. The DFL gene consists of a 1,236-bp open reading frame and encodes a putative protein of 412 amino acids, which is 63% identical to LFY and 70% to FLO. The expression patterns of DFL during the flower development were analyzed, and RT-PCR results showed that DFL was strongly expressed in the flower bud. In situ hybridization experiments showed that it is strongly expressed in the inflorescence bract, petal and stamen primordial tissues throughout the inflorescence development. Its expression signals were also detected in stems, leaf primordial tissues and developing inflorescence bracts.     

Gender modification in a monoecious species <Emphasis Type="Italic">Sagittaria potamogetifolia</Emphasis> (Alismataceae)

In order to find out if the inflorescences number variation has influences on the gender modification in plant species, we investigated the gender modification in a cultivated population of the monoecious species Sagittaria potamogetifolia. We also designed two nutrient levels to explore the impact of nutrient on gender modification in S. potamogetifolia. We found that the female and male flowers did not change with increasing plant size for each inflorescence at a low nutrient level. At a high nutrient level, the female flower numbers on each inflorescence did not increase with plant size; however, the male flower numbers had some positive correlation with the plant size. At the ramet level, the total male and female flower numbers increased with the plant size at both nutrient levels. The sex ratio (female to male flower ratio) decreased with the inflorescence numbers and the plant size (Midvein length). Although the nutrient variation had impact on the flower number production, it did not change the gender modification pattern. The high plasticity of inflorescence numbers, which caused the gender variation in S. potamogetifolia, and low plasticity of female and male flowers on a single inflorescence, indicates that the limited modification on gender in a single inflorescence may be compensated by inflorescence number variation at the ramet level.     

紫花含笑花被呈色过程中色素含量与超微结构的变化特征

为了探究色素含量以及细胞结构在紫花含笑花被呈色过程中的作用机理,该研究以绿色和紫色花被为材料,测定其花被色素含量,运用逐步回归方程分析花被呈色与色素含量的关系,采用石蜡切片及超薄切片技术观察花被细胞超显微结构变化.结果表明:(1)在紫花含笑花被呈色过程中,紫色花被表面明度L*值降低,a*值上升,b*值降低;花被花青素苷...     

中国大陆兰科植物新资料

报道了中国大陆兰科(Orchidaceae)一新记录种:闭花天麻(Gastrodia clausa T. C. Hsu, S. W. ChungC. M. Kuo),凭证标本馆藏于中国科学院华南植物园标本馆(IBSC)。闭花天麻以联合花被管短且闭合,花辐射对称,唇瓣花瓣状,合蕊柱腹部具显著附属物而易与该属其他种类区别。提供了该种的描述、解剖照片及分类学信息。     

UFO in the Arabidopsis inflorescence apex is required for floral-meristem identity and bract suppression

The UNUSUAL FLORAL ORGANS (UFO) gene of Arabidopsis encodes an F-box protein required for the determination of floral-organ and floral-meristem identity. Mutation of UFO leads to dramatic changes in floral-organ type which are well-characterized whereas inflorescence defects are more subtle and less understood. These defects include an increase in the number of secondary inflorescences, nodes that alternate between forming flowers and secondary inflorescences, and nodes in which a single flower is subtended by a bract. Here, we show how inflorescence defects correlate with the abnormal development of floral primordia and establish a temporal requirement for UFO in this process. At the inflorescence apex of ufo mutants, newly formed primordia are initially bract-like. Expression of the floral-meristem identity genes LFY and AP1 are confined to a relatively small adaxial region of these primordia with expression of the bract-identity marker FIL observed in cells that comprise the balance of the primordia. Proliferation of cells in the adaxial region of these early primordia is delayed by several nodes such that primordia appear “chimeric” at several nodes, having visible floral and bract components. However, by late stage 2 of floral development, growth of the bract generally ceases and is overtaken by development of the floral primordium. This abnormal pattern of floral meristem development is not rescued by expression of UFO from the AP1 promoter, indicating that UFO is required prior to AP1 activation for normal development of floral primordia. We propose that UFO and LFY are jointly required in the inflorescence meristem to both promote floral meristem development and inhibit, in a non-cell autonomous manner, growth of the bract.Shelley R. Hepworth and Jennifer E. Klenz contributed equally to this work.     

蝴蝶兰花发育的分子生物学研究进展

蝴蝶兰花非常独特且高度进化,如萼片瓣化、瓣片特化为唇瓣、雌雄蕊合生成合蕊柱及子房发育须由授粉启动等,是单子叶植物花发育研究的理想材料。近年来蝴蝶兰花发育分子生物学取得了重要进展。该文就近年来国内外有关蝴蝶兰开花转换及花器官发育相关基因研究以及B类基因与兰花花被的进化发育关系方面的研究进展进行综述。研究表明:MADS基因在蝴蝶兰开花转换及花器官发育过程中起重要作用,推测其中的DEF(DE-FICIENS)-like基因早期经过2轮复制,形成了4类不同的DEF-like基因,进而决定兰花花被属性。蝴蝶兰花发育分子生物学的深入研究,将极大地利于通过基因工程手段提高蝴蝶兰花品质如花色改良及花期调控等,推动分子育种进程。     

Micropropagation of wild beet (Beta maritima) from inflorescence pieces

In order to investigate the regeneration of wild beet (Beta maritima) from inflorescence pieces, the effects of growth regulator, genotype, explant source and stage of plant development on adventitious shoot formation and rooting in vitro and subsequent transplanting in the glasshouse were tested. Inflorescence tips produced more adventitious shoots than sub-apical segments and the best micropropagation was achieved on a Murashige and Skoog (MS) medium supplemented with 1.0 mg l^–1 BAP. Addition of auxin was not beneficial. The induction rate of adventitious shoots was genotype-dependent and influenced by the stage of plant development. Adventitious shoots were produced from the base of the flower buds, i.e. from the receptacle, not from axils or stalks and only a few buds on inflorescence tip explants produced adventitious shoots. Rooting was increased by using a MS medium with 3% sucrose supplemented with 1.0 mg l^–1 NAA. There was no variation in leaf morphology of the transplants. This work shows that inflorescence tips can be used successfully as explants for in vitro multiplication of sugar beet and wild beet.Abbreviations BAP benzylaminopurine - IBA indole-3-butyric acid - GA₃ gibberellic acid - MS Murashige and Skoog medium - NAA naphthaleneacetic acid Author for correspondence     

Comparative ontogeny of the cyathium in Euphorbia (Euphorbiaceae) and its allies: exploring the organ-flower-inflorescence boundary

We present a detailed comparative ontogenetic analysis of pseudanthia of representatives of all three subtribes of Euphorbieae (Euphorbiinae, Neoguillauminiinae, Anthosteminae) in order to clarify their homologies and interpretation. The cyathium of Euphorbia and its allies (subtribe Euphorbiinae) closely resembles a bisexual flower but is traditionally interpreted as an inflorescence bearing clusters of highly reduced male flowers surrounding a single terminal female flower. Previously unreported characters are (1) male flowers formed one above the other in the male inflorescences of some Euphorbiinae, (2) late-developing perianthlike structures in some male flowers of Neoguillauminia cleopatra, (3) evidence for a bracteate origin of the female perianth in Anthosteminae and Neoguillauminiinae, and (4) spatiotemporally independent formation of abscission zone and perianth. Indistinct boundaries between inflorescence, flower, and floral organs demonstrate that defining the cyathium neither as an inflorescence nor as a flower is entirely satisfactory and indicate a "hybrid" flower/inflorescence nature of the cyathium. Based on our current knowledge and the existing phylogenetic context, it is most parsimonious to suggest that the cyathium evolved from a determinate thyrse with a terminal female flower surrounded by dichasial male partial inflorescences. We speculate that the cyathium was formed because of strong condensation and possible overlap between expression zones of regulatory genes.     

Morphometric analysis of the genusHemerocallis L. (Liliaceae) in Korea

To better understand the patterns of variability and distributions ofHemerocallis in Korea, 53 locations were visited and measurements of 19 morphological and phenological characters were taken on plants directly from their natural habitats. For morphometric analysis, 10 plants from each of 34 populations and five herbarium specimens ofH. middendorffii were used and the data from 12 quantitative characters was analyzed using univariate analysis. Except the littoral populations of Cheju, Hong, Taehuksan, and Sohuksan Islands (H. hongdoensis M. Chung & S. Kang), three peninsular KoreanHemerocallis species can be recognized mainly in South Korea:H. hakuunensis Nakai (=H. micrantha Nakai, growing on southern, central, and northwestern Korea);H. thunbergii Baker (=H. coreana Nakai, found on southeastern and central Korea); andH. middendorffii Tr. et Mey. (central and northeastern Korea). Morphological and phenological features contributing to recognition of the three groups were; color of perianth, shape of roots, shape of inflorescence, flowering time, odor, length of inflorescence, width of the lowest bracts, length of perianth tube enclosing a ovary, width of the inner perianth lobes. Natural hybridization seems to be rare in KoreanHemerocallis. It appears that the KoreanHemerocallis species are relatively well characterized by their distribution patterns, phenology, and habitats compared with the JapaneseHemerocallis species.     

Biogeography and evolution of flower color in Veratrum (Melanthiaceae) through inference of a phylogeny based on multiple DNA markers

Veratrum (Melanthiaceae) comprises ca. 27 species with highly variable morphology. This study aims to construct the molecular phylogeny of this genus to infer its floral evolution and historical biogeography, which have not been examined in detail before. Maximum parsimony, maximum likelihood, and Bayesian analyses were performed on the separate and combined ITS, trnL-F, and atpB-rbcL sequences to reconstruct the phylogenetic tree of the genus. All Veratrum taxa formed a monophyletic group, within which two distinct clades were distinguished: species with white-to-green perianth formed one highly supported clade, and the species with black-purple perianth constituted another highly supported clade. Phylogenetic inference on flower color evolution suggested that white-to-green perianth was a plesiomorphic state and black-purple perianth was apomorphic for Veratrum. When species distribution areas were traced as a multi-state character, parsimonious optimization inferred that Veratrum possibly originated in East Asia. Our study confirmed previous phylogenetic and taxonomic suggestions on this genus and provided a typical example of plant radiation across the Northern Hemisphere.