Racemose inflorescences of monocots: structural and morphogenetic interaction at the flower/inflorescence level

Background

Understanding and modelling early events of floral meristem patterning and floral development requires consideration of positional information regarding the organs surrounding the floral meristem, such as the flower-subtending bracts (FSBs) and floral prophylls (bracteoles). In common with models of regulation of floral patterning, the simplest models of phyllotaxy consider only unbranched uniaxial systems. Racemose inflorescences and thyrses offer a useful model system for investigating morphogenetic interactions between organs belonging to different axes.

Scope

This review considers (1) racemose inflorescences of early-divergent and lilioid monocots and their possible relationship with other inflorescence types, (2) hypotheses on the morphogenetic significance of phyllomes surrounding developing flowers, (3) patterns of FSB reduction and (4) vascular patterns in the primary inflorescence axis and lateral pedicels.

Conclusions

Racemose (partial) inflorescences represent the plesiomorphic condition in monocots. The presence or absence of a terminal flower or flower-like structure is labile among early-divergent monocots. In some Alismatales, a few-flowered racemose inflorescence can be entirely transformed into a terminal ‘flower’. The presence or absence and position of additional phyllomes on the lateral pedicels represent important taxonomic markers and key features in regulation of flower patterning. Racemose inflorescences with a single floral prophyll are closely related to thyrses. Floral patterning is either unidirectional or simultaneous in species that lack a floral prophyll or possess a single adaxial floral prophyll and usually spiral in the outer perianth whorl in species with a transversely oriented floral prophyll. Inhibitory fields of surrounding phyllomes are relevant but insufficient to explain these patterns; other important factors are meristem space economy and/or the inhibitory activity of the primary inflorescence axis. Two patterns of FSB reduction exist in basal monocots: (1) complete FSB suppression (cryptic flower-subtending bract) and (2) formation of a ‘hybrid’ organ by overlap of the developmental programmes of the FSB and the first abaxial organ formed on the floral pedicel. FSB reduction affects patterns of interaction between the conductive systems of the flower and the primary inflorescence axis.     

A mutation at AP2 locus of Arabidopsis confers spermine resistance

A spermine-resistant mutant of Arabidopsis thaliana (L.) Heynh. was isolated from M2 population of ethylmethanesulphonate-mutagenized seeds. The mutant was resistant to seed germination inhibition by spermine, but was as sensitive as the wild-type to spermidine and putrescine. In addition, the mutant displayed developmental abnormalities such as frequent cauline leaves, increased number of branches with inflorescence, reduced apical dominance, flowers subtended by bracts, disrupted floral organs with homeotic conversions. Genetic analysis indicated a single recessive nuclear mutation that was allelic to apetala2-1 (AP2-1). The new mutant allele of AP2 locus was accordingly numbered as AP2-10. This revised version was published online in July 2006 with corrections to the Cover Date.     

Intra-ovarian trichomes in Jackiopsis ornata (Wallich) Ridsdale (Rubiaceae-Jackieae)

The ovary and young fruit of Jackiopsis ornata has internal, unbranched, septate hairs which are more or less evenly dispersed over the entire interior surface of the locules and present in quite large numbers. This is the first record of intra-ovarian trichomes in the Rubiaceae. The trichomes do not seem to have an obvious function in that they do not appear to serve as a specialized pollen transmitting tissue or play a role in directing pollen tube growth.     

Anatomy and morphology of Behnia (Behniaceae) and its relationships within Lilianae: Asparagales

The vegetative and floral anatomy, morphology, embryology and seedlings of Behnia reticulata (Thunb.) Didr. are described, and the relationships of the recently described endemic southern African monocot family Behniaceae Reveal are discussed. Recent molecular studies place the family with the Agavaceae, Hostaceae, Anthericaceae, Herreriaceae and Ane-marrhenaceae. Behnia shows some morphological similarities with this clade, such as the woody shrub habit, a secondary thickening meristem in the rhizomes, small flowers and baccate fruits; but differs in several features, such as reticulate leaf venation, cryptodioecious flowers and seeds lacking phytomelan. Embryologically, the Behniaceae agree with the other members of their clade, although there are no clear synapomorphies by which the group may be defined from other Asparagalean clades.     

Leaf anatomy and phylogeny of Ixioideae (Iridaceae)

Leaf anatomy is described in Ixioideae, the largest subfamily of Iridaceae, with particular reference to phylogeny and systematics. Leaves in many genera have two rows of opposing vascular bundles (found also in many other Iridaceae), sometimes (except in e.g. Pillansia) combined with typical ixioid features such as a prominent pseudomidrib, mesophyll cells often elongated at right angles to the leaf axis, and epidermal cells also sometimes slightly laterally elongated, frequently with markedly sinuous anticlinal walls, and a single row of papillae per cell. Other characters are limited to a few genera. Anatomical characters are used together with data from other sources to construct a cladogram for the group. Although anatomical characters in general show much homoplasy, the relationships of the existing three tribes, Pillansieae, Watsonieae and Ixieae, diagnosed mainly on the basis of floral and inflorescence characters, are largely upheld by analysis, with at least two potentially useful subtribal groupings within Ixieae.     

Plant regeneration and micropropagation of Brachypodium distachyon

Brachypodium distachyon (L.) P. Beauv. has several features of its genome and growth habit reminiscent of Arabidopsis thaliana (L.) Heyn. that may allow it to be developed as a model molecular genetic system representative of the temperate grasses. In order for B. distachyon to be exploited in this way, it will be necessary to develop tissue culture procedures. This report details initial studies of the characteristics of mature seed-derived callus and the production of fertile plants from callus of three ecotypes of B. distachyon. Optimum development of embryogenic callus occurred on LS (Linsmaier & Skoog 1965) and N6 (Chu et al. 1975) media containing 3.0% w/v sucrose and 11.25 M (2.5 mg l^-1) 2,4-dichlorophenoxyacetic acid. Plants were recovered at a high frequency from embryogenic callus of ecotype B200 maintained on growth regulator-free N6 medium and were easy to establish in compost. A method was also developed for the in vitro clonal propagation of shoots using MS (Murashige & Skoog 1962) medium supplemented with 4 to 13 M (1.0 to 3.0 mg l^-1) benzyladenine. It was concluded that B. distachyon performed well in tissue culture and was suitable for further studies aimed at genetic transformation and its continued development as a model molecular genetic system.Abbreviations BA benzyladenine - 2,4-d dichlorophenoxyacetic acid - LS Linsmaier and Skoog (1965) - MS Murashige & Skoog (1962) - NAA -naphthaleneacetic acid - MSO growth regulator-free Murashige & Skoog (1962)     

Difference in monotropoid mycorrhiza formation between Monotropastrum globosum and its forma roseum

Monotropoid mycorrhiza formation and its morphological characteristics on an achlorophyllous plant, Monotropastrum globosum f. roseum, were investigated. The forma formed typical monotropoid mycorrhizae, indicating that the forma is myco-heterotrophic. Morphological characteristics of the mycorrhizae and root systems of the forma were quite different from those of Monotropastrum globosum, suggesting that further investigation on host specificity and the phylogeny of the plants should be conducted.     

雌蕊的类型一节的教学改进

在植物“雌蕊的类型”一节的教学实践中,我们在课堂教学中采用理论教学与实验教学同步进行的“二合一”教学方法,并在教学过程中选用典型的、合适的实验材料应用电视——显微镜成像系统对其解剖观察和讲解,这不仅活跃了课堂气氛,而且提高了学生观察和动手能力;在学生对“雌蕊一节”各概念和实验技能基本掌握的前提下,再辅以现场教学,则进一步扩展了学生的知识面,所有这些,不仅使学生更好的理解各类雌蕊的结构组成特点,而且提高了学生的综合素质。     

Pollen presenters in the flowering plants–form and function

Pollen presenters are specific floral structures, other than anthers, from which pollen is distributed for cross fertilization between flowers. They occur in only five families of monocotyledons and 20 families of the dicotyledons. Presenters in 15 families are described here. In the largest plant family (Asteraceae) all taxa have pollen presenters, while in others (e.g. Myrtaceae) they occur in only some species in a few genera. Most presenters are associated with the gynoecium and there is a wide range of forms involving hairs or outgrowths of the stylar tissue. Despite the placement of self pollen close to the stigma most taxa are outcrossing and avoid self fertilization by protandry, with the stigma being covered at anthesis, or by precise placement of pollen so that is does not contact the stigma. Likely selective advantages in the development of pollen presenters include greater accuracy in pollen transfer than in the normal anther to stigma movement and avoidance of interference between male and female organs in the flower. In some groups there is enhanced ability for female choice because effective pollen delivery enables a choice from among many pollen grains, while in others pollen presenters enhance male reproductive success. Study of the pollination biology of plants requires a knowledge of which plants have pollen presenters and a full understanding of the structures in the flower which are associated with the pollen presentation action.     

重瓣紫蓝大岩桐组培苗的花同源异型现象(简报)

由于花同源异型突变体可作为研究花形态建成的分子遗传分析模式系统,近十几年来,人们对于花同源异型基冈的分离、鉴定及转化均产生了很大兴趣,并对花器官特征决定基因的功能提出了“ABC”控制模型J和“异时性”(heterchrrony)假说。我们在进行黄瓜子叶离体培养时,发现了离体培养黄瓜子叶直接成花现象,进而建立起黄瓜子叶离体培养直接成花及黄瓜去顶苗直接成花的实验系统。在栽培重瓣大岩桐组培苗的过程中,观察到六种花同源异型变异体,其表型难以简单地用“ABC”控制模型解释。通过统计还发现同源异型花的发生频率与节位有关。这一现象为进一步探讨花     

农杆菌介导单子叶植物遗传转化问题与对策

尽管十几年来农杆菌介导的单子叶植物遗传转化研究取得了较大的进步,但仍存在着基因型限制、转化率不高和外源基因表达活性低等问题。本文综述了近几年来此项研究在感受态细胞选择与调节、预培养及共培养体系优化、转化子的筛选及外源基因表达调控等方面的主要进展。     

Transformation of rice mediated by Agrobacterium tumefaciens

Agrobacterium tumefaciens has been routinely utilized in gene transfer to dicotyledonous plants, but monocotyledonous plants including important cereals were thought to be recalcitrant to this technology as they were outside the host range of crown gall. Various challenges to infect monocotyledons including rice with Agrobacterium had been made in many laboratories, but the results were not conclusive until recently. Efficient transformation protocols mediated by Agrobacterium were reported for rice in 1994 and 1996. A key point in the protocols was the fact that tissues consisting of actively dividing, embryonic cells, such as immature embryos and calli induced from scutella, were co-cultivated with Agrobacterium in the presence of acetosyringonc, which is a potent inducer of the virulence genes. It is now clear that Agrobacterium is capable of transferring DNA to monocotyledons if tissues containing competent cells are infected. The studies of transformation of rice suggested that numerous factors including genotype of plants, types and ages of tissues inoculated, kind of vectors, strains of Agrobacterium, selection marker genes and selective agents, and various conditions of tissue culture, are of critical importance. Advantages of the Agrobacterium-mediated transformation in rice, like on dicotyledons, include the transfer of pieces of DNA with defined ends with minimal rearrangements, the transfer of relatively large segments of DNA, the integration of small numbers of copies of genes into plant chromosomes, and high quality and fertility of transgenic plants. Delivery of foreign DNA to rice plants via A. tumefaciens is a routine technique in a growing number of laboratories. This technique will allow the genetic improvement of diverse varieties of rice, as well as studies of many aspects of the molecular biology of rice.     

樟科(Lauraceae)部分属种雌蕊群维管分布格局及其系统学意义

运用石蜡切片技术,对樟科的紫楠（Ｐｈｏｅｂｅ ｓｈｅａｒｅｒｉ（Ｈｅｍｓｌ．）Ｇａｍｂｌｅ）,浙江楠（Ｐｈ．ｃｈｅｋｉａｎｇｅｎｓｉｓ Ｓ．Ｂ．Ｓｈａｎｇ）香樟（Ｃｉｎｎａｍｏｍｕｍ ｃａｍｐｈｏｒａ （Ｌｉｎｎ．）Ｐｒｅｓｌ．）浙江桂（Ｃ．ｃｈｅｋｉａｎｇｅｎｓｉｓ Ｎａｋａｉ）,细叶香桂（Ｃ．ｓｕｂａｖｅｎｉｕｍＭｉｑ．）、江浙山胡椒（Ｌｉｎｄｅｒａ ｃｈｉｅｎｉｉ Ｃｈｅｎｇ）、钓樟（Ｌ．ｒ     

Morphogenesis of Pistillate Flowers of Cercidiphyllum japonicum(Cercidiphyllaceae)

Floral morphogenesis and the development of Cercidiphyllum japonicum Sieb.et Zucc.were observed by scanning electronmicroscopy(SEM).The results showed that the pistillate inflorescences were congested spikes with the flowers arrangedopposite.Great differences between the so-called"bract"and the vegetative leaf were observed both in morphogenesis andmorphology.In morphogenesis,the"bract"primordium is crescent-shaped,truncated at the apex and not conduplicate,has no stipule primordium at the base but does have some inconspicuous teeth in the margin that are not glandular.Theleaf primordium is triangular,cycloidal at the apex,conduplicate,has two stipule primordia at the base,has one gland-toothat the apex occurring at first and some gland-teeth in the margin that occur later.In morphology,the"bract"is also differentto the vegetative leaf in some characteristics that were also illustrated in the present paper.Based on the hypothesis thatthe bract is more similar to the vegetative leaf than the tepal,we considered that the so-called"bract"of C.japonicum mightbe the tepal of the pistillate flower in morphological nature.Therefore,each pistillate flower contains a tepal and a carpel.We did not find any trace of other floral organs in the morphogenesis of the pistillate flower.Therefore we consideredthat the unicarpellate status of extant Cercidiphyllum might be to highly reduce and advance characteristics that make theextant Cercidiphyllum isolated from both fossil Cercidiphyllum-like plants and its extant affinities.     

An updated angiosperm classification

DAHLGREN, C, 1989. An updated angiosperm classification. A new two-dimensional diagram, reflecting the system of classification of the angiosperms, is presented. It combines the dicotyledon diagram in G. Dahlgren (1989) and an adapted monocotyledon diagram after that in Dahlgren (1985) in a single diagram. An updated monocotyledon taxonomy is presented and the classification is appended.     

Quantitative developmental analysis of homeotic changes in the inflorescence of Philodendron (Araceae)

Background and Aims: The inflorescence of Philodendron constitutes an interestingmorphological model to analyse the phenomenon of homeosis quantitativelyat the floral level. The specific goals of this study were (1)to characterize and quantify the range of homeotic transformationin Philodendron billietiae, and (2) to test the hypothesis thatthe nature of flowers surrounding atypical bisexual flowers(ABFs) channel the morphological potentialities of atypicalbisexual flowers. Methods: Inflorescences of P. billietiae at different stages of developmentwere observed using SEM. The number of appendices in male, femaleand sterile flowers were counted on 11 young inflorescences(5–6 flowers per inflorescence). The number of staminodesand carpels on ABFs were counted on 19 inflorescences (n = 143).These data were used for regression and ANOVA analyses. Results: There was an average of 4·1 stamens per male flower,9·8 carpels per female flower and 6·8 staminodesper sterile male flower. There was an average of 7·3floral appendices per atypical flower. Staminodes and carpelsare inserted on the same whorl in ABFs. A negative exponentialrelationship was found between the average number of staminodesand the number of carpels in ABFs. If only the ABFs consistingof less than six carpels are considered, there is a linear relationshipbetween the number of carpels and the average number of staminodes.The value of the slope of the regression equation indicatesthat on average, in P. billietiae, 1·36 carpels are replacedby one staminode. Conclusions: In P. billietiae, the number of appendages in female flowersimposes a constraint on the maximum total number of appendages(carpels and staminodes) that can develop on ABFs. The quantitativeanalyses indicate that the average number of different typesof floral appendages on an ABF and the number of organs involvedin a homeotic transformation are two independent phenomena.