Floral anatomy and development of <Emphasis Type="Italic">Saxofridericia aculeata</Emphasis> (Rapateaceae) and its taxonomic and phylogenetic significance

Floral anatomy and development of Saxofridericia aculeata Körn was studied in a comparative approach to contribute to the understanding of the family. Flowers at different developmental stages were analysed with light and scanning electron microscopy, and the nature of the exudate secreted by the floral trichomes was investigated by histochemical tests. The anatomical characteristics observed in S. aculeata flowers were compared with those from other Rapateaceae species by a cluster analysis (UPGMA). The dendrogram generated reflects the groupings that emerged in phylogenetic molecular analyses, highlighting the usefulness of floral anatomy for taxonomy and for the understanding of infrafamilial relationships. The exudate secreted by the trichomes has a polysaccharidic composition. Such trichomes (colleters) occur in the sepals, petals, filaments and around the gynoecium; they are initiated at mid-stage of floral development and are an apomorphy of the family. The flowers are pentacyclic, presenting three initially free sepals, petals, stamens and carpels that mature in a centripetal order. The connate portion of the corolla, which is also adnate to the stamens, has a late development by zonal growth. Gynoecium formation is a combination of postgenital and congenital fusion processes. Data on floral organogenesis of Rapateaceae are first reported here and support the early diverging position of the family in Poales, close to Bromeliaceae.     

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。     

蓝堇草属(毛茛科)花形态发生的扫描电子显微镜观察

花的发生和发育过程研究可以发现早期进化的轨迹,为系统发育的研究提供重要线索。蓝堇草属(Leptopyrum)为毛茛科唐松草亚科一单种属,仅包含蓝堇草一种,其花的发生和发育过程仍为空白。为了深入理解唐松草亚科乃至毛茛科花发育多样性和演化规律,该文运用扫描电子显微镜(SEM)观察了蓝堇草各轮花器官的形态发生和发育过程。结果表明:该属植物所有的萼片、花瓣、雄蕊和雌蕊均为螺旋状发生,花器官排列式样也为螺旋状; 5枚萼片原基宽阔,5枚花瓣原基圆球形、位于萼片原基的间隔,且在后期表现为延迟发育现象,雄蕊原基较小、为圆球形;花瓣原基和雄蕊原基连续发生,无明显的时空间隔,但与萼片原基有时空间隔;心皮原基为马蹄形对折,柱头组织由单细胞乳突组成;胚珠倒生、具单珠被。该属花器官螺旋状排列、胚珠具单珠被在唐松草亚科中是独有的性状,花发育形态学证据支持了该属的特殊性。     

Type specification and spatial pattern formation of floral organs: A dynamic development model

A mathematical model simulating spatial pattern formation (positioning) of floral organs is proposed. Computer experiment with this model demonstrated the following sequence of spatial pattern formation in a typical cruciferous flower: medial sepals, carpels, lateral sepals, long stamens, petals, and short stamens. The positioning was acropetal for the perianth organs and basipetal for the stamens and carpels. Organ type specification and positioning proceed non-simultaneously in different floral parts and organ type specification goes ahead of organ spatial pattern formation. Computer simulation of flower development in several mutants demonstrated that the AG and AP2 genes determine both organ type specification and formation of the zones for future organ development. The function of the AG gene is to determine the basipetal patterning zones for the development of the reproductive organs, while the AP2 gene maintains proliferative activity of the meristem establishing the acropetal patterning zone for the development of the perianth organs.     

Comparative floral structure and systematics in the Asian palm genus Rhapis (Arecaceae,Coryphoideae)

A comparative study of the floral structure in the species of the genus Rhapis (Arecaceae, Coryphoideae, Rhapidinae) is presented. Flowers are mainly unisexual, with three sepals, three petals, 6 stamens or staminodes and three carpels or carpellodes. Some evidences of basal congenital and apical postgenital fusion of the carpels, first time reported in the genus, were observed in the gynoecium. Ovules are basally attached and crassinucellate; they appear to be slightly anatropous. The morphology of the filaments suggests a division of the species into two groups: Rhapis excelsa and R. subtilis exhibit thick and keeled filaments, whereas R. gracilis, R. humilis, R. laosensis, R. micrantha and R. multifida have slender, non-keeled filaments. Relationships of Rhapis with the rest of the genera of Rhapidinae are inferred on the light of floral structure.     

Floral morphology and structure of Phyllonoma (Phyllonomaceae): systematic and evolutionary implications

Phyllonoma, a small tree genus of four species distributed from Mexico to Peru, has been placed in various families (mainly in Saxifragaceae), but now, based on molecular evidence, is placed in a distinct family Phyllonomaceae in Aquifoliales. To better understand the morphological relationships of the genus and family, I studied its floral morphology, anatomy, and vasculature using P. tenuidens. Most of the external and internal floral characteristics were described more than 120 years ago. Although some of them were confirmed, some were substantially revised, mainly those concerning the gynoecial structure. Flowers are small and basically pentamerous, consisting of five sepals, five petals, five stamens, and a gynoecium composed of two carpels usually in transversal position. Comparisons with other Aquifoliales show that Phyllonomaceae share the inferior ovary, epiphyllous inflorescence and epigynous disc nectary with East-Asian Helwingiaceae (Helwingia only), but clearly differ from Helwingiaceae in having glandular trichomes on the sepal margins and a bicarpellate, unilocular gynoecium bearing many ovules on the parietal placentae. Evidence from floral morphology and structure supports the distinctness of Phyllonomaceae and its sister-group relationship with Helwingiaceae. Its floral characteristics suggest that Phyllonomaceae have evolved by adapting to distinct biological habitats in relation to pollination and seed dispersal.     

Floral development in Adonideae (Ranunculaceae)

Floral development and floral phyllotaxis in species of Adonis, Callianthemum, and Trollius (Ranunculaceae) were studied with scanning electron microscopy. The floral organs are initiated in spiral sequence and the flowers have spiral phyllotaxis. The sepal primordia are broad, crescent-shaped, and truncate, but those of petals, stamens, and carpels are rather hemispherical. A relatively long plastochron appears to be present between the last sepal and the first petal as compared with the short and equal plastochrones of all subsequent floral organs. Maturation of the stamens within the androecium appears to be centripetal. The carpels have a short ascidiate zone. Placentation is uniformly lateral, even in Adonis and Callianthemum, which have only one fertile ovule per carpel (versus median in other genera of Ranunculoideae with a single fertile ovule). In Adonis and Callianthemum at the tip of the carpel the ventral slit is gaping and the stigma is broadly exposed, whereas in Trollius the stigma is narrower and more pronouncedly decurrent along the ventral slit. The petals in Callianthemum and Trollius are more conspicuously delayed in development than those in Adonis as compared with sepals and stamens. A short carpel stipe is formed early in Callianthemum but later in Adonis and Trollius. In Trollius farreri (commonly having only five carpels in contrast to other species of Trollius) the carpels form a single (spiral) series. Thus floral development is similar in all three genera and, at a lower level, Adonis and Callianthemum are especially close but have different autapomorphies, which reflects the current classification of the genera.     

Cloning and expression of floral organ development-related genes in herbaceous peony (Paeonia lactiflora Pall.)

Herbaceous peony (Paeonia lactiflora Pall.) is an important ornamental plant that has different flower types. However, the molecular mechanism underlying its floral organ development has not been fully investigated. This study isolated six floral organ development-related genes in P. lactiflora, namely, APETALA1 (PlAP1), APETALA2 (PlAP2), APETALA3-1 (PlAP3-1), APETALA3-2 (PlAP3-2), PISTILLATA (PlPI) and SEPALLATA3 (PlSEP3). The expression patterns of these genes were also investigated in the three cultivars ‘Hangshao’, ‘Xiangyangqihua’ and ‘Dafugui’. Furthermore, gene expression during floral development was also analyzed in different organs. The results showed that PlAP1 was mainly expressed in the sepals, and PlAP2 was mainly expressed in the carpels and sepals. PlAP3-2 and PlPI had the highest expression levels in the stamens, followed by the petals. The expression levels of PlAP3-1 (from highest to lowest) were in the following order: petals, stamens, carpels and sepals. PlSEP3 was mainly expressed in sepals and carpels. With the depth of stamen petaloidy, the expression levels of PlAP1, PlAP2 and PlSEP3 increased, whereas those of PlAP3-1, PlAP3-2 and PlPI decreased, which showed that PlAP1 mainly determined sepals and petals of P. lactiflora. The PlAP2 not only determined the sepals and petals, and it participated in carpel formation. PlAP3-1, PlAP3-2 and PlPI mainly determined stamens and petals. PlSEP3 determined the identities of sepals and petals. This study would help determine the molecular mechanism underlying floral organ development in P. lactiflora.     

Floral development in Anemoneae (Ranunculaceae)

The floral development of two Clematis species and four Anemone species (including Pulsatilla) (Anemoneae, Ranunculaceae) is described. Shared features are: (1) sepals shortly after initiation broad, crescent‐shaped, as opposed to the other organs, which are narrow and hemispherical; (2) outermost organs of the androecium often smaller than the others and sometimes sterile; (3) carpels ascidiate, with distinctive stalk, stigma papillate, decurrent; the carpels have one median fertile ovule and a few lateral sterile ovules in all species studied; the fertile ovule appears before the carpel closes. Generic differences are: (1) In Clematis, four sepals are initiated in two pairs; sometimes one of the sepals in the second pair appears to be divided into two organs (double position) resulting in a pentamerous perianth; the first eight stamens are positioned in two alternating whorls, the outer whorl alternating with the four sepals. In Anemone, the perianth organs, if five, are initiated in spiral sequence; in the Pulsatilla group of Anemone, six sepals are initiated in two whorls; the first three organs of the androecium (staminodes) alternate with the inner sepals. (2) Further androecial organs are mostly in complex whorls (i.e. including double positions) in Clematis, but in an irregular spiral or in irregular complex whorls in Anemone. (3) Anther maturation is largely centripetal in Clematis, but centrifugal or bidirectional in Anemone. In Clematis macropetala, the outermost organs of the androecium lack anthers and the filaments expand and become petal‐like. In contrast, in the Pulsatilla group of Anemone, these organs retain sterile anthers and become small, capitate organs. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 162 , 77–100.     

Correlation between number and position of floral organs in Arabidopsis

Background and Aims

The study of variation in number, position and type of floral organs may serve as a key to understanding the mechanisms underlying their variation, and will make it possible to improve the analysis of gene function in model plant species by means of a more accurate characterization of mutant phenotypes. The present analysis was carried out in order to understand the correlation between number and position of floral organs in Arabidopsis thaliana.

Methods

An analysis of number and position of organs in flowers of wild type as well as in a series of mutations with floral organ position alterations was carried out, using light and electron microscopy. Variation common to different genotypes was analysed by means of individual diagrams, upon which generalized diagrams depicting variation in number and position of organs, were built by superimposition.

Key Results and Conclusions

It is shown that in the Arabidopsis flower a correlation exists between positions of petals and sepals, as well as between positions of stamens and carpels, whereas the position of carpels does not seem to depend on number and position of petals and stamens. This suggests that the position of organs in the basal (sepals) and apical (carpels) parts of the flower are determined before that in the intermediate zone. This assumption is consistent with the results of mathematical modelling and is supposed to be the consequence of stem-cell activity in the flower.     

MORPHOLOGY AND DEVELOPMENT OF THE FLOWERS OF BOOTTIA CORDATA,OTTELIA ALISMOIDES,AND THEIR SYNTHETIC HYBRID (HYDROCHARITACEAE)

The inferior ovary of Boottia cordata, Ottelia alismoides, and their hybrid is appendicular in nature, the carpels are congenitally only slightly connate, and they are unsealed. All floral organs except the sepals originate from common primordia in the female and bisexual flowers. A flat residual floral apex is pressnt. There is a vestigial superior ovary of three ontogenetically fused carpels in the male flower of Boottia cordata. The hybrid is intermediate in many characteristics and has partially fertile stamens and staminodia. The sequence of development in all flowers is acropetal. These plants appear to be related to the Butomaceae and they show evolutionary tendencies parallel to those in the Nymphaeaceae.     

Isolation and Characterization of an AGAMOUS-Like Gene from Magnolia wufengensis (Magnoliaceae)

The floral homeotic C function gene AGAMOUS (AG) plays crucial roles in Arabidopsis development by specifying stamen and carpel identity, repressing A-class genes, as well as regulating floral meristem determination. Although the function of AG homologs from other core eudicots appears highly conserved, the role of AG orthologs in the design of floral architecture in basal angiosperm remains unknown. We isolated and identified an AG ortholog from Magnolia wufengensis, a woody basal angiosperm belonging to the Magnoliaceae. Sequence and phylogenetic analyses revealed that it is a clade member of the euAG lineage, and hence, the gene is referred to as MAwuAG (M. wu fengensis AGAMOUS). Moreover, two highly conserved motifs specific to C proteins, AG motifs I and II, are found in the C-terminal regions of the MAwuAG protein, but the N-terminal extensions that usually appear in euAG lineage members from eudicots were not found in MAwuAG. The cDNA has the first in-frame ATG immediately preceding the MADS domain. A semi-quantitative PCR analysis showed that the expression of MAwuAG was restricted to reproductive organs of stamens and carpels. The transgenic Arabidopsis containing 35S::MAwuAG displayed extremely early flowering, bigger stamens and carpels, and homeotic conversion of petals into staminoid organs, but ectopic expression of MAwuAG in the first whorls failed to convert the sepals into carpeloid structures that are usually observed in the overexpression transgenic Arabidopsis of AG orthologs from other core eudicots. In addition, the phenotype of the transgenic 35S::MAwuAG Arabidopsis revealed that the abscission of the outer three floral whorls (sepals, petals, and stamens) was inhibited.     

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.     

Floral development of Dichocarpum, Thalictrum, and Aquilegia (Thalictroideae, Ranunculaceae)

We examined the floral development of Dichocarpum fargesii, Thalictrum fargesii, Thalictrum przewalskii, and Aquilegia yabeana in Thalictroideae, Ranunculaceae, by scanning electron microscope. The sepals are initiated spirally in D. fargesii and A. yabeana, and in two pairs (with four sepals) or spirally (with five sepals) in T. fargesii and T. przewalskii. The petals in D. fargesii and A. yabeana and the stamens and carpels are initiated in a whorled pattern in all three genera. The floral phyllotaxis is whorled in these genera. The primordia of sepals are lunular and truncate, but that of petals and/or stamens are hemispherical, rounded, and much smaller than the sepal primordia. A relatively long plastochron exists between the last sepal and the first petal in D. fargesii and A. yabeana or the first stamen in T. fargesii and T. przewalskii. The similarity between the primordia of petals and stamens may indicate an evolutionary relationship between petals and stamens. The petals develop slower than the stamens in D. fargesii, but faster than stamens in A. yabeana. The early developmental stages of the staminodes in A. yabeana are similar to that of stamens, so they may be phylogenetically homologous organs. The carpel primordia are initiated in a single whorl; are lunular in shape and plicate in A. yabeana and D. fargesii; and are initiated spirally and hemispheric in shape and ascidiate in T. fargesii and T. przewlaskii. The stigma is everted and decurrent with unicellular papillae in T. fargesii and T. przewalskii; the head has unicellular papillae in D. fargesii and is smooth in A. yabeana. The floral development features of Aquilegia are unique in Thalictroideae.     

Contributions to the systematic position of Hydrolea (Hydroleaceae) based on floral development

In the flower of Hydrolea palustris, unusually orientated with one sepal abaxially, organogenesis starts in following sequence: five sepals (2/5 sequence), five simultaneously initiated alternating petals, five episepalous stamens, two (seldom three) carpels forming a coenocarpous septate gynoecium. The two carpels are orientated rather in the diagonal floral plane than in the median one. Petal primordia fuse very late by forming interprimordial bridges (late sympetaly!). Many ovules develop on considerably widened placentas. On the very basis of the superior ovary a five-humped nectary disk is formed.Within Solanales (APG II 2003) late sympetaly, an intrastaminal disk and a 2-carpellate, septate, superior ovary are found in Hydroleaceae, Convolvulaceae, and Solanaceae. Enlarged axile placentas characterize Hydrolea, Solanaceae, and Sphenocleaceae but Sphenocleaceae differ considerably by early sympetaly. Montiniaceae differ by having a choripetalous corolla. Nearly diagonal orientation of the carpels seems to relate Hydrolea close to Solanaceae, but the orientation of the calyx is different.     

基于扫描电镜技术的天葵属(毛茛科)花器官发生研究

毛茛科天葵属为东亚特有类群,但其花器官的发生过程仍不清晰。该研究利用扫描电子显微镜观察了天葵［S. adoxoides (DC.) Makino］花器官的发生过程,以揭示毛茛科花形态的多样性和演化规律,为进一步探讨天葵属与近缘类群的亲缘关系提供发育形态学证据。结果表明：(1)天葵萼片、花瓣和雄蕊均为螺旋状发生,轮状排列;不育雄蕊的数目和位置不定,心皮轮状发生。(2)天葵萼片原基为宽阔的新月形,其他花器官为窄的半球形。(3)天葵花发育后期,花瓣有延迟发育现象,花瓣原基基部发育为浅囊状,心皮原基马蹄形对折,胚珠倒生、双珠被、具胎座附属物。(4)天葵属与耧斗菜属、尾囊草属的花发育性状存在相似性,支持分子系统学证据的三者近缘的观点;天葵属的花性状的特殊表现为：花直径较小,雄蕊、不育雄蕊和心皮数目较少,花器官没有形成明显的直列线,内珠被较长等。     

FLORAL DEVELOPMENT IN CAESALPINIA (LEGUMINOSAE)

Utilizing scanning electron microscopy, we studied the early floral ontogeny of three species of Caesalpinia (Leguminosae: Caesalpinioideae): C. cassioides, C. pulcherrima, and C. vesicaria. Interspecific differences among the three are minor at early and middle stages of floral development. Members of the calyx, corolla, first stamen whorl, and second stamen whorl appear in acropetal order, except that the carpel is present before appearance of the last three inner stamens. Sepals are formed in generally unidirectional succession, beginning with one on the abaxial side next to the subtending bracts, followed by the two lateral sepals and adaxial sepal, then lastly the other adaxial sepal. In one flower of C. vesicaria, sepals were helically initiated. In the calyx, the first-initiated sepal maintains a size advantage over the other four sepals and eventually becomes cucullate, enveloping the remaining parts of the flower. The cucullate abaxial sepal is found in the majority of species of the genus Caesalpinia. Petals, outer stamens, and inner stamens are formed unidirectionally in each whorl from the abaxial to the adaxial sides of the flower. Abaxial stamens are present before the last petals are visible as mounds on the adaxial side, so that the floral apex is engaged in initiation of different categories of floral organs at the same time.     

Early floral development of Pentaphylacaceae (Ericales) and its systematic implications

Early floral development of four species from the genera Anneslea, Cleyera, Eurya, and Ternstroemia of Pentaphylacaceae, was studied comparatively using scanning electron microscopy. Together with earlier studies in Euryodendron and Adinandra, 6 out of 12 genera of Pentaphylacaceae have now been studied for their floral development. The usually pentamerous flowers of these taxa share a number of developmental features: the perianth organs appear in a clockwise or anticlockwise spiral sequence on the floral apex with relatively long plastochrons between successive organs, resulting in conspicuous size differences among perianth organs during early developmental stages. The early development of the usually polystemonous androecium is characterized by an indistinct ring-primordium and a mostly concave floral apex; individual stamens appear subsequently on this ring-primordium. However, further development of the androecium differs conspicuously among taxa and we describe three main developmental patterns for the family including features such as centripetal stamen whorls and stamens fascicles. Unusual features of floral development and organization of Pentaphylacaceae include: (1) a pronounced spiral sequence of organ appearance during early floral development in perianth and androecium; (2) the occurrence of paired organs in the corolla and the androecium of some species; (3) sepals and petals that are positioned opposite from each other in the genera Anneslea and Ternstroemia; and (4) a concave floral apex at the beginning of androecium development. From a systematic point of view our results clearly support a close relationship between Anneslea and Ternstroemia and also suggest a closer relationship among Adinandra, Cleyera, and Euryodendron on the one hand and between Eurya and Visnea on the other. Further, our developmental study stresses the differences between Pentaphylacaceae and Theaceae, which earlier where thought to form a natural group of plants. While high stamen numbers are achieved via centripetal pattern of stamen formation in the former family, stamens are formed centrifugally in the latter.     

Eucalypt MADS-Box Genes Expressed in Developing Flowers

Three MADS-box genes were identified from a cDNA library derived from young flowers of Eucalyptus grandis W. Hill ex Maiden. The three egm genes are single-copy genes and are expressed almost exclusively in flowers. The egm1 and egm3 genes shared strongest homology with other plant MADS-box genes, which mediate between the floral meristem and the organ-identity genes. The egm3 gene was also expressed strongly in the receptacle or floral tube, which surrounds the carpels in the eucalypt flower and bears the sepals, petals, and numerous stamens. There appeared to be a group of genes in eucalypts with strong homology with the 3′ region of the egm1 gene. The egm2 gene was expressed in eucalypt petals and stamens and was most homologous to MADS-box genes, which belong to the globosa group of genes, which regulate organogenesis of the second and third floral whorls. The possible role of these three genes in eucalypt floral development is discussed.