FLORAL ORGANOGENESIS IN FIVE GENERA OF THE MARANTACEAE AND IN CANNA (CANNACEAE)

The paired flowers of all species of the Marantaceae studied, except Monotagma plurispicatum, are produced through the division of an apical meristem with a tunica-corpus structure. The solitary flowers of M. plurispicatum develop from a similar meristem which does not bifurcate. The paired flowers of Canna indica are produced in the axil of a florescence bract through the formation of a bract and an axillary flower on the side of the primordium which gives rise to the largest flower of the pair. The sequence of organ initiation for both families is: calyx, corolla and inner androecial whorl, outer androecial whorl, gynoecium. The sequence of sepal formation is opposite in the two families. In the Cannaceae it leads directly into the spiral created by the formation of the other organs, while in the Marantaceae the sequence of sepal formation follows a spiral opposite to that of the other floral organs. The members of the corolla and inner androecial whorl separate from common primordia. In general these common primordia separate into a petal and an inner androecial member through the initiation of two growth centers, at the same level, in the dorsal and ventral flanks of the primordium. In Ischnosiphon elegans and Pleiostachya pruinosa the stamen is initiated at a lower position than the petal in the ventral flank of the common primordium. A similar pattern of initiation is described for the callose staminode in Marantochloa purpurea and Canna indica. This pattern is interpreted as a variation on the more generalized pattern of inner androecial formation found in the other genera.     

地质时期樟科植物花化石及其系统演化意义

该研究对地质时期樟科植物花化石的主要类群,即Androglandula、Lauranthus、Mauldinia、Neusenia、Perseanthus和Potomacanthus属分别从属和种的形态特征、分布、地层以及系统意义进行了论述,并结合现代樟科植物从地层和分布、花序类型、花部形态特征和显微构造特征进行了分析。结果表明:(1)樟科植物在中晚白垩纪期,已经起源于劳亚古陆的中纬度区域。(2)樟科植物的花序类型为Mauldinia属的侧生花序类型和假伞形花序类型。(3)花为3基数的两性花,花被片6枚排列为2轮,雄蕊12或6,排列为4、3或2轮,最内轮雄蕊不育,第三轮雄蕊基部常见一对附属腺体,雄蕊药室瓣裂,4或2药室,雌蕊为单心皮。(4)花被片上常有大量的油细胞、并列型气孔器和单细胞毛。该研究结果中樟科花化石的发现,为樟科植物的系统演化提供了古生物学的证据和资料。     

HOMEOSIS IN THE FLOWERS OF THE ZINGIBERALES

Homeosis has played an important role in the evolution of the flowers of the Zingiberales, especially those of the Ginger Group. In the Zingiberaceae, two members of the outer androecial whorl are replaced by a lip, and two members of the inner androecial whorl are replaced by petaloid staminodes. Most of the androecium of the Costaceae has also been replaced by petaloid structures, and the single fertile stamen is often attached to an enlarged petaloid “filament.” The Cannaceae and Marantaceae have one-half of one fertile anther and three to four variously modified staminodes. In contrast, homeosis has played a minor role in floral evolution of the Banana Group. Only in the Heliconiaceae has a stamen been replaced by a staminode. In none of the families of the Zingiberales do the staminodes assume the total “form or character” of any perianth members. Because of this, it is reasonable to extend the definition of homeosis to include replacement by an organ like, but not identical to, some other part of the plant.     

Floral vasculature and ontogeny in Canna indica

The identity of the labellum is a hot point in Zingiberales, which has long been discussed by many authors. In this study, floral vasculature and ontogeny of Canna indica (Cannaceae) was observed by LM and SEM in order to ascertain the identity of the labellum and the functional stamen of this species and provide evidence for the homologies of the floral organs in Zingiberales. The results indicate that the labellum of C. indica have incorporated two androecial members from both outer and inner whorls, rather than three, one or half member, as previously suggested by morphologists of Cannaceae flowers. The two labellum traces are here interpreted as: one from the outer androecial whorl (diverging from the carpellary dorsal bundle), while the other from the inner androecial whorl (diverging from the parietal bundle). The functional stamen also incorporates two androecial bundles, the same as the labellum: one trace from the carpellary dorsal bundle, and the other (the petaloid appendage) from the parietal bundle. In addition, the origin of the vascular system in the androecium of Zingiberales and its systematic significance are discussed.     

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.     

ORGANOGENESIS IN FLOWERS OF THE HOMEOTIC GREEN PISTILLATE MUTANT OF TOMATO (LYCOPERSICON ESCULENTUM)

The flowers of a previously undescribed recessive mutant of tomato, green pistillate, show strong and consistent homeotic transformation of petals to sepals in whorl two and of stamens to carpels in whorl three. The phenotype at early and later stages is compared with wild type by scanning electron microscopy. Wild type and mutant show no difference in the pattern or timing of third whorl organ initiation, as shown by allometric analysis of scanning electron micrographs of early stages. This confirms that the mechanisms governing organ identity are distinct from those governing the positions and numbers of organs initiated; the former can be altered without changes in the latter. Mutant and wild type organs are compared by allometric analysis of dimensions of flowers dissected throughout development. The sepaloid petals (whorl 2) and the carpelloid stamens (whorl 3) in the mutant elongate at relative rates normal for the wild type organ of the whorls they occupy. This suggests that some aspects of organ growth, such as elongation rate, may also be independent of mechanisms governing organ identity.     

FLORAL DEVELOPMENT OF HYDROCHARIS MORSUS-RANAE (HYDROCHARITACEAE)

In both male and female flowers of H. morsus-ranae the primordia of the floral appendages appear in an acropetal succession consisting of alternating trimerous whorls. In the male flower a whorl of sepals is followed by a whorl of petals, three whorls of stamens, and a whorl of filamentous staminodes. The mature androecial arrangement therefore consists of two antisepalous stamen whorls, an antipetalous whorl of stamens, and antipetalous staminodes. Shortly before anthesis, basal meristematic upgrowth between filaments of adjacent whorls produces paired stamens, joining Whorls 1 and 3, and Whorl 2 with the staminodial whorl. A central domelike structure develops between the closely appressed filaments of the inner stamen and staminodial whorl, giving the structure a lobed appearance. After petal inception in the female flower a whorl of antisepalous staminodes develop, each of which may bifurcate to form a pair of staminodes. During staminode development a girdling primordium arises by upgrowth at the periphery of the floral apex. The girdling primordium rapidly forms six gynoecial primordia, which then go on to produce six free styles with bifid stigmas. Intercalary meristem activity, below the point of floral appendage attachment, leads to the production of a syncarpous inferior ovary with six parietal placentae. The styles and carpels remain open along their ventral sutures. During the final stages of female floral development, several hundred ovules develop along the carpel walls, and three nectaries develop dorsally and basally on the three antipetalous styles.     

Models of floral pattern in detached flowers of Silene coeli-rosa (L) Godr. (Caryophyllaceae)

Organ number per whorl was analysed in aberrant flowers of the long-day (LD) plant , Silene coeli-rosa , to test a hypothesis that organ number in a whorl takes its cue from an adjacent outer whorl and that perturbed organ number per whorl is not random but defaults to that of closely related taxa or genera of the Caryophyllaceae. When plants were grown under short-days (SD), transferred to LD and the shoot meristem excised and cultured in vitro under SD, the normal pattern of flower development was often disrupted. For example, we observed flowers which comprised floral whorls with an aberrant number of floral organs. In part, this was an effect of tissue culture; however, the over-and-above effect was the establishment of an alternative pattern of development. Our data indicate that two distinct and recurrent patterns occurred in the aberrant flowers we observed in five separate experiments. First, pairs of floral whorls were linked so that aberration in one whorl resulted in the next whorl being more aberrant than normal. Second, the number of organs in aberrant whorls was not random, but defaulted to an organ number which mimicked the flowers of closely related species of Silene or related genera in the Caryophyllaceae.  © 2002 The Linnean Society of London , Botanical Journal of the Linnean Society , 2002, 140 , 229−235.     

Flower development in Abrus precatorius (Leguminosae: Papilionoideae: Abreae) and a review of androecial characters in Papilionoideae

The jequirity bean (Abrus precatorius) is well known because of its shiny black and red coloured seeds and because of the poison (abrin) it contains. The genus Abrus is placed in a monogeneric tribe Abreae which is placed in a relatively isolated systematic position at the base of Millettieae. To contribute to a better understanding of this taxon, a detailed ontogenetic and morphologic analysis of its flowers is presented. Floral primordia are subtended by an abaxial bract and preceded by two lateral bracteoles which are formed in short succession. Sepal formation is unidirectional starting abaxially. All petals are formed simultaneously. The carpel is formed concomitantly with the outer (antesepalous) stamen whorl, which arises unidirectionally, starting in an abaxial position. In the inner, antepetalous stamen whorl two abaxial stamens are formed first, followed by two lateral stamen primordia. The adaxial, antepetalous position remains organ free (i.e. this stamen is lost). Later in development the nine stamen filaments fuse to form an adaxially open sheath. The filament bases of the two adaxial outer-whorl stamens grow inwards, possibly to provide stability and to compensate for the lost stamen. In the mature flower a basal outgrowth can be found in the position of the lost stamen. However this is more likely to be an outgrowth of the filament sheath rather than a remnant of the lost stamen. These ontogenetic patterns match in parts those found in other Millettieae (unidirectional formation of sepals and stamens, simultaneous petal formation). In contrast, the complete loss of a stamen is rather unusual and supports the isolated position of Abreae and probably justifies (among other characters) its tribal status. A review of androecial characters shows that androecial merosity is on the one hand extremely variable among Leguminosae, varying from a single stamen per flower to more than 500. On the other hand it is noteworthy that the number of stamens becomes stabilised in more derived Papilionoideae such as the large non-protein-amino-acid-accumulating clade (NPAAA clade). This indicates that the androecium has played an important role in the success of a major part of Leguminosae.     

FLORAL DEVELOPMENT IN MANGROVE RHIZOPHORACEAE

The flowers of mangrove Rhizophoraceae (tribe Rhizophoreae) are adapted to three different pollination mechanisms. Floral development of representative species of all four genera suggests that the ancestral flower of the tribe was unspecialized, with successively initiated whorls of separate sepals, petals, antisepalous stamens, and antipetalous stamens; at its inception, the gynoecium had a united, half-inferior ovary and separate stigmatic lobes. This developmental pattern is found in Rhizophora mangle (wind-pollinated) and Ceriops decandra (insect-pollinated). In Kandelia, all floral organs distal to the sepals are initiated simultaneously, and there has apparently been an evolutionary amplification in the number of stamens to about six times the number of petals. Explosive pollen release evolved independently in C. tagal and in Bruguiera. In the former, all stamens belong to one whorl and arise simultaneously upon a very weakly differentiated androecial ring primordium. In Bruguiera, the androecial ring is pronounced, and two whorls of stamens arise upon it; the primordia of the antisepalous whorl arise first but are closer to the center of the apex than the antipetalous stamen primordia. The antisepalous stamens bend toward and are enclosed by the petals early in development. In all genera, the inferior ovary develops by zonal growth of receptacular tissue; additional intercalary growth above the placenta occurs in Bruguiera. In general, floral specialization is accompanied by an increase in the width of the floral apex compared to the size of the primordia, increasing fusion of the stylar primordia, and decreasing prominence of the superior portion of the ovary. Apparent specializations of petal appendages for water storage, including the presence of sub-terminal hydathodes (previously unreported in any angiosperm), were found in two species in which flowers remain open during the day but were absent from two species normally pollinated at night or at dawn. Distinctive tribal characteristics that may aid in phylogenetic analysis include the mode of development of the inferior ovary; the aristate, bifid, usually fringed petals that individually enclose one or more stamens; the intrastaminal floral disc; and the initially subepidermal laticiferous cell layer in the sepals and ovary.     

Morphology, development and homologies of the perianth and floral nectaries in Croton and Astraea (Euphorbiaceae-Malpighiales)

New observations are presented on the ontogeny, vasculature and morphology of both staminate and pistillate flowers of Croton and Astraea. These data support earlier hypotheses that the filamentous structures in pistillate flowers represent reduced and transformed petals. Staminate flowers of both genera possess five free nectaries, which are vascularised by divergences of the sepal traces in Croton and unvascularised in Astraea. In pistillate flowers, there are five separate non-vascularised nectaries in Astraea, but in Croton there is a single nectariferous disk that is vascularised by divergences of the sepal traces. The nectaries are initiated late in floral development, but their location indicates that they could represent the outer stamen whorl transformed into secretory staminodes. Other glandular structures occur in pistillate flowers of most Croton species, resulting in flowers with two secretory organ whorls. In these cases, the inner whorl is formed by modified staminodes. Our observations support the recent segregation of Astraea species from the larger genus Croton. Despite strong similarities between the two genera, there are clear structural differences, including the presence of colleters in Astraea (absent in Croton), moniliform trichomes on petals (rather than simple trichomes in Croton), non-vascularised nectaries (vascularised in Croton) and reduced, non-secretory filamentous structures (well developed and secretory in Croton).     

RABBIT EARS is a second-whorl repressor of AGAMOUS that maintains spatial boundaries in Arabidopsis flowers

The RABBIT EARS (RBE) gene has been identified as a regulator of petal development in Arabidopsis thaliana. We find that second-whorl petals in rbe mutants can be replaced with staminoid organs, stamens or filaments and that some rbe flowers have increased numbers of sepals and exhibit fusion of sepals. We show that these rbe defects are due to AGAMOUS (AG) misexpression in the second whorl. Consistent with its role in maintaining the spatial boundary of AG expression, rbe enhanced the second-whorl defects present in ap2-1, lug-1 and clf-2 mutants. In the development of second-whorl organs, RBE acts in the same pathway and downstream of UNUSUAL FLORAL ORGANS (UFO). Enhanced first-whorl organ fusion in ap2-2 rbe-3, ant-4 rbe-3 and cuc2-1 rbe-3 double mutants supports an additional role for RBE in organ separation. RBE thus acts to maintain two different types of spatial boundaries in young flowers: boundaries between organ primordia within a whorl and boundaries of homeotic gene expression between whorls.     

Floral vasculature in Alpinia hainanensis in relation to the nature of the labellum in gingers

Observations presented here on floral vasculature in Alpinia hainanensis indicate that the labellum incorporates elements of five androecial members rather than two or three, as suggested by previous authors for Zngiberaceae flowers. The pedicel contains an outer ring and a central region of vascular bundles. Three carpellary dorsal bundles (CDs) and three alternatively arranged parietal bundles (PBs) separate from the central region successively. The remaining bundles of the central region run upwards and become the placental bundles to supply ovules. The placental bundles terminate between the top of the locular region and the base of the prolongation. The three PBs divides into about five strands respectively. Of which the outer strand enters into the petal being its midrib and the remaining strands move into the stamen adaxially being the vasculature of the functional stamen and the labellum abaxially being the lateral strands of the labellum. The three CDs divide into about five traces, of which the outer strand becomes the midrib of each sepal and the inner strand runs into the style. The remaining traces re‐unite, re‐divide again in the course up and the two adaxial sets of carpellary dorsals finally enter into the labellum being the marginal traces of it while the abaxial single strand enters into the labellum being its midrib. The two antero‐lateral glands receive small traces without lignified tube elements from the vascular plexus, which fonn in prolongation from both PBs and CDs and a few small strands in the ovary wall. There are no subulate appendages differentiated in the flower of Alpinia hainanensis. Hereby, the median of the sepals, both the marginal portions and the median of labellum, and the style have the same origin in vasculature from the CDs and so do the stamen, the lateral portions of labellum and the median of the petals from PBs. The labellum is supposed to represent three members of the outer androecial whorl by its two marginal portions and the median and two members of the inner whorl by its two lateral parts except the median.     

Functional analysis of B and C class floral organ genes in spinach demonstrates their role in sexual dimorphism

Background  

Evolution of unisexual flowers entails one of the most extreme changes in plant development. Cultivated spinach, Spinacia oleracea L., is uniquely suited for the study of unisexual flower development as it is dioecious and it achieves unisexually by the absence of organ development, rather than by organ abortion or suppression. Male staminate flowers lack fourth whorl primordia and female pistillate flowers lack third whorl primordia. Based on theoretical considerations, early inflorescence or floral organ identity genes would likely be directly involved in sex-determination in those species in which organ initiation rather than organ maturation is regulated. In this study, we tested the hypothesis that sexual dimorphism occurs through the regulation of B class floral organ gene expression by experimentally knocking down gene expression by viral induced gene silencing.     

FLORAL MORPHOLOGY OF HORSFIELDIA (MYRISTICACEAE)

The pistillate flowers of Horsfieldia are morphologically similar to those of Myristica and Knema, and are composed of a single whorl of thick, fleshy tepals, and an unsealed, monocarpellate pistil bearing a single ovule. The carpel is vascularized by two ventral bundles, a pair of dorsal bundles, and several supernumerary bundles. The ovule vascularization is derived from the supernumerary bundles. Paired dorsal vascular bundles are an uncommon feature of uncertain significance. Carpels of Myristica and Knema lack any clearly defined dorsal vasculature, and the ovule vascular supply is derived from both the ventral and supernumerary bundles. The organization of the staminate flowers of Horsfieldia agrees with the myristicaceous pattern observed in Myristica and Knema. Each androecium consists of a single whorl of anthers fused or partially fused to a massive connective column. Each anther consists of a pair of bisporangiate lobes and a single vascular bundle. The androecial forms observed are interpreted as forming a series of intermediates between the monadelphous type of androecia of two South American genera, Compsoneura and Dialyanthera, and one African genus, Brochneura, and the solid, columnar androecia which are predominate in the family. Accumulating evidence supports a proposed South American or west Gondwanaland origin of the Myristicaceae.     

Characterization of <Emphasis Type="Italic">SpAPETALA3</Emphasis> and <Emphasis Type="Italic">SpPISTILLATA</Emphasis>, B class floral identity genes in <Emphasis Type="Italic">Spinacia oleracea</Emphasis>, and their relationship to sexual dimorphism

Floral organ identity B class genes are generally recognized as being required for development of petals and stamens in angiosperm flowers. Spinach flowers are distinguished in their complete absence of petals in both sexes, and the absence of a developed stamen whorl in female flowers. As such, we hypothesized that differential expression of B class floral identity genes is integral to the sexual dimorphism in spinach flowers. We isolated two spinach orthologs of Arabidopsis B class genes by 3 and 5 RACE. Homology assignments were tested by comparisons of percent amino acid identities, searches for diagnostic consensus amino acid residues, conserved motifs, and phylogenetic groupings. In situ hybridization studies demonstrate that both spinach B class genes are expressed throughout the male floral meristem in early stages, and continue to be expressed in sepal primordia in reduced amounts at later stages of development. They are also highly expressed in the third whorl primordia when they arise and continue to be expressed in these tissues through the development of mature anthers. In contrast, neither gene can be detected in any stage in female flowers by in situ analyses, although northern blot experiments indicate low levels of SpAP3 within the inflorescence. The early, strong expressions of both B class floral identity genes in male floral primordia and their absence in female flowers demonstrate that B class gene expression precedes the origination of third whorl primordia (stamen) in males and is associated with the establishment of sexual floral dimorphism as it initiates in the first (sepal) whorl. These observations suggest that regulation of B class floral identity genes has a role in the development of sexual dimorphism and dioecy in spinach rather than being a secondary result of organ abortion.Electronic Supplementary Material Supplementary material is available for this article at Edited by G. Jürgens     

甘草腺体结构及对渗透胁迫的调节作用

甘草叶片上的腺体是其特殊的耐旱形态学结构,通过腺体分泌多糖调节叶肉细胞渗透势是其耐旱的重要生理特征。甘草叶片处于两面对称叶尚未展开期,部分腺体头部已分泌积累呈球状的多糖液,约占总腺体数的13.0%;部分腺体开始分泌多糖液,约占总腺体数的11.6%;75.3%的腺体尚未开始分泌多糖液,表明该期的腺体已有部分开始参与渗透调节。甘草发育成熟的功能叶上的所有腺体头部都分泌有呈球状的多糖液,表明该期所有的腺体都通过向外分泌多糖参与渗透调节。15%PEG+Hoagland培养的渗透胁迫比Hoagland培养的非渗透胁迫,叶内多糖增加了59.8%(P<0.01)。甘草通过腺体向腺体外分泌多糖液的作用,维持叶肉细胞适合的渗透势是甘草一种主动调节过程和方式。     

Early Floral Development of Endangered Euryodendron excelsum (Ternstroemioideae: Theaceae)

The floral development of a critically endangered plant Euryodendron excelsum from Ternstroemioideae (Theaceae) has been observed under scanning electron microscope (SEM) for the first time . The flower of E. excelsum is bisexual and teleianthous . Five sepal primordia are initiated 2&#1089839;5 spirally and arranged in one whorl when mature , and so are petals. Sepals and petals are initiated in the same order either clockwise or counterclockwise in the same flower . The androecial part is a ring primordium in the beginning . The first five stamen primordia are initiated on this ring primordium at antisepalous positions and then other stamen primordia appear on two sides of each of the first five primordia . Finally a total of 25 stamen primordia are initiated from the ring primordium and arranged in one whorl but could be grouped into 5 fascicles. Three sequentially initiated carpels compose an ovary which has an axile- central placenta with three locules and a truncateand indehiscent stigma . The floral development of E. excelsum is distinctly different from plants in Theoideae .