Unusual alternations of floral organs in <Emphasis Type="Italic">Paeonia</Emphasis>: Structure and possible mechanism of formation

Morphological analysis of flowers was carried out in Paeonia L. cultivars. Some unusual alternations of floral organs were described: sepal-(petal-stamen) × n-carpel, where 2 ≤ n ≤ 4 (appearance of an additional zone of petal and stamen formation in the medial flower part). The identity of floral organs was not affected in the flowers with this unusual alternation. It was shown on the basis of mathematical simulation of the genes responsible for flower development that these alternations may be determined by increased pool of stem cells, which may lead to delayed termination of flower development.     

HELICAL FLORAL ORGANOGENESIS IN GLEDITSIA,A PRIMITIVE CAESALPINIOID LEGUME

In order to determine the extent of floral ontogenetic differences among species of a genus, six species of Gleditsia were studied. Gledilsia is one of only two leguminous genera known in which there is completely helical succession of floral organs. Floral ontogeny was compared in three species (Gleditsia amorphoides, G. aquatica, and G. triacanthos), and late stages in six species (including the first three plus G. caspica, G. delavayi, and G. japonica). Other unusual primitive developmental features include the unequal-sized flower primordia which produce flowers of variable merosity. Order of floral development is also loosely controlled, so that flowers of different growth stages are intermixed in the inflorescence. Variable features include the occurrence of floral bracts, merosity of flowers, number of organs, and position of the first organ (sepal) initiated. The inflorescence type, while usually a raceme, often has lateral branches near the base, or fascicles of flowers at some points. A terminal flower often is present, although not in all species. Sex of flowers and inflorescences also varies, although floral initiation tends to include both stamens and carpel primordia. Suppression of one or the other may occur at different stages of development. Carpel orientation also varies; the cleft may be tilted or inverted occasionally. It is proposed that absence of subtending floral bracts influences development so as to favor radial symmetry and establishment of other “chaotic” characters seen in Gledilsia flowers.     

THE DEVELOPMENTAL BASIS FOR SEXUAL EXPRESSION IN CERATONIA SILIQUA (LEGUMINOSAE: CAESALPINIOIDEAE: CASSIEAE)

The flowers of Ceratonia siliqua, an anomalous caesalpinioid legume in the tribe Cassieae, are unusual in being unisexual and in lacking petals. Inflorescence development, organogeny, and flower development are described for this species. All flowers are originally bisexual, but one sex is suppressed during late development of functionally male and female flowers. Ceratonia siliqua is highly plastic in sexuality of individuals, inflorescence branching pattern, racemose or cymose inflorescences, bracteole presence, terminal flower presence, organ number per whorl, missing floral organs, pollen grain form, and carpel cleft orientation. Order of initiation is: five sepals in helical order, then five stamens in helical order together with the carpel. Each stamen is initiated as two alternisepalous primordia that fuse to become a continuous antesepalous ridge; in some flowers, the last one or two stamens of the five may form as individual antesepalous mounds. Petal rudiments are occasional in mature flowers. Position of organs is atypical: the median sepal is on the adaxial side in Ceratonia, rather than abaxial as in most other caesalpinioids. This feature in Ceratonia may be viewed as a link to subfamily Mimosoideae, in which this character state is constant.     

The Effect of Flower Maturity and Harvest Timing on Floral Extract fromBoronia megastigma(Nees)

Development of floral organs during maturation of flower budsinto fully open boronia flowers is described. The petals andfunctional anthers attain their maximum size prior to the non-functionalanthers and the stigma. Organoleptic properties of the floralextract change with successive stages of bud development. Theconcentrations of extract and volatiles in the extract (% byf. wt) increase as buds mature, the extract concentration beinghighest in large buds and open flowers and the concentrationof volatile compounds being highest in open flowers. The rateof flower and extract development was measured. Yields of flowermaterial and floral extract per plant, and the concentrationof total volatiles including ß-ionone reach maximumlevels when 70% of flowers have reached anthesis. All measuredfactors decline after this point, except extract concentration(% of f. and d. wt) which is maintained up to 83% open flowers. Boronia megastigma(Nees); brown boronia; Rutaceae; flower development; floral extract; solvent extraction; ß-ionone; essential oils     

Changes in polyamine pattern mediates sex differentiation and unisexual flower development in monoecious cucumber (Cucumis sativus L.)

Changes in the levels of polyamines are associated with fundamental physiological processes such as embryogenesis, induction of flowering, fruit development and ripening, senescence, and responses to environmental stresses, but the role of polyamines in sex differentiation and unisexual flower development has not been deeply studied. To extend the knowledge on the regulatory mechanisms of flowering in monoecious plant (producing unisexual flowers), we investigated the morphogenesis and free polyamine levels in Cucumis sativus during sex differentiation and unisexual flower development in vitro using histocytological and biochemical methods. As shown in our study, floral development in vitro was undisturbed and flowers of both sexes were produced. Sex differentiation relied on preventing the development of generative organs of the opposite sex, as we observed carpel repression in male flowers and stamen repression in female flowers. Pollen viability was negatively correlated with female flower development on the same node. Biochemical analysis revealed increased accumulation of aliphatic amines (tri, tetra‐amines) in generative (flower buds and flowers) compare to vegetative (axillary buds and leaves) organs. Undifferentiated floral buds contained elevated levels of agmatine, cadaverine, spermidine and spermine. Sex differentiation was associated with significantly decreased levels of agmatine and cadaverine. Our results showed that female flowers contained higher levels of total polyamine than male flowers. The increased level of cadaverine was associated with macrogametogenesis and female flower maturation. Putrescine was important for male flower development. Such results support the hypothesis that aliphatic amines are involved in unisexual flower development.     

Surprising absence of association between flower surface microstructure and pollination system

• The epidermal cells of flowers come in different shapes and have different functions, but how they evolved remains largely unknown. Floral micro‐texture can provide tactile cues to insects, and increases in surface roughness by means of conical (papillose) epidermal cells may facilitate flower handling by landing insect pollinators. Whether flower microstructure correlates with pollination system remains unknown.
• Here, we investigate the floral epidermal microstructure in 29 (congeneric) species pairs with contrasting pollination system. We test whether flowers pollinated by bees and/or flies feature more structured, rougher surfaces than flowers pollinated by non‐landing moths or birds and flowers that self‐pollinate.
• In contrast with earlier studies, we find no correlation between epidermal microstructure and pollination system. The shape, cell height and roughness of floral epidermal cells varies among species, but is not correlated with pollinators at large. Intriguingly, however, we find that the upper (adaxial) flower surface that surrounds the reproductive organs and often constitutes the floral display is markedly more structured than the lower (abaxial) surface.
• We thus conclude that conical epidermal cells probably play a role in plant reproduction other than providing grip or tactile cues, such as increasing hydrophobicity or enhancing the visual signal.

     

Genetic analyses of signalling in flower development using Arabidopsis

Flower development can be divided into four major steps: phase transition from vegetative to reproductive growth, formation of inflorescence meristem, formation and identity determination of floral organs, and growth and maturation of floral organs. Intercellular and intracellular signalling mechanisms must have important roles in each step of flower development, because it requires cell division, cell growth, and cell differentiation in a concerted fashion. Molecular genetic analysis of the process has started by isolation of a series of mutants with unusual flowering time, with aberrant structure in inflorescence and in flowers, and with no self-fertilization. At present more than 60 genes are identified from Arabidopsis thaliana and some of them have cloned. Although the information is still limited, several types of signalling systems are revealed. In this review, we summarize the present genetic aspects of the signalling network underlying the processes of flower development.     

Do floral herbivores respond to variation in flower characteristics in Gelsemium sempervirens (Loganiaceae), a distylous vine?

We tested the hypothesis that traits traditionally thought to function in pollination can also influence attack by floral herbivores. Because distylous species produce two different flower types, we used Gelsemium sempervirens, a distylous vine of southeastern USA, to examine the frequency and pattern of floral herbivory in relation to floral characteristics. Flowers of the short-styled morph had larger corollas but showed no difference in the volume or concentration of nectar produced. Over the 2 yr of this study, 20-30% of plants suffered floral herbivory. The pattern of damage was morph-specific. Long-styled flowers were more likely to have damaged pistils, while stamens were more often damaged in short-styled flowers. In this distylous species, exserted flower organs were more likely to be eaten. Such differential herbivory based on the position of floral organs within a flower may result in reduced fitness via either male (short-styled morph) or female function (long-styled morph).     

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。     

Does the morphological fit between flowers and pollinators affect pollen deposition? An experimental test in a buzz‐pollinated species with anther dimorphism

Some pollination systems, such as buzz‐pollination, are associated with floral morphologies that require a close physical interaction between floral sexual organs and insect visitors. In these systems, a pollinator's size relative to the flower may be an important feature determining whether the visitor touches both male and female sexual organs and thus transfers pollen between plants efficiently. To date, few studies have addressed whether in fact the “fit” between flower and pollinator influences pollen transfer, particularly among buzz‐pollinated species. Here we use Solanum rostratum, a buzz‐pollinated plant with dimorphic anthers and mirror‐image flowers, to investigate whether the morphological fit between the pollinator's body and floral morphology influences pollen deposition. We hypothesized that when the size of the pollinator matches the separation between the sexual organs in a flower, more pollen should be transferred to the stigma than when the visitor is either too small or too big relative to the flower. To test this hypothesis, we exposed flowers of S. rostratum with varying levels of separation between sexual organs, to bumblebees (Bombus terrestris) of different sizes. We recorded the number of visits received, pollen deposition, and fruit and seed production. We found higher pollen deposition when bees were the same size or bigger than the separation between anther and stigma within a flower. We found a similar, but not statistically significant pattern for fruit set. In contrast, seed set was more likely to occur when the size of the flower exceeded the size of the bee, suggesting that other postpollination processes may be important in translating pollen receipt to seed set. Our results suggest that the fit between flower and pollinator significantly influences pollen deposition in this buzz‐pollinated species. We speculate that in buzz‐pollinated species where floral morphology and pollinators interact closely, variation in the visitor's size may determine whether it acts mainly as a pollinator or as a pollen thief (i.e., removing pollen rewards but contributing little to pollen deposition and fertilization).     

Scanning Electron Microscopic Studies on the Development of the Organs of Litchi Flower

The pattern of development of the floral parts of litchi (Litchi chinensis Sonn.) flower was followed using scanning electron microscopy. Before making scanning electron microscopic observations, specimens were tannin-osmium impregnated and critical point dried. In the bisexual flower, floral organogenesis starts with the formation of protrusions near the floral apex. The two to three protrusions present at the apical region of the floral apex later expand and fuse to form the ovary. At the upper middle region of the ovary another protrusion develops which later becomes the style and the stigma. When the flower matures the tip of the style not only splits but also becomes twisted. On the upper side of the stigma there are numerous papillate cells. These cells are covered with mucilage when fully mature. The development of the filament and anther begins a little bit earlier than the gynoecium. The first sign of androecium development begins when protrusions start to develop around the floral apex. Each litchi flower possesses 6 to 10 anthers. In addition to forming bisexual flowers, litchi also produces a large number of male and female unisexal flowers. But under the scanning electron microscope it is very difficult to distinguish accurately between male and female flowers, because both flowers invariably give rise to some poorly developed organs of the opposite sex. Thus it seems that all flowers in litchi are potentially bisexual and only at the final stage of development (i.e. about 50 days after floral initiation) sex organs fail to develop properly in some flowers.     

Reproductive developmental complexity in the African oil palm (Elaeis guineensis, Arecaceae)

Species of the palm family (Arecaceae) are remarkably diverse in their inflorescence and floral morphologies, which make them a particularly interesting group for studies of reproductive development and its evolution. Using light and scanning electron microscopy, we describe inflorescence and flower development in the African oil palm Elaeis guineensis from the initiation of the inflorescence meristem to flower maturity. In mature palms, the inflorescence develops over 2-3 years and is characterized by individual stages within which differentiation may be either relatively slow, as in the case of early inflorescence meristem development, or rapid, as in the case of flower organogenesis. The female inflorescence bears floral triads composed of single pistillate flowers flanked by two abortive staminate flowers, whereas the male inflorescence contains single functional staminate flowers. This suggests a possible evolutionary movement from an ancestral hermaphrodite inflorescence form containing fully functional floral triads to the situation of temporal dioecy observed at present. Wild type flowers are compared to those bearing an epigenetic homeotic abnormality, known as mantled, involving an alteration of the identity of the organs in the fertile and sterile androecium.     

INFLORESCENCE AND FLORAL DEVELOPMENT IN HOUTTUYNIA CORDATA (SAURURACEAE)

The inflorescence of Houttuynia cordata produces 45–70 sessile bracteate flowers in acropetal succession. The inflorescence apical meristem has a mantle-core configuration and produces “common” or uncommitted primordia, each of which bifurcates to form a floral apex above, a bract primordium below. This pattern of organogenesis is similar to that in another saururaceous plant, Saururus cernuus. Exceptions to this unusual development, however, occur in H. cordata at the beginning of inflorescence activity when four to eight petaloid bract primordia are initiated before the initiation of floral apices in their axils. “Common” primordia also are lacking toward the cessation of inflorescence apical activity in H. cordata when primordia become bracts which may precede the initiation of an axillary floral apex. Many of these last-formed bracts are sterile. The inflorescence terminates with maturation of the meristem as an apical residuum. No terminal flowers or terminal gynoecia were found, although subterminal gynoecia or flowers in subterminal position may overtop the actual apex and obscure it. Individual flowers have a tricarpellate syncarpous gynoecium and three stamens adnate to the carpels; petals and sepals are lacking. The order of succession of organs is: two lateral stamens, median stamen, two lateral carpels, median carpel. The three carpel primordia almost immediately are elevated as part of a gynoecial ring by zonal growth of the receptacle below the attachment of the carpels. The same growth elevates the stamen bases so that they appear adnate to the carpels. The trimerous condition in Houttuynia is the result of paired or solitary initiations rather than trimerous whorls. Symmetry is bilateral and zygomorphic rather than radial. No evidence of spiral arrangement in the flower was found.     

Separation of AG function in floral meristem determinacy from that in reproductive organ identity by expressing antisense AG RNA

The Arabidopsis floral homeotic gene AGAMOUS (AG) is a regulator of early flower development. The ag mutant phenotypes suggest that AG has two functions in flower development: (1) specifying the identity of stamens and carpels, and (2) controlling floral meristem determinacy. To dissect these two AG functions, we have generated transgenic Arabidopsis plants carrying an antisense AG construct. We found that all of the transgenic plants produced abnormal flowers, which can be classified into three types. Type I transgenic flowers are phenocopies of the ag-1 mutant flowers, with both floral meristem indeterminacy and floral organ conversion; type II flowers are indeterminate and have partial conversion of the reproductive organs; and type III flowers have normal stamens and carpels, but still have an indeterminate floral meristem inside the fourth whorl of fused carpels. The existence of type III flowers indicates that AG function can be perturbed to affect only floral meristem determinacy, but not floral organ identity. Furthermore, the fact that floral meristem determinacy is affected in all transformants, but floral organ identity only in a subset of them, suggests that the former may required a higher level of AG activity than the latter. This hypothesis is supported by the levels of AG'mRNA detected in different transformants with different frequencies of distinct types of abnormal antisense AG transgenic flowers. Finally, since AG inhibits the expression of another floral regulatory gene AP1, we examined AP1 expression in antisense AG flowers, and found that AP1 is expressed at a relatively high level in the center of type II flowers, but very little or below detectable levels in the inner whorls of type III flowers. These results provide further insights into the interaction of AG and AP1 and how such an interaction may control both organ identity and floral meristem determinacy.     

DEVELOPMENT AND VASCULATURE OF THE FLOWERS OF LOPHOTOCARPUS CALYCINUS AND SAGITTARIA LATIFOLIA (ALISMACEAE)

The development of the bisexual flower of Lophotocarpus calycinus and of the unisexual flowers of Sagittaria latifolia has been observed. In all eases floral organs arise in acropetal succession. In L. calycinus, after initiation of the perianth, the first whorl of stamens to form consists of six stamens and is ordinarily followed by two alternating whorls of six stamens each. The very numerous carpels arc initiated spirally. In the male flower of S. latifolia the androecium develops in spiral order. A few rudimentary carpels appear near the floral apex after initiation of the stamens. There are no staminodia. The female flower has a similar developmental pattern to that of Lophotocarpus except that a prominent residual floral apex is left bare of carpels. The vascular system in all flowers is semiopen, with vascular bundles passing to the floral organs in a pattern unrelated to the relative positions of those organs. The androecia of these two taxa are similar to those of some Butomaceae and relationships based on ontogeny and morphology are suggested. The gynoecia are meristically less specialized but morphologically more specialized than the gynoecia of Butomaceae.     

Pollination Processes in Idiospermum australiense (Calycanthaceae), an arborescent basal angiosperm of Australia’s Tropical Rain Forests

Idiospermum australiense (Diels) S.T. Blake, a rainforest canopy tree restricted to a few small populations in northeast Australia, is the only southern hemisphere representative of the Calycanthaceae. Pollination processes in Idiospermum were investigated. Flowers are protogynous, with some populations of the species being andromonoecious, whilst others are hermaphrodite. Over their 10 – 16 day floral lifespan, movements of floral organs enforced spatial and temporal separation of male and female floral function. Changes in colour and intensity of fragrance may also influence their attractiveness to potential pollinators. Pollen is present in large quantities, and appears to act as a reward for floral visitors. Insect trapping was carried out both within flowers, and immediately adjacent to inflorescences. A wide variety of arthropods was trapped, with thrips being the most abundant. Other arthropods were trapped, including fourteen species of beetle. For arthropods other than thrips, the mean numbers of adults trapped on flowers remained more or less constant throughout the floral lifetime. However, there was a significant interaction between floral age and the number of pre-adult arthropods present – as the flower aged, the mean number of larvae and eggs per flower increased. The flowers appear to act as sheltered mating and brooding sites for small insects.     

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.     

Genomic approach to study floral development genes in Rosa sp

Cultivated for centuries, the varieties of rose have been selected based on a number of flower traits. Understanding the genetic and molecular basis that contributes to these traits will impact on future improvements for this economically important ornamental plant. In this study, we used scanning electron microscopy and sections of meristems and flowers to establish a precise morphological calendar from early rose flower development stages to senescing flowers. Global gene expression was investigated from floral meristem initiation up to flower senescence in three rose genotypes exhibiting contrasted floral traits including continuous versus once flowering and simple versus double flower architecture, using a newly developed Affymetrix microarray (Rosa1_Affyarray) tool containing sequences representing 4765 unigenes expressed during flower development. Data analyses permitted the identification of genes associated with floral transition, floral organs initiation up to flower senescence. Quantitative real time PCR analyses validated the mRNA accumulation changes observed in microarray hybridizations for a selection of 24 genes expressed at either high or low levels. Our data describe the early flower development stages in Rosa sp, the production of a rose microarray and demonstrate its usefulness and reliability to study gene expression during extensive development phases, from the vegetative meristem to the senescent flower.     

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.