Corolla and androecium development in someEudesmia eucalypts (Myrtaceae)

In the early stages of ontogeny, the corolline parts of theEudesmia eucalypts develop as compound structures directly comparable to the early stages of the petals ofAngophora and the bloodwood eucalypts, but with the onset of androecial formation a marked difference takes place. Rather than forming on the floral apex, the stamen primordia arise on the basal adaxial components of the young corolline parts; this basal component develops into the staminophore of the mature flower. The operculum consists only of the dorsal components of the corolline parts, the homologues of the dorsal keels of theAngophora petals. If the corolline parts remain more or less free in their early developmental stages, corresponding groups of stamens are produced. Early corolline continuity leads to a continuous ring of stamens. The staminophore is not an organ sui generis, but a derivative of the corolla. The bundles of stamens in some species are best referred to as epipetalous groups, not antepetalous fascicles.     

Operculum development inEucalyptus clöeziana andEucalyptus informal subg.Monocalyptus (Myrtaceae)

Flowers ofEucalyptus clöeziana have two clearly distinct perianth whorls. The small free parts of the outer (calycine) whorl cease growth early and are lost from the flower; the parts of the inner (corolline) whorl become continuous laterally by confluence of growth centres and form an operculum in the mature flower. The stamens are inserted on a circumfloral buttress (staminophore) that is homologous to the adaxial corolline component inAngophora and the bloodwood andEudesmia eucalypts. Flowers ofMonocalyptus have only one perianth whorl, which is opercular. The stamens are similarly inserted on a circumfloral buttress. Developmental study does not provide conclusive evidence for either a calycine or corolline determination of theMonocalyptus operculum, but comparison with other eucalypt groups, includingE. clöeziana (the sister taxon), predicts an essentially corolline composition.     

Operculum development in theEudesmieae B eucalypts andEucalyptus caesia (Myrtaceae)

In theEudesmieae B eucalypts and inEucalyptus caesia, the perianth of the mature flower consists of a single, anatomically continuous, opercular structure that is crowned by the tips of the original free and separate calycine and corolline whorls. Ontogenetic and comparative evidence supports the hypothesis that this operculum is mostly corolline in composition, and that the calycine parts have been elevated distally onto the dorsal surface. In theEudesmieae B eucalypts this condition appears to be due to precocious initiation of the corolline primordia, followed by expansion and continuity of their growth centres which incorporates the areas at or below the base of the still differentiating calycine whorl. InEucalyptus caesia the corolline primordia are not precocious, but a similar situation is effected by a seemingly retarded increase in receptacle diameter relative to lateral expansion of the corolline growth centre(s). In these two examples the same final perianth form apparently derives from two different sets of growth processes which, nonetheless, result in the same allometric relationships within the developing flower. Although identical at maturity, the operculum form in these two taxa is best described in terms of convergence, rather than homology.     

A comparative study of floral development inTrillium apetalon andT. kamtschaticum (Liliaceae)

Trillium apetalon Makino is unique amongTrillium in having apetalous flowers. Using scanning electron microscope, the early floral development was observed in comparison with that ofT. kamtschaticum Pallas ex Pursh having petalous flowers. Morphologically petal primordia closely resemble stamen primordia in their more or less narrow and radially symmetric shape and are clearly distinct from sepal primordia with broad bases. Early in floral development sepal primordia are first initiated and subsequently two whorls of three primordia each are formed in rapid sequence, the first three at the corners and the second three at the sides of the triangular floral apex. Based on comparison in position and early developmental processes of their primordia, petals and outer stamens ofTrillium kamtschaticum are equivalent to outer stamens and inner stamens ofT. apetalon. The replacement of petals by outer stamens apparently leads to the loss of petals inTrillium apetalon flowers. Such a replacement can be interpreted in terms of homeosis. The replacement of the petal whorl leads to the serial replacement of the subsequent whorls: outer stamens by inner stamens, and inner stamens by gynoecium inTrillium apetalon. The term ‘serial homeosis’ is introduced for this serial replacement.     

Floral ontogeny inMazus pumilus (Scrophulariaceae)

InMazus pumilus, all the floral appendages are initiated in acropetal sequence in the second cell layer (except stamens) of the floral primordium by periclinal divisions. The actinomorphic calyx tube is formed due to zonal growth. The zygomorphy in corolla is evident from the inception of petal primordia which arise sequentially as independent units in order of one anterior, a pair of anterio-lateral followed by a pair of posterio-lateral. Later these primordia exhibit differential growth because of which zygomorphy becomes more pronounced. The upper corolla tube is formed by interprimordial growth and lower corolla tube by zonal growth. Stamens are initiated in the third layer of the floral apex. Unlike sepals and petals, in the development of stamens (4) underlying cells of corpus also contribute. Posterior stamen is absent. The stamens become epipetalous because of interprimordial and zonal growth in the common region below the bases of petals as well as stamens. The two carpel primordia arise as crescent shaped structures which become continuous due to interprimordial growth. The ovary is formed by a ring of zonal meristem. The style develops later between stigma and ovary because of intercalary growth. The residual apex grows vertically along with the ovary and forms the septum of the ovary. All the floral appendages exhibit similar pattern of histogenesis and early growth suggesting thereby the appendicular nature of these appendages.     

Cytokinins in cut carnation flowers. II. Relationship between endogenous ethylene and cytokinin levels in the petals

Tentative identification using HPLC and RIA techniques indicated the presence of zeatin-O-glucoside, zeatin, ribosylzeatin, dihydrozeatin, iso-pentenyladenine and iso-pentenyladenosine in the petals of carnation flowers. Dihydrozeatin is apparently responsible for most of the biological activity. Within the petals most activity was detected in the basal parts which also senesced much slower than the upper parts of the petals. Treatment with AOA extended petal longevity and reduced ethylene production. This was associated with higher cytokinin-like activity in the basal parts of the petals.These higher levels of cytokinins were not observed in the petals of ACC treated flowers or in the detached control flowers. It is suggested that cytokinin transport and/or metabolism may play an important role in regulating ethylene production in cut carnations.     

Floral development and systematics ofCistaceae

The floral development of representatives of six genera ofCistaceae has been studied. Calyx development involves the formation of a ring primordium in several taxa. Androecium development in species with intermediate or higher stamen numbers starts with the formation of a ring meristem on which the stamens are initiated in a centrifugal direction. In many taxa five alternipetalous leading stamen primordia can be observed. In the apetalous (cleistogamous) flowers ofTuberaria inconspicua androecium development appears to be unordered; this is probably due to the lack of petals. InLechea intermedia (also cleistogamous) the corolla is trimerous and three complex stamen primordia are produced, which give rise either to one or three stamens. Relationships withinCistaceae are discussed. Floral development inCistaceae is compared with that in otherMalvanae. Among the eight families ofMalvanae from which information on floral development is availableCochlospermaceae andBixaceae exhibit the greatest similarities toCistaceae. InCistaceae the leading stamen primordia are alternipetalous. InBixa the same condition seems to be present. InMalvales s. str. mostTiliaceae also show earliest stamen initiation in alternipetalous sectors, whereas the stamens of the innermost alternipetalous position are retarded early or even suppressed inSterculiaceae, Bombacaceae, andMalvaceae. WithinMalvales s. str. the diversity of androecial developmental patterns seems to decrease inBombacaceae andMalvaceae due to increasing synorganization in the mature androecium. The derivation of polyandry inMalvanae from diplo- or obdiplostemony is discussed by comparison with the sister clades ofMalvanae as shown in recentrbcL studies (i.e.Sapindales, Rutales, the glucosinolate producing clade, andMyrtales).     

Sites of ethylene production in the pollinated and unpollinated senescing carnation (Dianthus caryophyllus) inflorescence

Production of endogenous ethylene from the styles, ovary and petals of pollinated and unpollinated flowers of Dianthus caryophyllus L. was measured. The rate of ethylene production of cut, unpollinated flowers aged in water at 18°C was low until the onset of petal wilting, when a rapid surge of ethylene occurred in all tissues. The flower ethylene production was evolved mostly from the styles and petals. The bases of petals from unpollinated, senescing flowers evolved ethylene faster and sometimes earlier than the upper parts. Treatment of cut flowers with propylene, an ethylene analogue, accelerated wilting of flower petals and promoted endogenous ethylene production in all flower tissues. Pollination of intact flowers also promoted endogenous ethylene production and caused accelerated petal wilting within 2–3 days from pollination. Although the data are consistent with the hypothesis that ethylene forms a link between pollination of the style and petal wilting, in the unpollinated flower the style and petals can evolve a surge of ethylene independently of each other, about the time when the petals irreversibly wilt. The results are discussed in relation to the role of ethylene in flower senescence.     

Homeosis, morphogenetic gradient and the determination of floral identity in the inflorescences ofPhilodendron solimoesense (Araceae)

A comparative developmental study of the inflorescence ofPhilodendron solimoesense was conducted using scanning electron microscopy. The spadix ofP. solimoesense is characterized by unisexual flowers. Staminate flowers are initiated on the upper portion of the spadix while pistillate flowers develop on the lower portion of the spadix. An intermediate zone located between the upper male and lower female portion of the inflorescence consists of sterile male flowers. Within this intermediate zone a row of flowers exhibit polarity with respect to the identity of sexual organs. Stamens are initiated on the flank of the floral meristem facing the upper male zone and carpels are initiated on the portion of the floral meristem facing the lower female zone. The resulting flowers therefore assume a bisexual identity. At the level of the inflorescence, all floral buds are initiated along a series of contact parastichies and the continuity of these parastichies is not disrupted at any level in the male, intermediate, and female zones on the spadix. Results from this study support the presence of a morphogenetic gradient acting at the level of the inflorescence and appears to be independent of the boundaries of floral primordia.     

Theligonum cynocrambe: Developmental morphology of a peculiar rubiaceous herb

The annual Mediterranean herbTheligonum cynocrambe shows a peculiar combination of morphological characters, e.g., switch from decussate to spiral phyllotaxis with 90–100° divergence, combined with a change from interpetiolar to lateral stipules, anemophily, lack of calyx, flowers often dimerous to trimerous, corolla fused in both male and female flowers, male flowers extra-axillary, with 2–19 stamens per flower, female flowers axillary, with inferior uniovulate ovary, basilateral style and perianth, nut-like fruits with elaiosome. In male flowers the androecium emerges as an (uneven) elliptical rim with a central depression. This common girdling primordium is divided up into several stamen primordia. In male flowers with low stamen number the stamen primordia may occupy the corners alternating with the corolla lobes. There are no epipetalous androecial primordia that secondarily divide into stamens. Male flowers occasionally show a hemispherical base that may be interpreted as remnant of the inferior ovary. In female flowers a ring primordium grows into a tube on which the petal lobes arise. The perianth and style become displaced adaxially by uneven growth of the inferior ovary. The ovary is basically bilocular. The lower region of the ovary is provided with a septum that is overtopped and hidden by the single curved ovule.Theligonum is referred to theRubiaceae-Rubioideae, with theAnthospermeae andPaederieae as most closely related tribes.     

Pollination biology ofTernstroemia laevigata andT. dentata (Theaceae)

The flowers of two species ofTernstroemia from Central Amazonia were observed to be pollinated by female bees performing vibrational foraging. The anthers of these flowers are longitudinally dehiscent. They are completely included in a petal tube, which opens by a small pore at the apex. Pollen is expelled out of this pore when the bees vibrate the flower while curling over the apex of the petal tube. The much elongated connectives probably transmit the vibrations from the petals to the anthers. The possible occurrence of this mode of pollination in other species ofTernstroemia is briefly discussed.     

Spatial fragrance patterns in flowers of Silene latifolia: Lilac compounds as olfactory nectar guides?

Floral odour can differ qualitatively and quantitatively between different parts of the flowers, and these spatial fragrance patterns within the flowers can be used by pollinators for orientation on flowers. Here we present results of spatial fragrance patterns within flowers of the dioecious Silene latifolia (Caryophyllaceae). Volatiles were collected and analysed using a highly sensitive dynamic headspace method, which allows dramatically reducing the sample time. From all flower parts, especially the petals and the anthophore emitted the typical flower volatiles of S. latifolia. However, compounds emitted from the petals differed from compounds emitted by the anthophore. The anthophore emitted the monoterpenoids lilac aldehydes and alcohols, whereas, all other typical scent compounds (e.g. benzoids, other monoterpenoids) were emitted by the petals. Lilac aldehydes are known to be behaviourally very attractive for noctuid moths, and they may serve as nectar guides in S. latifolia.     

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

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

Competition between the oligolectic beePtilothrix plumata (Anthophoridae) and the flower closing beetlePristimerus calcaratus (Curculionidae) for floral resources ofPavonia cancellata (Malvaceae)

The flowers ofPavonia cancellata, a creeping ruderal half-shrub of northeastern Brazil, open synchronously at 6:00 h with all anthers already dehisced. The oligolectic beePtilothrix plumata was the most effective pollinator. During 90—180 min, female bees make up to 40 brief pollen collection trips to provision their brood cells. The pollen of about 40 flowers ofP. cancellata is needed to feed one bee larva. The most frequent flower visitors, however, are the specialized curculionid beetlesPristimerus calcaratus, which do not crosspollinate the flowers. They perforate the epidermis with their mouthparts, provoking dehydration, and then actively close the loose petals with their legs. Two hours after opening, half of the flowers had already been closed by the beetles. We interpret the fast, uninterrupted pollen foraging ofPtilothrix plumata bees as a strategy adapted to synchronous pollen presentation ofPavonia and to competition withPristimerus calcaratus: the female bees have to provision their brood cells before the beetles succeed in closing the flowers.     

The role of growth regulators in the differentiation of flowers and inflorescences

Growth regulators participate in the differentiation of floral parts, determining the developmental path of the respective type of inflorescence. The effect depends on the expression of the peculiarities of floral part differentiation, the recognition of the character of endogenous substances in certain stages and the choice of the suitable regulator for application. In the primitive flower ofPapaver petals and stamens are formed from the peripheral meristem with a lower content of auxins and a higher level of gibberellic substances. The pistil arises later from central tissues with a higher level of auxins and inhibitory substances. The stamens are more sensitive to the higher level of auxin substances, and by a suitable application of GA₃ and BAP they can be transformed into petals; in this way double flower forms arise. In the differentiation of floral parts ofCampanula, Rosa andMelandrium similar regularities assert themselves in time successions, but in another spatial arrangement. Sex differentiation of diclinous flowers ofMelandrium is based on differences in heterochromosomes XY and XX. The rise of the zygomorphic flower ofVeronica is accompanied by a different distribution of endogenous substances which affect the development of petals, stamens and the pistil. The differentiation of flowers in the racemose inflorescence occurs in the acropetal succession, and lateral primordia inCampanula develop into actinomorphic regular flowers, whereas inDigitalis they are zygomorphic and only the terminal flower is peloric. In the initial phases the staminate tassel and the pistillate ear in maize are identical. Earlier differentiation of the terminal pistillate tassel is connected with a higher level of gibberellins and the later development of the lateral pistillate ear is accompanied by the increase in auxin-like substances and inhibitions. Similar correlations were found in the development of staminate catkins and the differentiation of pistillate flowers in terminal buds ofJuglans regia. By the application of auxin-like substances it is possible to achieve the transformation of primordia of the staminate tassel into the pistillate ear in maize or to regulate the number of staminate catkins and pistillate flowers on twigs of the walnut tree. In the capitulum of the sunflower differences arise between peripheral pistillate ray flowers and hermaphrodite tubular ones. By applying GA₃ and BAP the number of ray flowers is increased. If the normal course of inflorescence differentiation is affected with a suitable type of regulator, a range of floral abnormalities appears which permit to assess the intervention in different developmental stages and the reaction of the primordium to the applied type of regulator. Abnormalities also suggest some phylogenetic correlations.     

Developmental analyses reveal early arrests of the spore-bearing parts of reproductive organs in unisexual flowers of cucumber (<Emphasis Type="Italic">Cucumis sativus</Emphasis> L.)

To understand the regulatory mechanisms governing unisexual flower development in cucumber, we conducted a systematic morphogenetic analysis of male and female flower development, examined the dynamic changes in expression of the C-class floral organ identity gene CUM1, and assessed the extent of DNA damage in inappropriate carpels of male flowers. Accordingly, based on the occurrence of distinct morphological events, we divided the floral development into 12 stages ranging from floral meristem initiation to anthesis. As a result of our investigation we found that the arrest of stamen development in female flowers, which occurs just after the differentiation between the anther and filament, is mainly restricted to the primordial anther, and that it is coincident with down-regulation of CUM1 gene expression. In contrast, the arrest of carpel development in the male flowers occurs prior to the differentiation between the stigma and ovary, given that no indication of ovary differentiation was observed even though CUM1 gene expression remained detectable throughout the development of the stigma-like structures. Although the male and female reproductive organs have distinctive characteristics in terms of organ differentiation, there are two common features regarding organ arrest. The first is that the arrest of the inappropriate organ does not affect the entirety of the organ uniformly but occurs only in portions of the organs. The second feature is that all the arrested portions in both reproductive organs are spore-bearing parts.Abbreviations SEM Scanning electron microscopy - TEM Transmission electron microscopy - TUNEL TdT-mediated dUTP nick-end labeling     

Floral scent and intrafloral scent differentiation inMoneses andPyrola (Pyrolaceae)

Floral scent was collected by headspace methods from intact flowers, petals, and stamens of four species ofPyrolaceae. The scent samples were analyzed by coupled gas chromatography-mass spectrometry (GC-MS). The floral scent inPyrola spp. is differentiated into a characteristic petal scent—phenyl propanoids and a characteristic stamen scent—methoxy benzenes. InMoneses the scent is characterized by isoprenoids and benzenoids, with a larger proportion of benzenoids in the stamens compared to the petals. Specific anther scents may promote foraging efficiency in buzz-pollinated species and enhance flower fidelity. Variation in floral scent composition is consistent with the taxonomic relationships among the genera and species examined.     

Studies in the morphology and systematics of berberidaceae

The floral vasculature in three allied genera,Plagiorhegma, Jeffersoria andAchyls is investigated, and the results are compared with those ofEpimedium andVancouveria which are related closely toPlagiorhegma andJeffersonia. The vasculature in the receptacle ofPlagiorhegma andJeffersonia is similar, but that ofAchlys is much simpler. Slightly different trace patterns are observed in the sepals ofPlagiorhegma andJeffersonia. InJeffersonia, the 3-trace condition leaving 2 or 3 gaps is most frequently observed, but inPlagiorhegma traces of a double nature leaving a single gap are more frequent. The traces to the innermost sepals, petals and stamens are usually of a double nature leaving a single gap in both genera. Regular division and fusion are not observed in the receptacular stele. The vascular differentiation between sepals and petals is more advanced inPlagiorhegma andJeffersonia than inEpimedium andVancouveria. InAchlys, the traces are all staminal and single throughout their course. Two parts recognized in the pistils ofPlagiorhegma, Jeffersonia andAchlys are traversed by independent vasculature. The comparisons of pistil morphology including vasculature ofPlagiorhegma, Jeffersonia, Achlys, Epimedium andVancouveria lead to the interpretation that the pistils are based on the same morphological plan. The probable evolutionary trend in pistil is then suggested in these five genera.     

Carpels as leaves: meeting the carbon cost of reproduction in an alpine buttercup

We investigated the role of photosynthesis by reproductive organs in meeting the carbon costs of sexual reproduction in the snow-buttercup, Ranunculus adoneus. The exposed green carpels of snow-buttercup flowers have 1–2 stomata each. Net carbon assimilation rates of flowers are negative during bud expansion, but rise to zero at maturity, and become positive during early fruit growth. Experimental removal of separate whorls of flower parts demonstrated that the showy, nectary-housing petals account for most of the respiration cost of flower presentation. Conversely, photosynthesis by female organs contributes to a flower's carbon balance. Dipteran pollinators of R. adoneus are most active in sunny mid-morning to mid-afternoon intervals. At this time of day, rates of carpel photosynthesis (A_max) meet respiratory costs of pollinator attraction in fully expanded flowers. Achenes remain photosynthetically active until dispersal, and positive net carbon assimilation rates characterize infructescences throughout fruit maturation. Photosynthetic rates of achenes are positively correlated with infructescence growth rates. We tested the causal basis of this relationship by experimentally shading developing infructescences. Mature achenes from shaded infructescences were 16–18% smaller than those from unshaded controls. Leaf photosynthetic rates did not differ between plants bearing shaded and unshaded seed heads. Since female reproductive organs are only 8% more costly in terms of caloric investment than male ones and contribute to their own carbon balance, it is plausible that the energy cost of male function equals or exceeds that of female function in this hermaphroditic species.