Stamen Primordia Research Articles

DORNRÖSCHEN-LIKE, an AP2 gene, is necessary for stamen emergence in Arabidopsis

To identify novel genes in petal and stamen development, a genetic screen was carried out for enhancers of the unusual B class mutant pistillata-5 (pi-5). In pi-5 flowers, second whorl organs develop as sepals rather than petals, but third whorl stamens are normal. One pi-5 enhancer, dornröschen-like-2 (drnl-2), results in third whorl positions developing as filamentous organs. In addition to enhancing the pi-5 phenotype, drnl-2 mutants also exhibit a phenotype in a wild-type PI background. Although stamen primordia are morphologically visible during early stages of flower development, they fail to enlarge in drnl-2 mutants. DRNL, which encodes a single AP2 domain protein, is expressed in a dynamic pattern in the embryo, seedling, and flower. Analysis of both the drnl-2 mutant phenotype and the DRNL expression pattern in flowers suggests that DRNL plays a critical role in stamen emergence in Arabidopsis.

Characterization and Identification of a Novel Mutant fon( t) on Floral Organ Number and Floral Organ Identity in Rice

The floral-organ-number mutant fon( t) was firstly discovered in the progeny of a cross between a diploid (Chunjiang 683) and a haploid ( SARIV-620 -A) rice cultivar. The fon( t) mutant showed normal vegetative development and produced normal inflorescence structures. Difference between the mutant and the wild type was observed when the stamen primordia began to form. The mature flowers of fon( t) mutant showed open-hull phenotypes, which resulted in the exposure of stamens and stigmas. Normally, a single fon( t) floret consisted of six to nine stamens and one or two pistils. In addition, stamen/pistil-like structures and bulged tissues near ovaries were also observed in a few fon( t) florets. But homeotic transformation of lodicules into palea/lemma-like organs was observed almost in all the open-hull florets. The phenotypes of fon( t) flowers also suggested that fon( t) gene might affect flower organ identity in the inner whorls. Genetic analysis showed that the fon( t) mutant was controlled by a single recessive gene.

Flower structure and development in Tupidanthus calyptratus (Araliaceae): an extreme case of polymery among asterids

Flowers of Tupidanthus show an extreme case of floral polymery among asterids. Floral development and gynoecium structure have been examined. The floral meristem has a complex folded shape. The tiny calyx is initiated as a continuous ring primordium. The corolla is initiated as a lobed ring and develops into a calyptra. All stamen primordia appear simultaneously as a single whorl. The carpels, also in a single whorl, tend to alternate with the stamens. Some Schefflera species related to Tupidanthus are also studied. The flower of Tupidanthus is interpreted as a result of fasciation. Further investigation should determine whether mutation(s) in gene(s) of the CLAVATA family are responsible for the fasciation here. The significance of Tupidanthus for understanding spatial pattern formation in flowers of Araliaceae, and both functional and developmental constraints in angiosperm flowers with a single polymerous carpel whorl are discussed.

The influence of ethylene perception on sex expression in melon (Cucumis melo L.) as assessed by expression of the mutant ethylene receptor, At-etr1-1, under the control of constitutive and floral targeted promoters

Sexual diversity expressed by Curcurbitaceae species is a primary example of developmental plasticity in plants. Ethylene, which promotes femaleness (carpel development), plays a key role in sex determination. We sought to determine the critical location for ethylene perception in developing floral primodia. The dominant negative Arabidopsis ethylene response mutant gene, etr1-1, was introduced into melon (Cucumis melo L.) plants under control of the constitutive cauliflower mosaic virus (CaMV) 35S promoter, or floral-targeted Apetela3 (AP3) and Crab’s Claw (CRC) promoters, which in Arabidopsis, promote expression in petal and stamen, and carpel and nectary primordia, respectively. Based on effects of exogenous ethylene, it was predicted that inhibition of ethylene perception by carpel primordia would inhibit carpel development. Constitutive expression of etr1-1 caused several phenotypes associated with ethylene insensitivity, verifying that etr1-1 inhibits ethylene perception in the heterologous melon system. Carpel-bearing bud production was essentially abolished in 35S::etr1-1 melons, providing direct demonstration of the requirement for ethylene perception for carpel development. CRC::etr1-1 plants, however, showed enhanced femaleness as manifested by earlier and increased number of carpel-bearing buds, and production of female (rather than bisexual) buds. Despite increased carpel-bearing bud formation, a greater proportion of the CRC::etr1-1 carpel-bearing buds aborted before anthesis. AP3::etr1-1 plants showed increased maleness by nearly exclusive staminate flower production, and poorly developed carpels in the rare bisexual flowers. These results indicate that ethylene perception by the stamen (or petal) primordia plays a critical role in promoting carpel development at the time of sex determination, while ethylene perception by the carpel is important for maturation of carpel-bearing flowers to anthesis.

The Discovery of Polyandry in Curculigo (Hypoxidaceae): Implications for Androecium Evolution of Asparagoid Monocotyledons

Individual flowers of the monocot Curculigo racemosa (Hypoxidaceae, Asparagales) are regularly polyandrous. To evaluate the significance of this almost unique character among Asparagales for flower evolution of asparagoid monocots, flowers of C. racemosa were studied comparatively. Anthetic flowers as well as early floral developmental stages were studied by light and scanning electron microscopy. Despite the polyandry, floral development is similar to that of other Asparagales with a developmental gradient from adaxial to abaxial. Stamens initiate simultaneously and the diameter of staminal primordia is about half of that in species with six anthers. The number of stamens is not fixed (12-26) and varies within the same inflorescence. Surprisingly, the gynoecium can be four- or six-locular, besides the normal trimerous state. The discovery of a polyandrous Curculigo reveals plasticity of stamen number at the base of Asparagales. Orchidaceae - sister to all other Asparagales - has a reduced stamen number (three, two or one), whereas in Hypoxidaceae - part of the next diverging clade - either the normal monocot stamen number (six), polyandry (this study) or the loss of three anthers (Pauridia) occurs. However, at present it is impossible to decide whether the flexibility in stamen number is autapomorphic for each group or whether it is a synapomorphy. The small size of stamen primordia of Curculigo is conspicuous. It allows more space for additional androecial primordia. Stamens are initiated as independent organs, and filaments are not in bundles, hence C. racemosa is not secondarily polyandrous as may be the case in the distantly related Gethyllis of asparagoid Amaryllidaceae. The increase in carpel number is a rare phenomenon in angiosperms. A possible explanation for the polyandry of C. racemosa is that it is a natural SUPERMAN-deficient mutant, which shows an increase of stamens, or ULTRAPETALA or CARPEL FACTORY mutants, which are polyandrous and changed in carpel number.

Floral Ontogeny of the Afro-Madagascan Genus Mitrasacmopsis with Comments on the Development of Superior Ovaries in Rubiaceae

Members of Rubiaceae are generally characterized by an inferior ovary. However, Mitrasacmopsis is cited in the literature as having a semi-inferior to superior ovary. It has previously been hypothesized that the gynoecial development of Rubiaceae with semi-inferior to superior ovaries takes place in the same way as in Gaertnera, one of the most commonly cited rubiaceous genera with a superior ovary. To test this hypothesis, a floral ontogenetic study of Mitrasacmopsis was carried out with special attention paid to the gynoecial development. Floral ontogeny and anatomy of Mitrasacmopsis were examined using scanning electron and light microscopy. At an early developmental stage, a concavity becomes visible in the centre of the floral apex simultaneously with the perianth initiation. A ring primordium surrounding this concavity expands vertically forming the corolla tube (early sympetaly). Stamen primordia develop inside the corolla. From the bicarpellate gynoecium only two carpel tips are visible because the ovary is formed by a gynoecial hypanthium. In the basal part of each carpel, a placenta primordium is initiated. Two septa divide the ovary into two locules. In each locule, the placenta becomes mushroom shaped and distinctly stalked. Eventually, the inferior ovary of Mitrasacmopsis develops into a beaked capsule. Only very late in the fruiting stage, the continuously expanding ovary is raised above the insertion point of the persistent calyx, changing the ovary position of Mitrasacmopsis from basically inferior to secondarily semi-inferior. Mitrasacmopsis follows an epigynous pattern of floral development. However, the presence of a prominent beak in the fruiting stage gives the whole ovary a semi-inferior appearance. This kind of secondarily semi-inferior ovary is shown to be different from the secondarily superior ovary observed in Gaertnera.

Two AGAMOUS‐like MADS‐box genes from Taihangia rupestris (Rosaceae) reveal independent trajectories in the evolution of class C and class D floral homeotic functions

Duplicate genes may be retained by sub- and/or neofunctionalization through changes in gene expression and/or coding sequence, and therefore have the potential to contribute to the genetic robustness and diversification of an organism. In this study, two MADS-box genes were isolated from Taihangia rupestris, a core eudicot species belonging to the Rosaceae. Sequence and phylogenetic analyses revealed that they are clade members of the euAG and PLE lineages, respectively, and hence the two genes are named TrAG (Taihangia rupestris AGAMOUS) and TrSHP (Taihangia rupestris SHATTERPROOF). Southern blot analysis shows that TrSHP is a single-copy gene in the T. rupestris genome. In situ hybridization analyses show that both TrAG and TrSHP are mainly expressed in the stamens, carpels, and ovules. When the stamen primordia are firstly observed, TrAG is initially expressed in the floral meristem domain that will initiate stamens and carpels. In contrast, no TrSHP signal is observed at this developmental stage. At late stages of carpel development, TrAG expression is detected in the ovules, ovaries, and developing styles and stigmas, whereas TrSHP expression is tightly restricted to the ovules. The transgenic Arabidopsis plants containing 35S::TrAG and 35S::TrSHP, respectively, showed similar phenotypes, including homeotic conversions of sepals into carpelloid structures bearing ovules and petals into staminoid organs, and the fruits shattering prematurely along the dehiscence zone. In addition, the phenotype of the transgenic 35S::TrSHP Arabidopsis plants revealed that perianth abscission was inhibited. Yeast two-hybrid assays indicated that TrAG can interact with TrSEP3, whereas TrSHP cannot. The data suggest that the euAG and PLE paralogs, TrAG and TrSHP, may have subfunctionalized and/or neofunctionalized through changes in expression patterns and accumulating variations in the coding regions. Taking these findings together with those available expression and functional data from Arabidopsis and other species, we conclude that the compensatory ways vary among the euAG and PLE lineage pairs in eudicot species.

Establishment of a highly efficient regeneration system for in vitro culture of young wheat spikes

AbstractThis study used three winter wheat (Triticum aestivum L.) genotypes (H6756, H311 and SP8581) to compare the effects of sampling time, callus induction media, differentiation media and rooting media on in vitro culture of young spikes in wheat. In all these three genotypes, the frequencies of green plantlet differentiation were high when their young spikes were cultured between the stages of protective glume primordium formation and pistil and stamen primordium formation, but low at other stages. The optimum medium for callus induction was Murashige and Skoog (MS) medium+2 mg/l 2,4-dichlorophenoxyacetic acid (2,4-D). The optimum green plantlet differentiation medium was MS medium. Some abnormal plantlets regenerated from calli. When these plantlets were transferred to another differentiation medium [MS+1.0 mg/l 1-naphthaleneacetic acid (NAA)+0.2 mg/l 6-benzylaminopurine (6-BA)], shoot formation and elongation were induced. This allowed 90.91% of them to develop into normal green plantlets. The optimum rooting medium was 1/2MS+0.2 mg/l 3-Indolylacetonitrile (IAA)+80 g/l sucrose. An efficient regeneration system for young spike culture of wheat was set up based on such methods. Using this wheat-regeneration system, young spikes and immature embryos of 17 genotypes of wheat were in vitro cultured to study and compare the callus induction frequencies and green plantlet differentiation frequencies. The results of two successive years showed that in 15 out of the 17 genotypes (88.24%) the green plantlet differentiation frequencies were higher than those of immature embryos by 6.2–65.1%. These results showed that the regeneration system established in this trial for young spike culture of wheat was effective.

The Floral Scales in Hellmuthia (Cyperaceae, Cyperoideae) and Paramapania (Cyperaceae, Mapanioideae): An Ontogenetic Study

In 1976 the monotypic genus Hellmuthia was placed in the Hypolytreae s.l., but was subsequently ascribed to the Mapanioideae, tribe Chrysitricheae, mainly because of the presence in Hellmuthia of two lateral, mapanioid-like floral scales with ciliated keels, the anatomy of the nutlet, the embryo and the inflorescence. Recently, based on cladistic analyses and supported by pollen ontogenetic evidence, Hellmuthia was transferred to a Cyperaceae, tribe Cypereae, clade mainly consisting of Ficinia and Isolepis. In this study, the floral ontogeny in Hellmuthia was investigated and compared with the floral ontogeny in Paramapania, with special attention for the floral scales. Freshly collected inflorescences of Hellmuthia membranacea and Paramapania parvibractea were investigated using scanning electron and light microscopy. In the conical 'spikelet' in Hellmuthia, proximal bracts occur, each axillating an axis with empty glume-like structures, or a reduced spikelet. Hence, it is a reduced partial inflorescence. In Hellmuthia, the stamen primordia originate before the primordia of the perianth-gynoecium appear. Moreover, a third adaxially positioned 'floral scale' was observed for the first time. The position and relative time of appearance of the floral scales in Hellmuthia are typical for perianth parts in Cyperoideae. The basal position of Hellmuthia within a clade of species with usually perianthless flowers, allows the presence of rudiments of a perianth in Hellmuthia to be interpreted as a primitive state. Development of the lateral 'scales' in Paramapania follows a different pattern. Therefore, it was decided that the lateral 'scales' in Paramapania are different from the lateral perianth parts in Hellmuthia. The pollen grains in Hellmuthia are cyperoid, with one polar and five lateral apertures, of which the membrane is covered with sexinous bodies. The pollen surface is granulate and perforate with microspines. The floral ontogeny in Hellmuthia occurs according to the general cyperoid pattern. The lateral scales in Hellmuthia are perianth parts, and they are not homologous to the lateral 'scales' in Paramapania.

Flower development and anatomy of Clusia valerioi, a Central American species of Clusiaceae offering floral resin

The present paper is part of a study dealing with various aspects of reproduction of two Costa Rican Clusia species offering resin as a floral reward. It provides data on the floral development and flower (especially stamen and staminode) anatomy of one of the species, Clusia valerioi. In the early stages, both male and female flowers develop in the same manner. The bracts are distinguished by a decussate arrangement from the five sepals and five petals, which emerge in a spiral manner. In the male flowers the apical meristem forms five meristematic mounds (common stamen primordia) that are pentagonally arranged around the apical meristem in epipetalous position. From these mounds, the primordia of the proper stamina emerge in 3–5 whorls. Direction is centrifugal. In the centre, five hemispherical bulges arise which develop into carpel primordia. These, however, cease growth, stay rudimentary and are hidden by the stamens in the mature male flower. The adult stamens consist mainly of a thick angular filament column, while the two anthers situated at the flattened top are very small. One anther is annular and surrounds a second, hemispherical one right in the centre. At the periphery, these two pollen sacs (provided with a distinct wall of customary anatomy) are surrounded by a ring-like protuberance of the filament. The resin canals are situated at the periphery of the filament. Their schizogenous development is documented in cross sections. At anthesis, the resin is released from the ring-like filament protuberance by burst of the single-layered epidermis. In the female flower, the five meristematic mounds produce two whorls of staminode primordia. The development of the staminodes does not essentially differ from that of the fertile stamens, but some staminodes lack the central pollen sac and the other tissues do not develop into pollen grains. An attempt is made to derive the peculiar stamen morphology of Clusia valerioi and similar species from conventional stamens. Three hypotheses are proposed and discussed.

Patterns of anomalous floral development in the Asian Passiflora (subgenus Decaloba: supersection Disemma)

Approximately 22 species of Passiflora are native to the Old World. All of these species are placed in subgenus Decaloba, supersection Disemma. Within Disemma, three species vary in stamen and carpel number (≤ eight stamens and five carpels). The mode of development was determined for two of the anomalous species, P. moluccana var. glaberrima and P. siamica. Ontogenetic patterns were compared to normal development in P. perakensis and P. holosericea. Passiflora siamica develops additional stamens through dédoublement of a single widened stamen primordium, while P. moluccana var. glaberrima exhibits congenital dédoublement where stamens emerge already doubled. Phylogenetic analysis using ITS and the trnL-F intron and spacer resolve the anomalous species as monophyletic and sister to P. perakensis. This signifies a single loss of genetic regulation in stamen and carpel number within Disemma. Floral whorls were examined across the Passifloraceae, Malesherbiaceae, Turneraceae, and Flacourtiaceae s.l.. Similar doubling in these families suggests that this Eurosid lineage may have a genetic propensity for variability in floral whorl number.

Calceolariaceae: floral development and systematic implications

The recent establishment of the new family Calceolariaceae, separated from Scrophulariaceae on the basis of molecular evidence, is complemented here by a scanning electron microscopy study of floral morphology and development of 12 species encompassing all genera (Calceolaria, Jovellana, and Stemotria [= Porodittia]). All species showed a similar pattern of organ initiation. The slightly zygomorphic, four-merous calyx is the first floral organ series initiated, with the primordia emerging consecutively in a unidirectional (dorso-ventral) succession. The two entire corolla lips in Calceolaria and Jovellana arise as uniform meristematic ridges (sometimes with a central emargination, especially in Jovellana), kept apart by two lateral stamen primordia. Later the margins of the lips fuse across the backs of the young stamens, giving rise to the short corolla tube (late sympetaly). Stemotria stands out by having three stamens instead of two and a bilobed lower lip, resulting in a trimerous corolla. Similar architecture was found in teratological flowers of Calceolaria. The perianth of Calceolariaceae is shown to be derived from a tetramerous condition, not from pentamery as traditionally believed. This is in agreement with the separation of Calceolariaceae from Scrophulariaceae and with their placement in succession of Oleaceae and Tetrachondraceae in the basal Lamiales. The hitherto puzzling molecular evidence is thus supported by morphological-developmental features of the flower.

Morphological development of the spikelet and the floret in Dendrocalamus ronganensis (Gramineae: Bambusoideae)

Morphological development of the spikelet and the floret in Dendrocalamus ronganensis has been studied for the first time under scanning electron microscope (SEM). The developmental sequence of spikelet is: spikelet primordium→primordium of the first glume→primordium of the second glume→primordium of the first lemma→primordium of the first floret→primordium of the second lemma→primordium of the second floret. The spikelet is a pseudospikelet consisting of two glumes and 1–2 florets. The developmental sequence of floret is: primordium of palea→primordia of stamens→primordium of pistil. The palea originates from two distinct protuberances in its early development, and the two parts gradually unite in late stage of development. The palea has been confirmed to be of a double origin. The primordia of stamens initiate nearly in two whorls. The central part of the floret primordium changes directly into gynoecium. The development of lodicules cannot be observed in the whole process. The floret, consisting of stamens and pistil subtended by lemma and palea, is quite reduced because of the absence of the perianth. The evolution of the spikelet and the floret in the Bambusoideae is discussed based on the comparison of the morphological development of the spikelet and the floret in Dendrocalamus with that in its closely related genera.

Floral ontogeny of Hardenbergia violacea (Fabaceae: Faboideae: Phaseoleae) and taxa of tribes Bossiaeeae and Mirbelieae, with emphasis on presence of pseudoraceme inflorescences

The floral ontogeny of several Australian papilionoid taxa has been studied in Hardenbergia violacea L. (Phaseoleae); Kennedia rubicunda (Phaseoleae; inflorescences only); Bossiaea cordigera (Bossiaeeae); Gastrolobium truncatum, Mirbelia oxylobioides, and Pultenaea daphnoides (Mirbelieae). Species studied of Hardenbergia, Pultenaea, and Brachysema have pseudoracemose inflorescences comprised of triads of flowers, Kennedia rubicunda has paired flowers that resemble reduced pseudoracemes, while Gastrolobium truncatum and Mirbelia oxylobioides have pseudoracemes comprised of 2–10 flowers per ultimate unit. Pseudoracemes are a significant and overlooked feature in many taxa of tribes Bossiaeeae and Mirbelieae. Hardenbergia violacea has ultimate axillary units of three flowers, each with a subtending bract but no bracteoles. Floral ontogeny in H. violacea and P. daphnoides shows acropetal order among whorls, and unidirectional order starting from the abaxial side in sepal, petal, and stamen whorls, as in most papilionoid flowers. The carpel is initiated concurrently with the first antesepalous stamen primordium. Pultenaea daphnoides and Bossiaea cordigera have unidirectional sepal initiation starting abaxially, but simultaneous petal initiation, an unusual feature among papilionoids. In late stages of H. violacea and B. cordigera, a diadelphous stamen tube or sheath is formed, while in taxa of Mirbelieae the stamens remain free. The flowers in all taxa studied become strongly zygomorphic as evidenced by three petal morphs and upturning of the free portions of style and stamens late in development.

Floral organogenesis of Handeliodendron bodinieri (Sapindaceae) and its systematic implications

Floral organogenesis and development of Handeliodendron bodinieri (Sapindaceae), a species endemic to China, were studied under scanning electron microscope and optical microscope. The results are as follows: the inflorescence primordium initiates at first, forming 2 unequal flower primordia. The sepal primordia initiate in spiral order and are not synchronous. Four to five petal primordia initiate in whorls simultaneously. The petal and stamen primordia initiate separately, and there is no petal-stamen complex. Seven to eight stamen primordia initiate nearly at the same time and grow more quickly than the petal primordia. At last, 3 carpel primordia appear simultaneously and close up gradually to form the ovary. The flowers of H. bodinieri are unisexual. In the female flower, the ovary bulges and the stamens degenerate, whereas the male flower, the stamens grow normally but the ovary degenerates. The systematic implications of floral organogenesis and development of H. bodinieri are discussed.

REVISION OF PLETHIANDRA HOOK.F.: A POLYSTAMINATE, EAST ASIAN GENUS OF MELASTOMATACEAE

Plethiandra (Melastomataceae–Melastomatoideae–Dissochaeteae) comprises seven species in Borneo and one (P. sessiliflora) in the southern part of Peninsular Malaysia and central Sumatra. Plethiandra is easily recognized by its polystaminate androecium, having 16–40 stamens with short, straight, inappendiculate anthers. The closely related Medinilla has a diplostemonous androecium with 8–12 stamens and variously appendaged anthers. Ontogenetic studies in P. hookeri show that the increase in stamen number in Plethiandra results from subdivision of the stamen primordia into three or more subprimordia.This paper provides a key, genus and species descriptions including diagnostic characters, distribution maps and ecological notes. One species, P. tomentosa, is newly described. During field observations on P. hookeri and P. cuneata pollination by bees and dispersal by birds and squirrels were observed.

Gene expression profiling in rice young panicle and vegetative organs and identification of panicle-specific genes through known gene functions

In rice, at the stage from pistil and stamen primordia formation to microsporocyte meiosis, the young panicle organs (YPO) make a great contribution to grain productivity. This period corresponds to the onset of meiosis and marks the transition from vegetative to reproductive stages. By comparing gene expression profiling of YPO with that of rice aerial vegetative organs (AVO), it is possible to gain further molecular insight into this period that is developmentally and functionally important. In this report, a total of 92,582 high-quality ESTs from 5'-end sequencing, including 44,247 from YPO and 48,335 from AVO, were obtained and classified. There were 12,884 (29.12%) ESTs from YPO and 16,304 (33.73%) ESTs from AVO matched to known genes, which generated 1,667 and 2,172 known genes, respectively, after integration of these ESTs. From the functions of known homologous genes, we identified some tissue- and developmental-stage-specified genes in YPO. The expression of these genes clearly reflected the unique functional characteristics of YPO. Furthermore, we estimated that there are about 10,000 mRNAs specifically expressed in rice YPO.

Organogenesis of the Inflorescence and Flowers in Platycarya strobilacea (Juglandaceae)

The reproductive structures of the monotypic genus Platycarya (Juglandaceae), in particular the nature of the fruit wings, have been interpreted variously. We investigated organogenesis of inflorescence and flowers with scanning electron microscopy (SEM). This is the first SEM study to show the whole developmental process of male, female, and bisexual flowers in a member of the Fagales. In staminate and bisexual flowers, only a subtending bract is present, while bracteole and perianth are absent. Four to 10 stamen primordia of different sizes are arranged as an irregular circle or two semicircles. With further development of the stamens, the receptacle, which is fused to the base of the bract, enlarges, and the whorled arrangement of stamens becomes less and less distinct. In pistillate flowers, the transversely ellipsoidal floral primordium develops a central depression. Two bracteoles are initiated in the lateral position of the floral primordium. Soon, the inconspicuous circular perianth primordium appears around the central depression, and two carpels are initiated bordering the central depression opposite to the bracteoles. The perianth is highly reduced and fused with the ovary wall from the initial stage. Each wing of the fruit of Platycarya strobilacea is formed by a combination of one bracteole and the lateral lobe of the perianth.

OsMADS22, an STMADS11-like MADS-box gene of rice, is expressed in non-vegetative tissues and its ectopic expression induces spikelet meristem indeterminacy

We report the cDNA sequence and gene expression patterns of OsMADS22, a novel member of the STMADS11-like family of MADS-box genes, from rice. In contrast to previously reported STMADS11-like genes, whose expression is detected in vegetative tissues, OsMADS22 is mainly expressed during embryogenesis and flower development. In situ hybridization analysis revealed that OsMADS22 expression is localized in the L1 layer of embryos and in developing stamen primordia. Ectopic expression of OsMADS22 in transgenic rice plants resulted in aberrant floral morphogenesis, characterized by a disorganized palea, an elongated glume, and a two-floret spikelet. The results are discussed in terms of rice spikelet development and a novel non-vegetative role for a STMADS11-like gene.

Floral initiation and development in three field-grown Allium species belonging to different sub-genera

SummaryFloral development and inflorescence structure in three Allium species, A. sphaerocephalon, A. rosenbachianum and A. cowanii, were investigated using scanning electron microscopy (SEM). Inflorescence initiation occurred as an enlargement of the shoot apex followed by spathe initiation. Flower primordia appeared at the top of the enlarged shoot apex, and formed basipetally in A. sphaerocephalon. In both A. rosenbachianum and A. cowanii, primary flower primordia appeared in the lower position of the enlarged shoot apex, and formed acropetally. Secondary flower primordia in A. rosenbachianum and A. cowanii were formed basipetally in the lower position of the primary flower primordia, similar to flower clusters, giving rise to the composite inflorescence. A. rosenbachianum had a large number of flower clusters, whereas A. cowanii produced only a few flower clusters. During flower primordia development, the inner perianth primordia and outer stamen primordia appeared almost simultaneously. A. sphaerocephalon and A. cowanii initiated inflorescences in mid-February (early Spring) and early October (Autumn) respectively. Floral development then progressed steadily until their respective flowering in mid-June (early Summer) and late April (Spring). In A. rosenbachianum, inflorescence initiation was started in mid-July (Summer), and floral development progressed slowly until the formation of pollen mother cells in mid-March (early Spring), and bloom started in early May (late Spring).