Carpel Primordia Research Articles

Phyllotaxic diversity in Magnolia flowers

Impermanent initials and thus the shift of the axis in the stochastic meristems are postulated to be responsible for ontogenetic phyllotactic diversity in plants. In the gynoecium of <i>Magnolia acuminata</i> the main Fibonacci pattern develops in much less than 50% of individual generative shoots. There is also an extremely wide spectrum of other patterns, among them even the rarest I, 3, 8, 11 ... pattern is present. Regarded sometimes as "impossible", the pattern has been documented in SEM for the first time. Beside the presence of various patterns, frequent ontogenetic transformations of phyllotaxis have been found in <i>Magnolia</i>. These are indicated by dislocations in the periodic distribution of carpel primordia. In other magnolias, exemplified by <i>M. soulangeana</i>, the Fibonacci pattern prevails, but not as much as in coniferous vegetative shoots, where, as demonstrated earlier, it reaches 95%. Other pattern numbers are also different. This suggests the involvement of the genetic factor and may be attributed to the higher frequency of discontinuous phyllotactic transformations in some species. The stochastic character of the meristem is perhaps more pronounced in some plants, which leads in turn to more frequent transitions and greater pattern diversity.

Comparative floral ontogeny of single-flowered and double-flowered phenotypes of Alcea rosea (Malvaceae)

A comparative study of floral ontogeny in single- and double-flowered Alcea rosea L. was conducted using epi-illumination light microscopy. In both floral types, floral differentiation starts with the appearance of three epicalyx lobes, which subsequently subdivide to produce a 7–10-parted epicalyx. Five sepals appear then in a unidirectional or possibly spiral sequence. In single flowers, a corolla-androecium common primordium is formed and subsequently differentiated into five androecial sectors (= primary androecial primordia). Petals are developed at the base of the androecial sectors and secondary androecial primordia are initiated centrifugally in two rows on each sector. Later, tertiary androecial primordia are formed by the subdivision of secondary androecial primordia, which then differentiate into androecial units. Three types of double flowers were identified regarding androecial development. The first type of double flowers shows a more or less disorganised nature. However, 10 proliferation zones can be indentified in the proximal and distal tips of the androecial sectors. In the second and third types of double flowers, androecial development follows similar developmental pathways to that of single flowers. However, in second-type double flowers, the secondary androecial primordia differentiate into petals and the stamens then develop from the free space between the two rows of secondary androecial primordia. In third-type double flowers, after complete primordial partitioning, some primordia on the marginal parts of each androecial sector develop into petaloids or intermediate appendages. The gynoecium appears similarly in both floral types as numerous congenitally united carpel primordia. The double-flowered phenotypes of Alcea appear to fit the criteria for homoheterotopy with complete or partial replacement of stamens with petals, as well as for neoheterotopy, with the formation of stamens in a new position. Based on mutant phenotypes, it is suggested that different functions possibly contribute to the proliferation and differentiation of common primordia.

The differentiation and development of pistils of hermaphrodites and pistillodes of males in androdioecious Osmanthus fragrans L. and implications for the evolution to androdioecy

The evolutionary pathway between hermaphroditism and dioecy draws widespread interests, and androdioecy is rarely achieved as an intermediate state between the two breeding systems. Flower bud differentiations in the pistils of hermaphrodites and the pistillodes of males in androdioecious Osmanthus fragrans L. were investigated by paraffin sectioning to elucidate the evolution to androdioecy. Results showed that the regularity and rhythm in flower bud differentiation between males and hermaphrodites were almost consistent and included six main stages. However, the hermaphrodites always lagged behind the males at each stage. The apical floret in the same inflorescence developed earlier than did the lateral ones in both hermaphrodites and males. The most significant difference between males and hermaphrodites was observed at the carpel differentiation stage. Two carpel primordia appeared inside the stamens of both males and hermaphrodites at the initial stage. These two carpels gradually fused with each other in hermaphrodites and eventually developed into a normal pistil with a stigma, a style, and an ovary. However, a cavity grew conspicuously over time between two carpels as developed in males. The two carpels eventually developed into a pistillode with two independent bracteal tissues. However, from the whole development process, the male retained the developmental residue of the hermaphrodite. Thus, the pistillodes of males could be traced to the pistils of hermaphrodites. This finding shows that males may be derived from hermaphrodites in O. fragrans. On the basis of this finding and previous studies on Oleaceae, androdioecy could be regarded as a transition from hermaphroditism to dioecy in this family.

Elucidating the unusual floral features ofSwartzia dipetala(Fabaceae)

In this study, we evaluated the floral ontogeny of Swartzia dipetala, which has peculiar floral features compared with other legumes, such as an entire calyx in the floral bud, a corolla with one or two petals, a dimorphic and polyandrous androecium and a bicarpellate gynoecium. We provide new information on the function of pollen in both stamen morphs and whether both carpels of a flower are able to form fruit. Floral buds, flowers and fruits were processed for observation under light, scanning and transmission electron microscopy and for quantitative analyses. The entire calyx results from the initiation, elongation and fusion of three sepal primordia. A unique petal primordium (or rarely two) is produced on the adaxial side of a ring meristem, which is formed after the initiation of the calyx. The polyandrous and dimorphic androecium also originates from the activity of the ring meristem. It produces three larger stamen primordia on the abaxial side and numerous smaller stamen primordia on the adaxial side. These two types of stamens bear morphologically similar ripening pollen grains. However, prior to the dehiscence of thecae and presentation of pollen in the anther, only the pollen grains of the larger stamens contain amyloplasts. Two carpel primordia are initiated as distinct protuberances, alternating with the larger stamens, in a slightly inner position in the floral meristem, constituting the bicarpellate gynoecium. Both carpels are able to form fruit, although only one fruit is generally produced in a flower. The increase in gynoecium merism probably results in an increase in the surface deposition of pollen grains and consequently in the chance of pollination. This is the first study to thoroughly investigate organogenesis and the ability of the carpel to form fruit in a bicarpellate flower from a member of Fabaceae, in addition to the pollen ultrastructure in the heteromorphic stamens associated with the ‘division of labour’ sensu Darwin. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 173, 303–320.

Comparative ontogeny of perfect and pistillate florets in Senecio vernalis (Asteraceae)

We studied the inflorescence, and in particular ontogeny and development of the florets in Senecio vernalis as a representative member of Asteraceae, using epi-illumination microscopy. Initiation and subsequent development of florets on the highly convex inflorescence apex occur acropetally, except for pistillate ray florets, which show a lag in initiation. Receptacular bracts derive from the receptacular surface after development of all florets. The order of whorl initiation in both disc and ray florets include corolla, androecium and finally the pappus, together with the gynoecium. Development of corolla lobes from a ring meristem occurs in bidirectional order starting from the lateral side, whereas stamens incept unidirectionally from the abaxial side. Concurrently with the inception of two median carpel primordia, a ring meristem develops at the base of the corolla from which pappus bristles differentiate in later stages. Pistillate ray florets show significant differences from perfect disc florets as reflected by the zygomorphic shape of the floral apex and a shift of floral merosity from pentamery to tetramery. Loss of stamens in ray florets occurs due to abortion of primordia after initiation.

Comparative Ontogeny of Hermaphrodite and Pistillate Florets in Helianthus annuus L. (Asteraceae)

The inflorescence of Helianthus annuus L. has two types of flowers (or florets) on a single capitulum; central hermaphrodite disc florets and peripheral pistillate ray florets. In both florets, reproductive development starts with the conversion of apical meristem into floral meristem that will produce floral organ primordia. The only difference between hermaphrodite and pistillate florets in apical meristem stage is that apical meristem of the pistillate florets is not as apparent and curvaceous as apical meristem of the hermaphrodite florets. The differentiation of apical meristem into floral meristem is in the same progress in both florets. In hermaphrodite florets, flower organs; petals, stamens and carpels develop from floral meristem. Differentiation of five petal primordia takes place in the same way in both florets. Firstly filament and then anther differentiates in a stamen. Two carpel primordia appear below the stamen primordia in hermaphrodite florets. In following stages, carpel primordia are lengthened and formed inferior ovary, style, stigma respectively. In pistillate florets, flower organs; petals and carpels develop from floral meristem. They pass directly from the periant initiation to the start of carpel formation. Stamen primordia don’t appear and the further development of carpel primordia stops in a short time, as a result, stigma and style do not exist in pistillate florets. However, an inferior ovary with no ovule forms. In the capitulum of hermaphrodite florets, the development takes place in a centripetal manner; it starts firstly on the outermost whorl, and it proceeds towards inner whorl. However, this is not the case in pistillate florets.

Inflorescence and floral development in Ranunculus and three allied genera in Ranunculeae (Ranunculoideae, Ranunculaceae)

The development of inflorescences and flowers of three species of Ranunculus and three allied genera (Ceratocephala, Halerpestes, and Oxygraphis) (Ranunculeae, Ranunculaceae) was studied comparatively using scanning electron microscopy (SEM). Our results showed that both the inflorescence branching patterns and the floral morphogenesis in Ranunculeae are extremely labile. Inflorescences range from a thyrsoid to a solitary flower, with intermediate branching patterns in which sometimes only the terminal flower of the inflorescence main axis fully develops, such as in Ceratocephala and Halerpestes. Only in Oxygraphis is the flower truly solitary. In all species, sepal primordia are broad, crescent-shaped, and truncate, and the primordia of petals, stamens, and carpels are rather small and hemispherical, and very similar to each other. The plastochron between the last sepal and the first petal is relatively long. At the onset of androecium or gynoecium development, the regular spiral pattern of the perianth may become irregular in Ceratocephala and Oxygraphis, whereas spiral and whorled patterns may co-occur in Ranunculus and Halerpestes. The development of the petals is delayed with regard to that of the other floral organs in all species studied here, except for Oxygraphis. Our study confirms that, for solitary flowers, increased number of petals and the shape of the ventral nectary may have evolved independently many times, as suggested by earlier molecular phylogenetic studies and ancestral character reconstructions. With respect to the remainder of the tribe, Oxygraphis displays several autapomorphies, such as nondelayed development and increased number of petals, which will be of interest for comparative molecular developmental studies.

Gynoecial anatomy and development in Cyperoideae (Cyperaceae, Poales): congenital fusion of carpels facilitates evolutionary modifications in pistil structure

Background and aims – In Cyperaceae, the single-ovuled, usually triangular gynoecia are widely considered to have a basic number of three carpels, often reduced to two, resulting in dimerous pistils. However, laterally flattened dimerous pistils cannot be explained by any existing carpel reduction theories, because a single stigma in median position replaces the two adaxial stigmata. This paper presents a comparative study of the ontogenetic and anatomical adaptations facilitating the origin of new pistil forms in Cyperoideae, focusing on modified gynoecia. It includes a re-evaluation of Blaser’s (1941) anatomical studies in Cyperaceae. We aim to test Blaser’s hypothesis that is based on an acropetal developmental model of the floral vasculature and the general Cyperoid ontogenetic model of Vrijdaghs et al. (2009), which states that cyperoid ovaries originate from an annular primordium. Methods – SEM, dark field and phase contrast microscopy. Key Results – All cyperoid pistils studied develop according to a cyperoid floral ontogenetic pattern, in which carpel primordia are congenitally fused. In Pycreus sanguinolentus (and other species), separate procambial initiation zones were observed in both the flower receptacle and separate floral primordia, which connect (or not) at later developmental stages. Conclusions – The presence of an annular ovary primordium instead of individual carpel primordia, combined with the bidirectional development of the pistil vasculature liberate the developing gynoecium from the structural constraints proper to a typical carpellate organisation. Procambial initiation zones in the receptacular vascular plexus and in individual floral primordia constitute the basis for the formation of a flexible vascular system in cyperoid flowers. Moreover the development of the ovary and ovule are decoupled. Consequently, in Cyperoideae the acquired developmental freedom of the pistil resulted in various adaptations.

Structural Analysis of Reproductive Development in Staminate Flowers of Laurus nobilis L.

Male (staminat) flower development, being separated in 8 phases, was investigated in Laurus nobilis (Lauraceae) through the usage of histological sections and scanning electron microscopy (SEM) analysis. Flower development starts when apical meristem differentiates, followed by the conversion of this structure to floral meristem. Initial development phases comprise incidents similar to the ones of the female flower. 4 tepals and 8-10 stamens primordia develop through floral meristem in turn. In early stages of the development, sexual dimorphism occurs when the carpel primordium arrests. Filaments carry 2 nectaries in stamens which arise in 3 whorls. Anther wall consists of epidermis, endothecium, 2 or 3 middle layers and a single-layered glandular tapetum. Anthers are bisporangiate. Meiotic division is regular in pollen mother cells, and pollen grains do not contain aperture. Beside the pollen scattered individually within the pollen sacs, groups which contain some pollen tied to each other are rarely observed, as well. Pollen grains seldom germinate within microsporangium. Anthers are opened with 2 valves which widen from the base through the top. Accumulation of polysaccharides, lipids and proteins were identified by histochemical methods in stamens. These organic substances are greater within and around the vascular bundle compared to other tissues.

Different Patterns of Floral Ontogeny in Dimorphic Flowers of Pseudostellaria heterophylla (Caryophyllaceae)

Pseudostellaria heterophylla, a cleistogamous species belonging to the Caryophyllaceae, was studied ontogenetically with SEM to investigate floral development in chasmogamous (CH) flowers and cleistogamous (CL) flowers. Comparative ontogenetic studies of this cleistogamous species revealed significant differences between CH and CL flowers. As opposed to other findings for cleistogamous species, the results of this study showed that divergence in the development of the floral forms occurs at inception, not later during organ growth. The floral organ inception in the CH flower is as follows: five sepal primordia are initiated in a helical sequence, 10 stamen primordia are initiated in two whorls (an antesepalous whorl and an antepetalous whorl sequentially), petal primordia are initiated by the division of common stamen-petal primordia, and three carpel primordia are initiated last. The floral organ inception in the CL flower is as follows: four sepal primordia are initiated in two pairs alternatively, two ...

The expression patterns of the genes VvTFL1, VFL, VAP1, VvAG1 and VvSEP3 during bud and flower development in the “Xiangfei” grapevine (Vitisvinifera L.)

In this study, the differentiation of buds, inflorescences and flowers of the “Xiangfei” grapevine (Vitis vinifera L.) was examined, and the roles of the genes VvTFL1, VFL, VAP1, VvAG1 and VvSEP3 in the initiation and development of these organs were studied. We found that the structure of burst buds included an apical point, a leaf primordium, an inflorescence or tendril primordium, bract and stipule primordia. The original floral primordium formed lateral meristems for branching inflorescence primordia and continued to differentiate into floret primordia in lateral bud. VvTFL1 gene expression was detected in the apical meristems of swelling buds, but it was not detected during the entire process of inflorescence initiation and flower development. VFL and VAP1 genes were strongly detected in inflorescences and developing flowers. Furthermore, the VFL gene strongly detected in inflorescence meristems and flower organ primordia. VAP1 expression was detected in the branching of the pedicel region of burst buds, and after petal, stamen and carpel primordium development, VAP1 transcripts were clearly detected. The expression of VvAG1 and VvSEP3 began to be detected in the placental region of anatropous ovules at later stages of flower development, and VvAG1 had earlier effects than VvSEP3. These results suggest that those genes might play a different role in grapevine.

Floral ontogeny of Schisandra chinensis (Schisandraceae): implications for androecial evolution within Schisandra and Kadsura

The organogenesis of staminate and carpellate flowers of Schisandra chinensis (Schisandraceae) was investigated with scanning electron microscopy, with observations on the development of tepals reported for the first time. The results showed that there is no interval between the initiation of the last tepal and that of the first stamen or carpel, and that the shapes of tepal, stamen, and carpel primordia are similar. The tepals and stamens of staminate flowers are initiated acropetally in a continuous spiral Fibonacci phyllotaxis, with no carpel structures observed; the filaments are not connate. The organogenesis of the carpellate flowers is similar to that of the staminate flowers, but with no evidence of stamen development. The carpels are ascidiate without postgenital fusion. Three androecial characters of Schisandra and Kadsura are discussed in a phylogenetic context. The subglobose or obovoid androecium of Schisandrapropinqua and Schisandra plena may be homologous with that in sections Kadsura and Sarcocarpon. The plesiomorphic form of the androecium within the two genera is likely to be elongate with more than ten free stamens.

Geometric parameters of the apical meristem and the quality of phyllotactic patterns in Magnolia flowers

The ratio of primordium size to the meristem size (<em>P/M </em>ratio) is regarded by some geometrical models of phyllotaxis as the parameter, which determines the quality of spiral and whorled patterns of lateral organ arrangement. This assumption was tested on floral meristems in four genets representing four <em>Magnolia </em>taxa: <em>M. </em>× <em>salicifolia</em>, <em>M. stellata</em>, <em>M. denudata </em>and <em>M. acuminata</em>. In successive zones of <em>Magnolia </em>flower, lateral organs are initiated in specific phyllotactic patterns and at specific values of the meristem and primordia sizes. The elements of perianth, usually positioned in three trimerous whorls, are initiated as large primordia on relatively small meristem. The switch in the identity of primordia, from tepals to stamens is accompanied by an abrupt increase in the size of the meristem and decrease in the primordia size. Small values of <em>P/M </em>ratio and frequent occurrence of qualitative transformations of phyllotaxis contribute to the exceptionally rich spectrum of spiral patterns in androecium zone. New spiral patterns emerge when bigger primordia of carpels are initiated on the meristem, which at the same time starts diminishing in size either abruptly (<em>M. </em>× <em>salicifolia</em>, <em>M. stellata</em>, <em>M. acuminata</em>) or slowly (<em>M. denudata</em>). Spiral patterns identified in gynoecia have lower numbers of parastichies than the patterns of androecia and occur in frequencies specific for the genet. Although noted ranges of the meristem and primordia sizes, justify the occurrence of phyllotactic patterns observed in successive zones of <em>Magnolia </em>flower, they do not explain genet-specific frequencies of the patterns observed in gynoecium zone. The lack of straightforward relationship between frequency of the patterns and <em>P/M </em>ratio in gynoecium suggests that more complex geometrical factors or factors of non-geometrical nature are engaged in determination of <em>Magnolia </em>floral phyllotaxis.

Le déterminisme du sexe chez les cucurbitacées

Sex determination in plants leads to the development of unisexual flowers from an originally bisexual floral meristem. Cucurbits are not only species of agronomic interest but they also represent model species for the study of plant sex determination, because of their ability to harbor different sexual types. Such sexual forms are controlled by the identity of the alleles at the following loci: andromonoecious (a) and gynoecious (g) in melon, or androecious (a), Female (F), and Monoecious (M) in cucumber. We firstly showed that the andromonoecious a gene in melon encodes for an ACC synthase (CmACS7) and demonstrated that andromonoecy results from a mutation in the active site of the enzyme. Expression of the active enzyme inhibits the development of the male organs and is not required for carpel development. Because the a gene in melon and M gene in cucumber control the same sexual transition, monoecy to andromonoecy, we isolated the andromonoecy M gene in cucumber using a candidate gene approach in combination with genetic and biochemical analysis. We demonstrated the co-segregation of CsACS2, a close ortholog of CmACS7, with the M locus, and showed that the cucumber andromonoecious phenotype is also due to a loss of ACS enzymatic activity. CsACS2 is expressed specifically in carpel primordia of female flowers and should play a similar role to that of CmACS7 in melon in the inhibition of stamina development. Finally, we also showed that the transition from male to female flowers in the gynoecious lines results from epigenetic changes in the promoter of a C(2)H (2) zinc-finger transcription factor, CmWIP1. This epigenetic change is elicited by the insertion of a DNA transposon, which causes the spreading of DNA methylation to the CmWIP1 promoter. Expression of CmWIP1 leads to carpel abortion, resulting in the development of unisexual male flowers. From all these results, we built a model in which CmACS7 and CmWIP1 interact to control the development of male, female and hermaphrodite flowers in melon.

Flower and early fruit development in a diploid strawberry, Fragaria vesca

The diploid woodland strawberry, Fragaria vesca, is being recognized as a model for the more complex octoploid commercial strawberry, Fragaria×ananassa. F. vesca exhibits a short seed to seed cycle, can be easily transformed by Agrobacteria, and a draft genome sequence has been published. These features, together with its similar flower structure, potentially make F. vesca a good model for studying the flower development of other members of the Rosaceae family, which contains many economically important fruit trees and ornamental plants. To propel F. vesca's role in genetic and genomic research and to facilitate the study of its reproductive development, we have investigated in detail F. vesca flower and early fruit development using a seventh generation inbred diploid line, Yellow Wonder 5AF7. We present here standardized developmental staging and detailed descriptions of morphological changes associated with flower and early fruit development based on images of hand dissected flowers, histological sections, and scanning electron microscopy. In situ hybridization with the F. vesca AGAMOUS homolog, FvAG, showed expression in young stamen and carpel primordia. This work lays the essential groundwork and standardization for future molecular, genetic, and genomic studies of F. vesca.

Flower Development and Anatomy of Agapanthus praecox ssp. orientalis (Leighton) Leighton

Floral buds of Agapanthus praecox ssp. orientalis were observed under dissecting and optical microscope to characterize floral organs development and to study relationships between anther development and microsporogenesis. Floral organs differentiation was comprised of 6 distinct stages including nought differentiation, inflorescence bud differentiation, floret primordia differentiation, tepal primordia differentiation, stamen primordia differentiation, and pistil primordia differentiation. Six tepals differentiated almost simultaneously which cross arranged in space and appeared in hexagonal distribution pattern. Six stamens were differentiated inside the tepals at the same time. Finally, 3 carpel primordia differentiated and formed syncarpous pistil. The whole process of floral bud differentiation took approximately 40 d with the first 3 stages developing more slowly than the later 3 stages. Morphology and color of the anther underwent obvious changes during the period between stamen primordia differentiation and anther maturation. Microspores also underwent significant development during this same interval. The relationship between the process of microsporogenesis and anther development has already been made clear by the squash technique.

Inflorescence and floral ontogeny inOsteospermum ecklonis(Asteraceae)

Development of the capitulum inflorescence with different types of florets in Asteraceae is an interesting issue in the field of plant evolution and development. In this study, ontogeny of the inflorescence and florets of Osteospermum ecklonis (DC.) Norl., an ornamental and evergreen subshrub, was investigated using epi-illumination light microscopy. The initiation and subsequent development of florets on the highly convex inflorescence apex occurred acropetally, except for the ray florets, which showed a lag in initiation. Organogenesis in disc florets started with unidirectional initiation of corolla lobes from the adaxial side and then proceeded by simultaneous appearance of five stamen and finally two median carpel primordia. Significant developmental features included the lack of pappus differentiation, formation of nonsyngenesious stamens, and formation of the ovule-less ovary. Ray florets showed significant differences from disc florets as reflected by the zygomorphic shape of floral apex and shift of floral merosithy from pentamery to tetramery. Also, expansion of corolla lobes to form the ligule and the formation of staminodia were observed. It is hypothesized that the actinomorphic pentamerous disc florets are most primitive among the family from which the tetramerous ray florets are derived. Accordingly, ray florets evolved from disc florets under long-term selective pressure and play a crucial role in enhancing reproductive success.

DORNRÖSCHEN-LIKE expression marks Arabidopsis floral organ founder cells and precedes auxin response maxima

Live imaging during floral development revealed that expression of the DORNRÖSCHEN-LIKE (DRNL) gene encoding an AP2-like transcription factor, marks all organ founder cells. Transcription precedes the perception of auxin response maxima as measured by the DR5 reporter and is unaffected in early organogenesis, by mutation of four canonical auxin response elements (AuxREs) in the DRNL promoter. DRNL expression identifies discrete modes of organ initiation in the four floral whorls, from individual or pairs of organ anlagen in the outer whorl of sepals to two morphogenetic fields pre-patterning petals and lateral stamens, or a ring-shaped field giving rise to the medial stamens before carpel primordia are specified. DRNL function only overlaps in the central stem cell zone with that of its paralogue, DORNRÖSCHEN (DRN). drnl mutants are affected in floral organ outgrowth, which functionally interplays with boundary specification as organ fusions are sensitized by loss of CUP-SHAPED COTYLEDON (CUC) gene activity, and synergistic interactions exist with mutants in local auxin biosynthesis and polar transport. DRNL apparently monitors and contributes to cellular decisions in the SAM and thus provides a novel molecular access to the interplay of founder cell specification, organ anlage and organogenesis in the SAM peripheral zone.

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

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

Temporal and spatial regulation of DROOPING LEAF gene expression that promotes midrib formation in rice

Genes involved in the differentiation and development of tissues and organs are temporally and spatially regulated in plant development. The DROOPING LEAF (DL) gene, a member of the YABBY gene family, promotes midrib formation in the leaf and carpel specification in the flower. Consistent with these functions, DL is initially expressed in the central region of the leaf primordia (presumptive midrib) and in the presumptive carpel primordia in the meristem. To understand the regulatory mechanism underlying DL expression, we tried to identify cis-regulatory regions required for temporal and spatial expression of this gene. We found that the cis region responsible for the presumptive midrib-specific expression in the leaf primordia is located in intron 2. Next, we confined the region to a sequence of about 200bp, which corresponds to a conserved non-coding sequence (CNS) identified by phylogenetic footprinting. In addition, a sequence termed DG1, incorporating a 5' upstream region of about 7.4kb, and introns 1 and 2, was shown to be sufficient to induce DL in the presumptive midrib, and to suppress it in other regions in the leaf primordia. By contrast, the regulatory region required for carpel-specific expression was not included in the DG1 sequence. We modified Oryza sativa (rice) plant architecture by expressing an activated version of DL (DL-VP16) in a precise manner using the DG1 sequence: the resulting transgenic plant produced a midrib in the distal region of the leaf blade, where there is no midrib in wild type, and formed more upright leaves compared with the wild type.