Early Floral Development Research Articles

Floral Morphology and Development inAragoa(Plantaginaceae) and Related Members of the Order Lamiales

Inflorescence and floral morphology and development were investigated in Aragoa (Plantaginaceae) and related genera. Each inflorescence of Aragoa is a reduced, axillary raceme, on which the actinomorphic floral apices generally arise successively. The inflorescences of Aragoa and Plantago are polytelic and lateral. The five sepals emerge from the abaxial to the adaxial side of the floral apex, but at maturity, the calyx is actinomorphic. The four stamens arise simultaneously and before emergence of the petals. The four petals emerge unidirectionally united, but the corolla becomes actinomorphic. Aestivation is cochlear ascendent. The two united carpels initiate simultaneously. The abaxial‐adaxial inception of the calyx and corolla during early floral development in genera such as Aragoa, Digitalis, Plantago, and Veronica may indicate that the zygomorphic condition is ancestral in those genera. The tetramerous corolla, which is actinomorphic during middle and late development, and the presence of four stam...

Comparative Floral Development and Androecium Structure in Malvoideae (Malvaceae s.l.)

Floral development and androecium structure were studied in eight genera of the Malvoideae (Malvaceae s.l.). All core Malvoideae (Malvaceae s.s.) share a uniform pattern of floral development and have several characteristic androecium structures in common. A corolla/androecium ring wall is formed and subsequently differentiated into five androecial sectors (=primary androecial primordia) that give rise to the androecium and corolla. Petals are developed at the base of the androecial sectors and are shifted slightly clockwise or counterclockwise relative to the androecial sector. Secondary androecial primordia are initiated centrifugally in two rows on each sector in an alternate pattern. The first secondary androecial primordium is initiated on the opposite side of the androecial sector from the petal. The secondary androecial primordia later subdivide longitudinally and differentiate into functional androecial units, which each have a two‐locular theca with a single longitudinal dehiscence zone. In some taxa, sterile tips are formed at the distal end of the androecial tube in an antepetalous position. In Matisieae, sister to core Malvoideae, the early floral development is nearly identical to that in core Malvoideae. In later development and at anthesis, Matisieae and core Malvoideae show more pronounced differences. In Matisieae, a subdivision of secondary androecial primordia occurs generally transversely as compared with longitudinally in core Malvoideae. While the androecium of core Malvoideae consists of a long tube with lateral stalked androecial units, the androecial tube of Matisieae is stouter and bears sessile androecial units mostly on lobes. These lobes, however, do not correspond to the androecial sectors, as do the sterile androecial tips of core Malvoideae. The sterile androecial tips of core Malvoideae have the same position as androecial units at the tip of androecial sectors in other Malvaceae and could be remnants of these structures. The androecial lobes in Matisieae are, however, positioned alternipetalously and might correspond to remnants of a second whorl of androecial structures found in other Malvaceae or Malvales.

Early Floral Development and Nature of the Calyptra in Eupomatiaceae (Magnoliales)

Early floral development in Eupomatia bennettii and Eupomatia laurina was studied with scanning electron microscopy and serial microtomy to focus on initiation and development of the calyptra and initiation and phyllotaxis of the floral organs. Phyllomes preceding the calyptra are distichous or spirodistichous in arrangement. In both species, the calyptra is initiated as a smooth ring meristem encircling the floral apex. There are no traces of distinct organ primordia on this ring. After initiation, the calyptra rapidly elongates into a tubular structure, and its rim closes by irregular lobation and local formation of hairs. These lobes also behave differently than young organs in their growth pattern. The closed rim ceases to enlarge and forms a minute closed pore at anthesis. A long plastochron follows initiation of the calyptra, and the floral apex widens considerably during this time. Since a perianth is lacking, stamens and staminodes are the first floral organs initiated. They appear in a regular spiral phyllotaxis according to a Fibonacci pattern, with the contact parastichy sets of 13 and 21 for E. bennettii and eight and 13 for E. laurina (with fewer floral organs). The carpels are also spirally arranged, with the contact parastichy sets of eight and 13 for E. bennettii and five and eight for E. laurina. The calyptra in Eupomatiaceae is best interpreted as a single, amplexicaul bract. This is indicated by the floral development of Eupomatiaceae and also by comparison with the closest relatives (Annonaceae, Magnoliaceae, Himantandraceae), which have calyptra‐like structures that more clearly correspond to bracts. For angiosperms in general, I suggest that bracts and tepals are not terms to be used at the same level; bracts represent a less differentiated ground state of phyllomes.

A morphological and quantitative characterization of early floral development in apple (Malus x domestica Borkh.).

Apple is an important crop and a focus of research worldwide. However, some aspects of floral commitment and morphogenesis remain unclear. A detailed characterization of bourse shoot apex development was undertaken to provide a framework for future genetic, molecular and physiological studies. Eight morphologically distinct stages of shoot apex development, prior to winter dormancy, were defined. Based on measurements of meristem diameter, two stages of vegetative development were recognized. Vegetative meristems were flat, and either narrow (stage 0) or broad (stage 1). Pronounced doming of the apex marked stage 2. During stage 3, the domed meristem initiated four to six lateral floral meristems and subtending bracts before converting to a terminal floral meristem (stage 4). The terminal floral meristem proceeded directly with bractlet and sepal initiation, while lateral floral meristems initiated bractlets (stage 5). Sepal initiation began on the basal lateral flower (stage 6) and continued in an acropetal direction until all floral meristems had completed sepal initiation (stage 7). In this study, only stage 0 and stage 7 apices were observed in dormant buds, indicating that stages 1-6 are transient. The results suggest that broadening of the apex (stage 1) is the first morphological sign of commitment to flowering.

Temporal analysis of alpha and beta-expansin expression during floral opening and senescence

We have identified a family of expansin transcripts that include seven α-expansins ( MjExp1 through MjExp7) and three β-expansins ( MjExpB1 through MjExpB3) from Mirabilis jalapa (Nyctaginaceae) that show dramatic changes in transcript abundance during the rapid expansion and subsequent senescence of the ephemeral flowers. In general, α-expansin expression was low in small buds, high during maximal elongation of the floral tube, reduced during floral display, and upregulated during calyx infolding and collapse. Transcripts encoding auxin responsive proteins (Aux/IAA) showed a similar pattern of expression. Northern analysis using a set of overlapping probes designed to the MjExp2 transcript demonstrated a gradient of sequence conservation along its length (high to low, from the 5′ to the 3′ end of the coding region), and identified the presence of floral senescence-specific expansins. Beta expansin transcripts were found to be preferentially expressed during early floral development and sharply downregulated coincident with rapid growth. All three β-expansin transcripts are highly related, and ψ MjExpB2 is an intronless pseudogene derived from MjExpB1. MjExpB3 appears to have derived from MjExpB1 in a separate gene duplication event, and is predicted to encode a truncated protein.

Ovary Position Diversity in Saxifragaceae: Clarifying the Homology of Epigyny

We discuss the structural homology of the gynoecium and the developmental variations associated with ovary diversity in Saxifragaceae. Diverse ovary positions are present within most of the major clades in the family. We demonstrate that superior ovaries, although widely reported for various members of the family, are unusual and limited to a few species of Micranthes and Saxifraga and to male flowers of the dioecious Tanakaea among investigated genera. Most species reported to have superior ovaries actually have developmentally epigynous flowers in which the ovary has a small portion below the insertion of the perianth and androecium. Such ovaries of epigynous flowers that mimic superior ovaries are termed “pseudosuperior.” Labile shifts in proportioned growth of that part of the ovary above the insertion of the perianth and androecium to that below their insertion have created extensive variation in ovary position among closely related taxa, e.g., in both Saxifraga and Micranthes. The heterostylous Jepsonia has differences in ovary position among the different style‐length morphs, and similar variation in ovary position may be present in the dioecious Tanakaea. Epigynous flowers of Saxifragaceae fit the model of appendicular epigyny. During the organogenetic phase of early floral development, they exhibit peripheral upgrowth of the apical region, which forms a central concavity. The initial gynoecial primordium forms on the inner slope of the concavity, zonal growth in the concave flank subjacent to the initial gynoecial primordium elongates, and subsequently, the tissue lining the concave flank below the initial gynoecial primordium differentiates as ovary.

Desenvolvimento floral e estaminal no clone CP76 de Anacardium occidentale L.: cajueiro-anão precoce (Anacardiaceae)

The early floral development as well as anther ontogeny in the Anacardium occidentale L. was studied. The flowers present five sepals and five petals with helical and unidirectional development, respectively, and androceum with a stamen with striking heterochronic and heteromorphic development in relation to the remaining nine stamens. At the terminal position an unilocular carpel arises. The histogenic processes is identical in both stamens. At the end of ontogeny both anther types possess four sporangia, with epidermis, endothecium, two middle layers and secretory tapetum, as parietal layers and a sporogenic tissue. The inner portion of the tapetum does not arise from the connective.

Molecular Genetic Regulation of Early Floral Development in Brassica oleracea

Molecular Genetic Regulation of Early Floral Development in <i>Brassica oleracea</i>

Evolutionary Lability of Symmetry in Early Floral Development.

Floral symmetry is the product of organogeny plus subsequent organ development. In terms of floral apical meristem activity, radial symmetry results from equilateral organ initiation on a radially symmetrical apical meristem followed by equilateral development among like organs. Bilateral symmetry results from restriction of organ initiation to two planes that are perpendicular to one another. Zygomorphy can result either from zygomorphic organogeny (successive from one side of the flower) or from differential enlargement among like organs in a flower that has radial symmetry in earlier stages. Asymmetry results in rare instances when (a) the floral apex is asymmetric and initiates organs in asymmetric order or (b) when the floral apex is radially symmetrical but when differentiation among the organs of a whorl produces unlike structures. Evolutionary lability in symmetry has usually not involved the shape of the floral apex, except in a few examples, such as Labichea in Fabaceae. More frequently, such lability has resulted from postinitiation events, such as selective organ differentiation or heterochrony.

Changes in cytokinin activities before, during and after floral initiation in Polianthes tuberosa

The contents of endogenous cytokinin in tuberose corms ( Polianthes tuberosa) at vegetative, early floral initiation, and flower development stages were investigated. We also determined the influence of exogenous cytokinin treatment on the corm apex at three different growth stages in relation to floral initiation and development in tuberose. The exogenous cytokinin effectively induced floral initiation and development, especially at the early floral initiation and flower development stages. Endogenous cytokinins were higher in early floral initiation and development stages in comparison to the vegetative stage. During floral initiation stage, the zeatin and dihydrozeatin increased significantly, while the cytokinins, zeatin riboside, dihydrozeatin riboside, 6N- ( δ 2 -isopentenyl) adenine, and 6N -( δ 2 -isopentenyl) adenine riboside at consistently low levels. The increase of cytokinin levels in tuberose corms during floral induction suggests a role for cytokinins in tuberose apex evocation. Moreover, these results indicate that cytokinins seem to promote the development of flower buds rather than inducing flowering in tuberose.

Phosphorylation-dependent interactions between enzymes of plant metabolism and 14-3-3 proteins.

Far-Western overlays of soluble extracts of cauliflower revealed many proteins that bound to digoxygenin (DIG)-labelled 14-3-3 proteins. Binding to DIG-14-3-3s was prevented by prior dephosphorylation of the extract proteins or by competition with 14-3-3-binding phosphopeptides, indicating that the 14-3-3 proteins bind to phosphorylated sites. The proteins that bound to the DIG-14-3-3s were also immunoprecipitated from extracts with anti-14-3-3 antibodies, demonstrating that they were bound to endogenous plant 14-3-3 proteins. 14-3-3-binding proteins were purified from cauliflower extracts, in sufficient quantity for amino acid sequence analysis, by affinity chromatography on immobilised 14-3-3 proteins and specific elution with a 14-3-3-binding phosphopeptide. Purified 14-3-3-binding proteins included sucrose-phosphate synthase, trehalose-6-phosphate synthase, glutamine synthetases, a protein (LIM17) that has been implicated in early floral development, an approximately 20 kDa protein whose mRNA is induced by NaCl, and a calcium-dependent protein kinase that was capable of phosphorylating and rendering nitrate reductase (NR) sensitive to inhibition by 14-3-3 proteins. In contrast to the phosphorylated NR-14-3-3 complex which is activated by dissociation with 14-3-3-binding phosphopeptides, the total sugar-phosphate synthase activity in plant extracts was inhibited by up to 40% by a 14-3-3-binding phosphopeptide and the phosphopeptide-inhibited activity was reactivated by adding excess 14-3-3 proteins. Thus, 14-3-3 proteins are implicated in regulating several aspects of primary N and C metabolism. The procedures described here will be valuable for determining how the phosphorylation and 14-3-3-binding status of defined target proteins change in response to extracellular stimuli.

Early floral development of Camellioideae (Theaceae)

The early floral development of Camellioideae was studied. Two major evolutionary lineages were recognized for this subfamily. The earlier evolved lineage (Camellia, Polyspora, and Pyrenaria) has normally 11-14 perianth members, which are initiated in a continuous spiral and are differentiated into sepals and petals at late floral development, and numerous stamens initiated individually and centrifugally on the whole androecial region. The later derived lineage (Franklinia, Hartia, Schima, and Stewartia) has five sepals and five petals arranged in two whorls, and numerous individual stamens originating centrifugally from the five petal-opposed zones. Hartia-Stewartia and Franklinia-Schima further diverged as two branches - the former is characterized by having androecial fascicles and axile-basal placentation. The androecial fascicle is considered to be derived within this subfamily. The latter exhibits a higher degree of carpellary congenital fusion and axile-central placentaion, and as a whole, is concluded to be the most advanced group in the Camellioideae. A taxonomic treatment of the Camellioideae at the tribal level is also proposed.

The symplasmic coupling of L 2 -cells diminishes in early floral development of Iris

The transition from vegetative to reproductive development involves extensive revisions of cellular collaboration at the apical meristem and results in the production of novel appendages. In Dutch Iris (Iris xiphium) the transition from vegetative apical meristem to inflorescence meristem was morphologically signalled by the appearance of a `spathe leaf '. After enlargement of the inflorescence meristem, a second spathe leaf and a double floral meristem were formed. The then undulated surface corresponded to general topological changes and a beginning of altered cell division patterns. Throughout, all cells produced in the meristem remained in contact via plasmodesmata (Pd), thus maintaining the symplasmic unity of the meristem. Since the symplasm harbours part of the signal network that coordinates the activities of the meristem cells, we investigated if alterations in Pd numbers could underlie meristem transitions. Prior to Pd counting, potentially important borders inside the meristem, representing primary and secondary cell contacts, were identified by the construction of a symplasmetric map. During the transition, significant alterations did take place at some of the borders defined by the map. Within the second tunica layer (L2), and between the L2 and adjacent cells, Pd numbers were strongly reduced. Within the first tunica layer (L1) and within the corpus they remained the same. The reduction was 25% between L2-cells, and between L2- and L1-cells; it was 40% between the L2 and the outer corpus layer. The reductions appeared to be due to a lowered production of primary and secondary Pd by L2-cells towards each other and towards adjacent cells. As a result of this the integration of all L2-cells and, as a consequence, of the L1 as a whole in the symplasmic network of the meristem was reduced. The implied gain in autonomy of the individual L2-cells and of the L1-layer may reflect their new functions in the floral meristem.

Overexpression of a soybean gene encoding cytosolic glutamine synthetase in shoots of transgenic Lotus corniculatus L. plants triggers changes in ammonium assimilation and plant development.

A soybean cytosolic glutamine synthetase gene (GS15) was fused with the constitutive 35S cauliflower mosaic virus (CaMV) promoter in order to direct overexpression in Lotus corniculatus L. plants. Following transformation with Agrobacterium rhizogenes, eight independent Lotus transformants were obtained which synthesized additional cytosolic glutamine synthetase (GS) in the shoots. To eliminate any interference caused by the T-DNA from the Ri plasmid, three primary transformants were crossed with untransformed plants and progeny devoid of TL- and TR-DNA sequences were chosen for further analyses. These plants had a 50-80% increase in total leaf GS activity. Plants were grown under different nitrogen regimes (4 or 12 mM NH4+) and aspects of carbon and nitrogen metabolism were examined. In roots, an increase in free amino acids and ammonium was accompanied by a decrease in soluble carbohydrates in the transgenic plants cultivated with 12 mM NH4+ in comparison to the wild type grown under the same conditions. Labelling experiments using 15NH4+ were carried out in order to monitor the influx of ammonium and its subsequent incorporation into amino acids. This experiment showed that both ammonium uptake in the roots and the subsequent translocation of amino acids to the shoots was lower in plants overexpressing GS. It was concluded that the build up of ammonium and the increase in amino acid concentration in the roots was the result of shoot protein degradation. Moreover, following three weeks of hydroponic culture early floral development was observed in the transformed plants. As all these properties are characteristic of senescent plants, these findings suggest that expression of cytosolic GS in the shoots may accelerate plant development, leading to early senescence and premature flowering when plants are grown on an ammonium-rich medium.

TOUSLED participates in apical tissue formation during gynoecium development in Arabidopsis.

Mutations at the TOUSLED (TSL) protein kinase locus in Arabidopsis cause reduced differentiation of apical gynoecial tissues and eliminate the fusion of the style and septum. TSL expression becomes confined to the developing style by stage 13, where it may promote expansion of tissues. Double mutant analysis suggests that ETTIN interacts with TSL, possibly by restricting TSL expression to apical regions. TSL, LEUNIG, and PERIANTHIA appear to participate in pathways of redundant function during the development of specific gynoecial tissues. TSL and LEUNIG most likely function in similar pathways during ovule development. TSL acts independently of the function of the organ identity genes AGAMOUS and APETALA2, and it is required for the formation of specific tissues in ectopic carpels. Mutations in TSL, ETTIN, PERIANTHIA, and LEUNIG all affect floral organ number as well as gynoecium morphology. Their respective wild-type loci must therefore play important roles in early floral meristem development during initiation of organ primordia in addition to their functions during regional differentiation within developing gynoecial primordia.

Studies on the early floral development inCleomoideae (Capparaceae) with emphasis on the androecial development

Floral ontogeny ofCleome spinosa, Cleome violacea andPolanisia dodecandra subsp.trachysperma was studied in the context of the question whether the fascicled androecium ofReseda andCapparis (with fused fascicles) or the 2 + 4-pattern of theBrassicaceae is primitive in theCapparales. InPolanisia dodecandra, the 9–18 stamens show unidirectional initiation from the adaxial side toward the abaxial side of the flower. InCleome violacea, the six stamens also are formed in an unidirectional order, but development starts abaxially and a zigzag-like pattern is superimposed. InCleome spinosa, two stamen primordia in transversal (lateral) position are followed by four stamens which arise on a somewhat higher level in two pairs in front of the median sepals. It is assumed that the evolutionary steps in the androecial development proceed fromReseda viaCapparis andPolanisia/Cleome toBrassicaceae. This interpretation is supported byrbcL-studies (Chase & al. 1993,Rodman & al. 1993).

An analysis of the early floral development ofPittosporum tobira (THUNB.) AITON and some remarks on the systematic position of the family Pittosporaceae

An analysis of the early floral development ofPittosporum tobira (THUNB.) AITON and some remarks on the systematic position of the family Pittosporaceae

An analysis of the early floral development of Pittosporum tobira (THUNB.) AITON and some remarks on the systematic position of the family Pittosporaceae

AbstractIn Pittosporum tobira all floral organs are initiated in a strictly acropetal succession. It is striking that sepals and petals show an extremely early hyponastical development. Important floral characters for placing the family Pittosporaceae near the Apiales (Araliaceae and Apiaceae) are the early sympetaly, only gradual differences in the gynoecium development and placentation, and the fact that a nectar secreting area is situated at the base of the dorsal carpel flanks (ovary superior in Pittosporaceae, inferior in Apiales).Viscid latex, which plays an important role in the dispersal of the seeds by exozoochory, is produced by the multicellular epidermal hairs in the septal (placental) region.

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.

Heat Injury during Early Floral Bud Development in Cowpea

Heat stress during the vegetative and early reproductive stages induces floral bud abortion in cowpea [Vigna unguiculata (L.) Walp.] and several other crop species growing under long days, and can substantially reduce productivity. The objective of this study was to determine whether there is a specific developmental stage when heat stress causes abortion of floral buds. Cowpea plants were grown in four reach‐in growth chambers under either metal halide‐based (MH) or fluorescent‐based (FL) lighting systems with 14‐h photoperiod and thermoperiod. Heat injury to floral bud development was quantified as floral bud suppression; the percentage of peduncles on the first five reproductive nodes that did not produce at least one flower. In all cases, floral buds were initiated on these nodes. Light quality influenced plant responses, but similar responses to temperature were obtained when red/far red ratios were 1.3 for the MH system and 1.6 for the FL system. High night temperature (30 °C) caused complete suppression of floral buds, whereas development was normal at a night temperature of 20 °C. Transfer and heat‐pulse experiments demonstrated that plants were not sensitive to high night temperature at a particular stage of development but that the duration of heat experience may be critical for the suppression of floral bud development. Two weeks or more of consecutive or interrupted hot nights during the first 4 wk after germination caused complete suppression of the development of the first five floral buds on the main stem. Mechanisms for the effects of heat stress on floral bud development are discussed.