Floral Organogenesis Research Articles

Aspects of Floral Development in Philodendron grandifolium and Philodendron megalophyllum (Araceae)

This study deals specifically with floral organogenesis and the development of the inflorescence of Philodendron grandifolium and Philodendron megalophyllum. Pistillate flowers are initiated on the lower portion of the inflorescence, and the staminate flowers are initiated on the distal portion. The presence of extracellular calcium oxalate is observed on the surface of immature stamens of P. megalophyllum. An intermediate zone consisting of sterile male flowers and bisexual flowers with fused or free carpels and staminodes is also present on the inflorescences. This zone is located between the male and female floral zones. In general, the portion of bisexual flowers facing the male zone forms staminodes, and the portion facing the female zone develops an incomplete gynoecium with few carpels. In P. grandifolium, the incomplete separation of some staminodes from the gynoecial portion of the whorl shows that they belong to the same whorl as the carpels. The bisexual flowers of P. grandifolium and P. megalophyllum are believed to be a case of homeosis in which carpels have been replaced by sterile stamens on the same whorl.

Obdiplostemonie in der Gattung Allium L.

Summary Early floral organogenesis has been investigated in a number of Allium species from various subgenera and sections (A. ramosum, A. angulosum, A. galanthum, A. sphaerocephalon, A. oreophilum, A. cernuum, A. moly). Comparative studies and earlier results show a considerable uniform pattern of the sequence of floral organ inception in the genus as a whole. Fusion of extended filament bases and shifting outwards of the originally inner stamina has been observed in Allium oreophilum after stamina differentiation only. A disturbance of alternation in the androeceum has been detected in Allium kujukense, A. umbilicatum, and A. ferganicum as well. Those configurations and that of Trillium apetalon can be described by the term “obdiplostemony”, applied in a broad sense also to flowers with a perianth, not differentiated into calyx and corolla. According to this definition, mature flowers with two stamen whorls are obdiplostemoneous in the case of an interrupted alternation between androeceum and perianth, with stamina of the outer stamen whorl opposite the parts of the inner whorl of the floral envelope and/or stamina of the inner stamen whorl opposite the parts of the outer whorl of the floral envelope. In the genus Allium obdiplostemony occurs in several subgenera and sections of different flower traits. In the case of Allium oreophilum and A. kujukense however, a special type of obdiplostemony suggests a close relationship.

Sexual development and sex chromosomes in hop.

The stages of floral development in staminate and pistillate plants of hop (Humulus lupulus) were defined using scanning electron microscopy and light microscopy. Vegetative meristems of male and female plants are morphologically indistinguishable. On transition to the reproductive phase, inflorescence apices reduce greatly in size and striking developmental sex differences become apparent. The first sex-specific differences occur extremely early in floral ontogeny. Both male and female plants initiate inflorescence meristems at each leaf node, each meristem being enclosed within a bract. Male secondary inflorescence meristems give rise to clusters of asynchronously developing flowers. Female inflorescence meristems produce flowers arranged in 'cones'. Each male floral meristem initiates a whorl of five sepal primordia, followed by an inner whorl of five stamen primordia. There is no sign of carpel development at any stage. In females, two carpel primordia are initiated, surrounded at their base by a vestigial perianth whorl. No stamen development is observed. Several monoecious lines carry bisexual flowers, either within cymose panicles or within the basal bracts of terminal female inflorescences. Bisexual flowers usually possess perianth, stamen and carpel whorls. The central whorls are often highly variable, and range from a pair of stigmas fused to a thin central filament to a well developed gynoecium. Chimaeric central whorls consisting of fused staminoid-carpelloid structures also occur. Sex differences in unisexual hop flowers are determined at an extremely early stage in ontogeny. The inappropriate set of sex organs is suppressed before it becomes visible or, more probably, it is not initiated at all. Genes directing the development of sex are likely to act at an extremely early stage, well in advance of floral organogenesis. The sex chromosomes of dioecious hop plants are described, as well as the chromosome constitutions of monoecious plants and those carrying bisexual flowers.

NOZZLE regulates proximal-distal pattern formation, cell proliferation and early sporogenesis during ovule development in Arabidopsis thaliana.

With the characterisation of the NOZZLE gene we aim at a better understanding of the molecular and genetic mechanism underlying pattern formation and growth control during floral organogenesis. Our data indicate that NOZZLE links these processes during ovule development. In the ovule primordium NOZZLE plays a central role in the formation of the nucellus through antagonizing the activities of BELL, AINTEGUMENTA and INNER NO OUTER, all encoding putative transcription factors, in the prospective nucellar region. We provide evidence that NOZZLE and BELL are chalaza identity genes that share overlapping functions in establishing the prospective chalaza of the ovule. In addition, NOZZLE plays a role in controlling the cell number and by this means the length of the funiculus, again through antagonizing AINTEGUMENTA and INNER NO OUTER function. NOZZLE is also required for the development of the integuments. We show that during the initial phase of this process NOZZLE is transcriptionally regulated by AINTEGUMENTA and INNER NO OUTER. NOZZLE thus represents a downstream target of these two genes in the integument development pathway.

A spectrum of genes expressed during early stages of rice panicle and flower development

To unravel gene expression patterns during rice inflorescence development, particularly at early stages of panicle and floral organ specification, we have characterized random cloned cDNAs from developmental-stage-specific libraries. CDNA libraries were constructed from rice panicles at the stage of branching and flower primordia specification or from panicles undergoing floral organogenesis. Partial sequence analysis and expression patterns of some of these random cDNA clones from these two rice panicle libraries are presented. Sequence comparisons with known DNA sequences in databases reveal that approximately sixtyeight per cent of these expressed rice genes show varying degrees of similarity to genes in other species with assigned functions. In contrast, thirtytwo per cent represent uncharacterized genes. cDNAs reported here code for potential rice homologues of housekeeping molecules, regulators of gene expression, and signal transduction molecules. They comprise both single-copy and multicopy genes, and genes expressed differentially, both spatially and temporally, during rice plant development. New rice cDNAs requiring specific mention are those with similarity to COP1, a regulator of photomorphogenesis in Arabidopsis; sequence-speciAEc DNA binding plant proteins like AP2-domain-containing factors; genes that specify positional information in shoot meristems like leucine-rich-repeat-containing receptor kinases; regulators of chromatin structure like Polycomb domain protein; and also proteins induced by abiotic stresses.

A unique Hawaiian Schiedea (caryophyllaceae: Alsinoideae) with only five fertile stamens

The floral organogenesis and subsequent ontogenies of the Hawaiian endemic species Schiedea pubescens from Maui, Moloka'i, and Lana'i, and the Wai'anae Mountains, O'ahu, populations previously considered to be varietally distinct, were examined using the scanning electron microscope (SEM). The O'ahu population consistently produced only five fertile stamens, those of the inner whorl. The five stamens of the alternisepalous or outer whorl abort prior to microsporogenesis and fail to elongate. Additional vegetative differences between the two taxa, combined with the floral morphology characters, merit the description of the O'ahu population as a new species, S. pentandra, described herein.

Studies in the Alismataceae. X. Floral organogenesis in Luronium natans (L.) Raf.

Floral organogenesis of Luronium natans (L.) Raf. occurs at first in an alternating trimerous pattern typical of Alismataceae, with the formation of three sepals, then three bulges, corresponding to the petal-stamen primordia described in some other Alismataceae, alternating with the sepals. A petal is initiated on each bulge and a pair of stamens is initiated either on it or close to it. After this, development no longer follows a trimerous plan. Six carpels are initiated in positions alternating with the six stamens, and further carpels may then arise above and between the first six. The carpels ultimately lie in a whorled arrangement if there are only six; if more, they may appear whorled or irregularly arranged. After the initiation of the stamen pairs, floral organ primordia appear simply to be positioned between pre-existing primordia as in other phyllotactic systems. It is suggested that the number of carpel primordia formed is probably determined by the size of primordia relative to the floral apex, and the extent of continued growth of the floral apex. Luronium reinforces the concept that a form of trimery is fundamental for the Alismataceae up to the formation of three stamen pairs and adds to the possibilities for variation after this point. It is suggested for the Alismataceae in general that, according to taxon, trimerous development may be terminated at any point after the initiation of the stamen pairs, and after this the primordia are positioned individually in relation to pre-existing primordia. The switch from stamen to carpel initiation is not necessarily correlated with these phyllotactic changes.

AtZFP1, encoding Arabidopsis thaliana C2H2 zinc-finger protein 1, is expressed downstream of photomorphogenic activation.

C2H2 zinc-finger proteins play important roles in plant development including floral organogenesis, leaf initiation, lateral shoot initiation, gametogenesis and seed development. The gene for one such protein from Arabidopsis, AtZFP1 (Arabidopsis thaliana zinc-finger protein 1), is expressed at high levels in the shoot apex, including the apical meristem, developing leaves and the developing vascular system. In light-grown seedlings, AtZFP1 expression is induced about three days after germination, before the expansion of the true leaves. Dark-grown plants, in which photomorphogenesis is repressed, have no detectable AtZFP1 expression in the shoot apex. Under conditions which induce or mimic photomorphogenic development including growth in the light, shifting dark-grown plants to continuous light or growth on cytokinin in the dark, high levels of AtZFP1 expression are detected. Furthermore, AtZFP1 expression does not depend on active photosynthesis as shown by analysis of plants grown on the carotenoid biosynthetic inhibitor norflurazon. These results are discussed in relation to a possible role for AtZFP1 in shoot development, downstream of photomorphogenic activation.

Inflorescence architecture: A developmental genetics approach

We are characterizing a suiteof Pisum sativum mutants that alter inflorescence architecture to construct a model for the genetic regulation of inflorescence development in a plant with a compound raceme. Such a model, when compared with those created forAntirrhinum majus andArabidopsis thaliana, both of which have simple racemes, should provide insight into the evolution of the development of inflorescence architecture. The highly conserved nature of cloned genes that regulate reproductive development in plants and the morphological similarities among our mutants and those identified inA. majus andA. thaliana enhance the probability that a developmental genetics approach will be fruitful. Here we describe sixP. sativum mutants that affect morphologically and architecturally distinct aspects of the inflorescence, and we analyze interactions among these genes. Both vegetative and inflorescence growth of the primary axis is affected byUNIFOLIA TA, which is necessary for the function ofDETERMINATE (DET).DET maintains indeterminacy in the first-order axis. In its absence, the meristem differentiates as a stub covered with epidermal hairs.DET interacts withVEGETATIVE1 (VEG1).VEG1 appears essential for second-order inflorescence (I2) development.veg1 mutants fail to flower or differentiate the I2 meristem into a rudimentary stub,det veg1 double mutants produce true terminal flowers with no stubs, indicating that two genes must be eliminated for terminal flower formation inP. sativum, whereas elimination of a single gene accomplishes this inA. thaliana andA. majus. NEPTUNE also affects I2 development by limiting to two the number of flowers produced prior to stub formation. Its role is independent ofDET, as indicated by the additive nature of the double mutantdet nep. UNI, BROC, and PIM all play roles in assigning floral meristem identity to the third-order branch.pim mutants continue to produce inflorescence branches, resulting in a highly complex architecture and aberrant flowers.uni mutants initiate a whorl of sepals, but floral organogenesis is aberrant beyond that developmental point, and the double mutantuni pim lacks identifiable floral organs. A wild-type phenotype is observed inbroc plants, butbroc enhancesthe pim phenotype in the double mutant, producing inflorescences that resemble broccoli. Collectively these genes ensure that only the third-order meristem, not higher- or lower-order meristems, generates floral organs, thus precisely regulating the overall architecture of the plant.

Floral ontogeny in tribe Dalbergieae (Leguminosae: Papilionoideae):Dalbergia brasiliensis, Machaerium villosum s. l.Platymiscium floribundum, andPterocarpus rotundifolius

Floral organogenesis and development of the tropical legume treesDalbergia brasiliensis, Machaerium villosum, Platymiscium floribundum, andPterocarpus rotundifolius were studied using scanning electron microscopy. The aims were to compare ontogenies and to elucidate if floral ontogenetic data will provide new character states diagnostic of the tribe Dalbergieae, which is considered a basal papilionoid tribe and primarily defined on fruit characters. Organ inception is principally acropetal in all taxa studied. Carpel inception is, however, consistently precocious. InD. brasiliensis sepals are initiated in an order not previously reported in Papilionoideae. It may be considered modified helical. InP. rotundifolius the inner whorl of stamens initiate in an unusual way, this is lateral two stamens first, then the two abaxial ones, and last the adaxial one, opposed to the unidirectional order usually seen in Papilionoideae. Generally the differences in flower development among the studied genera appear at initiation and late stage in ontogenesis, rather than at mid-stage.

Arabidopsis TSO1 regulates directional processes in cells during floral organogenesis.

Flowers of the previously described Arabidopsis tso1-1 mutant had aberrant, highly reduced organs in place of petals, stamens, and carpels. Cells of tso1-1 flowers had division defects, including failure in cytokinesis, partial cell wall formation, and elevated nuclear DNA content. We describe here two new tso1 alleles (tso1-3 and tso1-4), which caused defects in ovule development, but had little effect on gross floral morphology. Early ovule development occurred normally in tso1-3 and tso1-4, but the shapes and alignments of integument cells became increasingly more disordered as development progressed. tso1-3 ovules usually lacked embryo sacs due to a failure to form megaspore mother cells. The cell division defects described for the strong tso1-1 mutant were rarely observed in tso1-3 ovules. The aberrations in tso1-3 mutants primarily resulted from a failure in directional expansion of cells and/or coordination of this process among adjacent cells. Effects of tso1-3 appeared to be independent of effects of other ovule development mutations, with the exception of leunig, which exhibited a synergistic interaction. The data are consistent with TSO1 acting in processes governing directional movement of cellular components, indicating a likely role for TSO1 in cytoskeletal function.

Pattern formation and growth during floral organogenesis: HUELLENLOS and AINTEGUMENTA are required for the formation of the proximal region of the ovule primordium in Arabidopsis thaliana.

Our understanding of the molecular mechanisms that regulate and integrate the temporal and spatial control of cell proliferation during organ ontogenesis, particularly of floral organs, continues to be primitive. The ovule, the progenitor of the seed, of Arabidopsis thaliana has been used to develop an effective model system for the analysis of plant organogenesis. A typical feature of a generalized ovule is the linear arrangement of at least three distinct elements, the funiculus, chalaza and nucellus, along a proximal-distal axis. This pattern is supposed to be established during the early proliferative phase of ovule development. We provide genetic evidence that the young ovule primordium indeed is a composite structure. Two genes, HUELLENLOS and AINTEGUMENTA have overlapping functions in the ovule and differentially control the formation of the central and proximal elements of the primordium. The results indicate that proximal-distal pattern formation in the Arabidopsis ovule takes place in a sequential fashion, starting from the distal end. Furthermore, we show that HUELLENLOS also regulates the initiation and/or maintenance of integument and embryo sac ontogenesis and interestingly prevents inappropriate cell death in the young ovule.

Transcription pattern of a FIM homologue in Impatiens during floral development and reversion.

Flowering and reversion in Impatiens are characterised by gradual transitions of organ identity and constitute a unique system for the molecular and physiological study of floral organogenesis. The authors have isolated an Impatiens homologue of the FIM gene of Antirrhinum (UFO in Arabidopsis), Imp-FIM, and analysed its expression in three states of the terminal meristem: vegetative, floral, and reverted. In floral meristems, Imp-FIM transcription is associated with petal identity, as in Antirrhinum and Arabidopsis, but this is achieved through a novel transcription pattern, characterised by a high level of transcript within petal primordia. This novel transcription pattern could contribute to the more diffuse boundaries between organ types in Impatiens. In vegetative meristems, Imp-FIM is expressed in the axils of leaf primordia which are arranged in a spiral. A similar pattern is observed in reverted meristems in which leaf primordia are initiated in a whorled arrangement. This result indicates that the maintenance of floral phyllotaxis is not associated with a specific pattern of Imp-FIM transcription. Transcription of Imp-FIM in a non-reverting line is no different from that in the reverting line. Therefore, the lack of floral commitment in the reverting line does not seem to be responsible for Imp-FIM transcription within petals. The novel transcription pattern in petals, together with features of Impatiens that are reminiscent of fim and ufo mutant phenotypes suggest an evolutionary divergence for Imp-FIM regulation in this species.

STYLOSA and FISTULATA: regulatory components of the homeotic control of Antirrhinum floral organogenesis.

The identity and developmental pattern of the four organ types constituting the flower is governed by three developmental functions, A, B and C, which are defined by homeotic genes and established in two adjacent whorls. In this report we morphologically and genetically characterise mutants of two genes, STYLOSA (STY) and FISTULATA (FIS) which control floral homeotic meristem- and organ-identity genes and developmental events in all floral whorls. The morphology of the reproductive organs in the first and second whorls of sty fis double mutant flowers indicate that the two genes are part of the mechanism to prevent ectopic expression of the C-function in the perianth of wild-type flowers. This is verified by the detection of the expansion of the expression domain of the class C gene PLENA (PLE) towards the perianth. Interestingly, in the second whorl of sty and fis mutants, spatial differences in stamenoid features and in the pattern of ectopic expression of the PLE gene were observed. This suggests that, with respect to the negative control of PLE, petals are composed of two regions, a lateral and a central one. Mutation in ple is epistatic to most of the sty/fis-related homeotic defects. PLE, however, is not the primary target of STY/FIS control, because dramatic reduction of expression of FIMBRIATA, meristem identity genes (FLORICAULA and SQUAMOSA) and of class B organ identity genes (GLOBOSA) occur before changes in the PLE expression pattern. We propose that STY/FIS are hierarchically high-ranking genes that control cadastral component(s) of the A-function. SQUAMOSA as a potential target of this control is discussed. Retarded growth of second whorl organs, subdivision of third whorl primordia and the failure to initiate them in sty/fis mutants may be mediated by the FIMBRIATA gene.

Gametophyte-Sporophyte Interactions in Pollen-Pistil System after Compatible and Incompatible Pollination.

The gametophyte-sporophyte interactions govern the reproductive strategy of higher plants by forming different barriers to self-pollination in pollen-pistil system. Self-incompatibility, barrier was studied in the experimental system including 2 clones of petunia : (a) self-compatible (self-pollination results in adhesion, hydration and germination of pollen grains, growth of pollen tubes and fertilization), (b) self-incompatible (with the S-gene of incompatibility, the expression of which inhibits pollen tube growth in sporophyte style tissues). Thus, our experimental model permitted us to study signal systems capable of transmitting not only positive information favoring the growth of compatible pollen tubes to the ovary, but also a negative information preventing the penetration of incompatible pollen tubes. A concept of multilevel system controlling gametophyte-sporophyte interactions was put forward. Here, we provide evidence for the participation of sporophytic proteins and ethylene in the regulation of male gametophyte growth and development. The protein specificity in pollen-pistil system during floral organogenesis is characterized by common antigens to male and female systems, as well as by pollen-and pistil-specific antigens, which are synthesized at the late stages of flower development (including a unique S-antigen in sporophyte tissue of pistil). The pattern of lectin activity observed in pistil transmitting tissue is related to the lectin molecule functioning in the interactions between the cells of male gametophyte and those of pistil sporophytic tissues. We have shown that two enzymes are related to the operation of the gametophyte-sporophyte interactions : style RNase takes part in the gametophytic selfincompatibility mechanism, whereas cholinesterase is the most likely candidate for the specific recognition and signal transduction in pollen-pistil system. It is demonstrated that the sporophyte stigma tissues are the source of ethylene production during pollen tube growth in the pistil in the case of both compatible and incompatible pollination.

CaMADS1, a MADS box gene expressed in the carpel of hazelnut.

Hazelnut (Corylus avellana L.) is a species of economic interest that shows a peculiar floral biology. Unlike most of the angiosperms, which produce ovules during floral development such that they are ready for pollen at anthesis, hazelnut ovary development is delayed and triggered by compatible pollination. In order to elucidate the mechanisms regulating this unusual process and the role of the MADS box genes in ovary development, a cDNA library from pollinated styles of hazelnut was screened with a mixture of MADS box genes from different plant species. CaMADS1 (Corylus avellana MADS box), a floral-specific MADS box gene, was isolated, and characterized as belonging to the sub-family of the AGAMOUS genes. Northern blot, RT-PCR analyses and in situ hybridization experiments show a precise correlation between ovary development and CaMADS1 expression, indicating a role of this MADS box gene in the processes of floral organogenesis.

Comparative floral development and evolution in tribe Caesalpinieae (Leguminosae: Caesalpinioideae). Haematoxylum

Floral organogenesis and development of the tropical legume trees Haematoxylum campechianum (logwood) and H. brasiletto (brazilwood) were studied using scanning electron microscopy. The aims were to compare ontogenies, and to elucidate the relationships of Haematoxylum with other genera of Caesalpinieae, the basal tribe of Caesalpinioideae. Flowers of Haematoxylum are in racemes or fascicles, lack bracteoles, and are pentamerous, hermaphroditic, and either actinomorphic or zygomorphic. Whorls arise in acropetal order except for the carpel, which arises concurrently with the outer stamens. Sepal order is bidirectional (a rare condition) within the whorl in both. Petals and outer stamens are initiated bidirectionally in H. campechianum, and unidirectionally in H. brasiletto. Inner stamens are initiated unidirectionally in both. In H. campechianum, time of petal initiation overlaps with that of outer stamens, and initiation of the two stamen whorls overlap. In both, the gynoecium becomes stipitate, and a hypanthium forms late in development. Both show many plesiomorphic states at anthesis; H. brasiletto alone shows several specialized states (expressed late in development), including a fused, gibbous calyx cup, a zygomorphic corolla, lightly aggregated filaments held together by hairs, and fenestrations in the stamen column. Ontogenetic divergence late in ontogeny characterizes differences at anthesis between related species.

Functional interaction between the homeotic genes fbp1 and pMADS1 during petunia floral organogenesis.

The petunia MADS box floral binding protein (fbp) gene 1 represents a class B homeotic gene determining the identity of second and third floral whorl organs. Suppression of fbp1, which is highly homologous to the Antirrhinum gene globosa and Arabidopsis gene pistillata, results in the conversion of petals to sepals and stamens to carpels. In contrast to fbp1, the petunia homeotic gene pMADS1, encoding a protein homologous to the Antirrhinum protein DEFICIENS, has been shown to be involved in the formation of petals only. We demonstrated that the induction of fbp1 is established independent of pMADS1, whereas at later developmental stages, fbp1 is up-regulated by pMADS1 in petals. On the other hand, the induction and maintenance of pMADS1 expression are not affected by fbp1. To obtain information about the functional interaction between fbp1 and pMADS1, an fbp1 cosuppression mutant with mild phenotypic alterations was crossed with a green petals mutant in which pMADS1 expression was abolished. Progeny plants, heterozygous for the pMADS1 gene, had flowers with a more pronounced reversion from petals into sepals than was observed for the parent fbp1 mutant. The morphology of the third whorl organs was not changed. These observations, together with expression levels of pMADS1 and fbp1 in mutant flowers, provide evidence for functional control of fbp1 by PMADS1 in vivo.

Functional Interaction between the Homeotic Genes fbp1 and pMADS1 during Petunia Floral Organogenesis

Functional Interaction between the Homeotic Genes fbp1 and pMADS1 during Petunia Floral Organogenesis

In vitro shoot and floral organogenesis from stamen explants from a Rhododendron PJM group clone

Flower buds were collected from a clone from the Rhododendron PJM group during autumn and winter, disinfested, and dissected. Stamens were placed in vitro on media containing combinations of thidiazuron (TDZ) and isopentenyladenine (2iP) where they produced callus, adventitious shoots, and adventitious floral structures. There were significant interactions between the two cytokinins as well as significant main effects. The best shoot organogenesis was obtained generally when 1 μM TDZ and 25 μM 2iP were in the medium. Thidiazuron was the predominant cytokinin that stimulated the production of adventitious floral structures.