Cuticle characteristics and volatile emissions of petals in Antirrhinum majus

Floral volatiles, which are small and generally water-insoluble, must move from their intracellular sites of synthesis through the outermost cuticle membrane before release from the flower surface. To determine whether petal cuticle might influence volatile emissions, we performed the first analysis of petal cuticle development and its association with the emission of flower volatiles using Antirrhinum majus L. (snapdragon) as a model system. Petal cuticular wax amount and composition, cuticle thickness and ultrastructure, and the amounts of internal and emitted methylbenzoate (the major snapdragon floral scent compound) were examined during 12 days, from flower opening to senescence. Normal ( n -) alkanes were found to be the major wax class of snapdragon petals (29.0% to 34.3%) throughout the 12 days examined. Besides n -alkanes, snapdragon petals possessed significant amounts of methyl branched alkanes (23.6–27.8%) and hydroxy esters (12.0–14.0%). Hydroxy esters have not been previously reported in plants. Changes in amount of methylbenzoate inside the petals followed closely with levels of methylbenzoate emission, suggesting that snapdragon petal cuticle may provide little diffusive resistance to volatile emissions. Moreover, clear associations did not exist between methylbenzoate emission and the cuticle properties examined during development. Nevertheless, the unique wax composition of snapdragon petal cuticles shows similarities with those of other highly permeable cuticles, suggesting an adaptation that could permit rapid volatile emission by scented flowers.     

A member of the PLEIOTROPIC DRUG RESISTANCE family of ATP binding cassette transporters is required for the formation of a functional cuticle in Arabidopsis

Although the multilayered structure of the plant cuticle was discovered many years ago, the molecular basis of its formation and the functional relevance of the layers are not understood. Here, we present the permeable cuticle1 (pec1) mutant of Arabidopsis thaliana, which displays features associated with a highly permeable cuticle in several organs. In pec1 flowers, typical cutin monomers, such as ω-hydroxylated fatty acids and 10,16-dihydroxypalmitate, are reduced to 40% of wild-type levels and are accompanied by the appearance of lipidic inclusions within the epidermal cell. The cuticular layer of the cell wall, rather than the cuticle proper, is structurally altered in pec1 petals. Therefore, a significant role for the formation of the diffusion barrier in petals can be attributed to this layer. Thus, pec1 defines a new class of mutants. The phenotypes of the pec1 mutant are caused by the knockout of ATP BINDING CASSETTEG32 (ABCG32), an ABC transporter from the PLEIOTROPIC DRUG RESISTANCE family that is localized at the plasma membrane of epidermal cells in a polar manner toward the surface of the organs. Our results suggest that ABCG32 is involved in the formation of the cuticular layer of the cell wall, most likely by exporting particular cutin precursors from the epidermal cell.     

A SCANNING ELECTRON MICROSCOPIC STUDY ON THE INITIATION AND DEVELOPMENT OF FLORAL ORGANS OF BRASSICA NAPUS (CV. WESTAR)

The initiation and development of the floral organs of Brassica napus L. (cv. Westar) were examined using the scanning electron microscope. After transition of the vegetative apex into an inflorescence apex, flower primordia were initiated in a helical phyllotactic pattern. The sequence of initiation of the floral organs in a flower bud was that of sepals, stamens, petals and gynoecium. Of the four sepal primordia, the abaxial was initiated first, followed by the two lateral and finally the adaxial primordium. The four long stamens were initiated simultaneously in positions alternating with the sepals. The two short stamens were initiated basipetal to and outside the long stamens, and opposite the lateral sepals. The petals arose on either side of the two short stamens and the gynoecium was produced from the remainder of the apex. During development, the sepal primordia curved sharply at the tips and tightly enclosed the other organs. Stamen primordia developed tetralobed anthers at an early stage while filament elongation occurred just prior to anthesis. A unique pattern of bulbous cells was present on the abaxial surface of the anther. Growth of petal primordia lagged relative to the other floral organs but expansion was rapid prior to anthesis. The gynoecium primordium was characterized by an invagination early in development. At maturity, there was differentiation of a papillate stigma, an elongated style and a long ovary marked externally by sutures and divided internally by a septum. Distinct patterns of cuticular thickenings were observed on the abaxial and adaxial surfaces of the petals and stamens and on the surface of the style. The patterns were less obvious on the sepals and ovary. Stomata were present on both surfaces of the mature sepals, on the style and restricted areas on the abaxial surface of the anthers and nectaries but were absent from the petals, the adaxial surface of the stamens and the ovary. No hairs were present on any of the floral organs.     

Flower bud opening and senescence in roses (Rosa hybrida L.)

The flower is the most significant and beautiful part of plants. Flowers are very useful organs in plant developmental phenomenon. During flower bud opening, various events takes place in a well defined sequence, representing all aspects of plant development, such as cell division, cellular differentiation, cell elongation or expansion and a wide spectrum of gene expression. The complexity of flower bud opening illustrates that various biological mechanisms are involved at different stages. Senescence represents the ultimate stage of floral development and results in wilting or abscission of whole flower or flower parts. Senescence is an active process and governed by a well defined cell death program. Once a flower bud opens, the programmed senescence of petal allows the removal of a metabolically active tissue. In leaves, this process can be reversed, but in floral tissue it cannot, indicating that a highly controlled genetic program for cell death is operating. The termination of a flower involves at least two, sometimes overlapping, mechanisms. In one, the perianth abscises before the majority of its cells initiate a cell death program. Abscission may occur before or during the mobilization of food reserves to other parts of the plant. Alternatively, the petals may be more persistent, so that cell deterioration and food remobilization occur while the petals are still part of the flower. The overall pattern of floral opening varies widely between plant genera, therefore, a number of senescence parameters have been used to group plants into somewhat arbitrary categories. Opening and senescence of rose flower is still an unsolved jigsaw in the world of floriculture industry and the mechanism behind the onset of the very early events in the sequence still remains to be elucidated. Hence, for advancing the knowledge on the pertinent aspect of bud opening and senescence the literature has been cited under this review.     

Wrinkled petals and stamens 1, is required for the morphogenesis of petals and stamens in Lotus japonicus

Although much progress has been made in understanding how floral organ identity is determined during the floral development, less is known about how floral organ is elaborated in the late floral developmental stages. Here we describe a novel floral mutant, wrinkled petals and stamens1 （wps1）, which shows defects in the development of petals and stamens. Genetic analysis indicates that wpsl mutant is corresponding to a single recessive locus at the long arm of chromosome 3. The early development of floral organs in wpsl mutant is similar to that in wild type, and the malfunction of the mutant commences in late developmental stages, displaying a defect on the appearance of petals and stamens. In the mature flower, petals and stamen filaments in the mutant are wrinkled or folded, and the cellular morphology under L1 layer of petals and stamen filaments is abnormal. It is found that the expression patterns of floral organ identity genes are not affected in wpsl mutants compared with that of wild type, consistent with the unaltered development of all floral organs. Furthermore, the identities of epidermal cells in different type of petals are maintained. The histological analysis shows that in wpsl flowers all petals are irregularly folded, and there are knotted structures in the petals, while the shape and arrangement of inner cells are malformed and unorganized. Based on these results, we propose that Wpsl acts downstream to the class B floral organ identity genes, and functions to modulate the cellular differentiation during the late flower developmental stages.     

Conversion of leaves into petals in Arabidopsis

More than 200 years ago, Goethe proposed that each of the distinct flower organs represents a modified leaf [1]. Support for this hypothesis has come from genetic studies, which have identified genes required for flower organ identity. These genes have been incorporated into the widely accepted ABC model of flower organ identity, a model that appears generally applicable to distantly related eudicots as well as monocot plants. Strikingly, triple mutants lacking the ABC activities produce leaves in place of flower organs, and this finding demonstrates that these genes are required for floral organ identity [2]. However, the ABC genes are not sufficient for floral organ identity since ectopic expression of these genes failed to convert vegetative leaves into flower organs. This finding suggests that one or more additional factors are required [3, 4]. We have recently shown that SEPALLATA (SEP) represents a new class of floral organ identity genes since the loss of SEP activity results in all flower organs developing as sepals [5]. Here we show that the combined action of the SEP genes, together with the A and B genes, is sufficient to convert leaves into petals.     

Arabidopsis class I KNOTTED-like homeobox proteins act downstream in the IDA-HAE/HSL2 floral abscission signaling pathway

Floral organ abscission in Arabidopsis thaliana is regulated by the putative ligand-receptor system comprising the signaling peptide INFLORESCENCE DEFICIENT IN ABSCISSION (IDA) and the two receptor-like kinases HAESA and HAESA-LIKE2. The IDA signaling pathway presumably activates a MITOGEN-ACTIVATED PROTEIN KINASE (MAPK) cascade to induce separation between abscission zone (AZ) cells. Misexpression of IDA effectuates precocious floral abscission and ectopic cell separation in latent AZ cell regions, which suggests that negative regulators are in place to prevent unrestricted and untimely AZ cell separation. Through a screen for mutations that restore floral organ abscission in ida mutants, we identified three new mutant alleles of the KNOTTED-LIKE HOMEOBOX gene BREVIPEDICELLUS (BP)/KNOTTED-LIKE FROM ARABIDOPSIS THALIANA1 (KNAT1). Here, we show that bp mutants, in addition to shedding their floral organs prematurely, have phenotypic commonalities with plants misexpressing IDA, such as enlarged AZ cells. We propose that BP/KNAT1 inhibits floral organ cell separation by restricting AZ cell size and number and put forward a model whereby IDA signaling suppresses BP/KNAT1, which in turn allows KNAT2 and KNAT6 to induce floral organ abscission.     

Defective cell proliferation in the floral meristem of alloplasmic plants of Nicotiana tabacum leads to abnormal floral organ development and male sterility

Flowers of an alloplasmic male-sterile tobacco line, comprised of the nuclear genome of Nicotiana tabacum and the cytoplasm of Nicotiana repanda, develop short, poorly-pigmented petals and abnormal sterile stamens that often are fused with the carpel wall. The development of flower organ primordia and establishment of boundaries between the different zones in the floral meristem were investigated by performing expression analysis of the tobacco orthologs of the organ identity genes GLO, AG and DEF. These studies support the conclusion that boundary formation was impaired between the organs produced in whorls 3 and 4 resulting in partial fusions between anthers and carpels. According to the investigations cell divisions and floral meristem size in the alloplasmic line were drastically reduced in comparison with the male-fertile tobacco line. The reduction in cell divisions leads to a discrepancy between cell number and cell determination at the stage when petal and stamen primordia should be initiated. At the same stage expression of the homeotic genes was delayed in comparison with the male-fertile line. However, the abnormal organ development was not due to a failure in the spatial expression of the organ identity genes. Instead the aberrant development in the floral organs of whorls 2, 3 and 4 appears to be caused by deficient floral meristem development at an earlier stage. Furthermore, defects in cell proliferation in the floral meristem of the alloplasmic male-sterile line correlates with presence of morphologically modified mitochondria. The putative causes of reduced cell number in the floral meristem and the consequences for floral development are discussed.     

PETAL LOSS gene regulates initiation and orientation of second whorl organs in the Arabidopsis flower

PETAL LOSS is a new class of flower development gene whose mutant phenotype is confined mostly to the second whorl. Two properties are disrupted, organ initiation and organ orientation. Initiation is frequently blocked, especially in later-formed flowers, or variably delayed. The few petals that arise occupy a wider zone of the flower primordium than normal. Also, a minority of petals are trumpet-shaped, thread-like or stamenoid. Studies of ptl combined with homeotic mutants have revealed that the mutant effect is specific to the second whorl, not to organs with a petal identity. We propose that the PTL gene normally promotes the induction of organ primordia in specific regions of the second floral whorl. In ptl mutants, these regions are enlarged and organ induction is variably reduced, often falling below a threshold. A dominant genetic modifier of the ptl mutant phenotype was found in the Landsberg erecta strain that significantly boosts the mean number of petals per flower, perhaps by reinforcing induction so that the threshold is now more often reached. The second major disruption in ptl mutants relates to the orientation adopted by second whorl organs from early in their development. In single mutants the full range of orientations is seen, but when B function (controlling organ identity) is also removed, most second whorl organs now face outwards rather than inwards. Orientation is unaffected in B function single mutants. Thus petals apparently perceive their orientation within the flower primordium by a mechanism requiring PTL function supported redundantly by that of B class genes.     

Synthèse et hydrolyse du saccharose dans l'œillet alimenté avec une solution glucosée

Sucrose synthesis and sucrose hydrolysis in cut carnations (Dianthus caryophyllus) supplied with glucose solution .
Sucrose synthesis and hydrolysis in cut carnations supplied with a glucose solution have been investigated using both entire floral branches and floral branches without any of their organs (petals, non-petaloid pieces, leaves) and isolated organs. – The flower is a more active sink that the leaves. The transformationn of glucose into sucrose is essential for the ability of the flower to use the exogenous glucose. All organs of the floral branch (petals, ovaries and sepals, leaves, stem) are able to form sucrose. The hydrolysis of the obtained sucrose occurs nearly exclusively in the petals.     

Sucrose‐cleaving enzymes and carbohydrate pools in Lilium longiflorum floral organs

The activities of soluble invertase (EC 3.2.1.26), cell wall invertase (EC 3.2.1.26) and sucrose synthase (EC 2.4.1.13) were determined in Easter lily ( Lilium longiflorum Thunb. cv. Nellie White) floral organs during flower development. These enzyme activities were correlated with dry weight gains and carbohydrate pools to investigate the importance of their expression in maintaining sink strength of floral organs. In the early stages of flower bud development, anthers exhibited the highest rates of dry weight gain and activity of sucrolytic enzymes. Once anther growth was completed, the dry weight gain of tepal, filament, stigma and style increased with a concomitant increase in hexose concentrations and invertase activity. Although all three enzymes capable of catalyzing sucrose cleavage were present in every flower organ of L. longiflorum , soluble invertase was the predominant enzyme in all flower organs except stigma where cell wall invertase dominated. Soluble invertase activity was highly correlated with dry weight gain in most of the flower organs.     

Relationship between petal abscission and programmed cell death in <Emphasis Type="Italic">Prunus yedoensis</Emphasis> and <Emphasis Type="Italic">Delphinium belladonna</Emphasis>

Depending on the species, the end of flower life span is characterized by petal wilting or by abscission of petals that are still fully turgid. Wilting at the end of petal life is due to programmed cell death (PCD). It is not known whether the abscission of turgid petals is preceded by PCD. We studied some parameters that indicate PCD: chromatin condensation, a decrease in nuclear diameter, DNA fragmentation, and DNA content per nucleus, using Prunus yedoensis and Delphinium belladonna which both show abscission of turgid petals at the end of floral life. No DNA degradation, no chromatin condensation, and no change in nuclear volume was observed in P. yedoensis petals, prior to abscission. In abscising D. belladonna petals, in contrast, considerable DNA degradation was found, chromatin was condensed and the nuclear volume considerably reduced. Following abscission, the nuclear area in both species drastically increased, and the chromatin became unevenly distributed. Similar chromatin changes were observed after dehydration (24 h at 60°C) of petals severed at the time of flower opening, and in dehydrated petals of Ipomoea nil and Petunia hybrida, severed at the time of flower opening. In these flowers the petal life span is terminated by wilting rather than abscission. It is concluded that the abscission of turgid petals in D. belladonna was preceded by a number of PCD indicators, whereas no such evidence for PCD was found at the time of P. yedoensis petal abscission. Dehydration of the petal cells, after abscission, was associated with a remarkable nuclear morphology which was also found in younger petals subjected to dehydration. This nuclear morphology has apparently not been described previously, for any organism.     

Ultrastructural changes in the epidermis of petals of the sweet orange infected by <Emphasis Type="Italic">Colletotrichum acutatum</Emphasis>

Postbloom fruit drop (PFD) is an important disease caused by the fungus Colletotrichum acutatum. PFD is characterised by the formation of necrotic lesions on the petals and stigmas of flowers as well as premature abscission of the fruit in Citrus spp. We compare the ultrastructure of the epidermis of uninoculated Citrus sinensis petals with that of petals inoculated with the fungus to understand the changes that occur upon C. acutatum infection. Healthy petals have a cuticle with parallel striations covering the uniseriate epidermis. This pattern consists of vacuolated parietal cells whose cytoplasm contains mitochondria, plastids with an undeveloped endomembrane system and a slightly dense stroma, a poorly developed rough endoplasmic reticulum, polysomes, few lipid droplets, and a nucleus positioned near the inner periclinal wall. In damaged regions, the cytoplasm of some cells is densely packed with well-developed endoplasmic reticulum, a large number of hyperactive dictyosomes, numerous mitochondria, and many lipid droplets. The plastids have an electron-dense stroma, starch grains, and a large amount of electron-dense lipid droplets, which can be released into vacuoles or the endoplasmic reticulum. Multivesicular bodies and myelin bodies are frequently observed in the vacuole, cytoplasm, and periplasmic space. Vesicles migrate through the cell wall and are involved in the deposition of cuticular material. In the later stages of infection, there is deposition of new cuticle layers in plaques. The outer periclinal walls can be thick. These observations indicate that epidermal cells respond to the pathogen, resulting in cuticular and parietal changes, which may limit further infection.     

Hormonal control of floral abscission in zucchini squash (<Emphasis Type="Italic">Cucurbita pepo</Emphasis>)

In the zucchini squash, Cucurbita pepo, a well coordinated abscission of the female flower during fruit set is essential to obtain a fruit of commercial value. In Spain zucchini is mainly produced in greenhouses in Almería, where high temperatures during the spring-summer period provoke a cultivar-dependent defect in fruits known as the “sticky flower” syndrome. This disorder is characterised by an arrest in growth and maturation of floral organs, and a lack of female floral abscission, thus diminishing fruit shelf-life, commercial quality and value. The aim of the present work was to improve knowledge of the abscission process in C. pepo to better understand the fundamental causes of this disorder. The anatomical analysis of abscission shows a well defined male floral abscission zone (AZ), few hours after anthesis, which differs from the female zone which is not differentiated from the adjacent tissue until the abscission process has begun, and which occurs as a consequence of AZ cell enlargement and the dissolution of their cell walls. To evaluate the role of ethylene and auxins in the regulation of floral abscission in zucchini we performed several treatments, with: ethylene, added as 0.25% ethrel solution; AVG, the inhibitor of ethylene synthesis, at 100 μM; indol-3-acetic acid, 100 μM; and TIBA, the inhibitor of auxin polar transport, at 10 mM. These treatments show that ethylene is an accelerator of zucchini floral abscission, and also promotes abscission in isolated AZs of sticky flowers. On the other hand, IAA delays abscission of the female flowers, whilst the inhibitor of auxin polar transport promotes it. The activity of the cell wall hydrolytic enzymes, polygalacturonase and cellulase, sharply increased just before the shedding of zucchini floral organs (72 h after anthesis). Moreover, both enzyme activities were induced by ethylene, which partly explains the ethylene promoting effect.