Wet Stigmas Research Articles

Plant Hormone and Fatty Acid Screening of Nicotiana tabacum and Lilium longiflorum Stigma Exudates.

Pollen germination in vivo on wet stigmas is assisted by the receptive fluid-stigma exudate. Its exact composition is still unknown because only some components have been studied. For the first time, hormonal screening was carried out, and the fatty acid (FA) composition of lipid-rich (Nicotiana tabacum) and sugar-rich (Lilium longiflorum) exudates was studied. Screening of exudate for the presence of plant hormones using HPLC-MS revealed abscisic acid (ABA) in tobacco stigma exudate at the two stages of development, at pre-maturity and in mature stigmas awaiting pollination, increasing at the fertile stage. To assess physiological significance of ABA on stigma, we tested the effect of this hormone in vitro. ABA concentration found in the exudate strongly stimulated the germination of tobacco pollen, a lower concentration had a weaker effect, increasing the concentration did not increase the effect. GC-MS analysis showed that both types of exudate are characterized by a predominance of saturated FAs. The lipids of tobacco stigma exudate contain significantly more myristic, oleic, and linoleic acids, resulting in a higher unsaturation index relative to lily stigma exudate lipids. The latter, in turn, contain more 14-hexadecenoic and arachidic acids. Both exudates were found to contain significant amounts of squalene. The possible involvement of saturated FAs, ABA, and squalene in various exudate functions, as well as their potential relationship on the stigma, is discussed.

Pattern of ROS generation and interconversion on wet stigmas in basal and divergent angiosperms

Pattern of ROS generation and interconversion on wet stigmas in basal and divergent angiosperms

Embryology of Ficus tuerckheimii (subg. Spherosuke, Moraceae) and its relevance in interactions with its pollinator wasps, Pegoscapus sp. (Agaonidae)

• Ficus tuerckheimii has two female floral morphs with dimorphic stigmas. • Both floral morphs form showed cohesive synstigmas. • Wet stigmas are described for the first time within the genus Ficus. • The development of the anther wall in male flowers is a basic type. • Several evidence suggest that F. tuerckheimii is actively pollinated. Species in the Ficus (Moraceae) genus carry an inflorescence called syconium, formed by a fleshy, urn-shaped receptacle. This study aims to i) describe the embryology of Ficus tuerckheimii flowers at different developmental stages and ii) determine whether this species is pollinated actively or passively. The species is monoecious, with protogynous syconia and diclinous flowers. The syconia contain two pistillate floral morphs: one sessile with a long style and a symmetrically bilobed stigma, the other pedicellate with a short style and asymmetrical stigmatic lobes. The ovule of each flower type can develop into a seed or a (parasitic or pollinator) wasp. The gynoecium is pseudomonomerous; the flowers form a cohesive synstigma due to the proximity of the stigmatic papillae, which facilitates pollen concentration and pollen tubes growth in neighboring flowers. The staminate flowers are pedicellate and unistaminate. The anther dehiscence is longitudinal, rotating horizontally to open and release bicellular pollen grains. The syconium includes three different trichome types whose functions remain unknown. The drupelet fruit has a pericarp conformed of a tanniferous exocarp, a parenchymatic mesocarp, and a schlerenchymatic endocarp. We detected the following embryological characteristics that were previously undescribed for the genus and are potentially informative for the systematics of the family: i) wet stigmas, ii) a basic anther wall with a non-persistent epidermis and a multiplicative middle layer, iii) pollen grains that can germinate within the anther, iv) a profuse nucellus that later forms a perisperm, and v) a persistent perisperm. Altogether, the synstigma, the low anther-to-ovule ratio (0.12 SD ± 0.031), the smooth pollen ornamentation, and the specialized pollen collection and transport structures (corbiculae) of its pollinator wasps ( Pegoscapus sp., Agaonidae) suggest that F. tuerckheimii is actively pollinated.

First report of osmophores and wet stigma in Podostemaceae with notes on floral biology and pollination of Weddellina squamulosa Tul.

Weddellina squamulosa floral morphology, anthesis and pollination were investigated. Anatomical and histochemical analyses were carried out to clarify the stigma type and location of putative osmophores. Although bracts, tepals, stamens, and stigmas were stained after immersion in neutral red, osmophores were detected only in the tepals. The presence of osmophores is supported by the positive test for starch, and unique micromorphology of the tepals when compared with others floral structures, such as the presence of idioblasts with lipophilic contents. These results indicated the importance of a combined approach using floral biology and anatomy to determine the presence of osmophores. Stamen movement had an important function in delaying self-pollination in the early stages of anthesis, improving the opportunity for cross-pollination and promoting self-pollination in the last hour of anthesis in case of cross-pollination failure. Halictid bees were observed collecting pollen from anthers of W. squamulosa flowers, which may promote pollination. Some attributes of W. squamulosa flowers can attract floral visitors, and others contribute to spontaneous self-pollination. There is no evidence for anemophily in this species. This is the first report of wet stigmas and description of osmophores in Podostemaceae.

Evolution of Cell Wall Polymers in Tip-Growing Land Plant Gametophytes: Composition, Distribution, Functional Aspects and Their Remodeling.

During evolution of land plants, the first colonizing species presented leafy-dominant gametophytes, found in non-vascular plants (bryophytes). Today, bryophytes include liverworts, mosses, and hornworts. In the first seedless vascular plants (lycophytes), the sporophytic stage of life started to be predominant. In the seed producing plants, gymnosperms and angiosperms , the gametophytic stage is restricted to reproduction. In mosses and ferns, the haploid spores germinate and form a protonema, which develops into a leafy gametophyte producing rhizoids for anchorage, water and nutrient uptakes. The basal gymnosperms (cycads and Ginkgo) reproduce by zooidogamy. Their pollen grains develop a multi-branched pollen tube that penetrates the nucellus and releases flagellated sperm cells that swim to the egg cell. The pollen grain of other gymnosperms (conifers and gnetophytes) as well as angiosperms germinates and produces a pollen tube that directly delivers the sperm cells to the ovule (siphonogamy). These different gametophytes, which are short or long-lived structures, share a common tip-growing mode of cell expansion. Tip-growth requires a massive cell wall deposition to promote cell elongation, but also a tight spatial and temporal control of the cell wall remodeling in order to modulate the mechanical properties of the cell wall. The growth rate of these cells is very variable depending on the structure and the species, ranging from very slow (protonemata, rhizoids, and some gymnosperm pollen tubes), to a slow to fast-growth in other gymnosperms and angiosperms. In addition, the structural diversity of the female counterparts in angiosperms (dry, semi-dry vs wet stigmas, short vs long, solid vs hollow styles) will impact the speed and efficiency of sperm delivery. As the evolution and diversity of the cell wall polysaccharides accompanied the diversification of cell wall structural proteins and remodeling enzymes, this review focuses on our current knowledge on the biochemistry, the distribution and remodeling of the main cell wall polymers (including cellulose, hemicelluloses, pectins, callose, arabinogalactan-proteins and extensins), during the tip-expansion of gametophytes from bryophytes, pteridophytes (lycophytes and monilophytes), gymnosperms and the monocot and eudicot angiosperms.

Toward a predictive understanding of the fitness costs of heterospecific pollen receipt and its importance in co‐flowering communities

While we have a good understanding of how co-flowering plants interact via pollinator foraging, we still know very little about how plants interact via heterospecific pollen (HP) receipt. To fill this gap, we sought to illuminate the extent of HP receipt and quantitatively evaluate the fitness consequences of HP receipt. We consider plant traits that could mediate the fitness costs of HP receipt in an effort to better understand the potential consequences of pollinator sharing in natural communities. • We survey the literature for occurrence of HP receipt and assess variation in the fitness effects of a standard HP treatment. We develop a conceptual framework for understanding variation in fitness consequences of HP receipt. • We find evidence for variation in HP receipt and its costs. Our framework predicts that certain traits (self-incompatibility, small, highly aperaturate or allelopathic pollen) will lead to detrimental HP donors, whereas others (self-compatibility, small or wet stigmas, short styles) will lead to vulnerable HP recipients. We also predict that detrimental effects of HP receipt will increase with decreasing phylogenetic distance between donor and recipient. • Our framework can guide much needed additional work so that we can evaluate whether and which plant traits contribute to the variation in the effects of HP receipt. This will be a step toward predicting the consequences of HP receipt in natural communities, and ultimately transform our understanding of the role of postpollination interactions in floral trait evolution and pollinator sharing.

Comparative proteomic analysis reveals similar and distinct features of proteins in dry and wet stigmas

Angiosperm stigma supports compatible pollen germination and tube growth, resulting in fertilization and seed production. Stigmas are mainly divided into two types, dry and wet, according to the absence or presence of exudates on their surfaces. Here, we used 2DE and MS to identify proteins specifically and preferentially expressed in the stigmas of maize (Zea Mays, dry stigma) and tobacco (Nicotiana tabacum, wet stigma), as well as proteins rinsed from the surface of the tobacco stigma. We found that the specifically and preferentially expressed proteins in maize and tobacco stigmas share similar distributions in functional categories. However, these proteins showed important difference between dry and wet stigmas in a few aspects, such as protein homology in "signal transduction" and "lipid metabolism," relative expression levels of proteins containing signal peptides and proteins in "defense and stress response." These different features might be related to the specific structures and functions of dry and wet stigmas. The possible roles of some stigma-expressed proteins were discussed. Our results provide important information on functions of proteins in dry and wet stigmas and reveal aspects of conservation and divergence between dry and wet stigmas at the proteomic level.

Comparative analysis of pistil transcriptomes reveals conserved and novel genes expressed in dry, wet, and semidry stigmas.

Fertilization in angiosperms depends on a complex cellular "courtship" between haploid pollen and diploid pistil. These pollen-pistil interactions are regulated by a diversity of molecules, many of which remain to be identified and characterized. Thus, it is unclear to what extent these processes are conserved among angiosperms, a fact confounded by limited sampling across taxa. Here, we report the analysis of pistil-expressed genes in Senecio squalidus (Asteraceae), a species from euasterid II, a major clade for which there are currently no data on pistil-expressed genes. Species from the Asteraceae characteristically have a "semidry stigma," intermediate between the "wet" and "dry" stigmas typical of the majority of angiosperms. Construction of pistil-enriched cDNA libraries for S. squalidus allowed us to address two hypotheses: (1) stigmas of S. squalidus will express genes common to wet and dry stigmas and genes specific to the semidry stigma characteristic of the Asteraceae; and (2) genes potentially essential for pistil function will be conserved between diverse angiosperm groups and therefore common to all currently available pistil transcriptome data sets, including S. squalidus. Our data support both these hypotheses. The S. squalidus pistil transcriptome contains novel genes and genes previously identified in pistils of species with dry stigmas and wet stigmas. Comparative analysis of the five pistil transcriptomes currently available (Oryza sativa, Crocus sativus, Arabidopsis thaliana, Nicotiana tabacum, and S. squalidus), representing four major angiosperm clades and the three stigma states, identified novel genes and conserved genes potentially regulating pollen-pistil interaction pathways common to monocots and eudicots.

Lipids are required for directional pollen-tube growth.

Successful pollination and fertilization are absolute requirements for sexual reproduction in higher plants. Pollen hydration, germination and penetration of the stigma by pollen tubes are influenced by the exudate on wet stigmas and by the pollen coat in species with dry stigmas. The exudate allows pollen tubes to grow directly into the stigma, whereas the pollen coat establishes the contact with the stigma. Pollen tubes then grow into the papillae, which are covered by a cuticle. The components of the exudate or pollen coat that are responsible for pollen tube penetration are not known. To discover the role of the exudate, we tested selected compounds for their ability to act as functional substitutes for exudate in the initial stages of pollen-tube growth on transgenic stigmaless tobacco plants that did not produce exudate. Here we show that lipids are the essential factor needed for pollen tubes to penetrate the stigma, and that, in the presence of these lipids, pollen tubes will also penetrate leaves. We propose that lipids direct pollen-tube growth by controlling the flow of water to pollen in species with dry and wet stigmas.

Cladistic analysis of the Lythraceae sensu lato based on morphological characters

GRAHAM, S. A., CRISCI, J. V. & HOCH, P. C, 1993. Cladistic analysis of the Lythraceae sensu lato based on morphological characters. The Lythraceae s. I. comprise 31 mostly highly distinctive genera distributed worldwide. Cladistic analyses of the family were undertaken using 26 characters from anatomy, floral morphology, pollen, and seed morphology. Of four outgroup hypotheses, the Onagraceae offered the best heuristic assessment, generating 3746 trees with a tree length of 83 and consistency index and (C.I.) of 0.41. A strict consensus tree from the 3746 trees produced a basal monophyletic group of five genera (Sonneratia, Duabanga, Punka, Lagerstroemia, Lawsonia) characterized by anthotelic (determinate) inflorescences and wet stigmas, and a second clade with blastotelic (indeterminate) inflorescences, dry stigmas, and reduced carpel number. Successive weighting with Onagraceae as outgroup generated five most parsimonious trees with a tree length of 164 and C.I. of 0.75. Internal branches are weakly supported by only seven non-homoplasious characters. Significant results of the analysis include: (1) recognition of the two major clades and a total of seven monophyletic groups within the family; (2) the paraphyly of subfamily Lythroideae (Lythraceae s. s.); and (3) indication that genera endemic to the New World have been derived from more than one ancient Old World evolutionary line. The current taxonomic classification of the family is not closely correlated with results of the cladistic analysis.

Cladistic analysis of the Lythraceae sensu lato based on morphological characters

The Lythraceae s. l. comprise 31 mostly highly distinctive genera distributed worldwide. Cladistic analyses of the family were undertaken using 26 characters from anatomy, floral morphology, pollen, and seed morphology. Of four outgroup hypotheses, the Onagraceae offered the best heuristic assessment, generating 3746 trees with a tree length of 83 and consistency index and (C.I.) of 0.41. A strict consensus tree from the 3746 trees produced a basal monophyletic group of five genera ( Sonneratia, Duabanga, Punica, Lagerstroemia, Lawsonia) characterized by anthotelic (determinate) inflorescences and wet stigmas, and a second clade with blastotelic (indeterminate) inflorescences, dry stigmas, and reduced carpel number. Successive weighting with Onagraceae as outgroup generated five most parsimonious trees with a tree length of 164 and C.I. of 0.75. Internal branches are weakly supported by only seven non-homoplasious characters. Significant results of the analysis include: (1) recognition of the two major clades and a total of seven monophyletic groups within the family; (2) the paraphyly of subfamily Lythroideae (Lythraceae s.s.); and (3) indication that genera endemic to the New World have been derived from more than one ancient Old World evolutionary line. The current taxonomic classification of the family is not closely correlated with results of the cladistic analysis.

The floral biology of Groenlandia densa (L.) Fourreau (Potamogetonaceae)

The floral biology of the obligately aquatic plant species Groenlandia densa (L.) Fourreau was studied. It is effectively pollinated (1) in air above the water surface (anemophily), (2) at the water surface where the stigmas can pick up pollen grains directly from the surface of the water (epihydrophily), or (3) underwater with wet stigmas (hypohydrophily). Underwater, the pollen grains are associated with the air-water interface of bubbles, but they may be positioned on both sides of this interface. The breeding system is almost entirely autogamous with self-fertilization; a slight degree of proterogyny may permit some outbreeding.

Stigma form and surface in relation to self‐incompatibility in the Onagraceae

The Onagraceae is unique among families of comparable size in the heterogeneity of stigma form and physiology. Studies of the receptive surfaces of stigmas from representatives of all genera of the family have shown that a range of types exists from papillate to non‐papillate, and from “wet”, bearing a free‐running secretion, to “dry”, lacking such a secretion, most genera falling in the former category. Self‐incompatibility is wholly restricted to wet‐stigma species, and direct and circumstantial evidence indicates that it is always likely to be of the gametophytic type, as in certain Oenothera species that have been the subjects of detailed genetical and physiological research. Whilst Oenothera and most other self‐incompatible species in the family appear to reject incompatible pollen mainly in the stigma surface layers, the precise site is subject to both genetical and environmentally‐determined variation. Intraspecific polymorphy in sex function is known in the genus Fuchsia, most species of which have wet stigmas. Female sterility in the functionally male flowers of certain species of this genus appears simply to be due to a failure to produce adequate stigma secretion. All species of the dry‐stigma genera in the family are self‐compatible, but not all are inbreeding because of the existence of other mechanisms enforcing outcrossing. The stigmas of some possess certain unique features, apparently related to water conservation. Possible evolutionary trends in the family and in the breeding and pollination systems are briefly discussed in the light of what is now known of pollen‐stigma relationships.

Composition of the stigmatic secretions of long and medium styled flowers ofEichhornia

Like wet stigmas, the stigmatic secretions of dry stigmas ofEichhornia also have proteins, sugars, amino acids, phenols and fatty acids. No significant difference could be observed in the composition of stigmatic secretions of long and medium styled flowers except that the components were marginally higher in concentration in the former than the latter. The UV absorption profiles of the stigmatic secretions also showed no difference. Stigma surface esterases could be detected in both the stigmas from a very early stage of development.

Structural aspects of pollination in Amelanchier alnifolia (Maloideae)

The blossom structure of Amelanchier alnifolia conforms to the typical pattern of the Maloideae (Rosaceae). The bowl-shaped perianth of the open flower and the staminal whorls around the stigmas facilitate pollination by foraging insects. Each of the five stigmas is characterized by large vacuolate papillae. Stigmatic secretions begin during petal elongation resulting in a sticky lipidic exudate on the papillate surface at full bloom. The tricolpate pollen adhering to the wet stigmas produce pollen tubes that penetrate the stigmas in between adjacent papillae and grow through the intercellular spaces of the transmitting tissue toward the ovarian locules. Although the blossom structure encourages entomophily, anther proximity to the stigmas just prior to anthesis in conjunction with the preanthesis shedding of pollen suggests a developmental mechanism that promotes a limited amount of autogamy.

Stigma-surface Esterase Activity and Stigma Receptivity in Some Taxa Characterized by Wet Stigmas

Stigma-surface esterase activity and stigma receptivity through a sequence of developmental stages of the pistil have been studied in four taxa characterized by having wet stigmas-Petunia hybrida, Nicotiana tabacum, Crinum defixum and Amaryllis vittata. The style is solid in the first two and hollow in the latter two taxa. In all the taxa, stigma-surface esterase could be detected in a thin surface layer (pellicle) from a very early stage of pistil development, irrespective of the presence or absence of the exudate. However, the taxa showed variation in stigma receptivity. In Petunia and Nicotiana, stigmas from pistils of all the stages supported pollen germination and tube growth. In Amaryllis and Crinum, stigmas of only the mature pistils, when the exudate is present on the stigma, supported normal pollen germination and tube growth. It is inferred that in taxa characterized by a wet stigma and solid style, the factors required for pollen germination are present from an early stage of pistil development and the exudate per se is not involved in pollen germination. In taxa characterized by a wet stigma and hollow style, however, the pellicle does not carry the factors required for pollen germination and tube growth; they appear to be present in the exudate.

The Receptive Surface of the Angiosperm Stigma

This paper reports upon a study of the characteristics of the receptive surfaces of angiosperm stigmas, covering almost 1000 species of about 900 genera of some 250 families. In both monocotyledons and dicotyledons the major subdivision is into those stigmas which are 'dry' at maturity, having a hydrated, proteinaceous extracuticular layer or pellicle but no free-flowing secretion, and those which are 'wet' bearing such a fluid secretion when in the receptive state. Further subdivision may be made talcing into account the nature of the surface cells-whether or not the receptive surface is papillate or smooth, and if papillate, whether the papillae are unicellular or multicellular. When the genera are classified according to these criteria, various taxonotnic regularities emerge. Many families are homogeneous in stigma type, but some prove to be diverse. Among these are families such as the Liliaceae, a fact that may have phylogenetic significance. The physiological importance of stigma type is shown by the correlations that exist between the characteristics of the receptive surface and self-incompatibility system. Sporophytic self-incompatibility systems are associated with dry, papillate stigmas; most gametophytic systems with wet stigmas. Further relationships exist with pollen type and physiology. Trinucleate pollen, not readily germinated in vitro, tends to be associated with dry stigmas, while wet-stigma forms tend to have binucleate pollen, easily germinated in liquid or semi-solid media; binucleate pollen, however, occurs with both wet and dry stigmas.