Self-incompatibility and the pollen-stigma interaction inTradescantia ohiensis rafin

Summary Self-incompatibility (SI) is reported for an accession ofTradescantia ohiensis. Pollen tube inhibition is stigmatic. The stigma is wet and papillate, the papillr surface bearing conspicuous blebs particularly in the mid- and basal regions of the cell. A proteinaceous pellicle is present on the surface of the papillar cuticle. The penetration of the stains calcofluor white and alcian blue into the cell wall of fresh stigma papillae strongly indicates that the permeability of the papillae is greatest at the mid-region of the cell and not at the tip. When single pollen grains are attached to the tip of a papilla there is either no response at all or the pollen adheres to the papilla. When attached in the mid-region pollen adheres, and often germinates. It is concluded that the sites of pollen receptivity are the mid- and basal regions of the papular cell.     

Mechanism of Pollination in Gladiolus: Roles of the Stigma and Pollen-tube Guide

Gladiolus has a dry type of stigma. Compatible pollen grainsalight and germinate on the receptive surface of the papillae,penetrate the cuticle and grow towards the style through a sub-cuticularpollen-tube guide of mucilage. This is secreted from epidermalcells of the stylodium and style canal. The cuticle, which coversthe pollen tube guide mucilage, is continuous through the stylecanal to the ovary. The wet stigma of Lilium also has cuticulartissue running through the style canal, covering the mucilage.     

GYNOECIAL ONTOGENY AND MORPHOLOGY,AND POLLEN TUBE PATHWAY IN BLACK MAPLE,ACER SACCHARUM SSP. NIGRUM (ACERACEAE)

The black maple (Acer saccharum Marsh, ssp. nigrum [Michx. f.] Desm.) gynoecium displays classical involute carpel development; carpels form, in mid- to late-summer, as two separate, opposite, hood-shaped primordia bearing naked megasporangia on inrolled carpel margins. Megasporogenesis, integument initiation, and carpel closure occur in spring; carpels fuse, forming a biloculate ovary with a short, hollow style and two divergent, dry, unicellular papillose stigmas. Transmitting tissues consist of developmentally and morphologically similar trichomes that form along the apparent carpel margins. The path from stigma to micropyle is open, but pollen tubes do not grow entirely ectotrophically. Germinating at the tip of a stigma papilla, a tube grows, apparently under the cuticle, to the papilla base. It then grows between stigma cells to the style, emerging to grow ectotrophically through the style to the compitum, where it passes into one of the locules. Within a locule, the tube grows over placenta and obturator to the micropyle, then between megasporangium cells to the female gametophyte, spreading over the surface near the egg. This study adds to our sparse understanding of gynoecium development and transmitting tissue in relation to pollen tube growth in naturally pollinated woody plants.     

The Pollen-stigma Interaction: Pollen-tube Penetration in Crocus

In a compatible pollination in Crocus, pollen tube tips enterthe stigma papillae after the enzymic erosion of the cuticle,and the tubes continue downward growth towards the ovary betweenthe cuticle and the underlying pectocellulosic wall. The cuticleof the receptive zone of the stigma papilla is chambered, thechambers containing a secretion accumulated during the maturationof the stigma. Pollen exudates contain various acid hydrolases,but are incapable alone of eroding stigma cutin. Furthermore,there is no penetration when the proteins of the wall-held stigmasecretions are degraded enzymically. These facts are taken toindicate that the pollen contributes a ‘cutinase’precursor which is activated by a factor or factors held inthe stigma secretion. Pollens of certain Cruciferae producetubes capable of penetrating the Crocus stigma cuticle, suggestingthat notwithstanding the taxonomic remoteness of Cruciferaeand Iridaceae the enzyme activation systems are quite similar.     

Fine Structure and Cytochemistry of the Stigma Surface and Incompatibility in some Distylous Linum Species

The receptive surface of the stigma in distylous Linum grandiflorumand L. pubescens was studied by electron microscopy and cytochemicaltechniques. In both floral morphs a proteinaceous-lipoidal coatingis present on the papilla surface. In thrum stigmas the cuticleis highly irregular and pitted at the papilla tip. The cuticleis dislodged and torn at anthesis and an osmiophilic secretionproduct is released within a pectinaceous matrix. The secretionproduct stains for proteins and lipids and contributes to adhesionof pollen. In the larger pin papillae the cuticle is wavy, continuous,thicker than in thrum papillae and adjoins the cell wall. Inboth species the surface of the two types of pollen grains iscoated with lipids and protein. A similar behaviour of the male gametophyte is observed in incompatiblepollinations of L. pubescens, L. mucronatum and L. grandiflorum.In intramorph thrum pollinations pollen tubes are arrested withinthe stigma. In intramorph pin pollinations the majority of pollengrains fail to adhere to the stigma. Low permeability to waterin pin papillae, as determined by the neutral red test, maybe a factor preventing imbibition of the few adhering grains.Tubes of the few germinated grains are inhibited inside thestigma. On the part of the stigma, the difference in the major siteof inhibition in the two intramorph incompatible combinationsmay be accounted for by the dissimilar properties of the papillae,i.e. the occurrence of wet thrum stigmas and dry pin stigmas.Functionally, the unusual association of sporophytic incompatibilitywith wet thrum stigmas is attributed to retention of the secretorymaterial on individual papillae. Stigmatic papillae, cuticle, pollen coat, distyly, incompatibility, Linum grandiflorum, L. pubescens, L. mucronatum     

GYNOECIAL DEVELOPMENT,POLLINATION, AND THE PATH OF POLLEN TUBE GROWTH IN THE TEPARY BEAN,PHASEOLUS ACUTIFOLIUS

The gynoecium of Phaseolus acutifolius var. latifolius, a self-compatible legume, is characterized by a wet non-papillate stigma, an intermeditae hollow/solid style type, and secretory cells on the ventral surface of the ovary which direct pollen tube growth. The stigma is initially receptive 5–6 days prior to anthesis. Production of stigmatic secretions, composed primarily of carbohydrates and lipids, fragment the cuticle covering epidermal cells of the stigma early in ontogeny; the lipidic aspect of the copious secretions apparently serves to inhibit desiccation after the cuticle is ruptured. Stylar canal development occurs as a combination of elongation of a basal canal present early in development, and dissolution of part of a solid transmitting tract tissue just below the stigma. Anthers dehisce and the tricolporate pollen is released onto the receptive stigma one day before anthesis. Following initial growth in intercellular spaces in the transmitting tract of the stigma, pollen tubes adhere to epidermal secretory cells along the ventral side of the stylar canal and upper ovary; here the transmitting tract is apparently limited in the number of tubes it can accommodate, providing a possible site of selection of male gametes.     

Ultrastructure of the dimorphic pollen and stigmas of the cleistogamous species,Collomia grandiflora (Polemoniaceae)

Summary An ultrastructural study of the pollen and stigma of the dimorphic flowers in the cleistogamous speciesCollomia grandiflora reveals significant differences in cytoplasmic features in the pollen and wall features in the papillae. Both pollen types contain lipid and starch reserves, but the smaller CL (cleistogamous) pollen shows a much greater abundance of starch compared to the CH (chasmogamous) pollen. In addition to the papular size and shape differences between the two stigma types, there is a more extensive cuticular stretching and wall microfibrillar loosening over the CH papillar tip. There is no apparent pellicle on the cuticle surface of either type of papilla, only scattered lipidic deposits. It is proposed that these structural differences may contribute to the cross incompatibility between the two floral morphs.     

Esterases in pollen and stigma of Brassica

The dry type stigma of Brassica is covered with a continuous layer of cuticle. Cutinase and non-specific esterases may be involved in breakdown of this cuticle barrier during pollen-stigma interaction, but only a little is known about their nature and characteristics. We report here the presence of two distinct esterases from stigma and pollen of Brassica. A 33 kD esterase assayed using MU-butyrate substrate shows high activity in stigma papillae. A similar esterase from Tropaeolum pollen has been shown to possess active cutinase activity. The esterase activity in anther tissue is due to a 24 kD enzyme with substrate specificity toward acetate esters. Both enzymes require sulfhydryl groups for their catalytic activity. Immunogold labelling of antibodies raised against these esterases localised the proteins at the subcellular level. Antibodies for MU-butyrate hydrolase gave a positive signal in the cell walls of mature stigma papillae and in the tapetum and microspores during early stages of anther development. In the mature anther, a positive signal in the cytoplasm of pollen grains with some detectable localisation in the exine layer of the pollen wall was obtained. Similar results were obtained with acetate hydrolase antibodies. These esterases are thus spatially and temporally regulated in stigma and anther tissues.Abbreviations MU methyl umbelliferyl - pAbC anti-butyrate hydrolase polyclonal antibodies - pAbE anti-acetate hydrolase polyclonal antibodies     

The Structure and Cytochemistry of the Pistil of Hypericum calycinum: The Stigma

The pistil of Hypericum calycinum has a pentacarpellary, syncarpousovary with five slender styles, each terminating in a smallstigma. The stigma is dry and papillate with a thin lining ofpellicle. The cuticle is thin and continuous around the papillae.A large vacuole filled with tannins occupies the major partof the papillae and the cytoplasm forms a thin lining aroundthe vacuole. The cell wall of the mature papillae show two distinctlayers - an outer layer of loosely woven fibrils and an innerdenser layer with compact fibrils. A large number of small lipoidalbodies accumulate just below the cuticle. The papillae havefewer organelles than those typical of glandular cells. Dictyosomesobserved occasionally are without associated vesicles. The cytoplasmis rich in ribosomes. The basal portions of the papillae mergeinto the transmitting tissue made up of loosely arranged cells.The intercellular matrix of the transmitting tissue is richin lipids. Pollen grains are deposited between the papillae.Upon pollen germination, pollen tubes enter the stigma throughthe interstices between the papillae Hypericum calycinum, cytochemistry, pistil, pollen-pistil interaction, stigma, ultrastructure     

A light and electron microscopic study of stigmas inAneilema andCommelina species (Commelinaceae)

Summary The stigmas of species inAneilema andCommelina are trifid and comprise elongate papillae. Progressive degeneration of papular cells is observed in stigmas from open flowers and at anthesis papillae may be moribund and collapsed. Fluid emanating from the hollow style flows onto the surface through ruptures in the cuticle at the interpapillar junctions into the interstices at maturity. This secretion stains positively for protein. Stigmas are of the wet type.The cuticle overlying the papillar cells is ridged and at the final stages prior to flowering this cuticle becomes detached from the underlying cellulosic wall. The sub-cuticular space so formed is filled with secretion. InAneilema species detachment of cuticle is at the papillar tip and along the lateral walls. InCommelina species the anticlinal walls of adjacent papillae are strongly attached for much of their length and thus detachment of cuticle is restricted to the papillar tip. The cell wall at the tip in both genera may proliferate forming a rudimentary transfer-cell type wall. The secretion is considered to be produced by the papillar cells. It is PAS positive but fails to stain for protein and in both the light and electron microscopes appears heterogenous.Pollen attachment, hydration, germination and early tube growth are very rapid following self-pollination, the pollen tubes entering the neck of the style within ten minutes of attachment.A unique character combination involving pollen and stigmas in these genera indicates a monophyletic origin.     

INTERCELLULAR ADHESIONS IN THE POLLEN-STIGMA SYSTEM: POLLEN CAPTURE,GRAIN BINDING,AND TUBE ATTACHMENTS

Four independent pollen-stigma binding forces are differentiated after pollen contacts stigmas of Brassica oleracea var. capitata. Identification is based on their different rates and sequence of appearance during gametophyte development; on their differential occurrence after compatible and incompatible pollinations; and on their different stabilities to NaOH and hexane. The first binding force develops most rapidly, begins seconds after pollen-stigma contact, is complete within minutes, occurs on compatible or incompatible papillae, and dissociates in methanol. A second slower binding reaction begins about 15 min after contact, continues for at least 90 min (when pollen tubes emerge), results in a binding structure termed the ocreatine, develops only on compatible papillae, and is dissociated by NaOH. A third attractive mechanism binds the tip of the emerging tube to a cuticle, is detected only on incompatible papillae, and is not dissociated by NaOH or methanol. Ocreatine formation and tube development beyond the emergence stage are prevented by the incompatibility response. A fourth attraction mechanism occurs between the surfaces of papilla and elongating tubes. Reviews of physical and biochemical evidence indicate that van der Waals forces and enzymatically mediated lipid polymerization are alternatives to agglutination as mechanisms for binding male gametophyte to papilla.     

Heterostyly inPrimula. 1. Fine-structural and cytochemical features of the stigma and style inPrimula vulgaris huds

Summary The stigmas of the heterostylous genusPrimula are of the dry type without a free-flowing surface secretion. The papillae of the stigma surface cells of the two morphs, in pin (stigma exserted) and thrum (stamens exserted), bear a thin proteinaceous surface pellicle, overlying a discontinuous cuticle. The vacuoles of the papillate cells contain tannins, and tannin cells extend in files through the stigma heads and form a loose sheath surrounding the pollen-tube transmitting tract in the styles. The cells of the transmitting tissue in the stigma heads have a normal complement of organelles, and abundant ribosomal endoplasmic reticulum. The intercellular spaces contain an internal secretion which reacts cytochemically for both carbohydrate and protein. The transmitting tract in the styles forms a central core surrounded by several vascular strands. The cells are elongated, and the intercellular spaces here also have a carbohydrate-protein content. In a compatible pollination, thrum pollen tubes enter the stigma by penetrating the cuticle at the tip or on the flank of the pin papilla. Pin tubes on the thrum stigma enter between adjacent papillae, penetrating the thin cuticle at the base. The tubes grow through the transmitting tracts in the intercellular material.     

Structural analysis of stigma development in relation with pollen–stigma interaction in sunflower

Structural analysis of stigma development in sunflower highlights the secretory role of papillae due to its semi-dry nature. Production of lipid-rich secretions is initiated at the staminate stage of the flowers in stigma development and increases at the receptive stage, coinciding with an extensive development of elaioplasts and endoplasmic reticulum network in the basal region of the papillae. Transfer cells, earlier identified only in the wet type of stigma, are also present in the transmitting tissue of the sunflower stigma. Attainment of physiological maturity by the stigmatic tissue, accompanying development from bud to pistillate stage, appears to affect the initial steps of pollen–stigma interaction. The nature of self-incompatibility in Helianthus has also been investigated in relation with pollen adhesion, hydration and germination. Pollen adhesion to the stigma is a rapid process in sunflower and stigma papillae exhibit greater affinity for pollen during cross pollination as compared to self-pollination. Components of the pollen coat and the pellicle on the surface of stigmatic papillae are critical for the initial phase of pollen–stigma interaction (adhesion and hydration). The lipidic components of pollen coat and the proteinaceous and lipidic components from the surface of the papillae coalesce during adhesion, leading to the movement of water from stigma to the pollen, thereby causing pollen hydration and its subsequent germination. Pollen germination (both in self-and cross-pollen) on the stigma surface and the growth of the pollen tube characterize the flexibility of self-incompatibility in sunflower. Compatible pollen grains germinate and the pollen tube penetrates the stigma surface to enter the nutrient-rich transmitting tissue. The pollen tube from incompatible pollen germination, however, fails to penetrate the stigmatic tissue and it grows parallel to the papillae. Present findings provide new insights into structural and functional relationships during stigma development and pollen–stigma interaction.     

桦木科植物花柱适应风媒传粉的特征

植物体为适应自己的传粉系统, 表现出高度的适应特征。风媒花植物为适应风传播花粉, 要形成特殊的结构, 以扩大接受花粉粒的面积。利用扫描电镜观察了桦木科(Betulaceae)6属18种植物花柱的形态及花粉粒在花柱上的萌发过程, 探讨了桦木科植物花柱适应风媒传粉的特征。结果表明, 桦木科植物的二心皮(铁木、云南鹅耳枥稀为三心皮)雌蕊具柱状花柱, 柱头不发达, 花柱表皮细胞长条状, 纵向排列紧密。传粉时, 花柱表皮细胞能执行柱头的功能, 接受花粉粒, 为花粉粒萌发提供场所和萌发条件。桦木科植物花柱有2种类型: 一种是花柱表皮细胞能形成乳突, 花粉管经乳突细胞进入花柱; 另一种是花柱表皮细胞不形成乳突, 花粉管经过花柱表皮细胞或胞间隙进入花柱。无论花柱表皮细胞是否形成乳突, 乳突的形态、大小以及花粉管和乳突的结合方式等在族间、属间、属内种间存在差异。与基部被子植物相比, 桦木科植物的花柱呈现适应风媒传粉的进化特征。桦木科植物花柱表皮细胞形成的乳突与基部被子植物柱头乳突功能相同, 是桦木科植物风媒传粉的适应策略。     

The transmitting tract in Trimezia fosteriana (Iridaceae). III. Pollen tube growth in the stigma, style and ovary

Trimezia fosteriana is a self-incompatible plant with an open style. The stigma was found to be receptive for approx. three hours. Pollen tube growth in the entire transmitting tract was followed with LM, SEM and TEM. The cuticle that covers the mature papillae is continuous but in the rest of the transmitting tissue it is thin and ruptured. The pollen tubes grow in a mucilage mixed with cuticle remnants. In the style, however, larger parts of a cuticle film remains which gives the impression that pollen tube growth occurs under a cuticle. The secretion contains proteins and carbohydrates including pectic substances. The pollen tube growth rates were estimated to 2 mm/hour in the stigma, 1–2 mm/hour in the style and 0.5 mm/hour in the ovary.     

STRUCTURAL DIMORPHISM OF STIGMATIC PAPILLAE IN DISTYLOUS LINUM SPECIES

Intermorph differences in the wall structure and constituents of stigmatic papillae are described for distylous Linum pubescens and L. grandiflorum. In the long-styled morph of both species the wall portion around the apex of the papilla has a thickened cellulose-pectin layer. In the short-styled morph of L. pubescens a cap zone is interposed between the cuticle and apical portion of the papilla wall. The subcuticular cap space contains pectins and lipid particles. Similar particles are also present in deposits on the cuticle surface. Papillae of the short-styled morph in L. grandiflorum lack a cap zone and have only epicuticular lipid deposits. Other distylous Linum species in which the two morphs differ in wall structure of the papillae are L. mucronatum, L. flavum, L. perenne, L. austriacum, and L. maritimum. Studies of stigma dimorphism can help to elucidate evolutionary relations between dimorphic and monomorphic Linum species.     

Divergent pollination systems in the cleistogamous species,Collomia grandiflora (Polemoniaceae)

Summary A structural study of pollination in the dimorphic flowers ofCollomia grandiflora, a cleistogamous species, reveals significant differences in stigma behavior during pollination, stylar structure, the timing of generative cell division, and pollen tube growth rate patterns. The cleistogamous flower shows a loss of protandry and the stigma is receptive only after reflexing and closing of its lobes. In contrast, the chasmogamous stigma is receptive when reflexed and closes when pollen has been deposited on the lobes. Pollen tube penetration of the dry stigma papillae and entry into the style is similar in the two morphs. The chasmogamous style is solid and the cleistogamous style partly hollow. The matrix of secretion produced by the transmitting tract cells is mainly carbohydrate with a trace of lipids. It is fibrillar in nature and appears to be partly comprised of wall material from the transmitting tract cells. In the chasmogamous pollen, the generative cell enters the tube before division, which occurs between 30 and 60 min after pollination. This division correlates with an increased growth rate for the pollen tube. In the cleistogamous pollen, contact with the stigma triggers generative cell division inside the hydrated pollen grain before germination. The two resulting sperm cells exit the grain 15–30 min after pollination when the pollen tube is in the stigma lobes. The cleistogamous pollen tube shows only one phase of growth which occurs at a rate similar to that of the slow, first phase of the chasmogamous pollen.Abbreviations CH chasmogamous - CL cleistogamous - DAPI 4, 6-diamidino-2-phenylindole     

Structural and Cytochemical Characteristics of the Stigma and Style in Vitis vinifera L. var. Sangiovese (Vitaceae)

Studies were carried out on structural and cytochemical aspectsof the stigma and style ofVitis vinifera . The stigma is ofthe wet papillate type with a continuous cuticle and pellicle.During the development of the papillae, the cell walls increasein thickness and produce a secretion product constituted oflipids that pass through the wall forming the exudate. The styleis solid with a central core of transmitting tissue which hasconspicuous intercellular spaces that increase remarkably fromthe periphery to the centre where the cuticle is present. Theintercellular spaces, where the pollen tubes grow, contain amatrix that includes polysaccharides, pectic substances andscattered areas of lipidic nature. Cytochemistry; stigma; style; ultrastructure; Vitis vinifera     

POLLEN-PISTIL INTERACTIONS IN TRISTYLOUS PONTEDERIA SAGITTATA (PONTEDERIACEAE). I. FLORAL HETEROMORPHISM AND STRUCTURAL FEATURES OF THE POLLEN TUBE PATHWAY

Heteromorphic characters and structural features of the pollen tube pathway are described in tristylous Pontederia sagittata to assess their influence on the pollination process and in mediating self-incompatibility behavior. Heteromorphic characters that distinguish the floral morphs include style length, stigma depth, stigmatic papillae length, stylar parenchyma cell length, area of the stylar canal, stamen height, anther size, and pollen size. Unlike several distylous species that have been investigated, the exine of pollen in P. sagittata was not strongly differentiated among the pollen types, and no differences in stigma cytochemistry were apparent. Features common to the floral morphs were a wet stigma, a hollow trilobed stylar canal separating into two sterile and one fertile canal, and a single anatropous ovule with a highly elaborated integumentary obturator. The similarity in structural features of the pollen tube pathway of P. sagittata to those found in monocotyledonous taxa with gametophytic self-incompatibility suggests that phylogenetic constraints may have influenced the evolution of trimorphic incompatibility in the Pontederiaceae.     

Immunohistochemical studies on translocation of pollen S-haplotype determinant in self-incompatibility of Brassica rapa

The self-incompatibility system in Brassica is controlled by the S-locus, which contains S-receptor kinase (SRK) and S-locus protein 11 (SP11). SRK and SP11 control stigma and pollen S-haplotype specificity, respectively. SP11 binding to SRK induces the autophosphorylation of SRK, which triggers the signaling cascade that results in the rejection of self-pollen. The localization of SP11 protein during pollen development and pollination, however, have never been demonstrated. In this study, we examined the localization of S(8)-SP11 protein in the anther or pollinated stigma by immuno-electron microscopy. The immunostaining suggested that S(8)-SP11 was secreted from the tapetal cell into the anther locule as a cluster and translocated to the pollen surface at the early developmental stage of the anther. During the pollination process, SP11 was translocated from the pollen surface to the papilla cell, and then penetrated the cuticle layer of the papilla cell to diffuse across the pectin cellulose layer. Furthermore, SP11 protein could only penetrate the cuticle layer of the papilla cell in the presence of pollen grains, and could not penetrate on its own. This suggests that another factor from the pollen grain is needed for SP11 protein to penetrate the papilla cell wall.