Pistil Receptivity and Pollen Tube Growth in Relation to the Breeding System of Eucalyptus woodwardii (Symphyomyrtus: Myrtaceae)

Pistil structure, stigma receptivity and pollen tube growthwere investigated in relation to seed set of Eucalyptus woodwardii.Self-pollination resulted in reduced capsule retention and seeddevelopment as compared with cross-pollination. The pistil consistedof an ovary with five locules, a long style with a canal extendingfor two-thirds of its length, and a papillate stigma. Therewas no change in style length with time after anthesis, butboth stigma secretion and ability to support pollen germinationand tube growth increased to reach a peak at 7 d. Pollen germinatedon the stigma surface and in the stylar canal, but most tubegrowth occurred intercellularly in the transmitting tissue surroundingthe canal. At the base of the style the pollen tubes split intofive groups following the transmitting tissue strands to theovary. Each group grew through a septum dividing two loculesand entered the placenta. The tubes then emerged from the placentato penetrate the ovules at between 10 and 20 d after pollination.Fewer ovules were penetrated following self- than cross-pollination. Eucalyptus woodwardii Maiden, Lemon-flowered gum, Pistil receptivity, Pollen tube growth, Breeding system, Self-incompatibility     

The Pollen Tube Pathway in the Pistil of Lycopersicon peruvianum

The pollen tube pathway has been studied in unpollinated andpollinated pistils of Lycopersicon peruvianum using histochemicalstains for detection of proteins, lipids and arabinogalactansby bright-field microscopy, and decolourized aniline blue fordetection of pollen tubes by epifluoresence microscopy. Thepollen tube pathway is a continuous tract of mucilage from thestigma surface to the ovule micropyles, and is associated witha continuous tract of specialized, protein-rich transmittingcells comprising the stigmatic papillae, vertical files of stylartransmitting cells and the placental epithelium within the ovary.The superficial exudate of the stigma is hydrophobic and richin lipids. The mucilage of the style and ovary is hydrophilicand rich in arabinogalactans but low in proteins. Pollen tubesgrow between cells through the mucilage of the stigma and stylartransmitting tract, and across the surface of the placenta inthe ovarian mucilage. The structure of the junction of the stylartransmitting tract with the top of the ovary placenta assistseffective distribution of pollen tubes within the ovary. Lycopersicon, solanaceae, fertilization, pistil, pollen tube, pollination     

Pollen Tube Growth and Fertilization Efficiency in Salpiglossis sinuata: Implications for the Involvement of Chemotropic Factors

The possible involvement of chemotropic factors influencingpollen tube growth in the style and ovary of Salpiglossis wasstudied. Pollen deposited at the base of excised styles germinatedreadily, with pollen tubes penetrating the transmitting tissueand growing towards the stigma, implying that no chemotropicrequirement exists for pollen tube growth in the style. However,the position and high efficiency of seed set following limited-pollinationof intact pistils would support the involvement of localizedchemotropism operating within the ovary. Chemotropism, limited pollination, fertilization efficiency, Salpiglossis sinuata     

The Proteaceous Pistil: Morphological and Anatomical Aspects of the Pollen Presenter and Style of Eight Species Across Five Genera

The morphology and anatomy of pollen presenters, styles andpollen of species ofBanksia, Dryandra, Hakea, IsopogonandMacadamiawerestudied. Serial sections of pistils and SEM images of pollenwere quantified to determine whether the low fertility observedin the Proteaceae has a structural basis. Pollen access to thestigma was investigated. There were three types of stigmaticcavity. A groove in which the stigmatic papillae were enclosedwas present inDryandra, BanksiaandHakea. Macadamiahad a groovewith protruding papillae, andIsopogonhad a tube which enclosedthe papillae. Anatomical studies showed the pollen presenterto be structurally complex but overall to have similar internalanatomy across the species studied. The species could be groupedaccording to presence or absence of transfer tissue and presenceor absence of sclerenchyma, but these groups were not mutuallyexclusive. In the pistil there were three structural filtersto pollen tube passage. The first was at the stigma, where pollengrain access could be limited by the diameter or length of thestigmatic groove or the capacity of the pollination chamberin relation to pollen volume. The second and third related toa narrowing of the transmitting tissue tract within the pollenpresenter and in the lower style which could influence pollentube passage to the ovule.Copyright 1999 Annals of Botany Company Proteaceae,Banksia coccinea, Banksia ericifolia, Dryandra formosa, Dryandra nana, Dryandra quercifolia, Hakea bucculenta, Isopogon cuneatus, Macadamia integrifolia,stigmatic cavity, fertility, pollen presenter, structural limitation, stigma, pollen grain, image analysis, transfer tissue.     

Evidence for Stigmatic Self-incompatibility, Pollination Induced Ovule Enlargement and Transmitting Tissue Exudates in the Paleoherb, Saururus cernuus L. (Saururaceae)

Saururus cernuus, a species belonging to the primitive herbaceousangiosperm family Saururaceae, exhibits high rates of self-sterility.We investigated the structural and functional aspects of pollen-carpelinteractions following cross and self pollination to assessthe tissue specific site and timing of self-sterility and factorsimportant for successful cross pollen tube growth. Self-sterilitywas due to inhibition of self pollen germination at a dry stigma.Self pollination was associated with anomalous foot formation,reduced cell wall expansion and secretory activity of stigmaticpapillae, and callose production in stigmatic papillae. Followinggermination, cross compatible pollen tubes entered a solid coreof transmitting tissue and grew to the base of a short style.Entry of cross pollen tubes into the ovary was coincident withovule enlargement which placed the micropyle in the proximityof cross pollen tube tips. Ovule enlargement also occurred followingself pollination. Cross pollen tubes either entered an exudate-filledmicropyle directly from the style, or growth in the ovary waslocalized to the epidermis of the locule and outer integumentprior to entry into the micropyle. Prior to pollination, thetransmitting tract was void of secretions except for exudatein the micropyle. Growth of pollen tubes on the locule and integumentwas associated with exudate apparently arising from transmittingcells adjacent to growing pollen tubes. The present study providesthe first evidence in a primitive herbaceous species of stigmaticself-incompatibility (SI) in association with a dry stigma,pollination-induced signalling events affecting developmentof carpellary tissues, and micropylar exudates. Copyright 1999Annals of Botany Company SI evolution, dry stigma, exudates, pollen-carpel signalling, Saururaceae.     

The transmitting tissue of Nicotiana tabacum is not essential to pollen tube growth, and its ablation can reverse prezygotic interspecific barriers

The Nicotiana tabacum transmitting tissue is a highly specialized file of metabolically active cells that is the pathway for pollen tubes from the stigma to the ovules where fertilization occurs. It is thought to be essential to pollen tube growth because of the nutrients and guidance it provides to the pollen tubes. It also regulates gametophytic self-incompatibility in the style. To test the function of the transmitting tissue in pollen tube growth and to determine its role in regulating prezygotic interspecific incompatibility, genetic ablation was used to eliminate the mature transmitting tissue, producing a hollow style. Despite the absence of the mature transmitting tissue and greatly reduced transmitting-tissue-specific gene expression, self-pollen tubes had growth to the end of the style. Pollen tubes grew at a slower rate in the transmitting-tissue-ablated line during the first 24 h post-pollination. However, pollen tubes grew to a similar length 40 h post-pollination with and without a transmitting tissue. Ablation of the N. tabacum transmitting tissue significantly altered interspecific pollen tube growth. These results implicate the N. tabacum transmitting tissue in facilitating or inhibiting interspecific pollen tube growth in a species-dependent manner and in controlling prezygotic reproductive barriers.     

The Nutritional Role of Pistil Exudate in Pollen Tube Wall Formation in Lilium longiflorum: I. Utilization of Injected Stigmatic Exudate

A quantity of labeled stigmatic exudate, collected from detached Lilium longiflorum (cv. Ace) pistils labeled with d-glucose-1-¹⁴C, was fractionated on Sephadex G-100 and the polysaccharide component, G-100-I, was injected into the hollow styles of unlabeled detached pistils (cv. Ace) which had been removed on the day after anthesis from the plant. Injected pistils were immediately cross-pollinated with L. longiflorum (cv. No. 44) pollen. Eighty-four hours later, pistils were dissected to recover the pollen tubes, expended exudate, and labeled tissues of the stigma and style. Distribution of label revealed that at least 25% of the carbohydrate substance in excised pollen tubes was derived from G-100-I. The composition of expended exudate adhering to pollen tubes, of pollen tube cytoplasm, and of pollen tube walls suggests that utilization of exudate by growing pollen tubes involves uptake and incorporation into pollen tube cytoplasm of exudate polysaccharide fragments followed by extensive metabolism of at least a portion of the incorporated carbohydrate prior to its utilization for pollen tube wall biosynthesis. Results suggest the presence of at least two polysaccharide components in G-100-I, one which resists major degradation following injection into the style and another which undergoes measurable degradation both before and after entry into the pollen tube.     

Characterization of the pollen growth transition in self-incompatible <Emphasis Type="Italic">Petunia inflata</Emphasis>

In Petunia inflata, as in other species that shed bicellular pollen, early pollen tube growth in the pistil is slow, then increases 2- to 5-fold depending on the genotype of the female parent. We refer to the time point at which pollen tubes enter the accelerated phase of growth as the pollen growth transition (PGT). Here, we present evidence that pre-PGT and post-PGT growth are quantitatively and qualitatively different, and that the PGT is triggered when pollen tubes reach the transition zone (TZ) below the stigma. The capacity of various pistil zones to precipitate the PGT was tested through 'stump' pollinations: varying lengths of the pistil apex were excised, the cut surface of the remaining pistil (the stump) coated with stigmatic exudates then dusted with compatible pollen. Pollen applied to TZ tissues entered the PGT earlier than pollen growing in intact control pistils; the PGT was delayed in stylar stumps, largely because of delayed germination and reduced pre-PGT growth. In immature pistils, the PGT was delayed by several hours relative to its onset in mature pistils. The PGT fails to occur in pollen cultured in vitro. Collectively, the data suggest that pollen tubes become competent to enter the PGT when they reach a critical size, but the physicochemical environment of the transmitting tissue is necessary for triggering the cellular changes that result in accelerated growth. An analysis of the distribution of pollen tube tips before and after the PGT suggests that pollen competition is most intense during the pre-PGT phase.     

Stigmatic and stylar incompatibility in Prunus avium L.: Morphological and ultrastructural aspects

Abstract

Stigmatic and stylar structures of-sweet cherry (Prunus avium L.) «Malizia» were examined with light and electron microscopes (S.E.M. and T.E.M.).

It was demonstrated that the transmitting tissue, situated in the central portion of the style, extends below the stigmatic papillae and secretes an electrondense material accumulating in the intercellular spaces. Pollen tubes which germinated on the stigma, reached the ovules passing through this substance which facilitates their passage while trophic relations are established.

Some ultrastructural aspects of the pollen tubes observed inside the style were examined and discussed in relation to the phenomenon of self-incompatibility.     

Pollination and Pollen-pistil Interaction in Oil Palm, Elaeis guineensis

Structural and cytochemical aspects of the pistil and detailsof pollination and pollen-pistil interaction were investigatedin the African oil palm (Elaeis guineensis Jacq.), an importantperennial oil crop. The stigma is trilobed, wet and papillate.The branched papillae are confined to a narrow linear zone oneach stigmatic lobe. Each stigmatic lobe harbours a deep stigmaticgroove, which runs adaxially along the surface. The stigmaticgroove is bordered by a well-defined layer of glandular cells,each of which has a pectinaceous cap on the inner tangentialwall. The style is hollow. The canal cells show thickeningson the inner tangential wall. The stigmatic groove and stylarcanal contain an extracellular matrix secreted by the canalcells which is rich in proteins, acidic polysaccharides andpectins. The canal cells at the base of the style are papillateand loosely fill the stylar canal. The stigma becomes receptivewhen the stigmatic lobes separate, and remains so for 24 h.Pollination is mediated by weevils as well as by the wind. Undernatural conditions the pollination efficiency was 100%. Pollinationinduces additional secretion in the stigmatic groove and stylarcanal. During post-pollination secretion, the pectinaceous capsof the cells lining the stigmatic groove are degraded. Pollengrains germinate on the stigmatic papillae and tubes grow onthe surface of the papillae, entering the stigmatic groove andadvancing along it into the stylar canal to eventually gainaccess to the locules. Pollen tubes are seen in the ovules 18–20h after pollination. Copyright 2001 Annals of Botany Company Arecaceae, Elaeis guineensis, African oil palm, pollination, stigmatic grove, stylar canal, Tenera hybrid, weevil     

POLLEN TUBE ATTRITION IN ERYTHRONIUM GRANDIFLORUM

Seed set after selfing in E. grandiflorum is often reduced relative to seed set after crossing; however, the compatibility patterns seen are not due to genes of major effect (i.e., S alleles). There is quantitative variation in the proportion of pollen tubes reaching the base of the style after both self- and cross-pollinations. Pollen tubes require between 24 and 72 hr to reach the ovary, but pollen tube growth ceases after 72 hr. When styles were removed from the ovaries 5 days after pollination, between 10 and 80% of the pollen tubes in the stigma had not reached the base of the style. The number of pollen tubes at the base of the style is a much better predictor of seed set than is the number of pollen tubes in the stigma. Pollen tube attrition is not affected by the age of the recipient flower or by the number of pollen donors contributing to the stigmatic pollen pool. The number of pollen tubes reaching the base of the style is dependent upon the source of the pollen and appears to be a decelerating function of the number of pollen tubes present in the stigma.     

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

Stigma-surface esterase activity and stigma receptivity througha sequence of developmental stages of the pistil have been studiedin four taxa characterized by having wet stigmas — Petuniahybrida, Nicotiana tabacum, Crinum defixum and Amaryllis vittata.The style is solid in the first two and hollow in the lattertwo taxa. In all the taxa, stigma—surface esterase couldbe detected in a thin surface layer (pellicle) from a very earlystage of pistil development, irrespective of the presence orabsence of the exudate. However, the taxa showed variation instigma receptivity. In Petunia and Nicotiana, stigmas from pistilsof 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 normalpollen germination and tube growth. It is inferred that in taxacharacterized by a wet stigma and solid style, the factors requiredfor pollen germination are present from an early stage of pistildevelopment and the exudate per se is not involved in pollengermination. In taxa characterized by a wet stigma and hollowstyle, however, the pellicle does not carry the factors requiredfor pollen germination and tube growth; they appear to be presentin the exudate. Petunia hybrida Vilm, Nicotiana tabacum L., Crinum defixum, Ker-Gawl, Amaryllis vittata Ait., tobacco, pollination, pollen germination, stigmatic exudate, stigma receptivity, stigma-surface esterase, esterase activity     

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.     

Fluorescence and scanning electron microscopic study on self-incompatibility in distylous Averrhoa carambola L.

Various combinations of intermorph, selfing and intramorph pollinations were carried out in Averrhoa carambola and the pollinated pistils were observed under fluorescence and scanning electron microscopes in time-course experiments. In both compatible and incompatible pollinations, similar behavior of pollen germination and penetration was observed in the first 4 h after pollination. In compatible intermorph pollination, pollen tubes were found at the base of the transmitting tract of the style at 8 h and 24 h after pollination in both the pin and thrum morphs. With thrum flowers, selfing resulted in pollen tubes being uniformly arrested at the junction between the stigmatic and stylar tissues. Penetration of pollen tubes into the upper portion of style was observed in thrum intramorph pollination and, when the second member was treated as the gynoecial tissue under the same pollination, penetration of tubes was further enhanced. Pin flowers, on selfing, resulted in pollen tube penetration farther down the style than was the case with thrum selfing. Intramorph pollination of pin morph behaved in a similar manner to selfing and was not affected by genotypes. Beside the stamen-style dimorphism, the receptive surface of the cob stigma was larger in pin than thrum flowers. While pin pollen was round, thrum pollen was oblong in shape with pin to thrum ratio on the polar axis being 1.2 and on the equatorial axis 0.8. The stigma of pin morph belonged to the dry type, while that of the thrum resembled the wet type.     

POLLEN TUBE DISTRIBUTIONS IN NICOTIANA GLAUCA: EVIDENCE FOR DENSITY DEPENDENT GROWTH

I hand sectioned styles of Nicotiana glauca at intervals along their length and counted the number of pollen tubes in each section using fluorescence microscopy. Evidence of density dependent growth was found for three stages of pollen growth. Pollen germination on the stigma increased with increasing pollen population size. Pollen tube penetration in the stigma was unaffected by increasing density from low to moderate levels but was reduced at high densities. Pollen tube penetration in the style was enhanced by increasing density. This enhanced growth in the style was apparently confounded by interference among pollen tubes growing at high densities. In particular, the area of tissue able to support pollen tube growth decreases from the stigma into the lower style, which could cause overcrowding of pollen tubes growing at high densities. Enhanced pollen tube penetration with increasing density combined with interference among pollen tubes growing at high densities resulted in greater mean pollen tube lengths for populations with moderate densities. The shift from density independent growth in the stigma to positively density dependent growth in the style may represent a shift from autotrophic to heterotrophic growth stages of pollen.     

Pistil Exudate Production and Pollen Tube Growth in Lilium longiflorum Thunb.

Exudate production in the pistil of Lilium longiflorum was studiedin relation to pollen tube growth, using scanning electron microscopy(SEM), transmission electron microscopy and light microscopy.In contrast with conventional fixation for SEM, during whichthe exudate of L. longiflorum largely washes away, the exudateremains present through freezing in case of cryo-SEM. Usingthe latter method we observed that exudate production on thestigma and in the style started before anthesis. Just underneaththe stigma the exudate was first accumulated at the top of eachsecretory cell, followed by a merging of those accumulationsas exudate production proceeded. Exudate is also produced bythe placenta. It was however not possible to determine whetherany of this fluid originated from the micropyle. Apart fromthe cell shape and the cuticle present in between the secretorycells, the ultrastructure of the secretory cells covering theplacenta was comparable to those of the stylar canal. The transferwall of the secretory cells of the placenta originated fromfusing Golgi vesicles but the endoplasmic reticulum seemed tohave an important role as well. After pollination the pollen tubes grew across the stigma andentered the style through one of the slits in the three stigmalobes. The pollen tubes grew straight downward through the styleand were covered by exudate. As the pollen tubes approachedthe ovary their growth was restricted to the areas with secretorycells. In the cavity the pollen tubes formed a bundle and theybent from this bundle in between the ovules towards the micropylarside. There they bent again to stay close to the secretory cells.After bud pollination the pollen tube growth was retarded. Laterarriving pollen tubes had a tendency to grow close to the secretorycells of the style, which resulted in a growth between thesecells and preceding pollen tubes. If there was still a littleexudate produced, it resulted in a lifting up of the pollentubes, out of the exudate. The relationship between exudateproduction and pollen tube growth is discussed. Both the speedand the guidance of the pollen tube seemed determined by theproperties of the exudate.Copyright 1994, 1999 Academic Press Cryo-scanning electron microscopy, exudate, Lilium longiflorum, lily, ovary, pollination, pollen tube growth, secretory cell, stigma, style     

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.     

Sexual reproduction in the cork oak (Quercus suber L.). I. The progamic phase

 Cork oak (Quercus suber L.) is a monoecious wind-pollinated species with a protandrous system to ensure cross-pollination. To the best of our knowledge, this report provides the first insight into the sexual reproduction cycle in this species. The cork oak flowering season extends from April until the end of May. Our results show that, at anthesis, the pistillate flower is not completely formed and ovules are just starting to develop. Pollen reaching the dry stigmatic surface adheres to the receptive cells, germinates and penetrates the epidermis in aproximately 24 h, and grows through the intercellular spaces of a solid transmitting tissue. In cross-pollination, a sequential arrest of pollen tubes was observed along the style, providing preliminary evidence for a pollen tube competition mechanism. As a consequence, few pollen tubes reach the basal portion of the style. Furthermore, pollen tube growth is a discontinuous process since tubes are arrested in the basal portion of the style about 10–12 days after pollination. While tubes are latent, the ovarian loculus starts to develop from an emerging mass of sporogeneous cells which later will differentiate into the placenta and ovules. One and a half months after pollination ovules complete their differentiation, tubes resume growth and fertilisation occurs. Ovular abortion is frequent at this stage, and only one ovule will successfully mature during autumn into a monospermic seed. Received: 23 July 1998 / Revision accepted: 2 November 1998