Floral Structure, Stigma Receptivity and Pollen Viability in Relation to Protandry and Self-incompatibility in Silky Oak (Grevillea robusta A. Cunn.)

The reproductive biology of Grevillea robusta growing underexotic conditions in Kenya and Australia is reported. The speciesshowed both protandry and a self-incompatibility mechanism.The stigma was wet and papillate with a distinct groove in themiddle. The anthers dehisced prior to anthesis, when the perianthopened. Stigmatic receptivity began 1 d after anthesis, withthe greatest pollen germination rates and longest pollen tubesobtained 2 d after anthesis. Nectar secretion commenced withpollen dehiscence and was abundant at anthesis. Most stigmaticgrooves opened widely 1–2 d after anthesis and stigmasshowed taller papillae and abundant secretion. Controlled pollinationsgave a greater fruit set from cross-pollination (5.9% in Apriland 17.5% in July) than open-pollination (0.1% in April and3.3% in July). No fruit set from self-pollination was obtainedin April, and very few fruit set for geitonogamous (two outof 1622; 0.1%) or for autogamous (one out of 2707 flowers; 0.04%)pollination treatments in July. Following self-pollination,growth of pollen tubes was poorer than in other treatments,and was generally arrested in the upper style. Cross-pollinatedflowers produced normal and straight pollen tubes, while self-pollentubes had growth abnormalities. Most of the open-pollinatedflowers were found without pollen or with only self-pollen ontheir stigmas indicating that the amount of cross-pollen reachingthe stigma under open-pollination may be a factor limiting seedproduction. Flowers shed soon after the fertilization phasewere those with ungerminated pollen or no pollen. Although avery low rate of selfing may occur, G. robusta presents a self-incompatibilitysystem and allogamy is its primary breeding behaviour.Copyright2000 Annals of Botany Company Grevillea robusta, silky oak, Proteaceae, protandry, controlled pollinations, receptivity, pollen-tube growth, self-incompatibility, pollination     

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-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.     

In vitro propagation of two species of commelinaceae from bud cultures and repeated subcultures on a growth regulator-free medium

Summary In our wide-ranging research on in vitro propagation of some monocotyledonous plants, two Commelinaceae species were studied: Tradescantia fluminensis var. foliis variegatis and Tradescantia pallida. Initial cultures were established successfully using nodal and apical meristems that produced single shoots, many roots, and no callus, by utilizing growth regulator-free MS medium. Addition of growth regulators did not increase the activity of explants that produced single or multiple shoots, atypical roots, and no callus. Consecutive cultures were possible using the apical and nodal meristems of the previous generation. The behavior of the different generations in culture did not change and was similar to the initial cultures. Their growth capacity was maintained over many months, also on a growth regulator-free medium. In both species, the chromosome number in the root tips of the mother plant and all morphologically stable in vitro plantlets confirmed a constant ploidy level, in T. fluminensis 2n=72, and in T. pallida 2n=24.     

Structure and Cytochemistry of the Stigma and Pollen--Pistil Interaction in Zephyranthes

The stigma in Zephyranthes candida and Z. citrina is of thedry type with a continuous cuticle—pellicle. In some papillae,however, the terminal portion of the cuticle—pellicleis lifted upwards and occasionally even disrupted by the accumulationof a secretion product below it. Both non-specific esterasesand acid phosphatases are present on the stigma surface. Thestyle is solid with a central core of transmitting tissue whichhas conspicuous intercellular spaces containing a matrix thatincludes proteins, polysaccharides and pectic substances. Zephyranthes citrina is self-compatible while Z. candida isself-incompatible. Followng incompatible pollination in Z. candida,pollen germination is normal but pollen tube growth is inhibitedat the junction of the stigma and style. Self-incompatibilitycan be overcome by bud pollination. Protein synthesis is necessaryfor pollen germination in both species. Concanavalin A bindsto the stigma surface of both species, but does not affect pollentube penetration in Z. candida. In crosses between the two speciestypical unilateral incompatibility is observed when Z. candidais used as the pistillate parent. Zephyranthes, stigma-surface enzymes, dry stigma, pollen-pistil interaction, self-incompatibility, unilateral-incompatibility     

Pollen-stigma Interaction in the Leguminosae: Constituents of the Stylar Fluid and Stigma Secretion of Trifolium pratense L.

The style of T. pratense is hollow, and the canal contains awatery secretion which forms the medium through which the pollentubes grow after penetrating the stigma head. In self-incompatiblegenotypes, incompatible pollen germinates freely and the tubespenetrate the stigma, but they are arrested in the canal afterpassing an inflated zone (entasis) proximal to the stigma head.The stylar fluid contains sucrose, glucose and traces of galactoseand arabinose, as well as a range of proteins. Comparison ofthe proteins in the stigma eluate and stylar fluid by microgradientgel electrophoresis shows that the spectra are broadly similar;but in addition to various minor differences, two major glycoproteinsare present in the stigma secretion which are absent from thestyle, while one in the stylar fluid is not represented in thestigma. Six esterase isoenzymes are present in the stylar fluid,and three of these also in the stigma eluate; there are alsodifferences in acid phosphatase isoenzymes. Leguminosae, Trifolium pratense L., pollen-stigma interaction, self-incompatibility, stigma eluate secretion, stylar secretion     

Pollen Viability and Pollen-tube Growth Following Controlled Pollination and their Relation to Low Fruit Production in Teak (Tectona grandisLinn. f.)

Pollen released at 1100 h has the highest viability (92.2%)but is no longer viable 3 d (84 h) after anthesis.In vitropollen-tubegrowth is fast (140 µm h^-1) and increases significantlywithin the first 8 h.In vivopollen tubes also grow quickly andreach the base of the style within 2 h after pollination andenter the micropyle 8 h after pollination. There is no significantdifference between self- and cross-pollination in either therate and the number of pollen tubes in the pistil and the numberof ovules penetrated by a pollen tube. Teak has late-actinggametophytic self-incompatibility; the majority of pollen tubesgrow through the style but some do not continue to grow fromthe style towards the embryo sacs. Pollen-tube abnormalitiesinclude swollen, reversed, forked and tapered tips and irregularand spiralling tubes. These are most prevalent in self-pollination(20.4%). The index of self-incompatibility of 0.17 and low fruitset following self-pollination (2.49%) indicates that teak ismostly self-incompatible. Drastic fruit abortion occurs withinthe first week following controlled pollination. Within 14 d,fruit size and fruit set from cross-pollination is generallymuch greater than from self-pollination. Tectona grandis; pollen viability; pollen-tube growth; pollination; controlled pollinations; incompatibility.     

Pistil Structure and Pollen Tube Pathways in Leptospermum myrsinoides and L. continentale (Myrtaceae)

Pistil structure and pollen tube growth were investigated inLeptospermum myrsinoides and L. continentale (Myrtaceae). BothL. myrsinoides and L. continentale pistils consist of an ovarywith five locules, a style and a five-lobed dry, papillate stigma.A centrally located stigmatic cleft is present but extends onlyto the base of the stigma. Pollen germinates and grows intercellularlythrough the stigma into the central transmitting tissue of thestyle. Pollen tubes do not grow down the stigmatic cleft. Atthe base of the style the transmitting tissue separates intofive, each tract leading through the placenta to one of thefive locules. The pollen tubes continue to grow intercellularlythrough these five tracts entering the locules between the lobesof the placenta. Pollen tubes are smooth-walled and straightwhilst in the transmitting tissue of the style but produce shortlateral branches at regular intervals when in the locules. Branchingcontinues until pollen tubes enter ovules. It is suggested thatthe observed branching in the locules is a result of pollentubes following a chemotropic or thigmotropic pathway to theovules. This behaviour was consistent in all pistils examinedand no difference was observed in the behaviour of self- orcross-pollen tubes in the style or ovary.Copyright 1994, 1999Academic Press Leptospermum myrsinoides Schldl., Leptospermum continentale J. Thompson, pistil structure, pollen tube pathway, pollen tube branching     

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     

Pollen-pistil Interaction in a Non-pseudogamous Apomict,Commiphora wightii

Structural and cytochemical details of the pistil and the interactionof pollen and pistil were studied in a non-pseudogamous apomict,Commiphorawightii.The anthers in the male and bisexual flowers producefunctional pollen grains. The stigma is of the wet and papillatetype. The style is typically solid with two strands of transmittingtissue that traverse the entire length of the style. There isa marked reduction in the area occupied by the transmittingtissue from the stigma to the base of the style. The cells ofthe transmitting tissue are isodiametric in transverse as wellas longitudinal section and do not form longitudinal files ofelongated cells as reported for other taxa. Proteins could notbe localized in the intercellular matrix. Although pollen grainsgerminate on the stigma, pollen tubes do not grow beyond theproximal one third of the style. Changed orientation of thecells of the transmitting tissue and absence of proteins inthe intercellular matrix could account for the failure of thepistil to support pollen growth.Copyright 1998 Annals of BotanyCompany Guggul, pollen-pistil interaction, non-pseudogamous apomict,Commiphora wightii, transmitting tissue     

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     

Messenger RNA in the Ungerminated Pollen Grain: A Direct Demonstration of its Presence

The presence of presynthesized messenger RNAs in the mature,dehydrated pollen grains of Tradescantia paludosa L. has beendemonstrated by translation of total RNA and poly (A)⁺ RNA ina wheat germ cell-free system, and a comparison of in vitroand in vivo synthesized proteins by SDS-polyacrylamide gel electrophoresis.The mRNAs are capped at their 5'-termini with a guanosine 5'phosphate moiety which is methylated. messenger RNAs, guanosine 5' phosphate, pollen, Tradescantia paludosa L     

Pollen Tube Growth and Seed Set of Banksia coccinea R.Br. (Proteaceae)

Controlled hand pollinations and field observations were usedin conjunction with fluorescence and scanning electron microscopyand fruit and seed set to investigate the timing of stigma receptivity,pollen tube growth and self-incompatibility in relation to fertilityin B. coccinea. The species showed both protandry and partialself-incompatibility. Peak stigma receptivity as measured bypollen germination was recorded at 3 d after anthesis and maximumproduction of stigmatic exudate at 6 d. Pollen tubes reachedthe base of the style by 6 d after pollination. A 5 x 5 diallelexperiment was conducted and the results measured by pollentube growth. Self-pollinations generally resulted in poorertube growth than crosses and there was significant specificand general combining ability as well as reciprocal effects.Cross-pollination resulted in improved fruit set and seed toflower ratio over both selfing and open pollination. Spatiallimitations to fertility due to infructescence size were alsorecorded, but the combination of outcrossing mechanisms andspatial limitation did not entirely account for the low fertility.It is suggested that environmental conditions and the availabilityof resources may also exert an influence. Banksia coccinea R.Br., scarlet banksia, Proteaceae, pollination, stigma receptivity, pollen tube growth, self-incompatibility, breeding system, seed set     

Polysaccharide Secretion by the Watermelon Stigma

Secretion of the galactose-containing polysaccharide componentof the watermelon stigma exudate was studied using electronmicroscopy cytochemistry and autoradiography. Polysaccharidelocalization using the thiosemicarbazide–silver proteinatemethod stained the Golgi apparatus and secretory vesicles, thecell wall, wall thickenings and extracellular secretion. Thesame result was obtained at anthesis and at 18 h prior to anthesis,which coincides with the period of maximum secretion. Labellingof stigmas in vivo with D-(1-³H) galactose at 20 h prior toanthesis resulted in different labelling patterns after 2 h(18 h prior to anthesis) and 20 h (anthesis). At 18 h priorto anthesis label was present in the Golgi apparatus and secretoryvesicles, the cell wall and wall thickenings. By anthesis labelhad accumulated in the extracellular secretion in addition tothe Golgi apparatus, secretory vesicles, cell wall and wallthickenings. The results suggest that the polysaccharide componentof the stigma exudate is produced in the Golgi apparatus andsecreted via the cell wall and wall thickenings. Citrullus lanatus Thumb., Matsum and Nakai, watermelon, autoradiography, stigma, secretion, cytochemistry, polysaccharide     

Pollination Ecology ofChloranthus serratus(Thunb.) Roem. et Schult. andCh. fortunei(A. Gray) Solms-Laub. (Chloranthaceae)

Flowering and pollination biology ofChloranthus serratusandChloranthusfortuneiwere studied. Flowering took place from early Marchto mid–April inCh. fortunei, and from April to September,the whole growth period, inCh. serratus.The flowering periodof an inflorescence ofCh. serratusaveraged about 8 d and anthesisof a single flower was 5–6 d. Flowers are slightly protogynous.The flower emitted fragrance when the androecium became white.Both species are entomophilous with thrips as exclusive pollinators.Under natural conditions, fruit set occurs mainly as a resultof cross-pollination, but self-pollination and agamospermy mayoccur in some cases. In flowers ofCh. fortuneiandCh. serratus,theincurved androecium, the carpel and the spike axis form a nearlyclosed chamber that contains the anthers and stigma. The developmentof a floral-axial chamber may be an important step towards amore economical and effective pollination system. Floral morphology,pollination biology and fossil evidence suggest that the mainevolutionary trend in the genusChloranthusis towards developmentof ‘closed’ flowers. The fidelity of the relationshipbetweenChloranthusand thrips is regarded as a specialized featureof pollination biology and this relationship may have originatedearly in the evolutionary lineage.Copyright 1999 Annals of BotanyCompany Chloranthaceae,Chloranthus, Thysanoptera,flowering, floral-axial chamber, pollination, evolution trends.     

Physiology of Post-Pollination Exudate Production in Acacia

Marginson, R., Sedgley, M. and Knox, R. B. 1985. Physiologyof post-pollination exudate production in Acacia—J. exp.Bot. 36: 1660–1668. Stigmas of A. wattsiana produced 1260 nl of secretion by 90min after pollination. The optimum temperature for post-pollinationsecretion in A. baileyana, A. brownii and A. iteaphylla was20°C. Both self and cross intraspecific, interspecific andintergeneric pollinations produced a similar positive responsein A. iteaphylla and A. baileyana. In all cases aged pollenwas as effective as fresh pollen despite reduced fluorescencein the fluorescein diacetate test. Live yeast cells, fixed chickenerythrocytes, glass beads, talc and Biogel P150 did not stimulatesecretion, nor did pollen which had been washed in water orethanol despite high retention of viability in some cases Pollendiffusates dried on to glass beads produced a positive responsein A. iteaphylla and A. gracifolia. Intraspecific and interspecificpollinations involving fresh Acacia pollen resulted in pollengermination on the stigma and pollen tube growth in the styleof A. iteaphylla and A. baileyana. In contrast washed pollenfailed to germinate and pollen germination and tube growth werereduced at 35 °C as compared with 20 °C. Key words: Acacia, pollination, secretion     

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     

Pollination Biology in a TropicalAcaciaHybrid (A. mangiumWilld. xA. auriculiformisA. Cunn. ex Benth.)

Floral biology and pollination mechanism of theAcaciahybrid(A. mangiumWilld. xA. auriculiformisA. Cunn. ex Benth.) growingin Thailand are investigated using light and electron microscopy.The hybrid is andromonoecious. A floral spike consists of about150 loosely arranged flowers. Flowers are cream coloured, fragrantand have no floral nectaries. The pistil has a solid style witha smooth, wet stigma and amphitropous ovules with immature integuments.The anther consists of eight loculi, each bearing only one 16-grainpolyad. The flowers are weakly protogynous. Anthesis is completeat 0500–0600 h but peak female receptivity begins at 0200–0300h and is completed that day. The stigmatic exudate is of thelipophilic type and is secreted from the stigmatic cells bya holocrine mechanism. Pollen is the main floral reward forthe insect pollinators. There are several floral characteristicswhich facilitate pollen transfer from anthers and depositionon stigmas.Apis melliferaandCeratinasp. are the most effectivepollinators because they are the most common visitors and carrya heavy load of hybrid polyads. However, their behaviour inforaging for pollen in the same tree and weak protogynous dichogamymay promote self-pollination in the hybrid. The hybrid has lowpollination success due to low pollinator number. An increasein exposure time of flowers to pollinators or pollinator numbermay increase pollination success but may not affect the rateof pollen deposition on stigmas due to the relatively smallsize of the stigma in relation to the polyad.Copyright 1998Annals of Botany Company Acaciahybrid,Acacia mangium, Acacia auriculiformis, pollination, pistil receptivity, anthesis, pollinators.     

Early Inbreeding Depression and Pollen Competition inCalluna vulgaris(L.) Hull.

We investigated whether partial self-sterility inCalluna vulgarisresultsfrom abortion of selfed offspring owing to inbreeding depressionor a late-acting self-incompatibility mechanism, and whetherself-pollen interferes with normal functioning of cross-pollen.Self-pollination resulted in 75% less seed set than cross-pollination.Self-pollen tubes reached ovaries and penetrated ovules as oftenas those of cross-pollen. Following self-pollination, examinationof the size of undeveloped seeds showed that at least 70% resultedfrom ovule fertilization and arrest of development occurredat various stages. All self-pollinated plants produced seedsand self-fertility varied among plants. These results indicatethat the reduced seed set observed in self-pollination is morelikely the result of inbreeding depression rather than a late-actingself-incompatibility system. The fecundity component of inbreedingdepression was high (0.762). Seed set was reduced by an averageof 40% when self-pollen was mixed with cross-pollen, comparedto pure cross-pollination. Using genetic markers, we found about20% of seeds resulted from self-pollination in mixed-pollinatedfruits.C. vulgarisis likely to experience self-pollination innature and our data suggest this will reduce the number of ovulesthat might otherwise mature after cross-pollination.Copyright1999 Annals of Botany Company Calluna vulgaris(heather), self-pollination, pollen tube, ovule fertilization, early inbreeding depression, pollen interference.     

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