Pollen tube reallocation in two preanthesis cleistogamous species, Ranalisma rostratum and Sagittaria guyanensis ssp. lappula (Alismataceae)

Pollen deposition on stigmas and pollen tube growth in two apocarpous species, Ranalisma rostratum and Sagittaria guyanensis ssp. lappula (Alismataceae), were examined with fluorescence microscopy. The reallocation of pollen tubes among pistils was observed in both species. The percentage of pollinated stigmas per flower was only 22.0% in R. rostratum and 51.0% in S. guyanensis, though the seed/ovule ratios are higher than 65% in both species. The number of pollen grains on each single stigma ranged from 0 to 96 in R. rostratum, and from 0 to 125 in S. guyanensis. When more than one pollen grain deposited on a stigma, all pollen tubes grew to the ovary, but only one of them turned towards the ovule and finally entered the nucleus. The other tubes grew through the receptacle tissue into ovules of adjacent carpels whose stigmas were unpollinated or pollinated later. The intercarpellary growth of pollen tubes could be a mechanism to increase the efficiency of sexual reproduction in an apocarpous gynoecium with low pollination on the pistils.     

The timetable for development of maternal tissues sets the stage for male genomic selection in Betula pendula (Betilaceae)

The influence of the sequence of maternal tissue development in Betula pendula upon the potential for male gamete selection was investigated, and the timing of the fixed abortion of one of the two ovules was determined. We used scanning electronic microscopy, confocal laser scanning microscopy, and blue light microscopy. The stigmas remain fresh throughout male anthesis, and may also last after its end, depending on ambient temperatures. The presence of germinated pollen does not induce stigmatic necrotization, and grains may arrive at different times. The pollen tube tips remain within the stigma base until the end of female anthesis. The ovules will not develop until after necrotization of the stigmas. The pollen tubes thus have a fair start to the ovules, regardless of their different arrival times and of the original positions of the pollen grains at the stigma surface. Therefore, competition among different microgametophytes is possible, in spite of low pollination intensity. Our results indicate that when the first pollen tube penetrates an ovule, this ovule starts to outgrow the other one, and even if the other is also penetrated, its vascular support soon atrophies and the megagametophyte will shrivel. Fertilization of both ovules was never seen in this study.     

油橄榄授粉受精和胚胎发育过程观察

该研究以油橄榄“鄂植-8”为材料,应用压片荧光观察花粉在柱头和花柱中的萌发及生长情况,采用石蜡制片法观察油橄榄的胚珠结构特点和授粉受精过程。结果表明：油橄榄为1子房2心室4胚珠,珠心较发达,由多层细胞构成,属于厚珠心椭圆型胚珠,胚珠直生;花开时花粉粒落到柱头上立刻萌发,随后花粉管在花粉通道中生长,再后进入子房经子房内表面,大部分花粉管不能到达胚珠,仅少数沿胎座生长经珠柄进入珠孔,释放2个精子,2个精核分别进入卵细胞和极核,并与卵核及极核相互融合;观察到合子中雌、雄性核仁融合的过程。授粉受精各阶段经历的时间为花粉落到柱头上立刻萌发;授粉后6d左右,花粉管长入胚珠的珠孔,随后释放精子;10 d左右完成授粉受精,30 d左右形成心型胚,40 d左右胚发育几乎成熟。在进行子房石蜡切片中,共观察到612个完整子房切片,发育完整的子房为97.53％,完成授粉受精的胚珠为15.52％。油橄榄在自然授粉下,约85％的胚珠授粉受精过程不能完成,在一定程度上影响其坐果。该研究结果为油橄榄授粉受精、高效生产等提供了理论依据。     

CHEMOTROPIC ACTIVITY AND THE PATHWAY OF THE POLLEN TUBE IN LILY,

A study of the pollen tube pathway in Lilium leucanthum var. centifolium and in L. regale reveals that the entire pathway from stigma to ovule is lined with cytologically unique stigmatoid cells. Assays for chemotropic activity of tissues and exudates along the pathway of pollinated or unpollinated pistils showed that onset of chemotropic activity progressed basipetally (and, when pollinated, in advance of the pollen tubes), commencing at the stigma 3-5 days before anthesis and appearing in the ovules 1-2 days after anthesis. Activity persists about 10 days in ovules of pollinated pistils and for 14-16 days in ovules of non-pollinated pistils. Attempts to localize the source of the chemotropic factor showed that gynoecial tissues bearing stigmatoid cells are chemo-tropically active while slices of style or ovary wall lacking stigmatoid cells are inactive. When ovules were sliced transversely and the micropylar and chalazal halves assayed, only the micropylar half showed activity. We suggest that the ovules and the stigmatoid tissue along the pollen tube pathway are the sources of the chemotropic factor responsible for the directional growth of the pollen tube.     

Pollination Rates and Pollen Tube Growth in a Vulnerable Plant,Liriodendron chinense (Hemsl.) Sarg. (Magnoliaceae)

The limited seed production of insect-depended plant, Liriodendron chinense was once considered to be pollen-limited and insufficient cross pollination. In this study, we counted pollen grains deposited on stigmas in three populations in Guizhou, Hunan and Zhejiang provinces of China respectively. Over 61.9% stigmas were pollinated. From 1994 to 1996, the mean number of pollen grains on each stigma ranged from 4.4 to 42.6, much more than ovules(2) in each pistil. Based on observations of three years, both the pollination rate and pollen quantity on stigmas significantly affected seed set. When flowers opened without stamens dehiscencing at the early stage of anthesis, stigmas received considerable quantity of pollen grains. Pollen grains from different sources were able to germinate and pollen tube growth rates were not greatly variable. It is very likely that pollen grains arrived first would fertilize eggs. Since only several pollen tubes went through the stylar canal, the potential pollen competition may exist. In this case, there would be strong selection on floral syndrome which benefit early insect visits. Pollen grains from the early visits would have a greater chance to fertilize ovules than those from later visits, which implies that cross pollination is the predominant breeding system of this plant. The conclusion was also confirmed by following four artificial experiments. Three treatments, including flowers bagged, netted or with the perianth removed, all reduced seed set clearly, but flowers with the stamens removed (emasculation)had a higher seed production by open pollination. As the rates of deposited stigmas in three populations were 6～8 times more than full seed set, we considerthat lower seed production in this plant may not mainly be due to pollen limitation.     

Pollen tube growth in pistils of female-sterile and fertile plants ofOenothera mut.brevistylis

Summary Pollination and pollen tube growth was observed in pistils of fertile and female-sterile plants ofOenothera mut.brevistylis. The stigmas and styles of sterile plants were very irregularly formed and additional ovules often developed in the style. The malformations did not inhibit pollen tube growth but made it slower and less efficient. The pollen tubes grew in the ovary but did not find the ovules. Near their tips, pollen tubes branched or meandered without any clear direction. Lack of tropism caused by malfunction of the ovules is postulated in the female-sterile plant.     

Variation of pollination and resource limitation in a low seed-set tree, Liriodendron chinense (Magnoliaceae)

Pollen limitation and resource limitation have been documented as the major factors responsible for plants commonly producing more ovules than seeds, but few studies have examined pollen deposition directly in natural populations at different sites and times. We investigated the causes of low seed set in four populations of Liriodendron chinense (Magnoliaceae), an insect‐pollinated endangered tree endemic to southern China, over 2–3 years. One pistil potentially produces two ovules. The number of pistils per flower varies among populations, but in three of the four populations the variation in a given population was not significantly different among years. Overall, populations with higher pistil numbers tend to set more seeds per flower, but a positive correlation between pistil numbers and seed production per flower was observed in only one of the four populations. The numbers of pollen grains deposited per stigma varied from 0 to 60. The proportion of pollinated stigmas per flower ranged from 44% to 88% among populations and years. The numbers of pollen grains deposited per stigma and the percentages of pollinated stigmas were significantly different between populations, and two populations showed significant differences between years. A positive correlation between stigmatic pollen load and seed set was sought in ten population‐by‐year combinations but, in a given population, high stigmatic pollen loads did not always result in high seed set. Examination of pollen deposition, pistil and seed production over several sites and years showed that in addition to pollination, other factors such as resource or genetic loads were likely to limit the (lower than 10%) seed set in L. chinense. It appears that small, isolated populations experience severe pollination limitation; one population studied had seed/ovule ratios of 0.84% and 1.88% in 1995 and 1996. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society, 2002, 140 , 31–38.     

Intercarpellary growth of pollen tubes in the extragynoecial compitum and its contribution to fruit set in an apocarpous species, Schisandra sphenanthera (Schisandraceae)

? Premise of the study: Apocarpous plants possess carpels that are separated in the gynoecium. Extragynoecial compita, commonly occurring in basal angiosperms, have been proposed to have the potential to increase offspring quantity in apocarpous species through the intercarpellary growth of pollen tubes. To date, the impact of an extragynoecial compitum on fruit or seed set has not been studied in any species. This study investigated the pollen tube pathway between adjacent carpels and its contribution to fruit set in Schisandra sphenanthera. ? Methods: We investigated the fruit set ratio in the field and collected hundreds of gynoecia at their full flowering stage. Pollinated carpel ratio and pollen tube pathway observations were performed using fluorescence optics. ? Key results: Pollen grains germinated and tubes extended along the pseudostyle surface. Some of them turned and entered the ovules at the end of the stigmatic crest, whereas others subsequently grew into neighboring carpels through promontory connections located at the base of the unfused carpels. No tubes were found growing on the surface of the receptacle. More than 24 carpels could be fertilized by pollen tubes from one carpel through hand pollination. The pollinated carpel ratio was significantly lower than the fruit set ratio under natural conditions. ? Conclusions: Pollen tubes from one carpel can easily cross in the extragynoecial compitum between the adjacent carpels of S. sphenanthera, and this intercarpellary growth of pollen tubes can significantly increase the fruit set of apocarpous species, at least in S. sphenanthera.     

濒危植物安徽羽叶报春两种花型的繁育特性及其适应进化

二型花柱的维持机制和自然选择压力多年来一直是生态学和进化学研究领域的热点之一。通过实验室栽培和野外观察统计相结合的方法,对安徽羽叶报春两种花型(长柱花和短柱花)的形态特征、花粉活力、柱头可授性、花粉/胚珠比、自然授粉及结籽能力、自交亲和性等繁育特性进行了比较研究。结果表明:长、短柱花的花冠直径和裂片宽无明显差异,而花冠筒、雌蕊和雄蕊高、花粉数目及大小、P/O比均有显著差异。在自然条件下,长柱花所接受的总花粉数要明显高于短柱花的总花粉数,但所接受的异型花花粉数和平均每果结籽数两者无显著差异。长柱花和短柱花的花粉和柱头活力相似,均能在较长时间内维持较高活力,仅在开花末期显著下降。两种花型的花在自花授粉、同型异花授粉、异型花授粉条件下均能结籽,但异型花授粉的结籽数均明显高于自花授粉和同型异花授粉结籽数。在长柱花各种授粉方式中,花粉萌发率无明显差异,但异型花花粉管的生长速度明显比同型异花花粉和自花花粉的快,而在短柱花柱头上表现为异型花授粉的萌发率最高,但只要萌发后在花柱中的生长速度无显明差异。此外,综合上述结果,对二种花型花部综合征的维持机制及自然选择压力进行了探讨。     

Synchronicity of pollination and inoculation with Claviceps africana and its effects on pollen-pistil compatibility and seed production in sorghum

Sorghum ergot (caused by Claviceps africana) is a disease that affects sorghum seed development and yield. The interaction between pollen tube growth and hyphal development determines whether ovaries will be fertilized or colonized. Thus their respective deposition times on the stigma are critical. The effect of the time interval between pollination and inoculation on stigma receptivity and seed production was measured under field conditions in the male-sterile line A9 at Montecillo, State of México (2240m altitude). Pollination and inoculation treatments, from simultaneous application to 2 and 4h difference, were imposed when all stigmas on the panicle had emerged. Control panicles were either only pollinated or only inoculated. Eighteen hours later, pollen grains that adhered to, and germinated within the stigma, pollen tubes in the style and ovary, and fertilized pistils were counted. Pistils showing some disease expression (germinated spores, mycelium growth, or tissue necrosis) at 18, 48, and 72h were recorded. The number of diseased florets was registered at the dough growth stage, while number of seeds, grain yield and 100-seeds weight was measured at the physiological maturity. The pathogen applied in a water suspension of macro and secondary conidia caused a decrease in stigma receptivity; the greatest decrease (40-60%) occurred when the pollen and the inoculum were deposited almost simultaneously, regardless of which was deposited first. The route of the pollen tube was also the route for fungal infection. On average, treatments first inoculated had 60% more diseased florets and 36% less grain yield, 30% fewer seeds and seed size decreased 8%, than those first pollinated.     

COORDINATED TIMETABLES FOR MEGAGAMETOPHYTE DEVELOPMENT AND POLLEN TUBE GROWTH IN RHODODENDRON NUTTALLII FROM ANTHESIS TO EARLY POSTFERTILIZATION

Rhododendron nuttallii T. W. Booth (Ericaceae) was used to derive concurrent timetables for megagametophyte, pollen tube and early postfertilization development from anthesis through 3 wk after pollination, based on timed collections of self-pollinated pistils. Stages of development were determined for over 33,500 cleared ovules, including, for selected collection dates, stages on different portions of the placenta. Pollen tube information was obtained by fluorescence microscopy of pistil squashes stained with aniline blue. Because of the very large number of ovules observed, it was possible to recognize a much more closely graded series of stages in megagametophyte development than is usually the case. While a range of stages occurred on all days, development progressed steadily from a majority of functional spores and 2-nucleate gametophytes on the day of anthesis to mostly a late zygote-primary endosperm stage at 18 days, and some 2-celled endosperm stages at 21 days, after pollination. At all times the most advanced stages, including first pollen tube entries, occurred on the outer surface of the lower half of the placenta, and the youngest on the inner surface of the uppermost portion. Fertilizable ovules were not found in any frequency until 8 days after pollination (then in only about 34% of the ovules); a few fertilized ones were seen after 10 days but constituted less than 5% until 12 days after pollination, thereafter increasing to about 60%. Fertilization occurred in any one of three morphologically recognizable stages distinguished by position and state of fusion of polar nuclei. Pollen germinated on the stigma 1–2 hr after pollination, and pollen tubes grew at a rate of about 1–1.25 cm/day, reaching the top of the ovary in 8–9 days with the first ovule entries seen after 10 days. There was a close correlation between megagametophyte development and pollen tube growth, with large numbers of functionally mature ovules not being found until pollen tubes had reached the ovary. While nuclei within ovules could not be distinguished in the squashes, three gametophyte stages that could be recognized—unelongated, elongated either without or with a pollen tube—were tallied for almost 29,000 ovules. The progression in these general stages corresponded well with that documented in more detail from cleared ovules. Unpollinated pistils showed a similar progression of gametophyte stages until the time fertilization would start to occur, after which there was continued accumulation of functionally mature ovules. A variety of abnormally developed and/or collapsing(ed) ovules or gametophytes were seen; collectively, they averaged over 8.6% of all ovules.     

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     

Changes in proteins and peroxidases induced by compatible pollination in the ovary of Nicotiana tabacum L. ahead of the advancing pollen tubes

Proteins and peroxidases produced by the ovules and placenta of tobacco (Nicotiana tabacum L.) in response to compatible pollination were analyzed by two-dimensional polyacrylamide gel electrophoresis and by enzyme staining in flat-bed native isoelectric focusing gels. For two-dimensional gels, ovaries were sampled at 36 h after pollination, at which time pollen tubes have penetrated much of the length of the style but have not yet entered the ovary. At least 11 major proteins from pollinated ovaries had no detectable counterparts in unpollinated ovaries. These showed a range of molecular mass and pI. For peroxidase isozyme assays, ovaries were sampled at 0, 12, 24, 36 and 48 h after pollination. At 45–50 h, pollen tubes were beginning to enter the top of the ovary but could still be separated from the ovules and placenta during sampling. Ovules and placentae from unpollinated pistils showed only one form of peroxidase, whereas those from pollinated pistils showed additional isozymes at pH 5.4 and pH 10.0. Both new isozymes increased in staining intensity over the first 36 h after pollination. At 48 h, however, the acidic peroxidase had continued to increase, while the basic component had declined so as to be barely detectable. The observations are discussed in relation to accumulating evidence that some form of pollination-induced signal reaches the ovary ahead of the advancing pollen tubes. The nature of this signal and possible involvement of peroxidases are also briefly discussed.     

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.     

Observation of Pollen Tube Behaviour and Early Embryogenesis Following Interspecies Pollination Between Actinidia deliciosa and A. arguta

The pollen tube behaviour in the style and early embryogenesis following interspecies pollination between Actinidia deliciosa No. 26 and A. arguta were observed by means of fluorescence and light microscopy. Pollen grains germinated on the papillate stigma and pollen tubes grew along the V-shaped open-type style. Pollen tubes showed slower growth and reached the ovules 50--60 hours later than those of the control. Several abnormalities of pollen tubes have been observed at the base of the style, including wave-like pollen tubes, pollen tubes with swollen or pointed tips, with variable diameters, and a few with irregular growth. Random deposition of callose along pollen tube wall and even the whole wall was observed. About 26.74 % of the ovules were successfully fertilized and developed into seeds, among them 68.50% of the seeds were normal and 31.50% were abortive. About 11.41% were empty seeds without embryo and endosperm. Unfertilized small ovule was 61.45 %. Normal seed and its embryo were smaller than those of the control. The development of embryo was of the Soland type. The endosperm was cellular. The zygote remained quiescent for about 12-15 days before it started to divide, eventually forming a cotyledonary embryo 50 days after pollination.     

野菊与菊花杂交中花粉活力和柱头可授性及胚胎发育研究

应用石蜡制片、活体压片、光学显微镜及扫描电子显微镜观察等方法,研究了四倍体河南云台山野菊(Dendranthema indicum)与栽培菊花'钟山金山'(D.grandiflorum 'Zhongshanjinshan')种间杂交中父本花粉活力、花粉在柱头萌发、花粉管生长及胚胎发育情况等.结果发现,父本云台山野菊的花粉活力在授粉时为12%左右.人工授粉后的不同时间,在柱头上都观察到正常萌发的花粉粒,且花粉管都能进入柱头,其中,在授粉后0.5 h时,平均每柱头有5.9粒花粉萌发;12 h时,为59.9粒;而24和48 h时,则分别降为47.1和35.7粒.此外,在授粉后8、10、12和15 d时,分别在49.1%、40.8%、39.7%和38.5%子房内观察到正常发育的胚胎,最终杂交结实率为44.8%,而母本自然开放结实率为52.3%.研究表明,授粉前其多数母本雌蕊发育良好、授粉后多数花粉能在柱头正常萌发和花粉管正常生长,在受精后大部分胚胎发育正常是野菊与栽培菊种间杂交较高结实率的重要保证,而授粉前父本较低的花粉活力对杂交结实率影响不大.     

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     

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     

Expression of a polygalacturonase enzyme in germinating pollen of <Emphasis Type="Italic">Brassica napus</Emphasis>

Penetration of pollen tubes through stigmatic tissues in Brassica napus L. may involve the release of cell wall modifying enzymes from the pollen tube tip. We examined the expression of a pectin-degrading polygalacturonase (PG) enzyme in unpollinated and early and late pollinated stigmas via immunoblotting and immuno-light microscopy using a PG polyclonal antibody. Immunoblotting analysis indicated that PG enzyme was present at low levels in unpollinated stigmas and at high levels in pollinated stigmas. The level of PG did not detectably increase between early and late pollinated stigmas. Immuno-light microscopy demonstrated that PG enzyme was present in ungerminated pollen grains, stigmatic papillae and in the tip of pollen tubes growing into the papillar wall. This latter evidence suggests that PG enzyme may play an important role in papillar cell wall penetration during pollination although other interpretations of the role of pollen PG should not be discounted. Received: 9 November 2000 / Accepted: 7 December 2000