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     

Late-acting self-incompatibility in tea plant (<Emphasis Type="Italic">Camellia sinensis</Emphasis>)

The self-incompatibility of tea plant (Camellia sinensis (L.) O. Kuntze) was studied with the methods of aniline blue fluorescence assay and paraffin sections. The characteristics of pollen tube elongation after hand pollination was analyzed in 4 tea cultivars, including ‘Keemenzhong’, ‘Longjing-changye’, ‘Fuding-dabaicha’ and ‘Yabukita’, under self-pollination and cross-pollination, respectively. Although there were some difference among cultivars, pollen tubes elongated through the style and reach the ovary successfully at 48 h after pollination for both cross- and self-pollen tubes in all the four cultivars of tea. Pollen tubes entered into the ovule micropyles, however, only for cross-pollination, but not for self-pollination. Pollen tubes of selfing plants, failed in fertilizing, seemed have some difficulties to enter the ovule. All of which indicated that the self-incompatibility of tea plant is a late-acting self-incompatibility system (LSI) or an ovarian sterility (OS), in which the self incompatibility was due to none self pollen tube penetrating into the ovule and no fertilization.     

EFFECT OF FLORAL AGING ON THE GROWTH OF COMPATIBLE AND INCOMPATIBLE POLLEN TUBES IN LILIUM LONGIFLORUM

Compatible and incompatible pollen tube growth in detached styles of three Lilium longiflorum cultivare varies with the physiological age of the style. Before anthesis both compatible and incompatible pollen tubes grow, in 48 hr, only a fraction of the distance compatible tubes grow after anthesis. Incompatible pollen tubes are restricted to about half the distance of compatible tubes in the four days postanthesis, but thereafter increase up to or three-fourths or more the length of compatible tubes at the time of floral senescence. About 10 days after anthesis, growth of both types of pollen tubes decreases. The detached style method of pollen-tube cultivation is validated in the cultivar ‘Ace’ by seed set obtained following self-pollination in the 6- to 9-day interval and failure of seed set after either self- or cross-pollination after 9 days following anthesis. Also, in agreement with detached style data, self-pollination fails to produce seeds when attempted in bud stages or the five days following anthesis. Cross-pollinations are successful in this period. This material and technique appear well suited for study of the nature of the self-incompatibility reaction.     

Relationship between the self-incompatibility and cAMP level in Lilium longiflorum.

The elongation of pollen tubes in Lilium longiflorum cv. Hinomoto after self-incompatible pollination stopped halfway, but that after cross-compatible pollination (cross with cv. Georgia) did not. The elongation of pollen tubes after self-pollination was enhanced by exogenous cAMP and by pertussis toxin or cholera toxin, which activates adenylate cyclase. The level of endogenous cAMP in pistils after self-pollination was approximately one half of that after cross-pollination. Furthermore, the activity of adenylate cyclase in pistils after self-pollination was also approximately one half of that after cross-pollination. By contrast, cAMP phosphodiesterase in pistils after self-pollination was approximately 2 times as high as that after cross-pollination. A possible correlation between self-incompatibility and the low level of endogenous cAMP in lily pistils is discussed on the basis of these results.     

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.     

Pollen tube Growth and Self-Incompatibility in Heuchera micrantha var. diversifolia (Saxifragaceae)

A crossing study and an analysis of pollen tube growth were conducted in diploid and autotetraploid Heuchera micrantha var. diversifolia to distinguish between the possible mechanisms that could promote the high outcrossing rates observed and that could also result in the absence of fruit set following self-fertilization. The crossing study indicated that no fruit set occurred after self-pollination, whereas fruit set occurred in all of the hand-pollinated outcrosses. After 4 d, the self-pollinated flowers shriveled and abscised. Pollen tube growth following hand pollination was assessed in selfed and outcrossed flowers using fluorescence microscopy. The self-pollinated flowers exhibited far fewer pollen tubes than did the outcrossed flowers. Furthermore, in self-pollinated flowers, some of the pollen tubes extended into the style; fewer than one-half of the pollen tubes reached the base of the style and still fewer reached the ovules. The variable length of pollen tube growth, the uniform timing of floral abortion after self-pollination, and the absence of variability among individuals in the level of fruit set following self-pollination are all consistent with a system that lies somewhere between classic gametophytic self-incompatibility and late-acting self-incompatibility as the mechanism that is most likely operating in H. micrantha var. diversifolia. A similar "nonstandard" system may be present in other Saxifragaceae, such as Tolmiea and Lithophragma, as well as in Ribes, the sister group of Saxifragaceae. Our data also indicate that ploidal level (diploid vs. autotetraploid) has no influence on the extent or mechanism of self-incompatibiltiy in autopolyploid H. micrantha var. diversifolia.     

Floral Biology, Pollination, Pistil Receptivity, and Pollen Tube Growth of Teak (Tectona grandis Linn f.)

Teak flowers are weakly protandrous and pollen is shed withina few hours of flower opening. Pollen is tricolpate and 29 µmin diameter. The papillate stigma is of the wet type and isreceptive from 1100–1300h. The style is hollow throughoutits length. Nectar and pollen are the major floral rewards forpollinators. The major pollinators areCeratina sp. which carryteak pollen on most parts of their bodies, especially the specializedhair structures (scopal brushes) on the tibia. The most effectivepollination period in terms of flowers pollinated and pollenper flower is between 0900 and 1300h. At 1300h the number ofpollen per flower is the highest, ranging from 1–36 (average7). Pollen tubes grow very fast. Within 2 h after pollination8% of the pollen tubes have reached the micropylar end of theovule and pollen tubes first enter the embryo sac at 8 h. Onlyone to two pollen tubes enter the micropyles of a flower. Although78% of flowers were pollinated in open-pollination, the lowfruit set (3.5%) suggests that there are factors other thanpollination limiting fruit set. The main factor appears to bea high amount of selfing, and self-incompatibility occurs whenpollen tubes are arrested at the lower portion of the ovary. Tectona grandis ; floral biology; pollen tube growth; pollination; receptivity; pollinators     

Is Eucalyptus Cryptically Self-incompatible?

BACKGROUND AND AIMS: The probability that seeds will be fertilized from self- versus cross-pollen depends strongly on whether plants have self-incompatibility systems, and how these systems influence the fate of pollen tubes. METHODS: In this study of breeding systems in Eucalyptus urophylla and Eucalyptus grandis, epifluorescence microscopy was used to study pollen tube growth in styles following self- and cross-pollinations. KEY RESULTS: Pollen tubes from self-pollen took significantly longer than those from cross-pollen to grow to the base of the style in both E. urophylla (120 h vs. 96 h) and E. grandis (96 h vs. 72 h). In addition, both species exhibited reduced seed yields following self-pollination compared with cross-pollination. CONCLUSIONS: The present observations suggest that, in addition to a late-acting self-incompatibility barrier, cryptic self-incompatibility could be a mechanism responsible for the preferential out-crossing system in these two eucalypt species.     

Effects of Cross-pollination and Flower Removal on Fruit Set in Macadamia

Macadamia racemes were cross-pollinated and had flowers removedto determine whether manipulation of initial fruit set wouldaffect final fruit set or yield. Examination of flowers collected7 d after pollination indicated that the cross-pollination treatmentgenerally induced a small (13-19%) but significant increasein the number of pollen grains per stigma. All flowers possessedsome pollen grains, but in all cases cross-pollination approximatelydoubled the percentage of flowers with a pollen tube at thebase of the style (42-68% of flowers on cross-pollinated racemescompared with 21-35% of flowers on control racemes). Fruit setafter 14 d was always improved by cross-pollination, and thistranslated into increased final fruit numbers on two out offour occasions. In these two cases, kernel weights were increasedby 24 and 31% in the cross-pollinated treatments. This indicatesa possible xenic (paternal parent) effect in macadamia. Flowerremoval resulted in retention of a greater percentage of flowersas fruits, so that only severe reductions in flower number decreasedfinal fruit numbers. Improved efficiency of cross-pollinationin macadamia may increase both nut numbers and nut size.Copyright1994, 1999 Academic Press Macadamia integrifolia Maiden and Betche, Macadamia tetraphylla L. A. S. Johnson, Proteaceae, macadamia, pollination, pollen tube growth, flower number, fruit drop, fruit set, xenia     

Differential ovule development following self- and cross-pollination: the basis of self-sterility in Narcissus triandrus (Amaryllidaceae)

Self-pollination results in significantly lower seed set than cross-pollination in tristylous Narcissus triandrus. We investigated structural and functional aspects of pollen–pistil interactions and ovule–seed development following cross- and self-pollination to assess the timing and mechanism of self-sterility. Ovule development within an ovary was asynchronous at anthesis. There were no significant differences in pollen tube behavior following cross- vs. self-pollination during the first 6 d of growth, regardless of style morph type. Double fertilization was significantly higher following cross- vs. self-pollination. Aborted embryo development was not detected following either pollination type up to seed maturity. Prior to pollen tube entry, a significantly greater number of ovules ceased to develop following self- vs. cross-pollination. These results indicate that self-sterility in N. triandrus operates prezygotically but does not involve differential pollen tube growth typical of many self-incompatibility (SI) systems. Instead, low seed set following self-pollination is caused by a reduction in ovule availability resulting from embryo sac degeneration. We hypothesize that this is due to the absence of a required stimulus for normal ovule development. If this is correct, current concepts of SI may need to be broadened to include a wider range of pollen–pistil interactions.     

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     

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     

Anthecology and reproductive system of Mourera fluviatilis (Podostemaceae): Pollination by bees and xenogamy in a predominantly anemophilous and autogamous family?

The Podostemaceae are sessile hydrophytes restricted to habitats with waterfalls and seasonal flow variability. Mourera fluviatilis belongs to the family and has a disjunct distribution in the Amazon and northeastern Brazil. The following hypotheses were tested: (i) both autogamy and anemophily act on the pollination system of M. fluviatilis, and (ii) the highest reproductive success is achieved by cross-pollination. Natural populations were monitored in the rivers Pirangi and Ipojuca, northeastern Brazil. Floral visitors are the polylectic bees Apis mellifera, Trigona spinipes (Apidae), Augochlora sp. and Augochloropsis sp. (Halictidae), though only the latter three are effective pollinators. In experiments on the reproductive system and pollination there was a high percentage of fruit formation (>86%), both in treatment and control plants. Although the index of self-incompatibility is 0.86, there was a significant difference in the number of seeds produced among reproductive system treatments, and xenogamy produced more seeds. There was no significant difference in the number of penetrated ovules between control and manual cross-pollination (xenogamy) treatments, 24 h after pollination. However, there were differences among treatments, 48 h after pollination, except for the control and xenogamy treatments. The pollen tubes from cross-pollination treatments usually penetrate the micropyle in shorter time and in higher quantity. We found differences among pollination experiments, except for the control and non-emasculated treatments, and between emasculated treatments. In spite of the ambiguity of floral attributes (pedicel, filaments and anthers colors, sweet odor, reduced perianth, absence of nectar, small and dry pollen grains), wind pollination is less important for this species; what predominates instead are first allogamy mediated by bees and second self-pollination at the end of anthesis.     

‘晚大新高’梨授粉及受精过程的显微动态研究

应用荧光显微法和石蜡切片解剖法对‘晚大新高’梨授粉受精过程进行了系统观察研究。结果表明：‘晚大新高’梨自花授粉不结实;异花最佳授粉品种为‘黄花’,其次为‘翠冠’和‘丰水’。与选用‘黄花’为异花授粉品种相比,自花和异花的授粉受精过程存在明显差异,自花花粉在授粉后2h开始萌发,8h花粉管生长至离柱头约1／3处停止生长,顶端膨大呈球形,表现出自交不亲和性;异花花粉在授粉后1h开始部分萌发,8h花粉管生长至花柱中部,24h到达花柱基部并进入子房,48h进入胚囊,72h完成双受精过程。     

Pollen tube growth and self-incompatibility in three Ziziphus species (Rhamnaceae)

Self-incompatibility and synchronous protandrous dichogamy have previously been reported in Ziziphus species. In this work, we conducted a comparative analysis of fluorescence microscopy observations of pollen tube growth following controlled cross pollinations of emasculated flowers and self-pollinations of non-emasculated flowers in three Ziziphus species, Z. jujuba, Z. mauritiana and Z. spina-christi, with the aim to determine the type of the self-incompatibility system of each species. In addition, to test whether autonomous self-pollination, parthenocarpy or agamospermy occurs, flowers were emasculated (or not) and covered. Fruit set and seed viability were monitored. The presence of binucleate pollen grains and the cessation of pollen tube growth in the style suggest that the self-incompatibility system operating in the studied Ziziphus species is gametophytically controlled. Controlled self-pollination in Z. mauritiana resulted in fruits that dropped off before maturation, whereas in Z. spina-christi the flowers dropped off one or two days after pollination. Following controlled self-pollination, small fruits lacking viable seeds were obtained in Z. jujuba, probably due to the stimulus provided by pollination (stimulative parthenocarpy). In the cultivar Tamar of Z. jujuba, the relatively high percentage of seedless fruits obtained in emasculated bagged flowers without hand pollination suggests that this cultivar can set seedless fruits without any pollination stimulus.     

PROTANDRY,INCOMPATIBILITY, AND SECONDARY POLLEN PRESENTATION IN CEPHALANTHUS OCCIDENTALS (RUBIACEAE)

Cephalanthus occidentalis L. is protandrous and presents pollen secondarily on the stigma surface. Because self-pollen is present on the stigma, the degree of selling vs. outcrossing in this species will depend on 1) the phenology of pollen presentation and stigma receptivity; 2) whether the species is self-incompatible; and 3) the rates of self vs. crossed pollen tube growth. This study describes floral morphology and phenology, self-incompatibility, and pollen tube growth rates in self- and crosspollinations of C. occidentalis. Light and scanning electron microscopy were used to study stigma morphology after flower opening, while controlled pollinations tested for incompatibility. Stigmas were unreceptive initially but became receptive by the second day after flower opening. Ninety-two percent of cross-pollinated flowers set fruit, compared to 12% fruit set in self-pollinations. Pollen tubes from selfed and out-crossed pollen initially had similar growth rates. Out-crossed pollen tubes began to grow rapidly ca. 5 hr after pollination of a receptive stigma, whereas selfed pollen tubes ceased growth or grew slowly after this time. Pollen tubes from out-crossed pollen grew the length of the style within 24 hr after pollination, while selfed pollen tubes were inhibited at the stigma-style junction. Our results indicate that C. occidentalis has selfincompatibility, in addition to protandry and secondary pollen presentation. Protandry allows removal of self-pollen from the unreceptive stigma, while self-incompatibility prevents fertilization by unremoved self-pollen.     

Pollination and seed production in Xerophyllum tenax (Melanthiaceae) in the Cascade Range of central Oregon

Xerophyllum tenax is a mass-flowering, nectarless herb in which self-pollination is unavoidable as anthers shed pollen onto the three, receptive stigmatic ridges attached to each pistil within a few hours after expansion of the perianth. We compared the pollination system with reproductive success in this species through controlled, hand-pollination experiments. Ovaries of flowers sampled from unbagged inflorescences were visited by pollen-eating flies (primarily members of the family Syrphidae), beetles (primarily Cosmosalia and Epicauta spp.), and small bees, and produced normal-sized capsules and mature seeds. Ovaries of flowers from inflorescences bagged to prevent insect pollination produced small capsules containing undeveloped or no seeds. Epifluorescence analyses suggest that 0.95 of the uncovered flowers are cross-pollinated by insects with pollen tubes penetrating style and ovary tissue. Flowers show a "leaky" but early-acting self-incompatibility system. While hundreds of pollen tubes germinate on each stigmatic surface following self-pollination, few pollen tubes penetrate the stigmatic surface and none penetrate the ovary. In contrast, when stigmas are cross-pollinated by hand with pollen from a second inflorescence pollen tubes were seen penetrating style and ovary. Self-incompatibility in X. tenax parallels that of some species of Trillium, a sister genus within the Melanthiaceae.     

Pollen tube dynamics following half- and fully-compatible pollinations in self-compatible almond cultivars

. Pollen tube growth dynamics along the style at different times after self- and cross-pollination of four heterozygous self-compatible (SfSx) almond cultivars were studied by means of fluorescence microscopy. Results showed a reduction of pollen tube number along the style following both self-pollination (half-compatible reaction) and cross-pollination (fully-compatible). An important decrease in the percentage of pollen tubes present took place in the upper section of the style in both crosses. As expected in a gametophytic incompatibility system, a higher number of pollen tubes were stopped along the style in the case of the half-compatible crosses; however, the percentage of pollen tubes reaching the base of the style was similar in both cases. These results reveal the existence of other mechanisms controlling pollen tube growth along the style.     

The Effect of Brassica oleracea Stigma Extracts on the Germination of B. oleracea Pollen in a Thin Layer Chromatographic Bioassay

Hodgkin, T. and Lyon, G. D 1986. The effect of Brassica oleraceastigma extracts on the germination of B. oleracea pollen ina thin layer chromatographic bioassay.—J. exp. Bot. 37:406–411. A procedure for germinating Brassica oleracea pollen on thinlayer chromatography plates pretreated with 20 mol m^–3tris(hydroxymethyl) methyl-aminopropanesulphonic acid (TAPS)buffer, pH 8·0 has been devised and used to detect pollengermination inhibitors in B. oleracea stigma extracts. Inhibitory zones in extracts of stigmas, unpollinated, or collected0·5, 4, 8 and 24 h after self- or cross-pollination,differed little in R_F values and sizes. Extracts of stigmascollected 1 h and 2 h after self-pollination gave a small additionalinhibitory zone which was not detected in 1 h and 2 h cross-pollinatedstigma extracts. The results showed some differences from thoseobtained using Petunia hybrida pollen germinated on T.L.C. platesthat were not pretreated with buffer. The nature of the differencesbetween the two bioassays is discussed and some possible reasonsfor them indicated. Key words: Pollen, germination inhibitors, self-incompatibility, Brassica oleracea     

Characteristics of self-incompatibility in Schlumbergera truncata and S. x buckleyi (Cactaceae)

The influence of self-incompatibility (SI) on fruit set, seed set, and pollen tube growth was investigated in Schlumbergera truncata (Haworth) Moran and S.xbuckleyi (T. Moore) Tjaden. Four Schlumbergera clones were crossed in a complete diallel to verify the presence of SI. Fruit did not set when the clones were selfed or when two of the clones were crossed reciprocally, but all other outcrosses yielded fruit which contained 100–200 seeds each. Compatible outcrosses were characterized by large numbers of pollen tubes in the style and ovary cavity at 72 h after pollination. When pistils were selfed or incompatibly crossed, pollen tubes were inhibited in the upper third of the style and few pollen tubes reached the base of the style by 72 h after pollination. Schlumbergera exhibits several characteristics often associated with sporophytic SI systems (tricellular pollen and dry stigmas with elongate papillae), together with those commonly observed in gametophytic SI systems (stylar inhibition of incompatible pollen tubes and absence of reciprocal differences in outcrosses).Publication no. 3174 of the Massachusetts Agricultural Experiment Station