Dynamics of pollen tube growth under different competition regimes

Pollen tube dynamics following different competition regimes were studied in sweet cherry (Prunus avium L.). In the process from pollination to fertilization, a constant reduction in the number of pollen tubes that travel along the style is observed. There could be two main causes of this reduction. One is a physical or physiological constraint consisting of the progressive decrease in the reserves and space available for pollen tube growth along the transmitting tissue of the style, and the other is genetic interaction both among the male gametophytes and between the male gametophytes and the female tissues of the flower. To evaluate the roles that these two forces play in reducing the number of pollen tubes that travel along the style, pistils were subjected to various pollen competition regimes by applying different mixtures of live and dead pollen onto the stigmata. The results obtained were similar when the experiment was repeated with different genotypes over 2 years, both in the laboratory and in the field. The role of stylar constriction is important, but it is not the only cause of pollen tube attrition because with low pollen loads fewer pollen tubes reach the different parts of the style than could fit therein. The fact that under different pollen competition regimes the number of pollen tubes is reduced by the same proportion in each stylar level indicates that genetic interactions play an important role in the control of pollen tube attrition.     

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     

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     

Polyester and nylon powders used as pollen diluents preserve pollen germination and tube growth in controlled pollinations

Pollen acquisition for seed production, breeding programs and supplemental pollination can be costly and difficult. The identification of dry particulates for use as pollen diluents would facilitate the use of limited amounts of pollen and aid in accurate pollen application and dispersion. Four powders - Rilsan ES, polyester, wheat flour, and Lycopodium spores - were evaluated as pollen diluents using petunia as a model system. Diluents were combined with petunia pollen at a 5:1 (v/v) ratio. Two types of studies were conducted: (1) storage studies evaluated the viability of pollen combined and held with diluent for different durations; and (2) in vivo studies evaluated pollen tube growth in the styles of flowers pollinated with pollen-diluent mixtures. Pollen germination was not affected when stored as pollen-diluent mixtures for 4 days. Slight detrimental effects on pollen germination were observed after 6 days storage with Rilsan ES powders. Pollination with all the pollen-diluent mixtures resulted in fewer pollen tubes growing in the style compared to controls diluted with heat-killed pollen instead of diluent powders. Lycopodium-pollen mixtures were the most inhibitory, providing only 8% of the tube numbers observed in controls. Pollen mixed with polyester powders, Rilsan ES powders or wheat flour had tube numbers ranging from 47 to 61% of the control, but still had 175 or more pollen tubes per style, which would be sufficient for high rates of seed set in petunia. Wheat flour-pollen mixtures tended to clump and degrade pollen flow. Rilsan ES and polyester were identified as two promising pollen diluent powders that can facilitate accurate metering and distribution of pollen, produce large numbers of pollen tubes, and maintain pollen viability under storage.     

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     

Effects of pollen competitive environment on pollen performance in Mirabilis jalapa (Nyctaginaceae)

 We examined the influence of pollen competitive environment on pollen performance in Mirabilis jalapa. We used the number of pollen grains and the number of pollen tubes per pistil as measures of pollen competition. Pollen germination, pollen tube penetration into the style, and pollen tube growth rates were used as measures of pollen performance. All three measures of pollen performance were affected by the competitive environment. Pollen germination was greatest at intermediate pollen load sizes. The percentage of germinated pollen grains that penetrated the stigma and grew into the style decreased with pollen load size. Pollen tube growth rate in the style was greater and more variable with larger numbers of pollen tubes in the style. Controlling for the degree of selection at the stigma indicated that pollen-pollen or pollen-style interactions were the likely causes of increased growth rates. Received: 28 October 1996 / Revision accepted: 24 January 1997     

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.     

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.     

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.     

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.     

The pollen receptor kinase LePRK2 mediates growth-promoting signals and positively regulates pollen germination and tube growth

In flowering plants, the process of pollen germination and tube growth is required for successful fertilization. A pollen receptor kinase from tomato (Solanum lycopersicum), LePRK2, has been implicated in signaling during pollen germination and tube growth as well as in mediating pollen (tube)-pistil communication. Here we show that reduced expression of LePRK2 affects four aspects of pollen germination and tube growth. First, the percentage of pollen that germinates is reduced, and the time window for competence to germinate is also shorter. Second, the pollen tube growth rate is reduced both in vitro and in the pistil. Third, tip-localized superoxide production by pollen tubes cannot be increased by exogenous calcium ions. Fourth, pollen tubes have defects in responses to style extract component (STIL), an extracellular growth-promoting signal from the pistil. Pollen tubes transiently overexpressing LePRK2-fluorescent protein fusions had slightly wider tips, whereas pollen tubes coexpressing LePRK2 and its cytoplasmic partner protein KPP (a Rop-GEF) had much wider tips. Together these results show that LePRK2 positively regulates pollen germination and tube growth and is involved in transducing responses to extracellular growth-promoting signals.     

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.     

INFLUENCE OF THE PISTIL ON POLLEN TUBE KINETICS IN PEACH (PRUNUS PERSICA)

Pollen tube growth has been studied in peach and has been related to changes in the pistil structures which the pollen tube has to traverse in its way from the stigma down to the ovule. Growth of the pollen tubes along the pistil is not continuous. While pollen tubes reach the base of the style 7 days after pollination, fertilization does not take place until 12 days later. Pollen tubes stop for 5 days at the top of the obturator and they further stop for 3 days before entering the ovule. The pollen tube growth is heterotrophic; starch, present all along the pistilar tract at anthesis, vanishes as the pollen tubes pass by. Discontinuous pollen tube growth appears to be controlled by the pistil. At anthesis the pistil is not fully matured. Maturation of the pistil implies a number of secretory processes that occur in a basipetal way starting from the stigma down to the style and ending in the ovule. Some of these secretions at the stigma and the style are triggered by pollination; others appear to be a maturative stage of the pistil and are produced in a discrete way. The fact that the pollen tube depends on these secretions together with the fact that these secretions are not continuously produced confer upon the pistil a role of controlling pollen tube kinetics and point out that, for a successful fertilization, male gametophyte development and pistil maturation need to by synchronized.     

Stigma development and receptivity of two Kalanchoë blossfeldiana cultivars

Several members of the Kalanchoë genus are popular as ornamental plants. Cross-breeding and wide hybridisation are essential to continuously introduce novel traits into cultivated plant material. This study aimed to identify the major factors related to the stigma affecting cross-pollination in the Kalanchoë blossfeldiana. Pollen tube growth after pollination of K. blossfeldiana ‘Jackie’ and ‘Reese’ was examined at different stigma developmental stages. Five distinct developmental stages were identified based on changes in morphology and activity of stigmatic peroxidase. After reciprocal pollination at the five stigma developmental stages, fluorescence microscopy was used to estimate the number of pollen tubes in situ. Both cultivars had receptive stigmas from stage I to IV, which concurred with the continuous expansion of the stigma covered with exudates. No pollen tube growth was observed at stage V for both cultivars. The number of pollen tubes was significantly higher in carpels pollinated at stage III, characterized by loose arrangement of the papillae and maximal amount of exudates, compared to all other developmental stages. Stigmas showing drying exudates and absence of peroxidase exhibited a relatively decreased number of pollen tubes in situ. No pollen tubes germinated on wilting stigmas. The arrangement of the papillae, the presence of exudates and peroxidase activity affected the number of pollen tubes in cross-pollination of K. blossfeldiana cultivars ‘Jackie’ and ‘Reese’. These results will help breeders to better select the optimal time for effective pollination. The findings may be applicable for other cultivars of K. blossfeldiana and relevant for different species of Kalanchoë.     

Style-controlled wilting of the flower

Differences in rate of wilting in cross-, self-and unpollinated flowers of self-incompatiblePetunia hybrida L. clone W166H appeared to be significant. Wilting rate was fastest following cross-pollination and slowest in unpollinated flowers. The difference between wilting behaviour of cross- and self-pollinated flowers was not caused by rate of pollen tube growth and not by the incompatibility (recognition or rejection) reaction either. It is assumed, that, following pollination, the wilting reaction is only retarded after penetration of pollen tubes of the same genetic composition as the style (complete self-pollination). The number of viable pollen grains necessary to initiate a maximal wilting-rate of flowers following cross- and self-pollination is about 800, which means that a fifth of the stigmatic surface must be covered with living pollen grains. It is suggested that pollen tube penetration and injury of the style have a similar influence on the initiation of wilting.Wilting-rate following pollination is faster in young plants as compared with wilting in old plants. The wilting process of unpollinated and self-pollinated flowers started in the early morning and lasted till afternoon. Cross-pollinated flowers wilted independently of the hour of the day. The role of flower-wilting as a means of communication to the environment with regard to pollination of the style is discussed.     

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.     

Pollination in vitro: effects on the growth of pollen tubes,seed set and gametophytic self-incompatibility in Trifolium pratense L. and T. repens L.

Summary Growth of pollen tubes and seed set were compared after hand pollination in situ and in vitro in two self-incompatible species, Trifolium pratense and Trifolium repens. Adhesion of pollen grains to the stigma was greater in vitro for both species. After cross-pollination, in vitro culture gave a significant increase in the cumulative growth of pollen tubes in pistils of T. pratense compared to in situ conditions. After selfing in T. repens, pollen tube growth was significantly increased by in vitro culture of florets. Seed set after crossing in situ and in vitro was similar for both species. Seed set after selfing in vitro was not increased in T. pratense. Several genotypes of T. repens were classified as very good, good and poor selfers based on their capacity for seed set following selfing in situ. In vitro pollination increased self seed formation by 1.7-, 18.0- and 31.0-fold for each class, respectively. Ovules located nearest to the style were fertilized more often after selfing than after crossing.     

不同葡萄品种柱头、花柱发育与种子形成的关系

对‘京秀’、‘香妃’(二倍体)和‘黑奥林’、‘巨峰’(四倍体)葡萄品种的柱头、花柱发生发育以及花粉管在雌蕊中生长与坐果和果实中种子形成的关系进行了研究。结果显示:‘京秀’、‘香妃’的坐果率和果实中的种子数明显高于‘黑奥林’和‘巨峰’,而‘巨峰’葡萄的坐果率和种子数最低。开花期‘京秀’和‘香妃’的花柱直径略小于‘黑奥林’和‘巨峰’,但花柱中部引导组织的直径和引导组织所占花柱的比例却大于‘黑奥林’和‘巨峰’;半实心花柱的比例也高于‘黑奥林’和‘巨峰’,说明花柱中引导组织的结构和发育状况可能与坐果和果实中种子形成有关;人工授粉24 h后,在‘京秀’和‘香妃’雌蕊中花粉管的生长速度快于‘黑奥林’和‘巨峰’,授粉后48 h‘京秀’和‘香妃’雌蕊中到达各部位的花粉管数要多于‘黑奥林’和‘巨峰’,授粉后72 h各品种到达子房各部位的花粉管数开始减少。表明‘京秀’和‘香妃’花柱中引导组织较为发达,而且半实心花柱比例也较高,有利于花粉管在雌蕊中的生长和完成授粉受精,使‘京秀’和‘香妃’的坐果率和果实中种子的形成都较高。     

Relationships of pollen size,pistil length and pollen tube growth rates in Rhododendron and their influence on hybridization

Summary Pollen size and pistil length data have been collected for 93 species of Rhododendron (Ericaceae) belonging to a number of different subgeneric taxa. For a sample of eight species in section Vireya, pollen tube growth in the style after selfor interspecific pollination has been quantified. Pollen volume and the time taken for pollen tubes to reach the ovary were both related to pistil length. Pollen-tube growth rates were generally greater for species with longer pistils and larger pollen. Increasing temperature increased the rate of pollen-tube growth. There was no detectable effect of pollen tube density on tube growth rate in the style. After interspecific pollinations tube growth rates in foreign styles could be faster or slower than in self styles. A semisterile individual with two viable pollen grains per tetrad and a plant grafted as scion to a longer-styled stock both showed more rapid pollen-tube growth than expected on the basis of pistil size. Data collected for 26 species in section Vireya showed that where extreme disparity of pollen/pistil size causes failure of interspecific crosses, one or more bridging species with intermediate pollen/pistil size can generally be selected.     

The relationship of the female reproductive success of Eucalyptus globulus to the endogenous properties of the flower

Low capsule and seed set is a major factor limiting seed production in Eucalyptus globulus seed orchards. Controlled pollination studies showed that the reproductive success (number of seeds produced per flower pollinated) was primarily determined by the female. We aimed to identify the factors contributing to the differences in reproductive success between female genotypes in terms of the physical and anatomical properties of the flower. We studied pairs of genotypes of high and low reproductive success from each of three races (Furneaux Group, Strzelecki Ranges and Western Otways) growing in a seed orchard. Controlled pollinations were performed on six females and along with flower physical measurements, pollen tube growth and seed set were assessed. Overall tree reproductive success was positively correlated with flower size, ovule numbers, style size, cross-sectional area of conductive tissue within the style (all of which were inter-correlated) and the proportion of pollen tubes reaching the bottom of the style. Significant positive correlations of reproductive success and flower physical properties between different ramets of the same genotypes across seasons suggests a genetic basis to the variation observed. The majority of pollen tube attrition occurred within the first millimetre of the cut style and appeared to be associated with differences in style physiology. When examined as pairs within races the difference in reproductive success for the Western Otways pair was simply explained by differences in flower size and the number of ovules per flower. Physical features did not differ significantly for the Strzelecki Ranges pair, but the proportion of pollen tubes reaching the bottom of the style was lower in the less reproductively successful genotype, suggesting an endogenous physiological constraint to pollen tube growth. The difference in reproductive success between the females from the Furneaux Group was associated with a combination of these factors.