Pollen Tube Growth In Style Research Articles

The neglected other half - role of the pistil in plant heat stress responses.

Heat stress coinciding with reproductive stage leads to a significant loss in reproductive organs viability, resulting in lower seed-set and crop productivity. Successful fertilization and seed formation are determined by the viability of male and female reproductive organs. The impact of heat stress on the male reproductive organ (pollen) is studied more often compared to the female reproductive organ (pistil). This is attributed to easier accessibility of the pollen coupled with the notion that the pistil's role in fertilization and seed-set under heat stress is negligible. However, depending on species and developmental stages, recent studies reveal varying degrees of sensitivity of the pistil to heat stress. Remarkably, in some cases, the vulnerability of the pistil is even greater than the pollen. This article summarizes the current knowledge of the impact of heat stress on three critical stages of pistil for successful seed-set, that is, female reproductive organ development (gametogenesis), pollen-pistil interactions including pollen capture on stigma and pollen tube growth in style, as well as fertilization and early embryogenesis. Further, future research directions are suggested to unravel molecular basis of heat stress tolerance in pistil, which is critical for sustaining crop yields under predicted warming scenarios.

Interspecific Hybridization Processes between Michelia yunnanensis and M. crassipes and Embryogenesis of the Heterozygote

The investigation of hybridization processes and embryogenesis of heterozygote is an effective approach for early hybrids’ identification, which could provide reliable information for successful crossbreeding. In this study, we reported the whole hybridization processes of the direct cross and reciprocal cross between Michelia yunnanensis Franch. ex Finet et Gagnep. and Michelia crassipes Law using fluorescence microscopy after aniline blue staining, with the pollen germination on stigmas, pollen tube growth in styles, and subsequent extension into the embryo sac as well as the double fertilization processes are documented in detail. The M. yunnanensis × M. crassipes combination displayed considerable cross-compatibility, and the heterozygote embryogenesis was further observed with an approach of modified cryosectioning technique. Besides, the whole formation processes of hybrid seeds from artificial pollination to maturation were successfully observed. However, in the reciprocal cross, we found incompatibility between pollen grains of M. yunnanensis and stigmas of M. crassipes for the reason of hysteretic identification, as well as the abnormal callose deposition which belongs to the prefertilization barriers. This is the first study in which the complete and clear hybridization processes in Michelia were reported. We inferred that unilateral incompatibility of M. crassipes detected in this study may also exist in some other Michelia species. In artificial hybridization practices, we suggest some special treatments for overcoming prefertilization barrier should be taken when treating M. crassipes as the maternal parent.

Anther response to high-temperature stress during development and pollen thermotolerance heterosis as revealed by pollen tube growth and in vitro pollen vigor analysis in upland cotton.

Pollen tube growth in styles was strongly inhibited by temperature above 35 °C, and the yield of cotton decreased because of the adverse effect of high temperatures during square development. High-temperature stress during flowering influences the square development of upland cotton (Gossypium hirsutum L.) and cotton yield. Although it is well known that square development is sensitive to high temperature, high-temperature sensitive stages of square development and the effects of high temperature on pollen tube growth in the styles are unknown. The effect of high temperature on anther development corresponding to pollen vigor is unknown during anther development. The objectives of this study were to identify the stages of square development that are sensitive to high temperatures (37/30 and 40/34 °C), to determine whether the abnormal development of squares influenced by high temperature is responsible for the variation in the in vitro germination percent of pollen grains at anthesis, to identify the effect of high temperature on pollen germination in the styles, and to determine pollen thermotolerance heterosis. Our results show that the stages from the sporogenous cell to tetrad stage (square length <6.0 mm) were the most sensitive to high temperature, and the corresponding pollen viability at anthesis was consistent with the changes in the square development stage. Pollen tube growth in the styles was strongly inhibited by temperature above 35 °C, and the yield of cotton decreased because of the effect of high temperature during square development. The thermotolerance of hybrid F1 pollen showed heterosis, and pollen viability could be used as a criterion for screening for high-temperature tolerance cultivars. These results can be used in breeding to develop new cotton cultivars that can withstand high-temperature conditions, particularly in a future warmer climate.

Recognition specificity of self-incompatibility in Pyrus and Malus

Pyrus displays gametophytic self-incompatibility controlled by a single highly polymorphic gene complex termed S locus, which comprises a stylar-expressed gene (S-RNase) tighlty linked with a pollen expressed gene, that determines the specificity of the self-incompatibility locus. Deduced amino acid sequence of ‘Meigetsu’ S 8 -RNase in Pyrus pyrifolia and ‘Kuerlexiangli’ S 28 -RNase in P. sinkiangensis showed 100% identity. S 3 -RNase in Malus spectabilis was also found to be similar to S 8 -RNase in P. pyrifolia with 96.9% identity in the deduced amino acid sequence. The intron, which is generally highly polymorphic between alleles, was also remarkably well conserved within these allele pairs. The intron of PpS 8 -RNase showed 95.3 and 91.9% identity with PsS 28 -RNase and MsS 3 -RNase, respectively. Pollen tube growth in styles, pollen tube length in artificial media containing different S-RNases and segregation of S haplotypes in F1 plants revealed commonality of the recognition specificity between PpS 8 -RNase and PsS 28 -RNase and between PpS 8 -RNase and MsS 3 -RNase. Results suggested that PpS 8 -RNase, PsS 28 -RNase and MsS 3 -RNase have maintained the same recognition specificity after the divergence of the two species and that amino acid substitutions found between PpS 8 -RNase and MsS 3 -RNase do not alter the recognition specificity.

Is Eucalyptus Cryptically Self-incompatible?

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. 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. 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. 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.

(239) Evaluation of Self-compatibility in Clethra alnifolia

Clethra alnifolia, which is commonly known as summersweet, is an attractive deciduous shrub that produces fragrant flower in mid-summer. Breeding efforts are hampered by a lack of information on the reproductive behavior of this native species. The objective of this study was to evaluate self-compatibility in C. alnifolia. Pollen germination and pollen tube growth in styles were examined following self- and cross-pollinations using fluorescence microscopy. Seed set and germination were compared following self- and cross-pollinations. While self-pollen tubes appeared to grow slightly slower than cross-pollen tubes, there was no indication of a self-incompatibility system acting at the stigmatic or stylar level in C. alnifolia. Self-pollinations of `Hummingbird' and `Ruby Spice' produced fewer seeds than did cross-pollinations of these cultivars. Germination of all seed obtained from this study was too poor to allow a comparison of germination rates of the self- and cross-pollinated seed. However, because a few self-progeny were obtained, emasculation is recommended when making controlled pollinations. The presence of a late-acting self-incompatibility system or early acting inbreeding depression was proposed as being responsible for the lower seed set following self-pollination.

Reproductive Biology of Clethra alnifolia

Breeding efforts in Clethra alnifolia L., an ornamental shrub native to the Eastern U.S., are hindered by a lack of information on the reproductive behavior of this species. The objective of this study was to evaluate self-compatibility, time of stigma receptivity, and the relationship between time of pollen shed and stigma receptivity in C. alnifolia. Stigma receptivity and changes in floral morphology were monitored over a 7-day period beginning at flower opening. Pollen germination and pollen tube growth in styles were examined following self- and cross-pollinations using fluorescence microscopy. Seed set and germination were compared following self- and cross-pollinations. Anthers began to dehisce in `Hummingbird' and `Ruby Spice' the day after flowers opened, but stigmas did not become fully receptive to pollen until 2 days later. An increase in the length of pistils was observed following flower opening. Maximum elongation of pistils occurred at approximately the same time stigmas became receptive and could be utilized as an indicator of receptivity. While self-pollen tubes appeared to grow slightly slower than cross-pollen tubes, there was no indication of a self-incompatibility system acting at the stigmatic or stylar level in C. alnifolia. Self-pollinations of `Hummingbird' and `Ruby Spice' produced fewer seeds than did cross-pollinations of these cultivars. Germination of all seed obtained from this study was too poor to allow a comparison of germination rates of the self- and cross-pollinated seed. However, because a few self-progeny were obtained, emasculation is recommended when making controlled pollinations. The presence of a late acting self-incompatibility system or early-acting inbreeding depression was proposed as being responsible for the lower seed set following self-pollination.

Distyly and variation in floral traits in natural populations of Psychotria ipecacuanha (Brot.) Stokes (Rubiaceae)

Psychotria ipecacuanha is a perennial, medicinal herb that grows in clusters in the understory of humid, shady areas of the Atlantic Rain Forest of southeastern Brazil. The present study characterized the variation in floral traits among 35 clusters from three natural populations of this plant species. Field observations showed that the clusters are isomorphic, that is, a given cluster will either set long-styled or short-styled flowers. Stigmas and anthers are reciprocally placed in each morph, a dimorphism characteristic of distyly. The populations are isoplethic, that is, a given population exhibits an equilibrium 1:1 ratio of floral morphs. Morphometric analyses revealed that anther length, stigma length, corolla diameter, and pollen grain diameter were consistently greater in short-styled flowers, regardless of the population investigated. Significant differences for floral traits in the short-styled morph were found among populations. Floral traits in the long-styled morph also showed some significant differences among populations, but not for stigma height and corolla length. Controlled pollinations carried out in natural populations showed that fruit production was higher after inter-morph pollination. Nevertheless, observations of pollen tube growth in style, and also fruit production after spontaneous self-pollination and intra-morph pollination, indicated partial intramorph compatibility in this plant species.

Pollination Biology of Hydrangea macrophylla

Little information is available on the reproductive behavior of Hydrangea macrophylla (Thunb. Ex J.A. Murr.) Ser. The objectives of this study were to investigate time of stigma receptivity, viability of pollen from sterile flowers, and self-incompatibility in this popular ornamental shrub. Pollen germination and pollen tube growth in styles were examined using fluorescence microscopy. Stigma receptivity was examined in cross-pollinations made from 1 day before anthesis to 8 days after anthesis. Maximum stigma receptivity for the two cultivars examined occurred from anthesis to 4 days after anthesis. Viability of pollen from sterile flowers was evaluated through pollen staining and observations of pollen tube growth. No significant difference in percent stainable pollen between fertile and sterile flowers was observed in any of the six taxa examined. Pollen germination and pollen tube growth were studied in cross-pollinations made using pollen from fertile and sterile flowers of two cultivars. For both cultivars, pollen tubes from fertile and sterile flowers grew to the same length and had entered ovules by 72 hours after pollination. Self-incompatibility was evaluated by comparing pollen germination and pollen tube growth in cross- and self-pollinations. In the five taxa examined, self pollen tubes were significantly shorter than cross pollen tubes in flowers that were examined 72 hours after pollination. This finding indicates the presence of a gametophytic self-incompatibility system in H. macrophylla.

Pollen tube growth in styles of apple and almond flowers after spraying with pesticides

SummaryThe timing of fungicide and antibiotic applications in fruit crops often overlaps flowering and pollination. Numerous studies report detrimental effects of chemical applications on pollination, fruit set and yield. However, field results can be quite variable even when similar compounds are tested on the same crop. Problematic is that field variables unrelated to the effects of pesticides on reproductive activities can mask results. In the current study, we specifically investigated the effects of selected pesticide sprays applied to stigmas, on subsequent pollen germination and tube growth. Using two model systems, apple and almond, sprays were applied to detached emasculated flowers under constant laboratory conditions using an electronically controlled robotic apparatus which simulated a field sprayer. flowers were pollinated at specific times after spraying, and pollen tube numbers and growth assessed using fluorescence microscopy. The pesticides evaluated were for apple: captan, myclobutanil and streptomycin; and for almond: azoxystrobin, myclobutanil, iprodione and cyprodinil. In apple, captan significantly reduced pollen germination, by 20% compared with water controls when pollination was conducted 18 h after treatment. The number of tubes that reached the basal part of the style within 20 h was not affected. In contrast, myclobutanil and streptomycin had no significant effect on pollen tube growth. With almond, none of the sprays significantly affected pollen germination or tube growth.

Optimal pollination environment of tetraploid ginger ( Zingiberofficinale Roscoe) evaluated by in vitro pollen germination and pollen tube growth in styles

Pollen germination percentages in vitro of a tetraploid ginger ( Zingiber officinale Roscoe), ‘4×Sanshu’, tended to be highest at around 20°C. Pollen tube growth in the styles was greatly enhanced at 17°C, i.e., pollen tubes penetrated into the entire stylar length in 66.7% of the styles used. Pollen stored for at least 3 h under 40–80% relative humidity (RH) almost completely lost its germinability, whereas pollen incubated for up to 3 h under 100% RH retained a relatively higher germinability. Moreover, the pollen germinability that was lowered under 40–80% RH did not recover when the pollen was re-humidified for 2 h under 100% RH before inoculation onto a medium. When stigmas were pollinated with fresh pollen at 17°C under 100% RH, pollen tubes penetrated into the entire stylar length in 26.7% of the styles tested. Under 40–80% RH, however, pollen tubes stopped growing at the middle or the base of styles. From these results, I concluded that the optimal pollination environment of the tetraploid ginger was at 17–20°C under 100% RH.

INTERSPECIFIC AND INTERGENERIC FERTILIZATION BARRIERS IN BROMELIACEAE

Bromeliaceae are tropical ornamentals with a variety of colours and inflorescence shapes. To remain the interest of the public, breeders create new cultivars using interspecific and intergeneric hand-pollinations. In our breeding studies, 4 genera were used: Aechmea (2 species), Guzmania (3 species), Tillandsia (1 species) and Vriesea (3 species). In preparation of crossing experiments, two important flower characteristics were studied: pollen quality and stigma receptivity. Pollen germination of different flower stages was determined by an in vitro germination test. All species, except two of the Guzmania species, possessed viable pollen and germination was always highest at anthesis. Stigma receptivity was studied by pollinating flowers before, at and after anthesis. Pollen germination and pollentube growth on stigma were visualised with fluorescence microscopy (aniline blue staining). All species showed optimal stigma receptivity and ovule penetration at anthesis. Interspecific and intergeneric hand-pollinations were performed with pollen and stigma at anthesis stage. Pollen germination on stigma, pollentube growth in style and ovary and fertilization of ovules was evaluated using fluorescence microscopy. Five species were self-compatible, making emasculation necessary. Half of the interspecific and all of the intergeneric crosses were classified as incongruent because no ovules were fertilised (prefertilization barriers) or no seedlings developed (postfertilization barriers). Prefertilization barriers occurred in the style, mostly the lower part of the style. Only in crosses with the self-incompatible Aechmea species as mother or the extremely short-styled Tillandsia species as father, pollentube growth stopped in the upper part of the style. To understand more about these style barriers, the morphology of the pistil was studied. Styles of all species consisted of a hollow channel, covered with protein-rich cells. These ‘feeder’-cells also appeared on the placenta and the ovule funiculus. In this way, pollen tubes could be guided towards the micropyles. Further, Ca-oxalate and starch grains were observed in the style.

Expression of stylar incompatibility in the Andean clonal tuber crop oca ( Oxalis tuberosa Mol . , Oxalidaceae )

Long-, mid-, and short-styled clonal accessions of oca (Oxalis tuberosa) were intercrossed in a complete diallelic design. Pollen tube growth in styles was monitored in all diallelic crosses. Pollen fertility was estimated by two tests: staining of pollen grains with aceto-carmine and detection of β-galactosidase activity by the substrate X-Gal. The two methods of pollen fertility estimation were equally useful to detect fertility levels. Pollen originating from short stamens had the highest fertility (85%) and pollen from long stamens had the lowest fertility (70%). Pollen fertility was high throughout, but its degree varied with the stylar morph on which the pollen was formed. Long-styled accessions had the highest rates of fertile pollen. Differences in pollen fertility at different anther levels in the same style morph were also apparent. Pollen grain diameter of the six morph-anther level combinations was inversely correlated with pollen fertility. Pollen grains from long stamens were the largest and pollen grains from short stamens were the smallest. Neither pollen fertility nor pollen grain size had an influence on pollen tube growth in the style or on fruit and seed set. Pollen tubes growing within the styles were inhibited at a different level for each of the 18 cross combinations in the diallel. Although legitimate crosses had greatest pollen tube growth, some of the illegitimate inter- and intramorph crosses had equally high scores. Of all illegitimate crosses, mid-styled seed parents had the lowest level of stylar incompatibility. Fruit and seed set were highly correlated with the extent of pollen tube growth in the style. The number of pollen tubes entering ovules in a flower was in good agreement with the number of seeds produced per fruit. Therefore, it is concluded that stylar incompatibility is the major determinant of limited seed formation in oca even in the most successful legitimate cross combinations.

Regulation of LAT52 promoter activity during pollen tube growth through the pistil of Nicotiana alata .

The pollen-specific promoter of the LAT52 gene is known to direct expression of marker proteins during the last stages of pollen maturation and in very early pollen tube growth.We have examined the expression of LAT52-GUS during later stages of pollen tube growth in style and ovary of the relatively long-styled species Nicotiana alata. GUS activity was detected histochemically and found to be present in germinating pollen grains of N. alata and in tubes growing through the upper part of the style. No GUS activity was detected in 99% of the pollen tubes growing through the lower part of the style, but activity was present in tubes within the ovary. This finding indicates that the LAT52 promoter is regulated in growing pollen tubes, and is most active during the earliest and latest stages of pollen tube growth. GUS activity was also detected in some ovules, where it presumably marked the release of pollen tube cytoplasm into the ovule. The distribution of ovules with GUS activity within the ovary is not consistent with high-precision pollen tube guidance to the ovule.

The genetic control of self-incompatibility in Linanthus parviflorus (Polemoniaceae)

The genetic control of self-incompatibility (SI) was studied in the spring-flowering annual, Linanthus parviflorus (Polemoniceae). Arrays of full-siblings were cross-pollinated in a full-diallel design and compatibility relationships were assessed by examining for pollen tube growth in styles. Two to four incompatibility types were observed in each sibship, some types were interincompatible, and reciprocal differences in incompatibility between types were found. The results demonstrated close agreement with expected patterns of incompatibility among full-siblings for sporophytic control of SI with linear dominance. Taken together, these results provide support for sporophytic SI in L. parviflorus. The crossing data presented here are contrasted with results of a previous study indicating gametophytic control of SI in Phlox drummondii, another polemoniaceous species.

The genetic control of self-incompatibility in Linanthus parviflorus (Polemoniaceae)

The genetic control of self-incompatibility (SI) was studied in the spring-flowering annual, Linanthus parviflorus (Polemoniceae). Arrays of full-siblings were cross-pollinated in a full-diallel design and compatibility relationships were assessed by examining for pollen tube growth in styles. Two to four incompatibility types were observed in each sibship, some types were interincompatible, and reciprocal differences in incompatibility between types were found. The results demonstrated close agreement with expected patterns of incompatibility among full-siblings for sporophytic control of SI with linear dominance. Taken together, these results provide support for sporophytic SI in L. parviflorus. The crossing data presented here are contrasted with results of a previous study indicating gametophytic control of SI in Phlox drummondii, another polemoniaceous species.

Influence of High Temperature on Pollen Grain Viability and Pollen Tube Growth in the Styles of Phaseolus vulgaris L.1

Abstract Four cultivars of Phaseolus vulgaris L. were studied in a growth chamber experiment to determine the effect of high temperature stress on pollen viability and pollen tube growth in styles. Compared with an optimal growing temperature (25/20°C, day/night), stress temperatures (35/20°, day/night or 35° constant) reduced the percentage of viable pollen for all cultivars, but cultivar differences were apparent. Beans generally produced only small quantities of pollen under normal growing temperatures but much more under high temperatures, again with cultivar differences. Finally, stress temperatures did not reduce the ability of pollen tubes to grow to the base of the style. Our results suggest that injury to pollen at high temperatures up to 35° is not likely to hinder the ability of beans to set pods.

Duration of Pistil Receptivity, Fruit Set, and Seed Production in Rabbiteye and Tetraploid Blueberries

Abstract Rate of pollen tube growth in styles of cross-pollinated rabbiteye (Vaccinium ashei Reade) and tetraploid highbush blueberries were adequate to induce a commercial fruit set when pollinated up to 6 days after emasculation. Varying intervals between emasculation and pollination, up to 6 days, did not consistently influence percentage fruit set and number of seeds produced per fruit.

Inactivation of self-incompatibility following temperature pretreatments of styles in Lilium longiflorum

Incompatible (self) pollen tube growth in styles of six cultivars of L. longiflorum is strikingly influenced by treatment of the styles for six minutes in 50°C distilled water prior to pollination. In pretreated detached styles the incompatible pollen tubes reach lengths normally attained by compatible pollen whereas in untreated styles they grow to only approximately two-thirds the length normally reached by compatible tubes. Pretreatment at either 25°C or 45°C for six minutes does not affect incompatible pollen tube growth. Both compatible and incompatible tubes grow only a few millimeters into styles treated at 55°C for six minutes. Stigmatoid cells in these styles appear necrotic. Pretreatment of attached styles at 50°C for six minutes resulted in fruit set following self-pollination. Seed number per capsule ranged from 6 to 114. Stylar pretreatment appears to be a highly promising approach to further investigation concerning the nature of the self-incompatibility reaction. It also appears to offer a suitable means of obtaining seed from self-incompatible plants.