Pollination adaptations of group-by-group stamen movement in a meadow plant with temporal floral closure

Floral sexual organ (stamen and pistil) movements are selective adaptations that have different functions in male-female reproduction and the evolution of flowering plants. However, the significance of stamen movements in the spatial–temporal function and separation of male and female organs has not been experimentally determined in species exhibiting floral temporal closure. The current study investigated the role of slow stamen (group-by-group) movement in male-female sexual function, and the effect of stamen movement on pollen removal, male-male and male-female interference, and mating patterns of Geranium pratense, a plant with temporal floral closure. This species uses stamen group-by-group movement and therefore anther-stigma spatial–temporal separation. Spatial separation (two whorls of stamen and pistil length) was shown to be stronger than temporal separation. We found that stamen movements to the center of the flower increase pollen removal, and the most common pollinators visited more frequently and for longer durations during the male floral stage than during the female floral stage. Petal movements increased both self-pollen deposition rate and sexual interference in G. pratense. The fruit and seed set of naturally and outcrossed pollinated flowers were more prolific than those of self-pollinated flowers. Group-by-group stamen movement, dehiscence of stamens, pistil movement, and male-female spatial–temporal functional separation of G. pratense before floral temporal closure may prevent male-female and stamen-stamen interference and pollen discounting, and may increase pollen removal and cross-pollination.     

Male × female interaction for a pre-copulatory trait, but not a post-copulatory trait, among cosmopolitan populations of Drosophila melanogaster

Sexual coevolution occurs when changes in the phenotype of one sex select for changes in the other sex. We can identify the "footprint" of this coevolution by mating males and females from different populations and testing for a male-female genotype interaction for a trait associated with male (or female) performance. Here we mated male Drosophila melanogaster from five different continents with females from their own and different continents to test for a male-female interaction for mating speed, a pre-copulatory trait, and female reproductive investment, a post-copulatory trait. We found a strong male-female interaction for mating speed, consistent with previous studies using different populations, suggesting that the potential for sexual coevolution for this trait is present in this species. In contrast, we did not detect a male-female interaction for female reproductive investment. Although a male-female interaction for mating speed is compatible with the hypothesis of ongoing sexual coevolution, the nature of our experimental design is unable to exclude alternate explanations. Thus, the evolutionary mechanisms promoting male-female genotype interactions for pre-copulatory mating traits in D. melanogaster warrant further investigation.     

湖北黄精大小孢子发生及雌雄配子体发育

【目的】研究湖北黄精花部形态结构特征和大小孢子发生及雌雄配子体发育过程,以丰富黄精属植物的生殖生物学理论,为进一步开展湖北黄精的品种选育提供依据。【方法】以不同发育时期的湖北黄精花芽为试验材料,用显微观察法观察花部形态结构特征,石蜡切片技术对单花雌雄蕊进行切片观察。【结果】湖北黄精的花被为白色或淡黄绿色,花被筒近喉部稍缢缩;具6枚雄蕊,花丝下端与花被合生,花药开裂方式为纵裂;雌蕊子房上位,3心皮,花柱与子房等长。湖北黄精花药壁由4层细胞组成,成熟的绒毡层具多核,绒毡层发育类型为分泌型;小孢子母细胞减数分裂为连续型,四分体呈左右对称型排列,成熟花粉粒为2-细胞型;存在小孢子发育不同步的现象。雌蕊胚珠具双珠被、厚珠心;四分体呈直线型排列,胚囊发育类型为蓼型;存在双胚囊胚珠现象。在雄蕊的花药壁和雌蕊的子房壁都观察到有束状草酸钙针晶。【结论】湖北黄精雌雄蕊具有较原始的发育特征,虽然在发育过程中都存在异常现象,但雄蕊最终能形成正常的雄配子体,雌蕊低频率的双胚囊现象对总体受精结果影响很小。湖北黄精杂交育种可以选择花药开裂前一时期的花粉,花药壁和子房壁观察到的束状草酸钙针晶无法作为湖北黄精物种鉴定的...     

柽柳大、小孢子发生和雌、雄配子体发育的观察

利用常规石蜡制片技术,对柽柳(Tamarix chinensis Lour.)的大、小孢子发生及雌、雄配子体发育过程进行了观察。主要结果如下:(1)花药壁由五层细胞组成,从外向内分别为表皮、药室内壁,两层中层和绒毡层。药壁的发育属于基本型。绒毡层为分泌型。(2)孢原细胞为多孢原起源。小孢子母细胞减数分裂过程中的胞质分裂为连续型,形成的四分孢子为四面体型;同一药室的小孢子母细胞减数分裂几乎完全同步。(3)成熟花粉粒为2细胞型,具3个萌发孔。(4)柽柳为三心皮构成的单室复子房,每子房具有10~20个胚珠,基底胎座,胚珠为双珠被、厚珠心、倒生型。大孢子母细胞减数分裂形成1+3排列的4个大孢子, 4个大孢子全部参与胚囊的形成。(5)胚囊发育为贝母型,反足细胞在胚囊成熟时充分发育。(6)同一朵花中,前期雄蕊的发育早于雌蕊的发育,后期当花粉成熟时,雌配子体也达到成熟,雌雄蕊发育趋于同步。     

羊草大、小孢子发生与雌、雄配子体发育的观察

利用常规石蜡制片技术研究了羊草大、小孢子发生及雌、雄配子体发育过程。主要结果是：(1)花药壁由4层结构组成,最外层为表皮,其次为药室内壁,1层中层,最内层绒毡层为分泌型;(2)小孢子母细胞减数分裂过程中的胞质分裂为连续型,四分孢子为左右对称型;(3)成熟花粉粒为3细胞型,具单萌发孔;(4)羊草为单子房、单胚珠,双珠被、薄珠心、倒生型胚珠,大孢子母细胞减数分裂形成线型或T型排列的4个大孢子;合点端大孢子具功能;(5)具有双孢原,双大孢子母细胞、双大孢子四分体和双胚囊的情况;(6)胚囊发育为蓼型,反足细胞经无丝分裂形成4～6个细胞的反足细胞群;(7)同一朵花中,前期雄蕊的发育早于雌蕊的发育,后期当花粉成熟时,雌配子体也达到成熟,雌雄蕊发育趋于同步。     

The arrest of development of abortive reproductive organs in the unisexual flower of<Emphasis Type="Italic"> Vitis vinifera</Emphasis> ssp.<Emphasis Type="Italic"> silvestris</Emphasis>

During the first stages of development, flowers of most dioecious species are hermaphroditic, with their transition to unisexual flowers being the result of the developmental arrest of one set of reproductive organs. In this work, we describe the development of male and female flowers of the dioecious wild grape species Vitis vinifera ssp. silvestris through scanning electron microscopy analysis and cytological observations, focusing our attention on the transition from bisexual to unisexual development. We divide floral development of the wild grape into eight stages. Differences between male and female flowers appear first at stage 6, when the style and stigma start to differentiate in female but not in male flowers. Cytological analysis of the slowly growing abortive pistil of male flowers shows that megagametophyte formation is, surprisingly, not inhibited. Instead of pistil abortion in the male flower, sexual determination is accomplished through programmed death of external nucellus cells and some layers of integumentary cells. Sterility of male structures in female flowers follows a different pattern, with microspore abnormalities evident from the time of their release from the tetrad. Sterile microspores and pollen grains in female flowers display an abnormal round shape, lacking colpi and possessing uniformly thickened cell walls that impede germination.     

ATP binding cassette transporters ABCG1 and ABCG16 affect reproductive development via auxin signalling in Arabidopsis

Angiosperm reproductive development is a complex event that includes floral organ development, male and female gametophyte formation and interaction between the male and female reproductive organs for successful fertilization. Previous studies have revealed the redundant function of ATP binding cassette subfamily G (ABCG) transporters ABCG1 and ABCG16 in pollen development, but whether they are involved in other reproductive processes is unknown. Here we show that ABCG1 and ABCG16 were not only expressed in anthers and stamen filaments but also enriched in pistil tissues, including the stigma, style, transmitting tract and ovule. We further demonstrated that pistil‐expressed ABCG1 and ABCG16 promoted rapid pollen tube growth through their effects on auxin distribution and auxin flow in the pistil. Moreover, disrupted auxin homeostasis in stamen filaments was associated with defective filament elongation. Our work reveals the key functions of ABCG1 and ABCG16 in reproductive development and provides clues for identifying ABCG1 and ABCG16 substrates in Arabidopsis.     

Gender specialization and factors affecting fruit set of the wind-pollinated heterodichogamous Juglans regia

Gender expression, flowering phenology, reproductive performance and factors affecting fruit set (i.e., flowering synchrony, size and distance to the nearest pollen donor) were investigated in a cultivated population of a wind-pollinated self-compatible heterodichogamous Juglans regia (Juglandaceae). Four flowering morphs, (i.e., protandrous, protogynous, male and female) were observed. The sexual functions of the protandrous and protogynous morphs were almost synchronous; however, they were not reciprocal, and the separation of male and female flowering within most monoecious individuals was not complete. Thus, within-morph mating and geitonogamous pollination may be common. The ratio of protandrous versus protogynous morphs was biased towards the protandrous morph, but the fruit set did not differ between the morphs, suggesting that the fruit set of the protandrous morph could be partly compensated by within-morph pollination. The ratio of the female flower number or fruit number to the total male catkin length was higher in the protogynous morph than in the protandrous morph and did not vary with plant size, suggesting that gender variation was not size dependent and that the sexual function of protandrous morphs was more male biased. Fruit set depended on plant size only for protandrous morphs. The fruit set of individual plants decreased with increasing distance to the nearest pollen donor regardless of morph, possibly because of pollen limitation. The fruit set of individual plants increased with flowering synchrony, indicating that flowering synchrony could affect reproductive success.     

Ovary and Gametophyte Development Are Coordinately Regulated by Auxin and Ethylene following Pollination

The differentiation and development of ovules in orchid flowers are pollination dependent. To define the developmental signals and timing of critical events associated with ovule differentiation, we have examined factors that regulate the initial events in megasporogenesis and female gametophyte development and characterized its progression toward maturity and fertilization. Two days after pollination, ovary wall epidermal cells begin to elongate and form hair cells; this is the earliest visible morphological change, and it occurs at least 3 days prior to pollen germination, indicating that signals associated with pollination itself trigger these early events. The effects of inhibitors of ethylene biosynthesis on early morphological changes indicated that ethylene, in the presence of auxin, is required to initiate ovary development and, indirectly, subsequent ovule differentiation. Surprisingly, pollen germination and growth were also strongly inhibited by inhibitors of ethylene biosynthesis, indicating that male gametophyte development is also regulated by ethylene. Detailed characterization of the development of both the female and male gametophyte in pollinated orchid flowers indicated that pollen tubes entered the ovary and grew along the ovary wall for 10 to 35 days, at which time growth was arrested. Approximately 40 days after pollination, coincident with ovule differentiation as indicated by the presence of a single archesporial cell, the direction of pollen tube growth became redirected toward the ovule, suggesting a chemical signaling between the developing ovule and male gametophyte. Taken together, these results indicate that both auxin and ethylene contribute to the regulation of both ovary and ovule development and to the coordination of development of male and female gametophytes.     

Distinct expression of members of the LHT amino acid transporter family in flowers indicates specific roles in plant reproduction

Sexual plant reproduction necessitates proper development of pollen, pollen germination and tube growth through various tissues of the pistil, the female organ of the flower. Finally, sperm cells are released to fertilize the female gametophyte. These processes require high metabolic activities of all tissues involved and rely on the delivery of nitrogen assimilates for success. However, transporters mediating nitrogen fluxes are mostly unknown. The presented work provides an expression analysis of members of the LHT amino acid transporter family in relation to pollen development and pollen–pistil interaction. Expression of Arabidopsis LHTs was analyzed during flower development and the location of LHT function resolved by transporter-GFP and promoter-GUS studies. GFP-LHT localization in onion cells indicates that all LHTs analyzed are targeted to the plasma membrane. We further showed that LHTs are expressed in anthers and male gametophytes where they are proposed to function in transport of amino acids for pollen development and maturation. Expression in germinating pollen, pollen tubes and transmitting tissue of the pistil points to a role of LHTs in support of the fertilization process. Overall, our study suggests that LHT function in flowers is cell or tissue specific, developmentally regulated and highly coordinated between male and female tissue.     

楸树大小孢子发生与雌雄配子体发育的研究

运用石蜡切片法和整体透明法对楸树(Catalpa bungei C.A.Meyer)大、小孢子发生及雌、雄配子体发育过程进行了研究.结果表明:楸树可育雄蕊2枚,花药4室,药壁发育属双子叶型,腺质异型绒毡层.小孢子母细胞减数分裂为同时型,四分体后小孢子不分离形成正四面体型四合花粉,偶有左右对称型和十字交叉型.成熟花粉为二细胞型,无萌发孔.子房上位,2室,中轴胎座,胚珠多数,倒生,单珠被,薄珠心,具珠被绒毡层.单孢原直接发育为大孢子母细胞,四分体线形排列,合点端大孢子发育为功能大孢子,胚囊发育为蓼型.雄蕊发育早于雌蕊,花开后雌、雄蕊趋于同熟.研究认为:虽然楸树雌、雄蕊发育过程中均存在一定比例的败育,但其花而不实"并非雄性或雌性不育所致.推测与其授粉受精和胚后发育有关.     

The joint evolution of mating system and pollen performance: Predictions regarding male gametophytic evolution in selfers vs. outcrossers

Studies of sexual selection in plants historically have focused on pollinator attraction, pollen transfer, gametophytic competition, and post-fertilization discrimination by maternal plants. Pollen performance (the speeds of germination and pollen tube growth) in particular is thought to be strongly subject to intrasexual selection, but the effect of mating system on this process has not been rigorously evaluated. Here we propose four predictions derived from the logic that pollen performance should evolve with mating system as an adaptive response to: (1) the competitive environment among pollen genotypes and (2) variation among female genotypes regularly encountered by a given pollen genotype. First, as previously predicted, due to the higher potential for intense selection among diverse pollen genotypes in outcrossing relative to selfing taxa, pollen should evolve to germinate and/or to grow more rapidly in outcrossers than in selfers. Second, due to stronger selection on pollen performance in outcrossing than in selfing taxa, heritable variation in pollen tube growth rate is more likely to be purged in outcrossers. In selfers, by contrast, genetic variation in pollen tube growth rates may readily accumulate because selfing reduces the number of genetically distinct male gametophytes likely to be deposited on any given stigma, thereby relaxing selection on male gametophytic traits. A summary of published studies presented here provides preliminary support for this prediction. Third, due to the high probability that the pollen of outcrossing individuals will be exposed to multiple pistil genotypes, we predict that the pollen of habitually outcrossing taxa will evolve to perform more consistently across female genotypes than the pollen of selfing taxa. Fourth, we predict that epistatic interactions between pollen and pistil genotypes are more likely to evolve in selfers than in outcrossers. We suggest several empirical approaches that may be used to test these predictions.     

Variation in sex allocation and male-female trade-offs in six populations of Collinsia parviflora (Scrophulariaceae s.l.)

Assumed trade-offs between male and female functions in hermaphroditic flowers have been difficult to demonstrate. Collinsia parviflora (Scrophulariaceae) is a winter annual that exhibits significant among-population variation in corolla size in British Columbia, Canada. We asked whether reduction in secondary male allocation (i.e., the attractive corolla), a preliminary indicator of mating system, was matched by a reduction in primary male allocation (i.e., pollen production), and whether there were allocation trade-offs between male and female function both within and among six study populations. Larger-flowered populations allocated more to male function (androecium and corolla biomass), and because populations did not vary in female biomass allocation (gynoecium and calyx), population differences were not due to simple allometric scaling. Populations also differed in per-flower gamete production (pollen and ovules). We found male-female trade-offs within populations between androecium and gynoecium mass and between corolla and calyx mass. Among populations, there was a marginal trade-off between pollen and ovule production and a significant within-male trade-off between pollen grain size and number. Trade-offs between the sexes were primarily apparent when we controlled for flower size in the analysis. Variation among populations in sex allocation may reflect different optima related to the mating system.     

高等植物受精过程中雌-雄相互作用的分子调控机制

从广义上讲,被子植物的受精过程是指花粉粒落到柱头上萌发形成花粉管,花粉管穿过柱头沿着引导组织生长进入子房内,最终在胚囊中实现精细胞与卵细胞以及中央细胞分别融合从而起始胚胎和胚乳的发育．被子植物的精细胞由于不具有鞭毛而无法自由移动,因此在受精过程中需要借助于花粉管来将精细胞运送到胚囊中．花粉管通过与雌性的孢子体组织之间的相互作用和识别将精细胞准确地运送到胚珠附近,而最终将精细胞准确地运送到胚囊内的过程则是受到了雌配子体细胞的控制．可以说,受精的成功实现有赖于雌性和雄性细胞之间的持续的识别和相互作用,这种互作具有多样性和阶段特异性．本文将主要综述被子植物受精过程中花粉粒以及花粉管与多种雌性孢子体组织以及雌配子体之间的信号互作研究．     

From pollination to fertilization in fruit trees

The phase that elapses from pollination to fertilization is re-examined giving special attention to pollen pistil interaction in compatible matings. Pollination induces an activation of the pistil. A number of changes take place in the different tissues of this organ that appear to support male gametophyte development and to assist fertilization. Thus pollination induces stigma secretion, the release of starch from the transmitting tissue and prolongs embryo sac viability. It appears that even those pollen grains that do not achieve fertilization have a synergistic role supporting others to do so.The pistil also has an effect on pollen tube growth. Pollen tube growth along the pistil is not continuous, accelerations and decelerations take place depending on the different tissues they traverse. The fact that pollen tube growth is heterotrophic, at the expenses of the pistil reserves, and that these reserves are not continuously produced confers the pistil with a role controlling pollen tube growth kinetics.     

Temperatures during flower bud development affect pollen germination,self‐incompatibility reaction and early fruit development of clementine (Citrus clementina Hort. ex Tan.)

• One of the key environmental factors affecting plant reproductive systems is temperature. Characterising such effects is especially relevant for some commercially important genera such as Citrus. In this genus, failure of fertilisation results in parthenocarpic fruit development and seedlessness, which is a much‐prized character. Here, we characterise the effects of temperature on flower and ovary development, and on pollen–pistil interactions in ‘Comune’ clementine (Citrus clementina Hort. ex Tan.).
• We examine flower bud development, in vitro pollen germination and pollen–pistil interaction at different temperatures (15, 20, 25 or 30 °C). These temperatures span the range from ‘cold’ to ‘hot’ weather during the flowering season in many citrus‐growing regions.
• Temperature had a strong effect on flower and ovary development, pollen germination, and pollen tube growth kinetics. In particular, parthenocarpic fruit development (indicated by juice vesicle growth) was initiated early if flowers were exposed to warmer temperatures during anthesis.
• Exposure to different temperatures during flower bud development also alters expression of the self‐incompatibility reaction. This affects the point in the pistil at which pollen tube growth is arrested and confirms the role of sub‐ and supra‐optimal temperatures in determining the numbers of pollen tubes reaching the ovary.

     

Arabidopsis hapless mutations define essential gametophytic functions

In flowering plants, the egg develops within a haploid embryo sac (female gametophyte) that is encased within the pistil. The haploid pollen grain (male gametophyte) extends a pollen tube that carries two sperm cells within its cytoplasm to the embryo sac. This feat requires rapid, precisely guided, and highly polarized growth through, between, and on the surface of the cells of the stigma, style, and ovary. Pollen tube migration depends on a series of long-range signals from diploid female cells as well as a short-range attractant emitted by the embryo sac that guides the final stage of tube growth. We developed a genetic screen in Arabidopsis thaliana that tags mutant pollen with a cell-autonomous marker carried on an insertion element. We found 32 haploid-disrupting (hapless) mutations that define genes required for pollen grain development, pollen tube growth in the stigma and style, or pollen tube growth and guidance in the ovary. We also identified genomic DNA flanking the insertion element for eleven hap mutants and showed that hap1 disrupts AtMago, a gene whose ortholog is important for Drosophila cell polarity.     

The evolutionary dynamics of self-incompatibility systems

Self-incompatible flowering plants reject pollen that expresses the same mating specificity as the pistil (female reproductive tract). In most plant families, pollen and pistil mating specificities segregate as a single locus, the S locus. In at least two self-incompatibility systems, distinct pollen and pistil specificity genes are embedded in an extensive nonrecombining tract. To facilitate consideration of how new S locus specificities arise in systems with distinct pollen and pistil genes, we present a graphical model for the generation of hypotheses. It incorporates the evolutionary principle that nonreciprocal siring success (cross-pollinations between two plants produce seeds in only one direction) tends to favor the rejecting partner. This model suggests that selection within S-allele specificity classes could accelerate the rate of nonsynonymous (amino acid-changing) substitutions, with periodic selective sweeps removing segregating variation within classes. Accelerated substitution within specificity classes could also promote the origin of new S-allele specificities.