3种生殖方式蒲公英花粉活力和柱头形态及可授性对比

利用离体萌发法、电镜扫描和联苯胺-过氧化氢法对有性生殖的东北蒲公英、专性无融合生殖的丹东蒲公英和兼性无融合生殖的蒙古蒲公英花粉活力、柱头表面形态及可授性进行观察和测定。结果显示:(1)3种蒲公英柱头均为干柱头,单细胞乳突,属于原始进化类型,都存在雌雄异熟和雌雄异位花部特征;东北蒲公英乳突饱满、紧密,蒙古蒲公英次之,丹东蒲公英干瘪、稀少。(2)东北蒲公英和丹东蒲公英柱头呈Y状时期花粉萌发率最高,分别为67.3%和19.8%,蒙古蒲公英柱头呈棒状时期萌发率最高,为23.3%。(3)3种蒲公英随着开花进行,柱头可授性增加,并且柱头在大Y状时期3种蒲公英为最佳授粉期,可授性柱头占样本柱头的比率分别是98.7%(东北蒲公英)、84.0%(蒙古蒲公英)、21.3%(丹东蒲公英)。研究表明,有性生殖蒲公英与无融合生殖蒲公英在花粉萌发力、柱头可授性和乳突上产生明显差别,为蒲公英在长期进化中性器官能量再分配提供证据。     

斜翼致濒原因探讨

斜翼是一个濒于灭绝的单型科植物。国内产地由于植被破坏导致居群及个体数量十分稀少。斜翼花开后自行脱落,胚囊成熟后逐渐退化、败育;花粉败育率为３８％。有性生殖障碍是该种植物个体数量稀少的主要原因,其生殖障碍可能主要是传粉和授精不能正常进行,并导致胚襄败育。应严格保护现有植株,并进行分株移植,以保存该物种。     

长春蒲公英雄性不育株形态学观察与败育细胞学研究

在长春蒲公英(Taraxacum junpeianum Kitam.)株群中发现雄性不育现象,为研究其败育机理及特点,探寻其不育基因,采用形态观察法、石蜡切片技术和染色体压片法,对长春蒲公英野生型及其雄性不育株的花药发育过程和花粉母细胞减数分裂过程进行了观察。结果表明:(1)长春蒲公英雄性不育株花药中部发红、干瘪、无花粉散出。与野生型比较,雄性不育株雄蕊更短,子房更窄,种子形态更加狭长;(2)长春蒲公英雄性不育株败育时期为四分体到单核小孢子前期,败育方式为小孢子自身异常发育,绒毡层异常分解,互相粘连败育;(3)长春蒲公英雄性不育株花粉母细胞减数分裂二分体时期出现落后微核,随后产生极少四分体,并且四分体产生大量染色体桥,小孢子营养物质流失,彻底败育。因此,长春蒲公英雄性不育株败育彻底、稳定,并且有种的特点。小孢子自身异常发育和绒毡层异常分解是导致败育的主要原因。     

稻类雄性不育系的花粉败育途径研究

对水、旱稻５ 个两系不育系和１ 个三系不育系的花粉败育途径的观察发现,野败三系不育系珍汕９７Ａ 和３ 个两系不育系是以核退化为典型特征的花粉败育途径,其败育时期发生在单核晚期。新选育成的旱稻昆植Ｓ－１ 和水稻昆植Ｓ－２两个两系不育系则是以核增生为典型特征的花粉败育途径。对两类花粉败育途径的细胞学特点和不育的稳定性进行了比较分析     

雄性不育小孢子发育的解剖结构及其生理变化

雄性不育花粉败育的类型和发生的时期是多种多样的,同一种植物在花粉发育过程中的每一个时期都可能发生败育。Laser等(1972)指出:不育化粉的败育,在双子叶植物中多发生于四分体形成之前,单子叶植物多发生于小孢子的后期或双核期。     

甜菜无融合生殖单体附加系M14花粉发生与发育的超微结构研究

运用透射电子显微镜技术,对甜菜无融合生殖单体附加系M14的小孢子发生、雄配子体发育以及相应的花药壁发育过程进行超微结构的观察研究,以阐明甜菜无融合生殖单体附加系M14花粉发生与发育超微结构特点以及花粉败育的时期和败育的细胞学特征.结果显示:(1)小孢子母细胞减数分裂正常,分裂期间细胞质具有明显的"细胞质改组"现象,主要表现在核糖体减少,质体、线粒体的结构发生规律性的变化,有利于孢子体向配子体的转变.M14减数分裂的胞质分裂为同时型,前期Ⅱ和中期Ⅱ形成"细胞器带";正常发育的花粉,小孢子分裂形成营养细胞和生殖细胞;生殖细胞脱离花粉壁,生殖细胞游离于营养细胞的细胞质中,最初具细胞壁,而后消失,且生殖细胞壁成分与花粉内壁成分相似.(2)三细胞型的成熟花粉含有一个营养细胞和两个具有尾突的精子;每个精子通过两层质膜与营养细胞隔开,含有一个大的精核,长尾突内含少量的细胞质以及纤丝状结构.(3)生殖细胞和精子中缺乏质体.(4)花粉的败育起始于小孢子,大部分受阻于单核-二细胞花粉期,其败育特征为花粉内液泡吞噬作用导致细胞器解体,绒毡层细胞过早解体或肥大生长致使营养供应受阻,可能是导致单核-二细胞花粉败育的主要细胞学原因.研究表明,白花甜菜第九号染色体的附加可能是导致M14大量花粉败育的遗传学因素.     

新疆蒲公英属一新种

本文报道了新疆产蒲公英属植物一新种——新源蒲公英Taraxacum xinyuanicum D．T．Zhai et Z. X．An,并对其模式产地种群中其它个体的形态变异做了进一步的说明,同时还指出它与药用蒲公英 T.officinale Wigg．和堆叶蒲公英T．compactum Schischk 的异同;花粉体积变异、败育率和染色体数目的统计表明它是一个二倍体,与后面的两个多倍体种有明显的差别。     

高温敏感不育水稻育性敏感期幼穗和叶片中的总RNA含量变化(简报)

在育性敏感的两个时期──花粉母细胞形成期和花粉母细胞减数分裂期,１３５６Ｓ和衡农Ｓ－２不育株幼穗的总ＲＮ Ａ含量极显著低于可育株,分别是可育株的４２．３％、４６．５％、４１．８％和４０．１％,这必然影响花粉母细胞形成及分裂所必需的蛋白质的合成,以致花粉不能正常发育,最终导致花粉败育。     

广东高州普通野生稻与粳稻杂交F1花粉育性及其发育特点

以粳稻台中65为母本,高州普通野生稻141个编号材料为父本,成功组配72个粳野杂种F1,分别对杂种F1的结实率、花粉育性及其发育特点进行研究。结果发现,粳野杂种F1平均结实率为68.30％,变化范围为30.29％～94.05％,大部分在50％～80％之间;花粉平均育性为76.49％,最低为33.23％,最高为95.72％,大部分都高于70％,表现正常。花粉败育类型包括染败、典败、圆败和大小花粉粒;花药的平均裂药指数为3.87,接近正常。粳野杂种F1花粉发育过程与栽培稻基本一致,可分为8个时期,包括小孢子母细胞形成期、小孢子母细胞减数分裂期、小孢子早期、小孢子中期、小孢子晚期、二胞花粉早期、二胞花粉晚期和成熟花粉期。研究结果表明广东高州普通野生稻可能具有决定杂种F1花粉育性的不同基因,包括花粉不育中性基因等。     

两份太空诱变玉米雄性不育突变体的遗传研究

从搭载神舟4号飞船的4份玉米自交系后代中选育出两份雄性不育突变体, 对其进行育性鉴定, 并分析不育性状的稳定性及遗传特点。以不育材料的不育株为母本, 同群体的可育株和其他自交系为父本进行杂交, 结合自交、回交分析其后代的育性表现; 同时, 以具有正常细胞质的自交系为母本, 育性完全恢复的测交F1植株为父本进行反交, 对其反交的F1及F2进行育性观察分析。结果表明：这两份不育材料不育株的花药内无花粉或含少量畸形花粉, 败育彻底, 花粉败育表现为典败型。不育性状在不同年份、不同季节、不同地点下稳定遗传, 属可遗传的单基因控制的隐性核不育类型。     

The Significance of Agamospermous Triploid Pollen Donors in the Sexual Relationships between Diploids and Triploids in Taraxacum (Compositae)

Abstract We review in this article the investigations of the significance of agamospermous triploid pollen donors in the sexual relationships between diploids and triploids in Taraxacum . Crossing experiments between diploid sexual mother plants and agamospermous polyploid pollen donors and recent isozyme analyses of the progeny have exhibited the following results: 1) Pollen from Agamospermous polyploid pollen donors have the potential to give rise to the polyploid agamospermous offspring when fertilizing diploid sexual plants. Ploidy level of the progeny is usually the same or higher, but occasionally lower, compared to the pollen donor. 2) Diploid progeny also occur from diploid (♀)-polyploid (♂) crosses, however, these diploids were in our results not hybrids but the results of self-fertilization of the diploids. The self-fertilization is regarded as a cosequence of the breakdown of the self-incompatibility barrier through the sterile triploid's pollen. This breakdown is in all probability a common phenomenon in diploid (♀)-polyploid (♂) crosses. Some examples suggest that agamospermous polyploids can increase their genetic diversity through obtaining genes from coexisting diploids. The evolutionary implications of this phenomenon and the reduction mechanism of chromosome number through agamospermous pollengenesis are discussed.     

Formation of a hybrid triploid agamosperm on a sexual diploid plant: evidence from progeny tests in Taraxacum platycarpum Dahlst.

Agamospermous dandelions of hybrid origin between a native sexual diploid species (Taraxacum platycarpum Dahlst. or T. japonicum Koidz.) and an alien agamospermous triploid [T. officinale Weber and T. laevigatum (Willd.) DC.] are now widely distributed throughout mainland Japan. These hybrid dandelions are known to be genetically variable. We hypothesized that this variability is maintained by repeated ongoing hybridization, based on the fact that triploid dandelions not only produce seeds agamospermously, but also produce some functional pollen grains that are able to sire seeds of sexual dandelions. To test this hypothesis, we examined whether heads of Japanese diploid dandelions produce new hybrid seeds after fertilization by pollen from triploid agamosperms under field conditions. One of the 430 tested plants grown from sexual dandelion seeds had morphological and molecular characteristics, which are consistent with a hybrid origin. The plant formed a hybrid surrounded by many individuals having recurved involucral bracts, in which frequency of T. officinale was very low (3.5 %). Cytological data and bagging experiments demonstrate triploidy and asexual seed production of the hybrid. Taken together, these results supported that the new hybrid is probably derived from a backcross of a hybrid to the native sexual species. Our findings provide evidence for the evolution of a new agamosperm through interspecific hybridization as a contemporary population process.     

Apomixis and ploidy barrier suppress pollen-mediated gene flow in field grown transgenic turf and forage grass (Paspalum notatum Flüggé)

Bahiagrass (Paspalum notatum Flüggé) is the predominant forage grass in the southeastern US. The commercially important bahiagrass cultivar ‘Argentine’ is preferred for genetic transformation over sexual diploid cytotypes, since it produces uniform seed progeny through apomixis. Pseudogamous apomictic seed production in Argentine bahiagrass may contribute to transgene confinement. It is characterized by embryo development which is independent of fertilization of the egg cell, but requires fertilization with compatible pollen to produce the endosperm. Pollen-mediated gene transfer from transgenic, glufosinate-resistant apomictic bahiagrass as pollen donor at close proximity (0.5–3.5 m) with non-transgenic sexual or apomictic bahiagrass cultivars as pollen receptors was evaluated under field conditions. Hybridization frequency was evaluated by glufosinate herbicide resistance in >23,300 seedlings derived from open-pollinated (OP) pollen receptor plants. Average gene transfer between transgenic apomictic, tetraploid and sexual diploid bahiagrass was 0.03%. Herbicide-resistant hybrids confirmed by immuno-chromatographic detection of the PAT protein displayed a single copy bar gene identical to the pollen parent. Hybrids resulting from diploid pollen receptors were confirmed as triploids or aneu-triploids with significantly reduced vigor and seed set as compared to the parents. Transmission of transgenes to sexual bahiagrass is severely restricted by the ploidy difference between tetraploid apomicts and diploid sexual bahiagrass. Average gene transfer between transgenic apomictic tetraploid and non-transgenic, apomictic tetraploid bahiagrass was 0.17%, confirming a very low frequency of amphimixis in apomictic bahiagrass cultivars. While not providing complete transgene containment, gene transfer between transgenic apomictic and non-transgenic bahiagrass occurs at a much lower frequency than reported for other cross-pollinating or facultative apomictic grasses.     

Attack of the clones: reproductive interference between sexuals and asexuals in the Crepis agamic complex

Negative reproductive interactions are likely to be strongest between close relatives and may be important in limiting local coexistence. In plants, interspecific pollen flow is common between co‐occurring close relatives and may serve as the key mechanism of reproductive interference. Agamic complexes, systems in which some populations reproduce through asexual seeds (apomixis), while others reproduce sexually, provide an opportunity to examine effects of reproductive interference in limiting coexistence. Apomictic populations experience little or no reproductive interference, because apomictic ovules cannot receive pollen from nearby sexuals. Oppositely, apomicts produce some viable pollen and can exert reproductive interference on sexuals by siring hybrids. In the Crepis agamic complex, sexuals co‐occur less often with other members of the complex, but apomicts appear to freely co‐occur with one another. We identified a mixed population and conducted a crossing experiment between sexual diploid C. atribarba and apomictic polyploid C. barbigera using pollen from sexual diploids and apomictic polyploids. Seed set was high for all treatments, and as predicted, diploid–diploid crosses produced all diploid offspring. Diploid–polyploid crosses, however, produced mainly polyploidy offspring, suggesting that non‐diploid hybrids can be formed when the two taxa meet. Furthermore, a small proportion of seeds produced in open‐pollinated flowers was also polyploid, indicating that polyploid hybrids are produced under natural conditions. Our results provide evidence for asymmetric reproductive interference, with pollen from polyploid apomicts contributing to reduce the recruitment of sexual diploids in subsequent generations. Existing models suggest that these mixed sexual–asexual populations are likely to be transient, eventually leading to eradication of sexual individuals from the population.     

Occurrence of unreduced pollen in diploid blueberry species,Vaccinium sect. Cyanococcus

Summary A total of 1475 individuals belonging to 43 natural populations of seven diploid (2x) blueberry species (Vaccinium section Cyanococcus) and two natural interspecific 2x hybrid populations were evaluated for unreduced pollen production. Significant differences were found in the frequency of unreduced pollen producers between species and within and between populations of the same species. Individuals with 1% or more unreduced pollen were considered unreduced pollen producers. The average frequency of unreduced pollen producers in these diploid species was 13.5%, ranging from 7.4% (V. corymbosum) to 18.4% (V. darrowii). The frequency of unreduced pollen grains in individual clones varied from <-1% to 28.6%. The production of unreduced pollen was not associated with male fertility. The widespread occurrence of unreduced pollen in the diploid species should allow the introgression of this germ plasm to the tetraploid level via unilateral sexual polyploidization.New Jersey Agricultural Experiment Station, Publication No. D-12163-18-91, supported by State and U.S. Federal funds, USDA-ARS Specific Cooperative Agreement No. 58-3615-9-068     

Evidence of 2n microspore production in a natural diploid population of Turnera sidoides subsp. carnea and its relevance in the evolution of the T. sidoides (Turneraceae) autopolyploid complex

Turnera sidoides is a complex of distylous perennial rhizomatous herbs that includes five subspecies. Since polyploidy has played a prominent role within this species (x?=?7), ongoing studies in T. sidoides are focused on the understanding of the mechanisms involved in the origin and the establishment of polyploids. Therefore, aiming to contribute to the understanding of the mode of polyploid formation, in this study we investigated the frequency of unreduced microspores in a natural diploid population of T. sidoides subsp. carnea by analyzing the size range of pollen and the constitution of the sporads. The results showed that some of the individuals studied produced 2n and 4n microspores, both in short- and long-styled floral morphs. The analysis performed documents the production of unreduced microspores in T. sidoides subsp. carnea and provides evidence that support the hypothesis of sexual polyploidization as one of the most probable mechanisms involved in the origin of polyploids within this species complex. The role of unreduced pollen in the establishment and persistence of newly formed polyploids in diploid populations of T. sidoides is also discussed.     

A population dynamic model for facultative agamosperms

Plants that can reproduce both sexually and agamically are called facultative apomicts. Some species, such as Taraxacum, contain both sexual diploids and triploid facultative apomicts. Triploids produce seeds without gamete fusion and recombination, and can also produce pollen and fertilize diploids. We present a population dynamic model that deals with gene flow and competition between diploids and triploids, with differing allocation towards reproductive investment in seeds and pollen. This paper examines whether diploids and triploids of plants with facultative agamospermy can coexist within a single population. We analyse the global behavior of such a dynamic system. Features of the system are significantly affected by the germination rates of diploids and triploids. Either diploids or triploids persist alone when the germination rate of diploids is sufficiently larger or smaller than that of triploids, respectively. Competitive exclusion occurs when both germination rates are sufficiently large. Coexistence is possible under certain specific conditions when: (I) the germination rates of both diploid sexuals and triploids are not sufficiently large, and (II) triploids produce sufficient pollen. When diploid sexuals and triploids coexist, triploids cannot exist alone, implying that the pollen of triploids is necessary to exploit diploid ovules.     

The role of tetraploids in the sexual-asexual cycle in dandelions (Taraxacum)

Apomictic plants often produce pollen that can function in crosses with related sexuals. Moreover, facultative apomicts can produce some sexual offspring. In dandelions, Taraxacum, a sexual-asexual cycle between diploid sexuals and triploid apomicts, has been described, based on experimental crosses and population genetic studies. Little is known about the actual hybridization processes in nature. We therefore studied the sexual-asexual cycle in a mixed dandelion population in the Netherlands. In this population, the frequencies of sexual diploids and triploids were 0.31 and 0.68, respectively. In addition, less than 1% tetraploids were detected. Diploids were strict sexuals, triploids were obligate apomicts, but tetraploids were most often only partly apomictic, lacking certain elements of apomixis. Tetraploid seed fertility in the field was significantly lower than that of apomictic triploids. Field-pollinated sexual diploids produced on average less than 2% polyploid offspring, implying that the effect of hybridization in the 2x-3x cycle in Taraxacum will be low. Until now, 2x-3x crosses were assumed to be the main pathway of new formation of triploid apomicts in the sexual-asexual cycle in Taraxacum. However, tetraploid pollen donors produced 28 times more triploid offspring in experimental crosses with diploid sexuals than triploid pollen donors. Rare tetraploids may therefore act as an important bridge in the formation of new triploid apomicts.     

On migration load of seeds and pollen grains in a local population

We have extended Wright's model of migration load to hermaphrodite plants showing variation at a single locus with two alleles. The model incorporates independent migration of seeds and pollen grains, the selection at both the haploid gametophyte and the diploid sporophyte stages, and a mixed mating system. The analytical relations between migration load and migration rate of seeds and pollen grains are explicitly formulated. The results show that under certain conditions, seed flow can have a more effect on migration load than pollen flow. Pollen selection at the gametophyte stage cannot substantially affect the migration load at the sporophyte stage. Selection at the diploid sporophyte stage is critical in determining the migration load of pollen grains. The relative migration loads of pollen versus seeds can be approximately estimated in predominantly outcrossing populations by the ratio of pollen flow to twice the seed flow, when the selection coefficient (s(T)) is greater than, or approximately equal to, the migration rate (m).     

Occurrence and Inheritance of 2 n Pollen in Musa

Sexual polyploidization explains the formation of most polyploidcrop species and provides means for their genetic improvement.This paper reports the occurrence and inheritance of 2n pollenin diploid and polyploidMusa . Pollen samples of male fertileaccessions available in the field gene bank of the InternationalInstitute of Tropical Agriculture were microscopically examinedthroughout a calendar year. Based on pollen diameter 2n pollenproducers were identified. The presence of 2n pollen in diploidspecies suggests that unilateral sexual polyploidization (2nxn) could have been involved in the origin of triploidMusa species.Segregation data suggests that at least one dominant gene controls2n pollen production inMusa . Further introgression of desirablealleles from diploid species to polyploids could be achievedeither through unilateral or bilateral (2nx2n ) sexual polyploidizationinMusa . Musa spp.; Musa hybrids; 2n gametes; evolution; ploidy manipulations; sexual polyploidization