Movement herkogamy in Kosteletzkya virginica: Effect on reproductive success and contribution to pollen receipt and reproductive assurance

Herkogamy may act as a mechanism to reduce interference between the reproductive functions of female and male organs, but too great a distance between stigmas and anthers may also decrease the outcross pollen transfer and male and female fitness. Our goal was to quantify the effect of movement herkogamy in Kosteletzkya virginica on reproductive success and its contribution to pollen receipt and reproductive assurance. Field investigations and hand-pollination experiments were performed to test: (1) the relationship between herkogamy before curvature of un-pollinated lobes and reproductive success under pollinator exclusion; (2) the contribution of movement herkogamy to pollen receipt; and (3) the relationship between pollen load and seed set. We noted that variation in herkogamy before curvature of un-pollinated lobes did not affect the outcome of autogamous self-pollination measured by fruit set and mean number of seeds per fruit. Under natural conditions, 39% of pollen grains deposited per flower were from autogamous self-pollination via movement herkogamy resulting in contact between anthers and stigmas. The relationship between the amount of pollen grains and the number of seeds per capsule was highly significant. Flowers producing four or five seeds received more pollen grains than those producing only one seed. Our data provides experimental evidence that movement herkogamy, which decreases the separation between anthers and stigmas and results in delayed self-pollination, contributes to pollen receipt and further enhances seed set when pollinators are scarce or absent.     

天仙子的花部特征及延迟自交机制

通过实验观察和野外控制授粉等方法,对天仙子的自交亲和能力和自交传粉机制进行了研究。结果显示:(1)天仙子的花不完全雌性先熟,开花进程中雄蕊伸长是维持其混合交配系统的重要花部特征。(2)野外控制授粉实验证明天仙子的自交亲和性高,具有主动自交能力,主动自交发生的时间集中在晚花期,与花药和柱头接触的时间吻合。(3)在花粉活力和柱头可授期内,花药与柱头的接触能够发生自花授粉,这种依赖花药与柱头接触发生的自花授粉机制属于典型的延迟自交类型。研究表明,天仙子不仅在花结构上首先选择了适于异交的特征,而且还利用雄蕊伸长成功实现自花授粉,通过异交与延迟自交混合的交配系统为该物种提供了灵活的遗传与繁殖保障。     

Corolla wilting facilitates delayed autonomous self-pollination in Pedicularis dunniana (Orobanchaceae)

Structural changes associated with corolla wilting may serve as a mechanism for effecting self-pollination. Low pollinator visitation, high seed production and a corolla that persists after anthesis indicates that Pedicularis dunniana is autogamous. Delayed autonomous self-pollination is facilitated by corolla wilting. Wilting of the upper lip (galea) brought the pollen laden anthers into contact with the stigma resulting in the deposition of self pollen on the stigma. The seed set of flowers either emasculated, or with restrained galeae thus preventing anthers brushing against the stigma, was significantly lower than that of open-pollinated flowers. This demonstrates that autogamy occurs in this species through corolla wilting. Germination experiments indicated that outcross seedlings were more vigorous than selfed seedlings as a result of inbreeding depression. It is likely that autogamy provides reproductive assurance for P. dunniana under conditions of pollinator scarcity.     

The pollination biology and breeding system of Monarda fistulosa (Labiatae)

Summary Successful cross-pollination of Monarda fistulosa is the result of a complex interaction among flower opening, the pollen-bearing areas of the pollinators and/or their behavior, and the maturation of the stigmas. The flowers open continuously from 0800–2000 h providing a temporally predictable rich source of nectar and pollen. Recently opened flowers may reduce the ability of bees to discriminate between resource rich and poor patches and encourage systematic foraging within patches. The continuous opening of flowers coupled with protandry also results in some flowers of most capitula being in the staminate and others in the pistillate phase. Autogamy is highly unlikely due to strong protandry and the spatial separation of anthers and stigmas. Geitonogamy, at least that mediated by Bombus is unlikely because the pollen is spread over a relatively large area of the wings, which reduces the likelihood of a stigma contacting just deposited pollen. Because pollen is transferred from the much smaller coxal area of Anthophora and other bees that mistake the stigmas of early pistillate phase flowers for stamens some geitonogamy seems inevitable. However, the delayed receptivity of young stigmas to self-pollen decreases the likelihood of self-pollen germinating on such stigmas. Older stigmas are equally receptive to self- and cross-pollen and the number of pollen grains germinating and pollen tubes reaching the base of the style increases with flower age.     

Movement herkogamy in Kosteletzkya virginica: Effect on reproductive success and contribution to pollen receipt and reproductive assurance

Herkogamy may act as a mechanism to reduce interference between the reproductive functions of female and male organs, but too great a distance between stigmas and anthers may also decrease the outcross pollen transfer and male and female fitness. Our goal was to quantify the effect of movement herkogamy in Kosteletzkya virginica on reproductive success and its contribution to pollen receipt and reproductive assurance. Field investigations and hand-pollination experiments were performed to test: (1) the relationship between herkogamy before curvature of un-pollinated lobes and reproductive success under pollinator exclusion; (2) the contribution of movement herkogamy to pollen receipt; and (3) the relationship between pollen load and seed set. We noted that variation in herkogamy before curvature of un-pollinated lobes did not affect the outcome of autogamous self-pollination measured by fruit set and mean number of seeds per fruit. Under natural conditions, 39% of pollen grains deposited per flower were from autogamous self-pollination via movement herkogamy resulting in contact between anthers and stigmas. The relationship between the amount of pollen grains and the number of seeds per capsule was highly significant. Flowers producing four or five seeds received more pollen grains than those producing only one seed. Our data provides experimental evidence that movement herkogamy, which decreases the separation between anthers and stigmas and results in delayed self-pollination, contributes to pollen receipt and further enhances seed set when pollinators are scarce or absent.     

Oleosin-like proteins are not present on the surface of tobacco pollen

Pollen-stigma interactions on wet- and dry-type stigmas involve similar processes: the hydration of the pollen, followed by pollen tube growth and penetration of the stigma. Furthermore, in some species, identical molecules, namely lipids, are used to achieve this. In addition to lipids, oleosin-like proteins of the pollen coat of dry-type stigma plants have been shown to be involved in pollen-stigma interactions. However, little information is present about the proteins on the surface of pollen of wet-type stigma plants, in particular that of the Solanaceae. To analyze proteins from the surface of pollen of Nicotiana tabacum (tobacco), a solanaceous plant, we used an antiserum raised against Brassica pollen coat, a dry-type stigma plant of the Brassicaceae. In addition we used a molecular approach to identify tobacco homologues of oleosin-like genes. Our results show that no proteins similar to Brassica oleracea pollen coat proteins are present on the surface of tobacco pollen, and that oleosin-like genes are not expressed in tobacco anthers or stigmas.     

Seed set after pollination with in-vitro-matured,isolated pollen of Triticum aestivum

Summary Immature pollen of two varieties of Triticum aestivum, at the stage right after the first pollen mitosis, was isolated from individual anthers and cultured in microcultures of microliter droplets. In a specifically designed medium, some of the pollen grains developed to maturity. These were applied to excised stigmas on agar, where they produced pollen tubes. Application to flowers in vivo led to seed set. Pollen was matured in vitro from a variety that produced a different protein banding pattern on SDS-PAGE as compared to the variety that was pollinated. The protein banding in the produced seeds showed the hybrid pattern, demonstrating that the seeds were not produced by self-pollination in this in-breeding species but by pollination with the in-vitro-matured pollen.     

Dichogamy in Salicornieae species: establishment of floral sex phases and evaluation of their frequency and efficacy in four species

Dichogamy in Salicornieae species is not clearly described in literature, and its efficiency remains untested. In this work we aim to establish the pathway for flower development, the degree of interaction between the two sexes, and the efficiency in overcoming selfing. Flower development was studied in six populations of four Salicornieae species at the Odiel Marsh Natural Park (Huelva, SW Spain) by calculating the percentage of different floral phases established in accordance with the position of their stamens and stigmas. To study the sexual functionality of each phase, the lengths of the perianth, stigma, and ovule were measured, and the number of germinated pollen grains on the stigmas was counted. In the Arthrocnemum macrostachyum and Salicornia ramosissima populations, the stigma protrudes from the perianth when the anthers have shed their pollen. In the Sarcocornia fruticosa and Sarcocornia perennis populations, anthesis starts with the extrusion of one anther, but in the most common pattern the stigma protrudes from the perianth while the anthers are shedding their pollen. All species studied were morphologically protandrous, but only in one population of Arthrocnemum macrostachyum was the number of germinated pollen grains on the stigma significantly greater when the stigma was exserted than in the previous phases.     

Stigma morphology in distylous and non-heterostylous species ofVillarsia (Menyanthaceae)

Stigma morphology was examined with the SEM in 14 of the 16 species ofVillarsia. In nine of the ten distylous species studied, stigmas of the floral morphs were strongly dimorphic in length, shape, configuration of the receptive surface, and in the size and density of their papillae. Thrum stigmas ofVillarsia, in contrast to those of most other distylous species, are not simply smaller versions of the conspecific pin stigmas, but generally exhibit an array of morph-specific characters. Thrum stigma lobes may be broader than those of pins, they may have undulate margins, lobes subdivided into secondary lobes, papillae more extensively distributed than in pins, and various combinations of these traits occur. The traits that distinguish thrum from pin stigmas achieve an increase in the receptive area and may enhance more efficient pollen capture by the shorter and less accessible thrum stigmas. The morphogenesis of the stigma shape dimorphism appears to involve processes more complex than inhibition of elongation in thrum styles. InVillarsia, the stigma dimorphisms are species-specific. No correlations were found between morphologies of the stigma and the different breeding systems in distylous species. Stigmas of the four non-heterostylous species examined resemble the thrum stigma type found in most distylousVillarsia species.     

An exception to Darwin's syndrome: floral position,protogyny, and insect visitation in Besseya bullii (Scrophulariaceae)

Darwin pointed out that plants with vertical inflorescences are likely to be outcrossed if the inflorescence is acropetalous (flowers from the bottom up), the flowers are protandrous (pollen is dispersed before stigmas are receptive), and pollinators move upward on the inflorescence. This syndrome is common in species pollinated by bees and flies, and very few exceptions are known. We investigated flowering phenology and pollinator behavior in Besseya bullii (Scrophulariaceae) and found that it did not fit Darwin's syndrome. The vertical inflorescence was acropetalous but the flowers were distinctly protogynous, so flowers with newly receptive stigmas appeared on the inflorescence above those with dehiscing anthers. A number of small insects visited B. bullii; bees in the family Halictidae (Augochlorella striata and Dialictus spp.) were most common. When insects moved between gender phases within inflorescences, they moved up more often than down (61% versus 39% of observations, respectively) but this difference was only marginally significant. Most visits were to male-phase flowers only, and this preference was more pronounced for pollen-foraging insects than for nectar-foraging insects. B. bullii was self-compatible, so its flowering characteristics potentially could result in considerable self-pollination. However, an average of 38% of the lowermost flowers opened before any pollen was available on the same inflorescence; these solo females had a high probability of outcrossing (though fruit set was relatively low in the bottom portion of the inflorescence). Upper flowers may also be outcrossed because downward insect movement was not uncommon. Therefore protogyny in B. bullii may not necessarily lead to more selfing than would protandry.     

The mechanism of delayed selfing in Collinsia verna (Scrophulariaceae)

Collinsia verna, blue-eyed Mary, has floral attributes of an outcrossing species, yet most flowers readily self-pollinate under greenhouse conditions. Here we describe the mechanism of self-pollination in C. verna via changes in relative positions of the stigma and anthers and late timing of receptivity, resulting in delayed selfing. Each flower contains four anthers that dehisce sequentially over ∼1 wk. Pollen that is not collected by pollinators accumulates in the keel petal and retains high viability (>80% pollen germination) up to the time of corolla abscission. The stigmatic surface does not become receptive until after the third anther dehisces. This overlap in the sexual phases is concurrent with a change in herkogamy during floral development. In most flowers (70%), the stigma has moved to the front of the keel and is positioned near the anthers when the third anther dehisces. Under field conditions, fruiting success of plants within pollinator exclosures was ∼75% of the fruiting success in open-pollinated plants (33% fruiting success via autogamy vs. 44% fruiting success, respectively). Collinsia verna plants in pollinator exclosures exhibit variation in autogamy rates within natural populations (range 0–80%). In addition, only half of naturally pollinated, receptive flowers examined had pollen tubes growing in their styles. In contrast, shortly after corolla abscission, nearly all flowers examined (96%) had pollen tubes in their styles. Thus we find that in C. verna, autogamy occurs late in floral development, which has the potential to provide substantial reproductive assurance, and that individuals vary in their ability to set fruit through this mechanism. We suggest that delayed selfing mechanisms may be overlooked in other species and that variable pollinator availability may play a significant role in the maintenance of mixed mating in species with delayed selfing, such as C. verna.     

Dry stigmas,water and self-incompatibility in Brassica

The evolution of dry stigmas has been accompanied by the development — in the pollen — of mechanisms for accessing water from the stigmatic epidermis. Development of self- and cross-pollen on the stigmatic surface has been examined in Brassica oleracea, focusing on the hydration of the grains. Unlike self-compatible (SC) Arabidopsis thaliana, pollen hydration of self-incompatible (SI) Brassica oleracea is preceded by a latent period of between 30–90 min, which is significantly shortened by inhibition of protein synthesis in the stigma. Physiological experiments, some with isolated pollen coatings, indicate that during the latent period signals passing from the pollen to the sigma are responsible for readying the stigmatic surface for penetration and — after self-pollination — activation of the SI system. The changes at the stigma surface include the expansion of the outer layer of the cell wall beneath the grain. This expansion does not occur following self-pollination, when coating-derived signals stimulate a stigmatic response which interrupts hydration and arrests grain development. Cell manipulation studies suggest that self grains are not inhibited metabolically, but are physiologically isolated from the subjacent stigmatic papilla. This focusing of the SI response at the pollen-stigma interface ensures that a single papilla can simultaneously accept cross-pollen and reject self-grains. The evolution of this highly efficient SI system is disussed in the perspective of pathogen-defence mechanisms known also to be located in epidermal cells.     

Pollen flow inPrimula veris (Primulaceae)

Observations on two natural and one artificial distylous populations ofPrimula veris in Britain revealed very high proportions of intramorph pollen on pin stigmas and moderate proportions of intermorph pollen on thrum stigmas. The average ratio of pin: thrum pollen production per flower was 2.4:1. Large amounts of pollen remained in dehisced anthers, perhaps reflecting low levels of pollinator activity. Population size and density had no clear effect on pollen flow patterns, which are asymmetrical for the two morphs.     

峨眉拟单性木兰的开花生物学特性与繁育系统

为阐明峨眉拟单性木兰(Parakmeria omeiensis)在自然条件结实率低的原因和确定最佳人工授粉时期,该文通过观察峨眉拟单性木兰的开花动态,采用杂交指数估算、花粉胚珠比、花粉活力及柱头活性检测、人工授粉试验等方法对其繁育系统进行了研究。结果表明:(1)植物园保育的峨眉拟单性木兰花期在4月底到5月中下旬,持续17～23 d,雄株始花期比雌株早3～4 d,但两者花期可遇。(2)两性花经检测雄蕊败育,实为功能上的雌性,部分雄株个体的雄花上残留1～2个心皮,其性别分化是通过雌、雄蕊选择性败育形成的,为隐性雌雄异株(cryptic dioecy)。(3)雄花、两性花开放经历佛焰苞开裂、花被片开裂、展开、闭合、二次开放、凋落6个阶段,历时4 d。(4)雄花初次展开时花粉活力最高,达92.8%,开花2 d后活力显著下降;两性花柱头在花被片展开期可授性最强,盛开后柱头部分可授。(5)杂交指数为5,P/O比为2.14×10~4。(6)套袋试验表明,峨眉拟单性木兰不能进行自花传粉,人工异花授粉的结实率和出种数显著高于自然授粉,且不存在无融合生殖。这说明峨眉拟单性木兰繁育系统为专性异交,传粉过程需要传粉媒介,自然条件下结实率低,主要是受传粉昆虫和柱头可授期短的限制。     

Pollen morphology and functional dioecy inSolanum (Solanaceae)

Dioecy has evolved independently several times in the large, mostly tropical genusSolanum. In all cases of dioecy inSolanum functionally male flowers have normal anthers, normal pollen and reduced stigmas while functionally female flowers have stigmas and anthers that appear normal but contain non-functional, usually inaperturate pollen. The inaperturate pollen has living cytoplasm, but apparently never germinates and it has been hypothesised that the pollen in these functionally female flowers is retained as a pollinator reward. Pollen morphology is compared in twelve of the thirteen known dioecious species ofSolanum, and some stages in the the development of inaperturate pollen in the anthers of functionally female flowers ofSolanum confertiseriatum of Western Ecuador are examined. Observations on the development and morphology of inaperturate pollen in functionally female flowers ofSolanum are related to hypotheses about the evolution of dioecy in the genus.     

Intergeneric hybridization between Diplotaxis siifolia,a wild species and crop brassicas

Summary Attempts were made to obtain intergeneric hybrids between Diplotaxis siifolia, a wild species, and cultivars of Brassica (B. campestris, B. juncea, and B. napus). The crosses showed unilateral incompatibility. When the wild species was used as female parent, pollen germination and pollen tube growth were normal, but hybrid seeds aborted due to post-fertilization barriers. Reciprocal crosses (cultivars as female parent) showed strong pre-fertilization barriers; although pollen grains showed germination, pollen tubes failed to enter the stigma. Hybrids were realized in two of the crosses, D. siifolia x B. juncea and D. siifolia x B. napus, through ovary culture. The hybrids were multiplied in vitro by multiplication of axillary shoots, or somatic embryogenesis. Detailed studies were carried out on the hybrid D. siifolia x B. juncea. F₁ hybrids had shrivelled anthers and were pollen sterile. Amphiploids of this hybrid showed 60% pollen fertility and produced seeds upon self-pollination as well as backcross pollination with the pollen of B. juncea.     

高山植物全缘叶绿绒蒿在不同海拔地区的传粉生态学研究北大核心CSCD

为了探明高山植物全缘叶绿绒蒿(Meconopsis integrifolia)的繁育系统特点和其对高山气候环境的繁殖适应特征,我们沿海拔梯度选择了5个样地(样地1(4 452 m)、样地2(4 215 m)、样地3(4 081 m)、样地4(3 841 m)、样地5(3 681 m))对其传粉生态学进行了连续2年的观察试验。结果发现,样地1、2的全缘叶绿绒蒿的单花寿命显著长于样地3、4和5。花开放早期柱头高于花药,之后花药不断伸长,并在开放中后期与柱头接触,说明全缘叶绿绒蒿具有不完全雌雄异位的花部特征。自然状态下,柱头可授能力持续期约8天(雌蕊先熟),但花药于开花第5天才散粉,花粉寿命约2天,说明全缘叶绿绒蒿为雌雄异熟,但存在一定的重叠期。人工授粉试验表明,全缘叶绿绒蒿自交部分亲和,且不存在无融合生殖现象。各样地中自然对照的结实率显著低于人工异交处理的结实率,说明自然状态下全缘叶绿绒蒿存在一定程度的传粉限制。传粉昆虫观察发现,样地1和2的传粉昆虫主要是蝇类,样地3、4和5的传粉昆虫主要是蝇类和蓟马(Thripidae spp.),蝇类在不同植株间的活动能够保证异花传粉结实,同时,蝇类和蓟马在花内的活动会引起"协助自交"。全缘叶绿绒蒿约65%的观察个体存在"自动自交"。蝇类在各样地的访花频率存在显著差异,样地1访花频率最低,样地2访花频率最高。各样地的结实由于异花传粉者的不足而受到传粉限制。两种不同类型的自交机制恰恰为该植物异花传粉者不足提供了一定程度的繁殖补偿。全缘叶绿绒蒿不分泌花蜜,当环境温度降低时,采取为昆虫提供保温庇护场所的方式来吸引传粉者。     

Bee-pollination inHibbertia fasciculata (Dilleniaceae)

In direct contrast to mostHibbertia spp., the flowers ofH. fasciculata R. Br. ex D. C. bear only a single whorl of stamens and these stamens are arranged separately (not in typical bundles). The short filaments are appressed to the three carpels so that the inflated, porose and introrsive anthers form a centralized cluster obscuring the three ovaries. The three slender styles emerge at right angles from between the filaments. These styles curve upward and the stigmas form the three points of a triangle; each stigma is approximately one millimeter outside the centralized cluster of anthers. The flowers are nectarless and bear a bright yellow corolla. A pungent and unpleasant fragrance appears to be concentrated within the pollenkitt. When native bees attempt to forage for the pollen, within the cluster of anthers, the ventrally deposited loads of pollen, on the bees' abdomens, contact the outer triangle of stigmas. The major pollinators ofH. fasciculata are female bees in the polylectic genera,Lasioglossum (subgenusChilalictus, Halictidae) andLeioproctus (Colletidae). These bees carry an average of more than two pollen taxa when they are caught foraging onH. fasciculata. 78% of the 47 bees, captured onH. fasciculata carried the pollen from at least one sympatric taxon bearing nectariferous flowers (e.g., genera in theMyrtaceae, Compositae, andEpacridaceae). The pollination biology ofH. fasciculata is assessed in relation to the known radiation of bee-pollinated flowers in the genusHibbertia, and within theDilleniaceae s. l.     

Asynchronous development of stigmatic receptivity in the pear (Pyrus communis; Rosaceae) flower

While stigma anatomy is well documented for a good number of species, little information is available on the acquisition and cessation of stigmatic receptivity. The aim of this work is to characterize the development of stigma receptivity, from anthesis to stigma degeneration, in the pentacarpellar pear (Pyrus communis) flower. Stigma development and stigmatic receptivity were monitored over two consecutive years, as the capacity of the stigmas to offer support for pollen germination and pollen tube growth. In an experiment where hand pollinations were delayed for specified times after anthesis, three different stigmatic developmental stages could be observed: (1) immature stigmas, which allow pollen adhesion but not hydration; (2) receptive stigmas, which allow proper pollen hydration and germination; and (3) degenerated stigmas, in which pollen hydrates and germinates properly, but pollen tube growth is impaired soon after germination. This developmental characterization showed that stigmas in different developmental stages coexist within a flower and that the acquisition and cessation of stigmatic receptivity by each carpel occur in a sequential manner. In this way, while the duration of stigmatic receptivity for each carpel is rather short, the flower has an expanded receptive period. This asynchronous period of receptivity for the different stigmas of a single flower is discussed as a strategy that could serve to maximize pollination resources under unreliable pollination conditions.