Reproductive conflicts ofPalicourea padifolia (Rubiaceae) a distylous shrub of a tropical cloud forest in Mexico

We studied a population of the distylousPalicourea padifolia (Rubiaceae) in a cloud forest remnant near Xalapa City, Veracruz, México to explore possible asymmetries between floral morphs in the attractiveness to pollinators, seed dispersers, nectar robbers, floral parasites, and herbivores. We first assessed heterostyly and reciprocal herkogamy by measuring floral attributes such as corolla length (buds and open flowers), style and anther heights, stigma and stamen lengths and the distance between the anther tip to the stigma lobe. We then estimated floral and fruit attributes such as flower size, anther height, number and size of pollen grains, fruit size, seed size, nectar production, and flower and fruit standing crops to assess differences between floral morphs in attracting and effectively using mutualistic pollinators and seed dispersers. Also, floral parasitism and nectar robbing were assessed in this study as a measure of flower attractiveness to antagonists. The system seems to conform well to classical heterostyly (e.g. reciprocal stamen/style lengths, pollen and anther dimorphism, intramorph incompatibility) yet, there were several tantalizing differences observed between pin and thrum morphs. Thrum flowers have longer corollas and larger but fewer pollen grains than pin flowers. Both morphs produced the same total number of inflorescences, developed the same number of buds, and opened the same number of flowers per inflorescence during the flowering season. Nectar production and sugar concentration were similar between floral morphs but the reward was not offered symmetrically to floral visitors throughout the day. Nectar concentration was higher in pin flowers in the afternoon. The numbers of developing, fully developed, and ripe fruits were the same between floral morphs, however, fruits and seeds were larger than those of thrums. The incidence of fly larvae was higher among thrum flowers and damage by nectar robbing was the same between floral morphs. Fruit abortion patterns of flowers manually pollinated suggest intra-morph sterility (self and intramorph incompatibility). There were no differences between morphs in fruit and seed set per flower following legitimate pollination although thrums were more leaky than the pins (intramorph compatibility).     

Is There ‘Anther-Anther Interference’ within a Flower? Evidences from One-by-One Stamen Movement in an Insect-Pollinated Plant

The selective pressure imposed by maximizing male fitness (pollen dispersal) in shaping floral structures is increasingly recognized and emphasized in current plant sciences. To maximize male fitness, many flowers bear a group of stamens with temporally separated anther dehiscence that prolongs presentation of pollen grains. Such an advantage, however, may come with a cost resulting from interference of pollen removal by the dehisced anthers. This interference between dehisced and dehiscing anthers has received little attention and few experimental tests to date. Here, using one-by-one stamen movement in the generalist-pollinated Parnassia palustris, we test this hypothesis by manipulation experiments in two years. Under natural conditions, the five fertile stamens in P. palustris flowers elongate their filaments individually, and anthers dehisce successively one-by-one. More importantly, the anther-dehisced stamen bends out of the floral center by filament deflexion before the next stamen''s anther dehiscence. Experimental manipulations show that flowers with dehisced anther remaining at the floral center experience shorter (1/3–1/2 less) visit durations by pollen-collecting insects (mainly hoverflies and wasps) because these ‘hungry’ insects are discouraged by the scant and non-fresh pollen in the dehisced anther. Furthermore, the dehisced anther blocks the dehiscing anther''s access to floral visitors, resulting in a nearly one third decrease in their contact frequency. As a result, pollen removal of the dehiscing anther decreases dramatically. These results provide the first direct experimental evidence that anther-anther interference is possible in a flower, and that the selection to reduce such interferences can be a strong force in floral evolution. We also propose that some other floral traits, usually interpreted as pollen dispensing mechanisms, may function, at least partially, as mechanisms to promote pollen dispersal by reducing interferences between dehisced and dehiscing anthers.     

异质生境对二型花柱植物雪地报春花性状分化的影响

该研究以生长在新疆北部的二型花柱植物雪地报春(Primula nivalis)为研究材料,对7个低海拔(1 657~2 013m)森林居群和7个高海拔(2 400~2 700m)草原居群的花型比例进行调查,对花部特征进行检测,并对长、短花柱植株在不同海拔居群的花性状分化进行了比较研究,以揭示该类群植物的演化与环境的关系。结果表明:(1)在高海拔草原居群中长花柱植株比例高于短花柱植株。(2)比较草原和森林生态系统中的雪地报春居群,长花柱花形态特征间存在显著差异,但短花柱花形态特征间的差异不显著。(3)高海拔草原居群中长花柱花的花冠筒长度、雄蕊长度、雌雄蕊距离、雌雄异位程度以及雌雄蕊空间位置是导致花性状分化的主要因素。(4)在草原居群中,长花柱花的雄蕊、雌雄异位程度及花冠口至雄蕊距离的变化减少了长短花柱花间的互补式对应性。研究认为,在异质生境中长花柱花性状的变化是导致该物种长短花柱花性状分化的主要因素。     

Isolation of a partial sequence of a putative nucleotide sugar epimerase, which may involve in stamen development in cucumber (Cucumis sativus L.)

Sex determination is the most widely studied subject in cucumber. The sex of cucumber plants can be monoecious, hermaphrodite, gynoecious, androecious, or andromonoecious. Besides environmental factors, three major genes, F/f, M/m, and A/a mainly govern the sex types in cucumber. Regardless of their sex all floral buds are bisexual at the early bud stage. A stage specific arrest of either stamen or carpel leads to unisexual flower development. The possible downstream product of the interaction of the sex determining genes that may directly allow the growth or selectively arrest stamen or pistil is not yet identified. Therefore, in the current study, we performed suppression subtractive hybridization using floral buds from nearly isogenic gynoecious and hermaphrodite cucumber plants and identified for the first time a cDNA homologous to nucleotide sugar epimerase. The expression level of the isolated putative nucleotide sugar epimerase is weak in female floral buds but strong in bisexual and male flowers. The weak level of the putative nucleotide sugar epimerase may be an indication for its improper functioning, which may influence stamen development in cucumber plants.     

Floral scent and intrafloral scent differentiation inMoneses andPyrola (Pyrolaceae)

Floral scent was collected by headspace methods from intact flowers, petals, and stamens of four species ofPyrolaceae. The scent samples were analyzed by coupled gas chromatography-mass spectrometry (GC-MS). The floral scent inPyrola spp. is differentiated into a characteristic petal scent—phenyl propanoids and a characteristic stamen scent—methoxy benzenes. InMoneses the scent is characterized by isoprenoids and benzenoids, with a larger proportion of benzenoids in the stamens compared to the petals. Specific anther scents may promote foraging efficiency in buzz-pollinated species and enhance flower fidelity. Variation in floral scent composition is consistent with the taxonomic relationships among the genera and species examined.     

Live-imaging provides an atlas of cellular growth dynamics in the stamen

Development of multicellular organisms is a complex process involving precise coordination of growth among individual cells. Understanding organogenesis requires measurements of cellular behaviors over space and time. In plants, such a quantitative approach has been successfully used to dissect organ development in both leaves and external floral organs, such as sepals. However, the observation of floral reproductive organs is hampered as they develop inside tightly closed floral buds, and are therefore difficult to access for imaging. We developed a confocal time-lapse imaging method, applied here to Arabidopsis (Arabidopsis thaliana), which allows full quantitative characterization of the development of stamens, the male reproductive organs. Our lineage tracing reveals the early specification of the filament and the anther. Formation of the anther lobes is associated with a temporal increase of growth at the lobe surface that correlates with intensive growth of the developing locule. Filament development is very dynamic and passes through three distinct phases: (1) initial intense, anisotropic growth, and high cell proliferation; (2) restriction of growth and proliferation to the filament proximal region; and (3) resumption of intense and anisotropic growth, displaced to the distal portion of the filament, without cell proliferation. This quantitative atlas of cellular growth dynamics provides a solid framework for future studies into stamen development.     

Expression of rolB in tobacco flowers affects the coordinated processes of anther dehiscence and style elongation

The effect of auxin on stamen and pistil development in tobacco flowers was investigated by means of the localized expression of rolB (root loci B), an Agrobacterium oncogene that increases auxin sensitivity in a cell-autonomous fashion. When rolB is driven by the promoter of the meiosis-specific Arabidopsis gene DMC1 (disrupted meiotic cDNA 1), expression occurs earlier in male than in female developing organs, resulting in a delay in anther dehiscence with respect to normal timing of pistil development. As a consequence of this developmental uncoupling, self-pollination is prevented in pDMC1:rolB plants. Histological analysis of pDMC1:GFP plants indicates that in tobacco, this promoter is active not only in meiocytes but also in somatic tissues of the anther. In contrast, simultaneous expression of rolB in anther and pistil somatic tissues, achieved by expressing a construct containing rolB under the control of the promoter of the petunia gene FBP7 (floral binding protein 7), results in a concomitant delay of both anther dehiscence and pistil development without affecting self-pollination of the plants. Analysis of plants harboring the pFBP7:GUS construct shows that in tobacco, this promoter is active not only in the ovules, as described for petunia, but also in pistil and anther somatic tissues involved in the dehiscence program. The delay in anther dehiscence and pistil development could be phenocopied by exogenous application of auxin. Jasmonic acid (JA) could not rescue the delay in anther dehiscence. These results suggest that auxin plays a key role in the timing of anther dehiscence, the dehiscence program is controlled by the somatic tissues of the anther, and auxin also regulates pistil development.     

Tristyly, self-compatibility and floral variation in Decodon verticillatus (Lythraceae)

Heterostyly typically involves reciprocal polymorphism in stamen and style lengths, physiological self- and intramorph-incompatibility, and a set of associated polymorphisms of pollen and stigma characters. This study examined floral morphology and compatibility relationships in the monotypic, herbaceous perennial Decodon verticillatus (Lythraceae). There have been conflicting reports on the occurrence of tristyly in the species, probably because of frequent loss of style morphsm from populations in parts of the species' range. Floral morphology was examined using material collected from natural populations throughout the range. Detailed floral measurements revealed discrete trimorphism in style length and anther positioning in three populations. Data from two dimorphic populations showed similar patterns of floral polymorphism, except that both were missing the mid-styled morph. In one dimorphic population, there was evidence for modification in the length of mid-level stamens. Measurements in three populations indicated pronounced floral variability, including high frequencies of modified phenotypes with reduced stigma-anther separation. Pollen size was only weakly differentiated among anther levels, and there were no differences in pollen production among anther levels or morphs. In contrast, stigma size and papilla length showed a strong negative correlation with style length; a pattern opposite to most heterostylous species. Experimental crosses performed under glasshouse conditions on plants from two populations showed a high degree of both self- and intramorph-compatibility. A comparative analysis of floral morphology showed that D. verticillatus is not unusual in terms of the precision and reciprocity of organ positioning compared with 13 other tristylous species.     

两性花的雄蕊运动:多样性和适应意义

雄蕊运动指雄蕊在自身能量支持下发生的主动运动,不包括雄蕊在访花者触碰下造成的被动位移。该文总结了雄蕊的应激运动、快速猛烈弹射、缓慢运动以及级联运动等4种主要类型,分析了这些运动类型的系统分布及繁殖适应意义等方面的研究进展。雄蕊的应激运动由访花者或其他外力诱发,可能起到促进散粉和实现繁殖保障的作用;雄蕊快速猛烈的弹射运动可将花粉猛然撒向空中或访花者身上,促进了花粉的风媒或虫媒散布;缓慢运动的雄蕊可能通过在不同花期改变雄蕊的空间位置和雌雄异位程度来调节繁殖策略,或主动将雄蕊花药移至特定部位(如柱头表面)实现自交;雄蕊逐一、依次发生的级联运动较为复杂,主要分布在刺莲花科、梅花草科、旱金莲科和芸香科中,目前还缺乏实验研究;但根据"花粉呈现理论"以及其他类型的雄蕊运动研究结果,雄蕊的级联运动可以将花粉分批呈现给不同的传粉者,通过不同传粉者的分别传粉来提高花粉的输出;而且可避免已散粉雄蕊对即将散粉雄蕊的干扰,同时可能也降低了雌雄功能干扰和(或)花内自交。在芸香(Ruta graveolens)中,级联运动之后的雄蕊还会在花末期再同时向花中央运动;这种多向、多次运动方式是目前发现的最复杂的雄蕊运动类型。雄蕊运动领域值得今后开展进一步实验研究的方向主要有:1)雄蕊运动尤其是级联运动对雌雄功能干扰(性别间干扰)、雄蕊与雄蕊的"性别内干扰"等植物繁殖格局的影响;2)雄蕊运动与雌雄异熟、雌雄异位等花部特征的相互作用;3)雄蕊运动复杂类型的生理与发育机制。     

短命植物甘新念珠芥（Neotorularia korolkovii）和宽翅菘蓝（Isatis violascens）的物候与性表达特征

甘新念珠芥（Neotorularia korolkovii）和宽翅菘蓝（Isatis violascens）是两种广泛分布于新疆准噶尔荒漠的十字花科早春短命植物。对其物候与性表达特征研究结果表明：(1) 二者种子均在3月下旬萌发,5月下旬和6月上旬果实完全成熟,生活周期分别为62d和71d,其中营养生长期约占1/3、生殖生长期约占2/3。(2) 花均为两性,四强雄蕊,单花开放时间较短,长雄蕊的花药开裂早于短雄蕊,但短雄蕊花药中的花粉数较长雄蕊的多。(3) 长、短雄蕊花药中花粉可育率均达90%以上,花粉活力的变化曲线基本相同,柱头可授期分别为9.0h和4.5h,花粉寿命及柱头可授期均短于单花花期,花粉活力最高的时期正是其柱头的最佳授粉期。柱头可授期与花粉活力及寿命在时间上的高度吻合,增加了在不可预测环境中授粉的机会与效率,从而保障生殖成功。(4) 二者的P/O（花粉/胚珠）值分别为108.07±17.17、992.10±272.16,属于自交繁育系统;对其传粉过程、套袋实验及荧光显微观察的结果也证明它们主要以自花传粉的方式来进行交配。(5) 两种植物从物候、花部性表达以及交配式样上均存在与其严酷荒漠环境相适应的特点,是长期适应准噶尔荒漠特殊生态环境的结果,对于保证繁殖成功并扩大种群具有重要的意义。     

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。     

Tristyly in the endangered Mascarene Island endemic Hugonia serrata (Linaceae)

Tristyly is a rare floral polymorphism known to occur in only five flowering plant families. One unresolved and potential additional case of tristyly concerns the genus Hugonia in the Linaceae. Here we confirm the existence of tristyly in the genus by reporting floral measurements made on Hugonia serrata Lam., an extremely rare species endemic to the Mascarene Islands of La Réunion and Mauritius in the southern Indian Ocean. We conducted an extensive search of all natural habitats on La Réunion Island where the species had been previously reported. Twenty-eight individuals were found, of which nine were in flower. Of the nine flowering individuals five had long-styled flowers with the stigmas placed above the two levels of anthers, three had intermediate length styles with the stigmas placed between the two anther levels, and one had stigmas placed below the two anther levels, i.e., three floral morphs could be identified based on the sequence of stigma and anther positions. Reciprocity and precision indices calculated for sexual organ length in each morph confirm that this variation is well within the range of values observed by previous workers on other tristylous species in other families. Our empirical data confirm the existence of tristyly in the genus Hugonia, thereby raising the number of known families in which tristyly occurs to six. Pollen size, pollen number, and anther length increased slightly with stamen length, but the low number of plants precludes statistical tests of these trends. A bibliographic survey suggests that tristyly may occur in several other species of the genus.     

荔枝草花的形态发生

在体式显微镜系统观察的基础上,对唇形科鼠尾草属植物荔枝草(Salvia plebeiaR.Br.)的花发育过程进行了扫描电镜观察.发现荔枝草的轮伞花序由多数交互对生的聚伞花序单位组成,花器官发育形式为向心式",各部分花器官从外向内依次形成;共形成4个雄蕊原基,其中2个雄蕊原基在形成后不再发育,另2个雄蕊原基每个均发育出1可育药室和1不育药室,不育药室膨大连接,并在花成熟之前参与组成特殊杠杆结构;子房四深裂"的形成实际是由4个原基分别发育,而后相互靠拢而成.     

Characterization of <Emphasis Type="Italic">SpAPETALA3</Emphasis> and <Emphasis Type="Italic">SpPISTILLATA</Emphasis>, B class floral identity genes in <Emphasis Type="Italic">Spinacia oleracea</Emphasis>, and their relationship to sexual dimorphism

Floral organ identity B class genes are generally recognized as being required for development of petals and stamens in angiosperm flowers. Spinach flowers are distinguished in their complete absence of petals in both sexes, and the absence of a developed stamen whorl in female flowers. As such, we hypothesized that differential expression of B class floral identity genes is integral to the sexual dimorphism in spinach flowers. We isolated two spinach orthologs of Arabidopsis B class genes by 3 and 5 RACE. Homology assignments were tested by comparisons of percent amino acid identities, searches for diagnostic consensus amino acid residues, conserved motifs, and phylogenetic groupings. In situ hybridization studies demonstrate that both spinach B class genes are expressed throughout the male floral meristem in early stages, and continue to be expressed in sepal primordia in reduced amounts at later stages of development. They are also highly expressed in the third whorl primordia when they arise and continue to be expressed in these tissues through the development of mature anthers. In contrast, neither gene can be detected in any stage in female flowers by in situ analyses, although northern blot experiments indicate low levels of SpAP3 within the inflorescence. The early, strong expressions of both B class floral identity genes in male floral primordia and their absence in female flowers demonstrate that B class gene expression precedes the origination of third whorl primordia (stamen) in males and is associated with the establishment of sexual floral dimorphism as it initiates in the first (sepal) whorl. These observations suggest that regulation of B class floral identity genes has a role in the development of sexual dimorphism and dioecy in spinach rather than being a secondary result of organ abortion.Electronic Supplementary Material Supplementary material is available for this article at Edited by G. Jürgens     

雄蕊合生植物半边莲的花部综合征与繁育系统

 为了解花内雄蕊合生结构的繁殖适应意义, 初步研究了雄蕊合生植物半边莲(Lobelia chinensis)的花部综合征、传粉特性和繁育系统。半边莲花大且鲜艳, 花瓣中下部弯折并合生成背部有裂缝的不封闭的花冠筒。5雄蕊的花药紧密合生成花药筒, 花丝中上半部也合生在一起, 只有花丝基部分离插生于花冠筒上。柱头被包裹在花药筒内。半边莲单花寿命可达5 d左右。雄性先熟, 柱头在伸出花药筒之后才具活性。花的主要访问者为蚂蚁、食蚜蝇和苍蝇类等小型昆虫。半边莲单花花粉数约为(5 200±130)粒、胚珠数约为(55±6)颗, 花粉胚珠比为94.54, 应属于兼性自交繁育系统, 但异交指数和其它特征都显示其以异交为主, 部分自交亲和。套袋和人工授粉实验发现, 半边莲不存在无融合生殖与自发自交, 但自交亲和性高。雄蕊合生(尤其是花药的合生)能把花药中的花粉聚拢在一起在传粉者的一次访问中就被同时带出, 与同样具有较低花粉胚珠比的花粉聚联(Pollen aggregation)传粉过程近似。半边莲的雄蕊合生结构(花药合生成筒、花丝上部也合生)可能与一些特定的花部特征, 如花被合生成未完全封闭的筒、雌雄异熟以及低花粉胚珠比等联系在一起, 形成了适应小型传粉者的“花部综合征”     

Morph-specific patterns of variation in stigma height in natural populations of distylous Jasminum fruticans

The purpose of this study was to describe morph-specific patterns of stigma–anther separation and style curling in the distylous Jasminum fruticans . We also examined whether variation in floral traits is correlated with variation in seed production. Stigma–anther separation is more variable in short-styled plants than in long-styled plants. In all populations studied, some plants bear flowers that lack any stigma–anther separation. These plants have the pollen characteristics (size and number) and compatibility relations of short-styled plants. Comparison with other distylous species illustrates that the variability of stigma–anther separation in short-styled plants is a novel finding for a distylous species. Long-styled plants have greater stigma–anther separation than short-styled plants, styles are often curled and protrude from the corolla, and anthers are placed well within the corolla tube. The frequency of long-styled plants with curled styles and the mean degree of style curling were significantly correlated with style length. Short-styled plants have larger corollas than long-styled plants and never have curled styles. Morph ratios are always 50:50 in natural populations. Mean values of each floral trait in the two morphs were significantly correlated among populations. There were no consistent differences in fecundity of the two morphs nor any correlation between floral traits and seed set for each morph in natural populations. We discuss the potential causes and significance of the two morph-specific patterns we describe; reduced stigma–anther separation in short-styled plants and the presence of curled styles in long-styled plants.     

单瓣与重瓣垂丝海棠花器官形态发育比较观察

为探究垂丝海棠重瓣花成花原因,该研究以单瓣垂丝海棠和重瓣垂丝海棠为实验材料,应用体式显微镜和扫描电镜观察垂丝海棠单瓣、重瓣品种花器官分化过程;解剖观察重瓣垂丝海棠大蕾期的花与盛开的花,统计其花器官的形态与数目;应用R语言对重瓣垂丝海棠的花瓣数目与其余各轮花器官数目进行相关性分析。结果显示：(1)单瓣和重瓣垂丝海棠的花器官分化均分为萼片原基分化期、花瓣原基分化期、雄蕊原基分化期、雌蕊原基分化期,且各轮花器官按照向心顺序依次分化发育。(2)在花瓣原基分化期,单瓣垂丝海棠仅分化出一轮(5枚)均匀分布于两枚萼片交汇处的花瓣原基,而重瓣垂丝海棠分化出两轮分布散列的花瓣原基,第一轮为5~7枚,第二轮为7~10枚。(3)在重瓣垂丝海棠各轮花器官中存在较多萼片瓣化、雄蕊瓣化、雌雄蕊异常发育的情况。(4)重瓣垂丝海棠各轮花器官数目间相关性分析结果显示,其花瓣数目与雄蕊数目以及瓣化中的雄蕊数目间存在明显的正相关关系,该现象与常规雄蕊瓣化植物表现的雄蕊数目减少、花瓣数目增多的现象不同。研究表明,重瓣垂丝海棠花瓣数目的增多并不完全依赖于雄蕊变瓣,暗示垂丝海棠重瓣花成花原因的多元性与复杂性。