New acritarch species from Holocene sediments in central West Greenland

Anther development, microsporogenesis, and microgametogenesis were studied using both light and TEM microscopy in the six accessible subdioecious/cryptically dioecious species of Consolea (Cactaceae). Anther wall development, microsporogenesis, and microgametogenesis are uniform in staminate flowers of all six species, and are typical for Cactaceae. Breakdown of microsporogenesis in male‐sterile anthers occurs early, at the onset of meiosis, and results in anthers bearing no pollen grains. The abortive process follows a common pattern in all investigated species. The tapetum is the first layer to deviate from normal male‐fertile anther development. Tapetal cells in male‐sterile anthers elongate at an early stage and have abundant rER with atypical configurations. Ultimately, the tapetum becomes hypertrophied and non‐functional. Male‐sterility in pistillate flowers appears to be directly related to these anomalies. In addition, other anther layers and tissues are affected, and normal patterns of programmed cell death (PCD) are disrupted. The relationship between these patterns and the pattern of PCD in normal male‐fertile anthers is discussed. We hypothesize a single origin for the cryptically dioecious/subdioecious breeding system of Consolea based on the uniformity of the anther's abortive processes in pistillate flowers.     

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.     

Cryptic dioecy and insect pollination in Rosa setigera Michx. (Rosaceae), a rare plant of Carolinian Canada

Rosa setigera is unique among known roses because it is truly dioecious, yet the plants and flowers are almost impossible to sex. Subtle differences in the inflorescences have been detected, for example, there are more flowers per inflorescence on male plants than on female plants and petal expansion from the day of opening to the next day is greater in females than in males; in addition, pollen from female plants appears somewhat collapsed and does not germinate. Pollinators ( Apis mellifera , other bees (Apidae), Eristalis tenax and other Syrphidae: Diptera) visit the blossoms mostly in the morning to collect pollen (there is no nectar) and in choice experiments do not discriminate between male flowers and female flowers on landing, but do spend significantly more time on the former. They do discriminate between freshly opened flowers and day-old flowers, and show marked preference for bouquets of five flowers vs . single flowers. The female plants, with smaller inflorescences and lesser interest to pollen foraging insects, seem to encourage them to forage at more flowers than do their male counterparts. This may be biologically significant for effective pollen flow in a dioecious pollenonly plant with pollenivorous pollinators.     

Microsporogenesis in male sterile Rosmarinus officinalis L. (Lamiaceae), an ultrastructural study

Within an extensive reproductive biology program on Rosmarinus officinalis a study of microsporogenesis in male sterile plants has been carried out. Two events, related to the two types of male sterile flowers found in this species (MS; Male sterile and INT; Intermediate male sterile flowers), are described. The first event is characterized by the early appearance of necrotic areas in the anther tissues during the final differentiation phases of the MS flowers, before meiosis takes place. Initially, these necrotic areas are small, later on they enlarge affecting the sporogenous tissue and tapetum. All the anthers in which necrosis has begun finally become aborted and lack pollen grains. The second event is manifested in the anthers of the INT flowers. Previous to the release of the microspores from the callosic envelope, vacuolisation of the tapetal cells takes place. The tapetum does not properly carry out its secretory function. It accumulates some substances in vacuoles and starch granules in plastids. The microspores degenerate in the vacuolate stage. In the epidermal and endothecial cells modifications are observed which may be related to the carbohydrate metabolism. Indehiscent, whitish anthers containing inviable microspores result. We have not found significant differences between the mitochondria in the anthers of the fertile flowers and MS or INT flowers. But we suggest, for both events, a metabolic failure, possibly controlled by cytoplasmic genes as the origin of male sterility. Paracrystalline material has been detected in microspore nuclei of developing INT anthers, though it does not seem to be related to the expression of male sterility.     

Dioecy in the endemic genusDendrocacalia (Compositae) on the Bonin (Ogasawara) Islands

Dendrocacalia crepidifolia Nakai (Compositae, Senecioneae), the only species of this arboreal genus endemic to Haha Island in the Bonin Islands, was found to be dioecious. Male flowers differ from female ones in having a stunted style (style in female exserted from corolla and deeply bifurcating) and anthers filled with fertile pollen (anthers in the female lacking pollen). The size of the corolla and number of florets per head were similar between male and female flowers. The crown area of this arboreal species was also similar in male and female plants. The sex ratio was 0.55 male, not significantly different from 0.5. Both sexes produced nectar of similar sugar concentration (ca. 50%). The flowers are pollinated by feral honeybees (Apis mellifera), but they are thought to have been pollinated by small, lesshairy, endemic solitary bees before honeybees were introduced and subsequently became the dominant bee species on the island. The evolution of dioecy ofDendrocacalia on the island is thought to stem from the deleterious effects of inbreeding that are inherent in plants with geitonogamy. The increased geitonogamy on the island has resulted from increased woodiness (i.e., increased number of flowers per plant) and the original dependence on endemic bee pollinators, which are now endangered.     

Morphological variation in the flowers of Jacaratia mexicana A. DC. (Caricaceae), a subdioecious tree

The Caricaceae is a small family of tropical trees and herbs in which most species are dioecious. In the present study, we extend our previous work on dioecy in the Caricaceae, characterising the morphological variation in sexual expression in flowers of the dioecious tree Jacaratia mexicana . We found that, in J. mexicana , female plants produce only pistillate flowers, while male plants are sexually variable and can bear three different types of flowers: staminate, pistillate and perfect. To characterise the distinct types of flowers, we measured 26 morphological variables. Our results indicate that: (i) pistillate flowers from male trees carry healthy-looking ovules and are morphologically similar, although smaller than, pistillate flowers on female plants; (ii) staminate flowers have a rudimentary, non-functional pistil and are the only flowers capable of producing nectar; and (iii) perfect flowers produce healthy-looking ovules and pollen, but have smaller ovaries than pistillate flowers and fewer anthers than staminate flowers, and do not produce nectar. The restriction of sexual variation to male trees is consistent with the evolutionary path of dioecy from hermaphrodite ancestors through the initial invasion of male-sterile plants and a subsequent gradual reduction in female fertility in cosexual individuals (gynodioecy pathway), but further work is needed to confirm this hypothesis.     

Programmed cell death promotes male sterility in the functional dioecious Opuntia stenopetala (Cactaceae)

Background and Aims

The sexual separation in dioecious species has interested biologists for decades; however, the cellular mechanism leading to unisexuality has been poorly understood. In this study, the cellular changes that lead to male sterility in the functionally dioecious cactus, Opuntia stenopetala, are described.

Methods

The spatial and temporal patterns of programmed cell death (PCD) were determined in the anthers of male and female flowers using scanning electron microscopy analysis and histological observations, focusing attention on the transition from bisexual to unisexual development. In addition, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling assays were used as an indicator of DNA fragmentation to corroborate PCD.

Key results

PCD was detected in anthers of both female and male flowers, but their patterns differed in time and space. Functionally male individuals developed viable pollen, and normal development involved PCD on each layer of the anther wall, which occurred progressively from the inner (tapetum) to the outer layer (epidermis). Conversely, functional female individuals aborted anthers by premature and displaced PCD. In anthers of female flowers, the first signs of PCD, such as a nucleus with irregular shape, fragmented and condensed chromatin, high vacuolization and condensed cytoplasm, occurred at the microspore mother cell stage. Later these features were observed simultaneously in all anther wall layers, connective tissue and filament. Neither pollen formation nor anther dehiscence was detected in female flowers of O. stenopetala due to total anther disruption.

Conclusions

Temporal and spatial changes in the patterns of PCD are responsible for male sterility of female flowers in O. stenopetala. Male fertility requires the co-ordination of different events, which, when altered, can lead to male sterility and to functionally unisexual individuals. PCD could be a widespread mechanism in the determination of functionally dioecious species.     

Reproductive trait variation in the functionally dioecious and morphologically heterostylous island endemic Chassalia corallioides (Rubiaceae)

Documenting the floral biology and breeding system of species throughout the Rubiaceae family provides data on the number of times heterostyly and dioecy may have evolved in this large family. The objectives of this paper are to quantify (a) whether Chassalia corallioides , a small tree endemic to La Reunion Island in the Indian Ocean, is another example of the evolution of dioecy from distyly and (b) whether reproductive traits linked to male and female function vary over the ecological distribution of this species. Quantification of pollen production and fruit set following controlled and natural pollinations demonstrate that this species is dioecious. Male flowers have longer corolla tubes than female flowers. Female flowers have long styles with stigmas placed above the anthers whereas males have short styles with stigmas placed below the anthers. Stigmas and anthers are reciprocally placed in each morph, illustrating that the species is morphologically heterostylous. Both fecundity and flower size are negatively correlated with altitude. In male plants, corollas are shorter and wider and anthers are placed closer to the mouth of the corolla tube with increasing altitude. Male plants flowered more often than female plants, the likely cause of the male biased sex ratio in each of the two years studied. The evolution of dioecy in relation to the island biogeography of the region and the diversification of the genus Chassalia is discussed.     

基因工程雄性不育烟草及其温度敏感性

将含有抗溴苯腈基因bxn和雄性不育基因的重组载体pTA29-Barnase/bxn导入农杆菌(Agrobacterium tumefaciens)后转化烟草(Nicotiana tabacum L.),得到33个转基因植株。在27℃/23℃培养的16株中,有7株表现部分不育,另9株全部可育。而在20℃/15℃培养的17株中,12株表现不育,5株表现部分不育。部分不育的植株上同时开放可育花朵和不育花朵,不过其中的不育花朵中的花粉萌发活力很低。将在20℃/15℃条件下表现不育的12个不育株从20℃/15℃温室移至27℃/23℃温室后30d左右,其中9株表现程度不同的育性恢复现象:5株表现部分可育,另4株表现完全可育;但仍有3株表现雄性不育。雄性不育花朵的花丝变短,花药皱瘪,不散粉。细胞学观察证明,转基因植株的花药绒毡层降解提早于四分体时期,至单核小孢子时期降解殆尽。     

Pollination Ecophysiology of Mercurialis annua L. (Euphorbiaceae), an Anemophilous Species Flowering all Year Round

Mercurialis annua L. is a dioecious anemophilous species thatflowers all year round in central and southern Italy. The flowersof both sexes are dimorphic: the female flower has a vestigialcalyx; the male flower consists only of a calyx that opens atanthesis. The anthers always dehisce after anthesis. The anthesisof male flowers seems to be temperature dependent, whereas antherdehiscence is related to relative humidity. The pollen grainsvary in volume according to the season: they are smaller whenrelative humidity is low and vice versa. They always decreasein volume after anther dehiscence and have the capacity to varyin volume and reach equilibrium with a changing environment.Viability is high, but may drop suddenly during heavy rain orhail that damage the exposed male flowers. The number of pollengrains per stigma varies from 0 to 300. The data is discussedin relation to the type of pollination and environmental characteristics.Copyright1994, 1999 Academic Press Mercurialis annua, dioecism, anthesis, anther dehiscence, pollen volume, pollen viability, anemophilous pollination, pollination ecology     

Dioecism of the genusCallicarpa (Verbenaceae) in the Bonin (Ogasawara) Islands

The morphology and function of the flowers of three species of the genusCallicarpa, C. glabra, C. nisnimurae andC. subpubescens, endemic to the Bonin Islands, revealed that all three species were dioecious. Male plants had short-styled flowers with sterile ovaries, while female plants had long-styled flowers with non-germinating inaperturate pollen grains. Such dioecism has never been reported from the family Verbenaceae. This curious sexual system with non-germinating pollen grains may have been maintained as a reward to insect pollinators.     

慈姑花的开放式样及其花粉流

对一野生慈姑（ＳａｇｉｔａｒｉａｔｒｉｆｏｌｉａＬ．）居群的性表达状态及其花粉流散布规律进行了观测。慈姑雌雄同株,单株雄花数是雌花数的３．６倍。雌雄花单花期均为１ｄ,但二者开放式样不同。尽管雌花的数目较少,但在１ｄ内开放较多的花,其花的开放速率比雄花快。在居群水平上表现出雌雄花比例随时间大幅度波动。在传粉者进行的２６１２次访花活动中,传粉者表现出偏“雌性”访问,对每朵雌花的访问是雄花的１．４倍。用番红染色法标记慈姑的花粉运动表明,花的不同开放式样影响花粉流的散布。当雄花数占高比例时,花粉主要在邻近的个体间散布;而雄花的比例较低、雌花相对较多时,花粉远距离散布的强度加大。     

FUNCTIONAL DIOECY AND ANDROMONOECY IN SOLANUM

Field and laboratory studies of 19 diclinous species endemic to Australia help to clarify the nature and evolution of andromonoecy, androdioecy, and dioecy in the genus Solanum. Ten species are andromonoecious; typically these species bear inflorescences with a single, large basal hermaphroditic flower and 12–60 distal, smaller staminate flowers. We suggest that the andromonoecious condition was derived from hermaphroditic-flowered ancestors in part by hemisterilization of flowers but largely by addition of staminate flowers. The resultant larger inflorescences are hypothesized to serve both to attract and to entrain pollinators, yielding more or higher-quality seed set in hermaphroditic flowers and/or greater dispersion of pollen from staminate flowers. We suggest that andromonoecy may also serve to reduce selling. Nine other species are morphologically androdioecious but functionally dioecious. In these species, staminate flowers, like those of the andromonoecious species, bear anthers with copious tricolporate pollen and a highly reduced gynoecium. The morphologically hermaphroditic flowers are functionally pistillate and borne singly in inflorescences, and they bear anthers with inaperturate pollen. The inaperturate pollen, although viable, never germinates and is hypothesized to be retained in pistillate flowers as a reward to pollinators in the nectarless Solanum flowers. All other species of Solanum studied with pollen dimorphism in which one pollen morph is inaperturate are also best treated as functionally dioecious. We conclude that there is no evidence for androdioecy in Solanum. A review of other families suggests that there is little support for this unusual breeding system in any other angiosperm group either. Preliminary analyses suggest that andromonoecy and dioecy are polyphyletic in Solanum. Furthermore, dioecy is as likely to have arisen from hermaphroditic as from andromonoecious ancestors.     

Stamens are not essential as an attractant for pollinators in females of cryptically dioecious Thalictrum pubescens Pursch. (Ranunculaceae)

 It has been hypothesized that females of some dioecious species maintain stamens that produce sterile pollen as a means of attracting pollinators to promote greater seed set. However, this hypothesis has rarely been tested. This paper examines the role of pollinators in the maintenance of sterile stamens in the cryptically dioecious species, Thalictrum pubescens. Wind was found to contribute to pollination; branches of female T. pubescens enclosed in cheesecloth to exclude insects but not wind were still able to set seed. Therefore, females may not need the stamens for pollination. In 1994, insects were found to discriminate against emasculated female flowers, but this discrimination did not lead to a significant difference in either the amount of pollen received or seed set. In 1995, emasculation was combined with the addition of pollen to determine if emasculated females were pollen limited. No significant effect of pollen addition or emasculation was found. Emasculated branches in the pollen-addition treatment appeared to have slightly lower seed set than non-emasculated branches that received pollen, indicating that the slight reduction in seed set was caused by emasculation rather than pollen limitation. Since stamens do not appear to be maintained as pollinator attractants, other explanations, such as genetic constraints, must be investigated. Received: 4 February 1997 / Revision accepted: 20 May 1997     

Studies in Garcinia, dioecious tropical forest trees: the phenology, pollination biology and fertilization of G. hombroniana Pierre

RICHARDS, A. J., 1990. Studies in Garcinia , dioecious tropical forest trees: the phenology, pollination biology and fertilization of G. hombroniana Pierre . Garcinia hombroniana is a facultative agamosperm which is pollinated by Trigona bees. Nectar is restricted to the large discoid stigma (or pistillode in male flowers), which also captures and hydrates pollen. The 'wet' stigma and binucleate pollen suggest that Garcinia arose from hermaphrodite plants with a gametophytic self-incompatibility system.
On stigmas, nectar is secreted early on three or four successive days. On male pistillodes, nectar is secreted when anthers dehisce, on the second morning after anthesis. Pollen is most viable when freshly collected, but some viability remains four days after collection. Pollen germinates within 24 h of hydration. Similar results to pollinations are obtained by germinating pollen in 1 % sucrose.
Garcinia hombroniana flowers principally from January to June. Cultivated females are considered as 'big bang' strategists. Male flowers are considered as 'steady state' strategists.     

西双版纳热带雨林对叶榕传粉生物学

研究了西双版纳热带雨林地区雌雄异株植物对叶榕(Ficus hispida L.)的生物学、传粉物候学以及榕小蜂(Ceratosolen solmsi marchali Mayr)的传粉和繁殖行为.研究结果表明:雌雄异株的对叶榕与其他雌雄同株的榕属植物不同,它的种子形成与传粉者有着更为复杂的相互关系.对叶榕一年结隐花果6～8次,结果高峰期4～5次,其中雄性植株仅产生花粉和孕育榕小蜂,而雌性植株(无雄蕊)则需榕小蜂带花粉进入隐花果内,进行传粉授精,使之发育成种子.对叶榕的成熟花粉不能从花药开裂处自行散发出来,必须由榕小蜂采集才能散落.榕小蜂雌蜂羽化、交配后,找到雄花区,用足、触角、口器在推动中采集花粉.雌蜂飞出熟榕果找寻雌株或雄株榕树上的幼嫩隐花果,一般需3～67 min;一部分雌蜂在雄株中寻找幼嫩的隐花果,进去产卵繁殖,另一部分雌蜂则寻找雌株雌花期嫩隐花果进去传粉.雌蜂在雌株榕树的隐花果内传粉时间为15～23 h,在雄株榕树的隐花果内产卵时间为6～9 h.对叶榕小蜂在雌株上进入单个隐花果的数量多少关系到雌花结实率;观察表明,每个隐花果最佳进蜂数为2头;榕小蜂传粉后榕树成熟种子形成率在54.1%～82.5%之间,平均为73.8%;而在雄株上雌蜂进蜂数量则关系到榕小蜂在隐花果内的产卵率,每个隐花果最佳进蜂数为3～4头,产卵率在72.3%～93.8%之间,平均为84.4%.     

Pollen Production in the Androdioecious Datisca glomerata (Datiscaceae): Implications for Breeding System Equilibrium

Abstract Androdioecy (the presence of males and hermaphrodites in a breeding population) is a rare reproductive system in plants, with Datisca glomerata (Datiscaceae) representing the only well-documented example. Recent reports of high outcrossing rates, inbreeding depression, and high male pollen production satisfy theoretical predictions for the continued maintenance of androdioecy in populations of this species. However, in prior studies pollen production was measured indirectly in terms of numbers of anthers per flower—based on the assumption that male and hermaphroditic plant have equal numbers of flowers and that anthers from the two sexual morphs produce equivalent amounts of pollen. Herein, we demonstrate that male and hermaphrodite plants do not differ significantly in terms of flower number, but that pollen production in anthers from hermaphroditic plants is 12.6% higher than in anthers from male plants, thus refining the estimate of relative pollen fecundity of male versus hermaphrodite plants. The differential lowers the frequency of males predicted by theory, but is still consistent with the maintenance of androdioecy in this species.     

灯盏花雄性不育种质鉴定与花药发育的细胞学研究

对云南泸西栽培灯盏花群体进行调查,发现了灯盏花雄性不育种质个体,其出现频率约为1.06×10-4.对所发现的灯盏花不育株形态特征及其花药发育过程进行了观察,并对花粉活力进行鉴定.结果显示:(1)灯盏花不育株根、茎、叶形态与正常可育植株基本相似,管状花小,花丝短,花药瘦小,无花粉粒散出或花粉无活力.(2)灯盏花在其花药发育的小孢子母细胞时期、四分体时期、小孢子时期和单核早期,由于绒毡层细胞液泡化、提前解体,不能为小孢子或花粉发育提供所需物质,导致小孢子母细胞和四分体解体,产生无花粉的花药;或小孢子和单核花粉胞内降解,形成不同形状和外壁纹饰的败育花粉.研究认为,灯盏花花药绒毡层异常是其花粉败育的主要原因.     

Dioecy in South American Deprea (Solanaceae)1

Dioecy in the Solanaceae is rare, occurring in < 1 percent of the species worldwide and known in only two species from South America. We report the occurrence of cryptic dioecy in the Neotropical genus Deprea. Studying herbarium material of the Venezuelan endemic D. paneroi revealed morphological distinctions that tentatively served to divide collections into male and female morphs. This discovery prompted investigation of population structure, crossing studies, and morphometric analyses of 95 individuals from the largest known wild population and a small sample of greenhouse‐grown plants. About 60 percent of the population was reproductive, and of these, nearly equal numbers exhibited female or male characteristics. Plants that bore fruit and small sterile anthers were characterized as female; those that lacked fruit but produced pollen in large anthers were characterized as male. The morphology, receptivity, and developmental phenology of pistils were identical in both forms. Crossing studies revealed significant enlargement of the ovaries in open‐pollinated female flowers and female X male hand‐pollinations. The ovaries in open‐pollinated male flowers and male X male hand‐pollinations never enlarged. These results suggest that the only legitimate combination is female X male. Dioecy in the family and possible mechanisms for the evolution and maintenance of dioecy in D. paneroi are discussed.     

An Examination of the Function of Male Flowers in an Andromonoecious Shrub Capparis spinosa

The pollen donor and pollinator attractor hypotheses are explanations for the functions of the male flowers of andromonoecious plants. We tested these two hypotheses in the andromonoecious shrub Capparis spinosa L. (Capparaceae) and confirmed that pollen production and cumulative volume and sugar concentration of nectar do not differ between male and perfect flowers. However, male flowers produced larger anthers, larger pollen grains and smaller ovaries than perfect flowers. Observations on pollinators indicated that two major pollinators (Xylocopa valga Gerst and Proxylocopa sinensis Wu) did not discriminate between flower morphs and that they transferred pollen grains a similar distance. However, there were more seeds per fruit following hand pollination with pollen from male flowers than from perfect flowers. Individuals of C. spinosa with a larger floral display (i.e. bearing more flowers) received more pollen grains on the stigma of perfect flowers. Female reproductive success probably is not limited by pollen. These results indicate that male flowers of C. spinosa save resources for female function and that they primarily serve to attract pollinators as pollen donors.