重唇石斛传粉生物学与显微动态研究

通过杂交和自交实验,对重唇石斛授粉亲和力和结实性进行分析,并对其开花期间花粉及蕊柱结构的动态变化进行显微观察,以探讨重唇石斛的最佳杂交授粉时间.结果表明:(1)花器表面结构差异较大,唇瓣、药帽、萼片表皮布满突起、钩刺等,花瓣表皮较平滑;(2)杂交时以重唇石斛为父本或母本均具有选择性,但作为父本亲和力强,杂交结实率可达100%,作为母本杂交结实率最高为60%;自交结实率非常低,为4.3%;(3)花粉培养的最佳配方为30%蔗糖+0.15 mg·L-1 CaCl2;(4)花开第4天后花粉发育饱满,第5～12天花粉发芽率稳定大于70%,蕊柱的乳突细胞于开花第6～10 天时发育饱满.研究表明,重唇石斛花开第5～12 天为最佳授粉时间.     

Pollination of Pteroglossaspis ruwenzoriensis (Rendle) Rolfe (Orchidaceae) by Beetles in Argentina

Beetle pollination by Euphoria lurida (Scarabaeidae: Cetoninae) is documented for Pteroglossaspis ruwenzoriensis (Orchidaceae: Epidendroideae: Cymbideae: Eulophiinae) in its natural habitat in Central Argentina (South America). Flower features with special emphasis on those related to beetle pollination are given. These include: long rigid and well exposed inflorescences, sturdy inconspicuous and deep flowers with small entrance, emission of a yeast-like fragrance, jelly-like nectar, short column, and a head-attaching pollinarium with a broad saddle-like viscidium. Pollinator behaviour and pattern of flower opening favour cross pollination and probably long distance pollen dispersal. Flowering, which lasts about 3 weeks, peaks in summer past mid-January. In natural conditions about 68 flowers are pollinated for every 100 pollinaria removals.     

14种石斛属(兰科)植物的花粉团形态及分类学意义

利用体式显微镜和扫描电镜观察了14种石斛的花粉团形态及其表面纹饰超微特征,为该属的物种划分和系统演化提供花粉形态证据。解剖镜下,14种石斛的花药里有4枚花粉团,表面金黄油亮呈蜡质,质地坚硬。根据每种石斛的4枚花粉团的总体轮廓形态和大小,可分为3种形态(心形、近心形和长心形)和4种类型(极小花粉团,小花粉团,大花粉团和超大花粉团)。根据单个花粉团边界轮廓的曲直,可将其分为4种类型(月牙型、弓型、棍状和米粒型)。扫描电镜下,14种石斛的花粉团表面纹饰类型有5种(光滑平整型、光滑带丝状突起型、光滑不平整型、粗网纹状型和皱波状型),在广东石斛和球花石斛的花粉团表面观察到晶体的存在。花粉团的形态大小和外壁纹饰特征在种间变化明显,对澄清石斛属的分类学问题有一定意义。     

Micropropagation and genetic stability of a Dendrobium hybrid (Orchidaceae)

Summary Dendrobium hybrids have great economic importance in a number of countries. Asymbiotic seed germination and the conventional vegetative method have been commonly used by growers to propagate these plants. To overcome somaclonal variation, which is commonly exhibited by Dendrobium (Nobile group) when micropropagated from protocorm-like bodies, a protocol for propagating Dendrobium Second Love in vitro using axillary buds in the presence of thidiazuron was developed. Random amplified polymorphic DNA analysis was also carried out to check for possible genetic alterations in plants originating from six consecutive subcultures. The results revealed that the established protocol was efficient for the in vitro cloning of this orchid hybrid and the plants obtained from the six subcultures did not exhibit any type of polymorphism.     

Genetic load,nutrient limitation,and seed production in Lupinus texensis (Fabaceae)

The interaction of mating system and nutrient limitation in determining seed production was investigated in the annual, self-compatible plant Lupinus texensis (Fabaceae). Abortion of developing seeds is a major factor limiting seed production in natural populations (17-28%). Selfing rates are generally low (0.02-0.21), suggesting that deleterious recessive genes may be maintained at significant levels in natural populations. The average inbreeding depression associated with seed development is δ = 0.24. Nutrient limitation reduced seed output across experimental treatments by a factor of 0.22 through decreased production of inflorescences, flowers, and ovules, and by a factor of 0.29 through increased abortion of fruits and of seeds within fruits. Competition for resources among fruits increased the frequency of seed abortion. Moreover, a greater proportion of selfed seeds were aborted as the overall abortion rate increased. Estimates of genetic load may therefore only be appropriate if undertaken in the field, and inbreeding depression may vary from year to year simply due to changes in environmental conditions rather than to underlying genetic changes in populations. The existence of inbreeding depression and the high frequency of abortions suggest that selective abortion favoring outcrossed progeny occurs in natural populations of L. texensis.     

Pollination and factors limiting fruit set of chasmogamous flowers of an amphicapric annual,Polygonum thunbergii (Polygonaceae)

We observed phenology and insect visitors of chasmogamous flowers of an amphicarpic annual, Polygonum thunbergii (Polygonaceae) in Kyoto, Japan, and clarified limiting factors for fruit set by bagging and hand-pollination experiments. Flowering season was one month from late September. Flowers were visited by various insect groups (total 30 families and 64 species) and effective pollinators were lower bees (Halictidae) and wasps (Vespidae) in the early flowering season, and middle-sized flies (Syrphidae and Calliphoridae) in the later season. Nectar was secreted at a constant rate (0.013mg sugar/hour) throughout a day and >90% of it was consumed by insects. The average number of flowers per ramet was 122, of which 95% were pollinated in the natural conditions. Bagging experiments showed that 47% of flowers were self-pollinated even under no pollinator visits. Despite of a high probability of cross pollination, the probability of fruit set within the ramet was 0.30 due to resource limitation. We discussed possible adaptive significance of cleistogamous flowers under the condition that seeds could be produced by chasmogamous flowers through self-pollination even under pollinator limited conditions.     

Development of simple sequence repeat (SSR) markers and their use in identification of Dendrobium varieties

The aim of this study was to develop simple sequence repeat (SSR) markers for Dendrobium varieties/species, many of which have medicinal and horticultural values. Two genomic DNA libraries of Dendrobium Sonia enriched with GA repeats and CA repeats were constructed. Fourteen polymorphic SSR markers were identified when screened against 42 popular commercial Dendrobium hybrids. The average allele number was 12.0 ± 1.9 and the observed heterozyosity was averaged at 0.70. All 42 hybrids tested, except for two tissue culture mutants, were uniquely identified with the markers used. Sibling hybrids were closely clustered. Hybrids were also closer to parents. These SSR markers can be used for molecular ecology research, genetic mapping and marker‐assisted breeding. They can also help protection for new Dendrobium varieties.     

温度对铁皮石斛生长及生理特性的影响

通过不同温度下的控制实验,研究了铁皮石斛光合作用与生长对温度的响应,以期为铁皮石斛的栽培提供理论依据。温度对铁皮石斛的光合速率（Pn）有明显影响,30℃处理的植株具有最高的饱和光合速率（Pmax）,其较高的光合速率与RuBP电子传递速率与羧化速率间相对平衡有关。温度对铁皮石斛茎的生长及多糖含量有明显影响,20℃处理的石斛多糖含量显著性的高于其他两个处理,而茎长、茎节数、茎鲜重等则是在30℃下最高。结果表明,30℃的温度对铁皮石斛的光合作用较为适宜,但在20℃条件下植株具有更高的多糖含量。     

Postpollination nectar reabsorption in the African epiphyte Aerangis verdickii (Orchidaceae)

Nectar reabsorption in flowering plants seems to be a rare phenomenon and to our knowledge it has not been reported previously in the Orchidaceae. In this study we present data that show statistically significant differences in nectar sugar concentrations before and after pollination. Virgin flowers of the African epiphytic orchid Aerangis verdickii showed mean sugar concentrations in the nectar of 14.4 and of 18.3% in 1994 and 1995, respectively (sucrose mass by mass equivalent). Sugar concentration in nectar from naturally pollinated flowers had a mean of 3.2 and of 8.7% for the same period. In an experiment in the wild 60 flowers were protected against nectar theft by the ants. Half of those flowers were hand-pollinated. Control (virgin) flowers had nectar with a mean value of 13.8%, while flowers measured 48 h after pollination had a mean sugar concentration of 4.3%. The mean volume of nectar based on measurements of 23 virgin flowers from nine different plants was 19 uL. We estimated an average energy value for the nectar produced of 684 J per plant per season. At the study site, over 60% of the unmanipulated flowers were robbed of all their nectar by arboreal ants, Polyrachis spp. (Formicinae). The adaptive significance of nectar reabsorption for A. verdickii is probably a function of the environmental stresses to which it has been exposed and the relative costs of nectar production.     

Interannual fluctuations in floral longevity, pollinator visitation and pollination limitation of an alpine plant (Gentiana straminea Maxim., Gentianaceae) at two altitudes in the Qinghai-Tibetan Plateau

Prolonged floral longevity and bumblebees as dominate pollinators in alpine ecosystem have been suggested to overcome pollination limitation of alpine plants arising from the decrease of pollinator activity with increasing altitude. However, this conclusion has never been examined in the Qinghai-Tibetan Plateau (QTP), the highest and largest plateau in the world. In this study, we intended to test year-to-year correlations between floral longevity, visiting frequency and pollen limitation of this species between two populations (at 3200 m and 4000 m) of Gentiana straminea in this plateau. Pollinator exclusion elongated both male and female phases greatly at both sites, and durations of both male and female phases in natural condition varied greatly over three years. The visiting frequency of bumblebees varied greatly at the higher altitude, but seemed to be stable at the lower altitude. Seed production was pollination limited in both populations in most studied years. The floral durations, pollinator frequency and pollination limitation showed no significant and consistent variations with the increase of altitude. The previous hypothesis that the prolonged floral longevity of alpine plants can compensate for low levels of pollinator visitation therefore could not be confirmed, and our results further suggested that in the QTP platform, the altitude shows no consistent effect on the reproductive performance of this species, despite that the fluctuation of visit frequency intensified at the higher altitude.     

Variable selection in Platanthera bifolia (Orchidaceae): phenotypic selection differed between sex functions in a drought year

We estimated selection on three morphological characters in the hermaphroditic, hawkmoth-pollinated orchid Platanthera bifolia and explored selection surfaces through male and female function. The work was carried out in northern Sweden during two flowering seasons (1994 and 1995) in one natural population and one season (1995) in another natural population. Fitness was estimated as number of pollinia removed (male function) and number of fruits produced (female function). We detected directional selection towards larger inflorescence size (flower number) through both sex functions in both populations in 1995. In 1994, with an unusually dry growing season, 78% of the individuals failed to set any fruit, and there was selection for larger inflorescences only through male function. In this year, there was selection towards longer flower spurs, which could be a direct or indirect effect of spurs being shortened by drought. The results demonstrate that selection patterns may vary temporally and spatially, and that the 'male function hypothesis' may be applicable as female function is more resource dependent than male function.     

Pollination of the orchidEpipactis thunbergii by syrphid flies (Diptera: Syrphidae)

The behavior of visitors to the flowers of the orchidEpipactis thunbergii was studied, with special attention to the role of the epichile in the pollination process. Only four species of syrphid flies legitimately pollinated the flower, among whichSphaerophoria macrogaster was regarded as the most effective pollinator. The movable epichile, possessing a furrow at its base, played a critical role in the pollination process: it threw the syrphid fly onto the stigmatic surface when both sides of the basal slanting surface of the furrow were presumably pressed in the direction of the hypochile by the fore (and middle) legs of the retreating syrphid fly. At this moment, the fly received a set of pollinia on the thorax.     

Crane flies and microlepidoptera also function as pollinators in Epidendrum (Orchidaceae: Laeliinae): the reproductive biology of E. avicula

Crane flies and microlepidoptera have been recorded as pollinators in unrelated orchid groups, but these insects have never been recorded in Epidendroideae, the most species‐rich orchid subfamily, which includes one of the most diverse genera among Orchidaceae, Epidendrum. Based on data on phenology, floral morpho‐anatomy, pollinators, pollination mechanisms and breeding system, the reproductive biology of E. avicula was studied in south‐eastern Brazil. Epidendrum avicula possess osmophores that produce a citric fragrance at night. The flowers attract Tipulidae flies and several families of microlepidoptera that drink the nectar produced in a tube formed by the adnation of the labellum and column. As is common in Epidendrum, after removing the pollinarium, both crane flies and micro‐moths get trapped by the proboscis, which frightens the insects and inhibits any possible intent to immediately visit another flower. The behavior of the pollinators on flowers, plus the retention of the anther cap by the pollinarium, results in a reduction in the occurrence of geitonogamy. Because E. avicula is self‐incompatible, the consequence of pollinator behavior and the floral mechanisms tend to reduce the pollen loss. As far as we know, this is the first study to report the reproductive biology of a species of Epidendroideae pollinated by crane flies and microlepidoptera. Based on more recent concepts of plant–pollinator interactions, although E. avicula is pollinated by several species belonging to two distinct orders, suggesting an unspecialized pollination system is involved, nectar‐seeking microlepidoptera and Tipulidae flies can be recognized as a single functional group.     

Experimental Studies on Male and Female Reproductive Success: Effects of Variation in Spur Length and Pollinator Activity on Platanthera mandarinorum ssp. hachijoensis (Orchidaceae)

Abstract Field experiments on an orchid, Platanthera mandarinorum ssp. hachijoensis , were carried out to investigate the effects of variations in spur (nectary) length and pollinator activity on reproductive success (RS) of individual plants. Experiments comprised two kinds of treatments: spur shortening and bagging to restrict pollinator activity. Plants with a natural spur lengths range show nearly equal RS, whereas plants with shortened spurs had decreased RS proportional to spur length reduction. Pollinaria attachment (a measure of male RS) to the pollinators seems to demand stricter morphological correspondence than pollen receipt (female RS). Decrease of male and female RSs in spur-treatments was smaller in the case of high pollinator activity than low pollinator activity. Results of the bagging experiments indicated that female RS was greater than male RS in cases of high pollen carryover. These facts suggest that (1) fecundity selection operates more intensely on both male and female functions in the case of low pollinator activity and more intensely on the male function in the case of high pollen carryover, and (2) individuals with different spur lengths in natural populations have nearly equal probabilities of RS after excluding the extreme variants through the reduction of male RS.