The effect of wild radish floral morphology on pollination efficiency by four taxa of pollinators

The effects of floral morphology on rates of pollen removal and deposition by different pollinators in generalist plant species are not well known. We studied pollination dynamics in wild radish, Raphanus raphanistrum, a plant visited by four groups of pollinators: honey bees, small native bees, butterflies, and syrphyd flies. The effects of anther position and other factors on pollen removal during single visits by all four pollinator taxa were measured. Flowers with high anther exsertion (i.e., anthers placed higher above the opening of the corolla tube) tended to have the highest numbers of pollen grains removed, but this effect was strongest for honey bees and butterflies. For all pollinator taxa, pollen removal increased with the number of pollen grains available on a flower and whowed a positive, decelerating relationship with the duration of the visit. The effects of stigma position and other factors on pollen deposition during single visits by honey bees and butterflies were also studied. The nectar-feeding butterflies had a higher pollination efficiency (percentage of pollen grains removed from anthers that were subsequently deposited on a stigma) than the nectar- and pollen-feeding honey bees. Flowers with intermediate stigma exsertion had the highest numbers of pollen grains deposited on their stigmas by butterflies, but stigma exsertion had no effect on deposition by honey bees. For both butterflies and honey bees, pollen deposition on the recipient flower increased with the amount of pollen removed from the donor flower, and there was a positive, decelerating relationship between deposition and time spent at the flower; these results are analogous to those for pollen removal. The effects of anther and stigma exsertion on pollen removal and denosition did not fit predictions based on patterns of floral correlations, but results for morphology, pollen availability, time spent per visit, and pollinator efficiency are in broad agreement with previous studies, suggesting the possible emergence of some general rules of pollen transfer.     

Floral homeotic gene expression defines developmental arrest stages inBrassica oleracea L. vars.botrytis anditalica

Brassica oleracea L. vars.italica (broccoli) andbotrytis (cauliflower) both undergo developmental arrests which result in heading phenotypes. We characterized these arrested tissues at the morphological and molecular levels, and defined the developmental changes that ensue after arrest has been broken. We found that the order of floral organ initiation and the positions of resulting floral organ primordia in this species differed in some respects from that ofArabidopsis, which is a member of the same family, Brassicaceae. We also cloned homologs of theArabidopsis floral homeotic genesAPETALA1 (AP1) andAPETALA3 (AP3) fromB. oleracea and characterized their expression patterns. We found that theAP1 homolog was expressed in some of the meristems of arrest-stage cauliflower, providing evidence that this tissue is florally determined. In broccoli, both the API andAP3 homologs were expressed. However, the spatial pattern of expression of the broccoliAP1 homolog differed from that ofArabidopsis. In addition, we identified a homolog of theCAULIFLOWER (CAL) gene,BoiCAL, from broccoli. The predicted amino acid sequence indicated that theBoiCAL gene product does not contain the mutation thought to be responsible for the early arrest exhibited in cauliflower (Kempin et al. 1995), but contains other changes that might play a role in the broccoli heading phenotype.The GenBank accession numbers for the sequences reported here are: U67451 (Boi2AP1); U67452 (Boi2AP1); U67453 (Boi1AP3); U67455 (Boi2AP3); U67456 (BobAP3); and U67454 (BoiCAL)     

黄瓜去顶苗直接成花的形态学研究

本文对黄瓜0—7天幼苗及去顶后0—8天诱导花芽分化苗与诱导营养芽分化苗的子叶节进行了系统石蜡切片观察,未发现0—7天幼苗的子叶叶腋存在潜伏芽。去顶后1—2天在子叶叶柄基部与切口之间的表皮下细胞分裂形成突起,去顶后6天诱花苗与诱芽苗的突起表现出形态差异,诱花苗突起的上端变钝,而诱芽苗突起的上端成尖锥状。去顶后8天诱花苗在子叶叶柄与切口之间形成完整的花芽。另发现有少量花芽起源于切口处细胞。对去顶后0—6天诱花苗与诱芽苗的子叶节还进行了电镜扫描观察,观察结果与石蜡切片基本一致。     

菊苣薄层培养花芽,营养芽分化中内源激素的动态变化

菊苣（Ｃｉｃｈｏｒｉｕｍ ｉｎｔｙｂｕｓＬ．）花梗薄层细胞培养于ＭＳ附加ＮＡＡ 和ＢＡ 或ＩＡＡ 和ＢＡ 的ＭＳ培养基上有花芽或营养芽分化． 花芽分化中内源ＩＡＡ、ＤＨＺ＋ ＤＨＺＲ、ｉＰＡ 含量明显增加,而Ｚ＋ ＺＲ变化不明显．营养芽分化中内源细胞分裂素含量增加明显,而ＩＡＡ 在培养前７ ｄ 含量下降,随后有所增加,在原基形成时含量达原初水平的２／３． 可见,花芽分化比营养芽分化所需内源ＩＡＡ／ＣＴＫ 比值要高     

Intraspecific Variation in the Amino Acid Content of Floral Nectar

In order to evaluate the constancy of amino acid composition and concentration, several randomly collected samples of genuine floral nectar from different flowers of several plant species were analysed. Although there seems to exist a rough pattern of species-specific nectar amino acid composition, amino acid concentration varied strongly from sample to sample. Apart from the lack of constancy in concentration of floral amino acids, our samples do not show amino acid concentration values as assigned typical for the pertinent pollination mode by other workers.     

Aspects of evolutionary differentiation of theHamamelidaceae and the LowerHamamelididae

New investigations on the flower and fruit structure of extantHamamelidaceae and other LowerHamamelididae together with new finds of fossil flowers and seeds from the Upper and Lower Cretaceous provide the outline of an increasingly more differentiated picture of the early evolution of the subclass. Three patterns of valvate anther dehiscence are recognized in the subfamilyHamamelidoideae (and the subclassHamamelididae). The basic (plesiomorphic) type within theHamamelididae has 2 valves per theca. The type with 1 valve but 2 pollen sacs per theca is both consistent and exclusive for the 5 southern genera of theHamamelidaceae. They seem to be the remnants of a homogeneous group that originated before the Upper Cretaceous. This is supported by fossil hamamelidaceous flowers from the Upper Cretaceous that have thecae with 1 valve. Since several-seededHamamelidaceae predate one-seeded forms in the fossil seed record (in Europe) and the systematic structure of the one-seeded group is relatively more homogeneous, several-seeded groups are considered to be more ancient. Several parallel evolutionary trends are recognized within theHamamelidaceae as well as within the LowerHamamelididae: anther dehiscence with 2 valves per theca 1 slit or 1 valve; pollen sacs per theca 2 1; pollen tricolpate polyforate; exine coarsely reticulate finely reticulate; loss of perianth (tepals or petals and sepals) and concomitant loss of fixed number of floral organs; differentiation of exposed nectaries.     

鸢尾属植物的传粉者吸引及异交策略

已知鸢尾属（Iris）植物约有280种且花部特征多变,具有较高的科研和观赏价值。尽管该属植物具备一定的克隆和自交繁殖能力,但传粉者介导的异交仍在其物种和遗传多样性的维持中发挥重要作用,然而目前仍缺乏对该属植物传粉者吸引及异交策略的系统性总结。本文首先简述了鸢尾属植物的传粉者种类及其适应动物传粉的花部构造,以明确其动物传粉概况。在此基础上,详细论述了该属植物如何通过视觉和嗅觉信号呈现花粉、花蜜和热量报酬供给等策略,实现对传粉者的有效吸引。在传粉者访问前后,鸢尾属植物还可通过合理的花展示、单花内雌雄功能的时空隔离以及传粉后的调控以实现最大程度的异交。此外,影响其传粉者吸引及异交的第三方生物和非生物因素,如食花者和资源配置,也应受到重视。今后随着相关研究的深入和技术手段的革新,研究者应针对鸢尾属植物传粉的热点或有争议的问题,采用花信号定量测定及异交率分子检测等先进技术,通过大范围的对比研究,深入揭示鸢尾属植物与传粉者的互作模式及其繁殖策略。     

Bumble bee behavior and selection on flower size in the sky pilot,Polemonium viscosum

Summary In alpine Polemonium viscosum, plants having sweet-scented flowers are primarily pollinated by queens of the bumble bee species, Bombus kirbyellus. In this paper we ask whether two aspects of the pollination effectiveness of bumble bees, visitation rate and pollination efficiency, vary significantly with flower size in sweet-flowered P. viscosum.(i) Bumble bees visited plants with large flowers on 80–90% of encounters, but visited those with smaller flowers on only 49% of encounters. (ii) However, the gain in pollination that large-flowered plants obtained via increased visitation was countered in part because bumble bees deposited fewer outcross pollen grains per visit on stigmas of large flowers than on those of small ones. When both visitation rate and pollination efficiency are taken into account, the predicted value of a single bumble bee encounter declines from 1.06 seeds for flowers larger than 18 mm in diameter to 0.55 seeds for flowers smaller than 12 mm in diameter. Our results suggest that bumble bee pollinators of P. viscosum prefer flower morphologies that are poorly suited for precise pollination. Such behavioral complexities are likely to place constraints on the evolution of optimal floral design.     

Morphological studies on the genusClematis linn. VIII. Floral and inflorescence anatomy inClematis patens with eight-sepaled flowers

The vascular anatomy of inflorescence axes and flowers ofClematis patens have been studied. The species shows a unique behaviour of the vascular bundles in the transition node from vegetative stem to pedicel: stelar bundles increase in number from six to eight as they ascend through the transition node so that the number of vascular bundles coincides with that of sepals. In the pedicel stele the resulting eight bundles are disposed opposite to eight sepals. respectively; each sepal receives its vascular supply from the bundle facing it. Morphological and anatomical evidence suggests that the calyx of eight sepals in this species should be interpreted as having consisted originally of four pairs of opposite organs, rather than as having been derived secondarily through chorisis of sepals from a calyx of four sepals as seen in most other species ofClematis.     

Reproductive timetable for the tropical Vireya rhododendron,R. Macgregoriae

Summary The reproductive development of Rhododendron macgregoriae F.v.M., Section Vireya (Ericaceae) has been followed from 10 days before anthesis to the production of mature germinable seeds about 145 days after anthesis. The species is self-compatible but shows both protandry and physical separation of pollen from the receptive stigma. Pollen is mature and viable from shortly before anthesis until the corolla and attached anthers abscise some 9–12 days after the flowers open. Spontaneous dehiscence, however, occurs mostly in the first few days after opening. The stigma becomes receptive 6–7 days after anthesis, and nectar is produced at this time. Female gametophytes are not mature until about 10 days after anthesis. Fertilization occurs about 6–7 days after pollination, and although the endosperm commences development immediately, development of the embryo proper does not begin until some 40–45 days later. Pollinations made with fresh pollen between 5 and 14 days after anthesis were successful, but those made on dry stigmas in the first 4 days after anthesis, or on senescing pistils 21 days after anthesis, gave little or no seed set. In nature, autogamy is probably uncommon, the majority of pollinations are likely to be geitonogamous, but there is considerable potential for outcrossing.