Differential reproductive success in Cassia fistula in different habitants-A case of pollinator limitations?

Differences in flower success patterns in two habitat types that differed drastically with respect to rainfall, tree density and species composition were studied at Mudumalai wildlife sanctuary, India. Observations on phenological patterns of two species, Cassia fistula and Gmelina arborea, were made from April 1988 through June 1990. Quantitative data on flower-fruit ratio, insect visitation rates, pollen grain per stigma and the number of fruits per tree were recorded. Data were also collected on the number of pollen deposited on the stigma after different types of bees visited the flower. The data suggested that only carpenter bees (Xylocopa spp) effect pollination in C. fistula. The differences in fruit-flower ratios were attributed to the differences in insect visitation rates to inflorescences between sites. The low pollen number per stigma and the resultant reduction in reproductive success in C. fistula are attributed to the competing species G. arborea receiving more visitations from pollinators in the wetter site. These results suggest that pollinator limitation is another constraint in reproductive success of plants.

玉兰花粉个体发育及绒毡层动态

苏联植物学家A．L．塔赫他间在<有花植物（木兰植物）分类大纲>(Ta-khtaian，1980)中认为广义的木兰目是最原始的和最古老的类群，由它产生被子植物所有其它主要分枝。根据这个观点，作者试图以木兰科玉兰(Magnol iadenudata Desr.)，花粉个体发育为主题，探讨它们的原始性状、特点及其在系统发育上的地位。 下面就其花粉个体发育顺序，扼要概括如下： 1．小孢子母细胞、减数分裂到四分体时期：细胞器发生重组，质体和线粒体发生脱分化与再分他的循环。在此期间，细胞中还有大量胞质小泡，高尔基体小泡参与胼胝质壁物质的形成，其他小泡与脂体物质的沉积有关。晚二分体时期，原外壁物质开始沉积，胞质小泡可能涉及原外壁的形成和未来萌发孔的位置。 2．游离小孢子时期：细胞器变得丰富而活跃，特别是粗糙内质网大量出现，它们与脂体的形成和运输有关。此时，外壁外层已形成，外壁内层和内壁开始发育。 3．两细胞花粉时期;质体出现极性分布，生殖细胞中不含质体。生殖细胞随着位置的推移，其形状和壁的结构、性质也发生变化，生殖细胞由凸透镜形变成球形以至梭形。同时，生殖细胞壁最初含纤维素和胼胝质物质，以后壁物质逐渐消失，当生殖细胞变为梭形时，在生殖细胞壁的双层膜间又出现亲锇物质沉积。有趣的是，在生殖细胞星球形时，营养细胞中的脂体紧挨并围绕生殖细胞，形成一层明显的脂体冠。 玉兰成熟花粉为远极单槽，营养细胞中造粉体里园球形，内部充满大量均匀小淀粉颗粒，生殖细胞形状特殊，在有丝分裂前两极具明显的细胞质延伸和突起。从花粉个体发育着，玉兰花粉壁带有若干裸子植物性状和原始特征。最重要的特点表现在：①外壁内层具片层状结构;②I柱：状层虽具稀疏小柱，但在孢壁分沁过程中，”在小柱之问还有大小不同的孢粉素颗粒;③在萌发孔处，外壁外层往往扩张、外折，形似穗花杉和香榧的残余气囊。玉兰花粉的内壁特殊，由内壁-l、内壁-2和内壁-3等三层形状和质地不同的结构组成。值得注意的是百合科的麝香百合内壁也呈明显不同的三层结构。 玉兰绒毡层为多层细胞，属分泌型。绒毡层细胞中细胞器很丰富，减数分裂期问达到高峰。细胞核明显地被质体和线粒体所包围。粗糙内质网常与膳体连在一起。四分体时期，原乌氏体排出，孢粉素在其上沉积。推测原乌氏体和孢粉素前体物质的形成与粗糙内质网活动和膳体形成有关，乌氏体有单个存在，也有以聚乌氏体或复合乌氏体形式出现。周绒毡层膜在二分体时期即开始形成，最初呈间断的薄膜小片，以后连续发育成膜。周绒毡层膜位于靠药壁细胞的绒毡层细胞四周及中层绒毡层细胞外切向面，而靠药室腔的绒毡层细胞则未见此膜。 总之，玉兰的生殖细胞特殊，附带脂体冠;后期呈梭形，两极具明显的胞质延伸和突起，不含质体。孢壁结构具明显原始性状，在某种意义上，一方面类似裸子植物，另一方面又有百合科的特点。绒毡层结构也有一些值得深入探讨的问题。

白皮松（Pinus bungeana）和青杄（Picea wilsonii）花粉脱壁技术建立及细胞学研究

花粉是种子植物受精过程中雄性生殖细胞的载体，在有性生殖过程中起着非常重要的作用。花粉与柱头、花柱、子房等都有相互作用，起识别作用的是细胞壁蛋白，而花粉粒的壁有明显的两层：内壁和外壁。裸子植物花粉与被子植物相比具有萌发时间长、生长缓慢、授粉－受精时间长等特点。花粉的内壁与外壁在花粉萌发和生长过程中的功能仍然缺乏研究，但是迄今为止现有的分子生物学技术在获得裸子植物花粉壁突变体方面并没有发挥作用。本研究以裸子植物白皮松(Pinus bungeana)和青杄（Picea wilsonii）花粉为材料建立裸子植物花粉脱壁的体系，包 括脱外壁花粉和花粉原生质体的制备，即将花粉的两层壁逐层剥离，并在此基础上进行了细胞学研究。 本文首先建立了裸子植物脱外壁花粉的分离技术。实验表明低浓度的酶组合短暂酶解后，辅以机械研磨，可以释放出大量的脱外壁花粉。其中在这两种裸子植物中的处理稍有不同，白皮松的脱外壁花粉在含12％蔗糖，0.5%纤维素酶和0.3%离析酶的溶液，pH 5.8 ，孵育半小时，辅以一定力度机械研磨的方法获得，而青杄脱外壁花粉的条件是0.8%纤维素酶和0.5%离析酶、12％蔗糖的溶液，其它条件类似。 其次我们成功建立了一种快速、有效、可重复的分离白皮松和青杄花粉原生质体的系统，分离频率可高达70%。对白皮松而言，最好的分离条件是2% 纤维素酶、1.5%离析酶、15%蔗糖、pH 5.8，黑暗、24℃条件下轻微振荡、酶解6 小时。3％纤维素酶和2％离析酶组合比较适宜青杄花粉原生质体的分离，同时需要较低浓度的蔗糖溶液（12％）。青杄花粉原生质体要远大于白皮松花粉原生质体，前者直径为80µm，后者为40µm。强烈的FDA 荧光显示很好的活性。在制备的过程中，酶的浓度、酶的配比、酶解时间、渗透压调节剂、起始材料对分离率都有影响。 运用免疫荧光标记技术显示，脱外壁花粉的表面存在纤维素、果胶质、阿拉伯半乳聚糖蛋白（AGPs）和凝集素结合位点，其中纤维素在整个表面都有分布，但在萌发孔附近的荧光最强;白皮松脱外壁花粉表面有胼胝质的存在，主要位于靠近气囊的部位，而青杄脱外壁花粉表面未能检测到胼胝质;酸性果胶质在白皮松脱外壁花粉靠近萌发孔处的荧光稍弱于其它部位，而在青杄脱外壁花粉的表面近极端的荧光要强于远极端;白皮松脱外壁花粉表面有酯化果胶的沉积，而青杄脱外壁花粉表面缺失酯化果胶;白皮松和青杄两种植物脱外壁花粉表面均有阿拉伯半乳糖的分布，而白皮松脱外壁花粉的荧光要远强于青杄;白皮松和青杄脱外壁花粉表面有伴刀豆凝集素（Conconavalin agglutinin, Con A ）和大豆凝集素（soybean agglutinin, SBA ）结合位点的分布，而缺失麦胚凝集素（wheat germ agglutinin, WGA）结合位点。另外，傅立叶红外光谱(FTIR) 分析结果也同样支持上述结论。

Lessons Learnt From Ragweed and Birch Studies

Here we review some of the most important aspects of recent work on Ragweed (Ambrosia) and birch (Betula) concerning: 1) sources, 2) trends & phenology and 3) dispersion and transformation. Sources: At Northern latitudes the birch fraction in forests usually exceeds 50% of all broadleaved trees and the abundance of birch decreases with latitude from 5%-20% in many mid-latitude regions and down to 0%-2% in more southern areas. Birches are also commonly found in small woodlands or planted as ornamental trees in urban areas. Ragweeds are herbaceous weed species that are associated with areas of disturbance. Ragweed is native to North America, but considered an invasive species in Europe, Australia and China. In Europe, the four main centres are: The Pannonian Plain, Ukraine, The Po Valley (Italy) and the Rhone Valley (France). Trends & Phenology: Birch pollen seasons have started earlier during the last decades. This trend appears have decreased during recent years despite increasing spring temperatures. Ragweed tends to experience less change in flowering date as ragweed flowering depends on photoperiod. Ragweed is increasing its distribution in Europe, but airborne concentrations of ragweed pollen are not universally increasing, e.g. due to control measures or pest attacks. Dispersion & transformation: The beginning of the birch pollen season is often heralded by episodes of Long Distance Transport (LDT) from the south. Similar LDT episodes are intermittently seen for ragweed, which can reach as far north as Scandinavia. Humidity and air pollution can modify pollen grains during atmospheric transport. This can cause a change in allergenic potential of the pollen grain and is a direction for future research including the effect of co-exposure of air pollution and the transformation of aeroallergens.

Plant-pollinator biodiversity and pollination services in a complex Mediterranean landscape

Mediterranean landscapes comprise a complex mosaic of different habitats that vary in the diversity of their floral communities, pollinator communities and pollination services. Using the Greek Island of Lesvos as a model system, we assess the biodiversity value of six common habitats and measure ecosystemic 'health' using pollen grain deposition in three core flowering plants as a measure of pollination services. Three fire-driven habitats were assessed: freshly burnt areas, fully regenerated pine forests and intermediate age scrub; in addition we examined oak woodlands, actively managed olive groves and groves that had been abandoned from agriculture. Oak woodlands, pine forests and managed olive groves had the highest diversity of bees. The habitat characteristics responsible for structuring bee communities were: floral diversity, floral abundance, nectar energy availability and the variety of nectar resources present. Pollination services in two of our plant species, which were pollinated by a limited sub-set of the pollinator community, indicated that pollination levels were highest in the burnt and mature pine habitats. The third species, which was open to all flower visitors, indicated that oak woodlands had the highest levels of pollination from generalist species. Pollination was always more effective in managed olive groves than in abandoned groves. However, the two most common species of bee, the honeybee and a bumblebee, were not the primary pollinators within these habitats. We conclude that the three habitats of greatest overall value for plant-pollinator communities and provision of the healthiest pollination services are pine forests, oak woodland and managed olive groves. We indicate how the highest value habitats may be maintained in a complex landscape to safeguard and enhance pollination function within these habitats and potentially in adjoining agricultural areas. (c) 2005 Elsevier Ltd. All rights reserved.

A New Species of Rhipsalis (Cactaceae) from Brazil

A new species of Rhipsalis (Cactaceae) from Rio de Janeiro State, in southwestern Brazil, is described and illustrated. The new Rhipsalis aurea is circumscribed in the subgenus Eryhtrorhipsalis and is morphologically most similar to R. pulchra Loefgr., but is distinct by the smaller, suberect habit, smaller secondary stem segments of determinated growth, golden yellow flowers, depressed-globose fruit, and epidermis and pollen grain features. Following the IUCN criteria this new species is vulnerable due to its restricted area of occurrence and reduction of the quality of habitat observed in the present and projected for the future. A taxonomic key to the subgenus Erythrorhipsalis is included.

Biologia da reprodução de Mimosa bimucronata: uma espécie ruderal

Com o objetivo de estudar a biologia reprodutiva de Mimosa bimucronata, o presente estudo foi realizado em Botucatu e Cachoeira Paulista, SP, no período de novembro de 2003 a junho de 2005. Determinou-se o número de flores por glomérulo, sua duração, os eventos da antese e outras características florais, como tamanho, formato, coloração, odor, presença de néctar e localização de osmóforos. A receptividade do estigma e a viabilidade do pólen foram avaliadas. Flores foram examinadas e documentadas em microscópio eletrônico de varredura, após tratamento adequado. Foram feitos testes para a determinação do sistema reprodutivo, visando avaliar a dependência dos polinizadores. A presença de visitantes florais foi observada no campo, sendo registrada a quantidade de visitas e o comportamento dos visitantes, além do tempo médio de permanência dos visitantes junto às flores. O padrão de floração de M. bimucronata é anual. Os grãos de pólen encontram-se reunidos em políades compostas por oito células, o que pode ser interpretado como uma adaptação para minimizar o efeito da mistura das cargas de pólen depositadas sobre o diminuto estigma. A formação de frutos em condições naturais foi baixa e não ocorreu agamospermia. A morfologia das flores e das inflorescências permite o acesso aos recursos florais para uma ampla variedade de visitantes (Hymenoptera, Diptera e Coleoptera). A maioria das visitas foi realizada por abelhas (56,4%). Os resultados permitem considerar que, embora M. bimucronata seja dependente de vetores de pólen para sua reprodução, é espécie entomófila generalista e, portanto, bastante adaptada aos ambientes ruderais, onde sua ocorrência é predominante.

Two novel reports of semidry stigmatic surface in Asteraceae

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Anther development, microsporogenesis and microgametogenesis in Heliconia (Heliconiaceae, Zingiberales)

Anther development, micro sporogenesis and microgametogenesis in several species of Heliconia were investigated as part of a complementary embryological study of the Heliconiaceae. All studied Heliconia species present bithecate and tetrasporangiate anthers with fertile pollen grains; only H. rivularis, a natural hybrid, presented sterile pollen grains of variable size and no content. The anther wall has an uniseriate epidermis and endothecium, the latter with helicoidal thickenings, although some cells of the middle layers also showed thickenings; the biseriate tapetum is of amoeboid non-syncytial type, since the tapetum cells did not fuse together forming a true plasmodium. The microsporogenesis is successive leading to isobilateral tetrads. The inaperturate pollen grains had a very reduced exine consisting of a thin, more or less continuous layer with small spines upon; the pollen grain shape is variable among the species, all of them presenting heteropolar pollen, except H. angusta with isopolar ones. Most of these characteristics were shared with other studied Zingiberales, although more studies need to be done. (c) 2006 Elsevier GmbH. All rights reserved.

Contribution to the embryology of Leiothrix fluitans (Eriocaulaceae : Poales)

This paper presents a contribution to the understanding of the embryology, especially microsporogenesis, the antipodal cell behavior, and the early stages of the micropylar seed operculum, in Leiothrix fluitans, to elucidate these aspects both within the subgenus Rheocaulon and within the genus in Eriocaulaceae. Contrarily to previous descriptions of this same species, our results show the following: microsporogenesis is of the successive type and results in isobilateral microspore tetrads; the antipodal cells gradually fuse together to form a conspicuous cyst; and the inner integument, which does not develop into an endothelium, shows evidence of the initiation of the seed operculum in its micropylar end. Such features are common to the family as a whole. Evidenced for the first time in the family, the chalazal end of the ovule differentiates into a hypostase closely associated to the antipodal cyst. These overall features of L. fluitalls point out previous misinterpretations on some of its embryological aspects, especially those concerning the only report of simultaneous microsporogenesis and proliferation of the antipodal cells. Furthermore, the results presented here allow us to reinforce the uniformity of the embryological aspects within the Eriocaulaceae, strengthening the cystic arrangement of the antipodal cells as a potential autapomorphy of the family within the other Poales (commelinids). (C) 2007 Elsevier B.V. All rights reserved.

Floral anatomy of Neotropical species of Mayacaceae

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Embryology and seed development of Syngonanthus caulescens (Poir.) Ruhland (Eriocaulaceae-Poales)

The embryology and the seed development of Syngonanthus caulescens are presented. This species possesses: a bithecous and tetrasporangiate anther, with a four-layered wall, a conspicuous endothecium of the baseplate type, a secretory tapetum formed by uninucleate cells, successive microsporogenesis resulting in isobilateral microspore tetrads, spiraperturate and binucleate pollen grains, an orthotropous, pendulous, bitegmic and terminucellate ovule, with a micropyle formed only by the inner integument, a megagametophyte of the Polygonum type, with formation of an antipodal cyst, free-nuclear and starchy endosperm, a broad and bell-shaped embryo, operculate and endotestal seeds, a seed coat derived from the inner layers of both integuments, and tanniniferous endotegmen. These embryological aspects are characteristic not only for Syngonanthus, but for the whole family, with few differences between genera. Furthermore, the pollen grain of the spiraperturate type and the cystic arrangement of the antipodals in the megagametophyte are peculiar and very distinctive features of Eriocaulaceae within the other Poales (commelinids). (c) 2006 Elsevier B.V. All rights reserved.

Estudos taxonômicos e anatômicos em Mayacaceae kunth

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Ontogenia do óvulo e da Antera de Cybistax antisyphilitica (Mart.) Mart. (Bignoniaceae)

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Embriologia e desenvolvimento de frutos e sementes de Eriocaulaceae e Cyperaceae (Poales)

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)