Reproduction in Seagrasses: Pollen Development in Thalassia hemprichii, Halophila stipulacea and Thalassodendron ciliatum

The general features of pollen morphogenesis in three marinemonocotyledons, Thalassia hemprichii, Halophila stipulacea andThalassodendron ciliatum, are described in this paper. Thalassia disperses spherical trinucleate pollen grains. Inthis genus simultaneous cytokinesis generally produces an isobilateraltetrad of microspores, but linear and T-shaped configurationsalso occur, together with configurations intermediate betweenisobilateral and T-shaped. Partitioning is followed by a phaseof cellular degeneration affecting one or two, never more, membersof the tetrad. Subsequent development of the surviving, functionalmicrospores does not differ essentially from the pattern ofmorphogenesis in terrestrial flowering plants. Halophila disperses strings of four reniform trinucleate pollengrains contained in a mucilaginous moniliform tube. These ariseby successive transverse partitioning of an elongate mothercell and the linear unit so formed is maintained throughoutpollen development. The tetrad tube substance originates inthe tapetal periplasmodium and deposition begins soon aftermeiosis. Thalassodendron disperses filiform trinucleate pollen grains.The characteristic form of the pollen in this genus is attainedduring post-meiotic growth and differentiation, as in othergenera belonging to the same family. This contrasts with thesituation in seagrasses belonging to the Zosteraceae where thefiliform shape is established before meiosis. Precocious divisionof the microspore nucleus in Thalassodendron launches the binucleatepollen phase soon after the spores separate from the tetrad.The division precedes the vacuolate period; again, this is afeature of the family. In Thalassia the tapetal periplasmodium is progressively transformedinto thecal slime. In Thalassodendron and Halophila the periplasmodialresidue forms a superficial coating on the pollen wall and tetradtube. These products could be implicated in attachment and recognitionof the pollen at the stigma surface. Thalassia hemprichii, Halophila stipulacea, Thalassodendron ciliatum, seagrasses, pollen development     

水鳖科9属15种植物花粉形态的研究

应用光学显微镜、扫描电镜和透射电镜对水鳖科Hydrocharitaceae 9属15种植物的花粉形态进行 了观察。水鳖科植物花粉为圆球形至近椭球形,无萌发孔或偶为单沟萌发孔,外壁纹饰通常为小刺状纹 饰,刺密集或稀疏,花粉表面具瘤状、疣状、颗粒状、皱波状突起或光滑。外壁由覆盖层、柱状层和基层组 成。覆盖层厚或较薄,柱状层小柱发育不明显,基层薄。水鳖科植物在花粉大小、纹饰类型、刺的长短、 密度、形态、萌发孔的有无以及花粉壁的结构等方面表现出了较为明显的差异,这些特征对探讨类群间 关系具有较重要意义。由于黑藻属Hydrilla和Stratiotes属花粉较为特殊,支持将它们各自作为一个独立 的族处理。水鳖科植物花粉外壁纹饰和结构特点表明该科与水雍科Aponogetonaceae、泽泻科Alismataceae 和花蔺科Butomaceae等近缘,而该科植物花粉大多无萌发孔等则反应了该科与茨藻目Najadales植物有密切联系。     

宁夏枸杞柱头和萌发花粉中钙分布特征

用焦锑酸钾沉淀法对宁夏枸杞柱头和花粉中的钙离子分布进行了研究.结果显示,宁夏枸杞柱头表皮有一覆盖层,其中有许多含钙沉淀颗粒的小泡,当花粉落到柱头后从覆盖层中吸水,在萌发孔的表面上聚集了较多的钙沉淀颗粒.同时,花粉内部出现许多含钙的小液泡,使花粉体积增大,内部产生膨压,花粉萌发;生长在覆盖层中的花粉管顶端穿过覆盖层小泡时,附近聚集了较多的钙沉淀颗粒,在花粉管壁上也附着较多的细小钙沉淀颗粒.萌发的花粉粒中由大液泡占据,在其亚顶端的细胞质中,聚集较多钙沉淀颗粒的线粒体膨大形成了一些含钙沉淀颗粒的小液泡,由这些小液泡融合形成的大液泡,将花粉管细胞质挤到其顶端,使其极性生长.这是首次发现在植物柱头覆盖层中有钙离子的现象,从体内证明了钙离子在花粉萌发过程中的现象.讨论了枸杞柱头组织中钙的分布和花粉管的萌发与生长的关系.     

Flavanoids in Pollen and Stigma of Brassica oleracea and Their Effects on Pollen Germination In Vitro

Brassica oleracea pollen was applied to a basic medium of 1.5per cent agar and 15 per cent sucrose to which flavanoids wereadded at three concentrations. Two types of agar were used;with agar 1, quercetin at a concentration of 0.5 x 10^–3per cent gave an increase in percentage germinating grains.With agar 2, an increase in germination occurred with kaempferoland naringin at concentrations of 0.5 x 10^–3 and 0.5 x10^–1 per cent respectively. Increase in pollen tube lengthoccurred with agar 2 and quercetin at a concentration of 0.5x 10^–3 per cent. The stigma tissue of B. oleracea contains at least three andthe pollen at least one glycoside of quercetin. The sugars inthe glycosides were not identified. Pollen germination and pollentube extension were not stimulated exclusively by the flavanoidspresent in the stigma. The flavanoid composition of the stigmadid not vary amongst five different S-allele genotypes, indicatingthat flavanoids are probably not directly involved in the incompatibilityreaction of B. oleracea.     

甘草花粉超微鉴定及花粉活力、柱头可授性荧光显微镜观察

对甘草的有性生殖特性进行了研究,利用扫描电子显微镜对乌拉尔甘草、光果甘草和胀果甘草花粉的超微结构进行观察,利用荧光显微镜确定乌拉尔甘草的授粉方式、花粉生活力和柱头活性以及授粉后受精时间.结果表明,花粉超微结构为甘草的鉴别提供了一定的形态学依据;甘草的授粉方式属于闭花受精;花粉生活力在每天12:00时最强,去雄后超过4d的柱头已经不具备接受花粉的能力;对授粉后不同时间的雌蕊进行研究得出授粉后6h花粉管进入胚珠进行受精.     

野生烟草花粉活力与柱头可授性及繁育特性研究

采用TTC法测定2个野生烟草材料(花烟草、哥西氏烟草)和1个栽培品种(K326)的花粉活力及其日变化情况,通过联苯胺-过氧化氢法测定3个烟草材料的柱头可授性、利用直接授粉法测定不同开花天数柱头可授性变化,并通过估算花粉胚珠比(P/O)、杂交指数(OCI)及授粉试验分析3个烟草材料的繁育特性。结果表明:(1)哥西氏烟草的花粉活性(74.9%)显著高于K326(52.2%)和花烟草(45.3%),且K326与花烟草间差异不显著;3个烟草材料花粉活力日变化均呈双峰曲线,峰值分别在13:00与15:00左右,且3个烟草材料的花粉活力日最低值与气温日最高值同时出现在14:00。(2)K326柱头可授性显著高于花烟草和哥西氏烟草,且2个野生烟草间可授性无显著差异;不同烟草的最佳授粉时期不同,哥西氏烟草自开花前1d至花后4d,一直保持较高的柱头可授性;花烟草的最佳授粉时期为花后2~3d;K326的柱头在开花前1d至开花后1d授粉最佳。(3)K326以自交为主,存在异交现象;哥西氏烟草繁育类型为兼性异交,自交亲和;花烟草繁育以异交为主,自交亲和性差。研究认为,野生烟草柱头可授性显著低于栽培品种从而影响其结实性,花烟草结实率低主要是由自交不亲和性造成的,而缺乏有效的传粉机制是造成哥西氏烟草结实性差的主要原因。     

Stigma Constriction in Pearl Millet, a Factor Influencing Reproduction and Disease

The sequence of events during pollination in pearl millet isdescribed. Four or five hours after pollination with compatiblepollen a constriction region located in the fused stylodia,consisting of a collar of parenchymatous cells, becomes apparent.The structural integrity of the constriction region is lostwithin 6 h of pollination, thereby eventually isolating theovary from other pollen and also from ovary pathogens whichnormally enter throught the stigma. The constriction developsin unpollinated gynoecia 4–5 d after stigma emergence,thereby contributing to out-crossing in the protogynous commercialhybrid commonly grown in the semi-arid tropics. The potentialsignificance of a stigma constriction character in a wider botanicalcontext is discussed, particularly as it is a hitherto unrecognizedincompatibility barrier. Pennisetum americanum (L.), pearl millet, Sorghum bicolor (L.), sorghum, pollination, stigma constriction, ergot, protogyny, incompatibility barrier     

RNA Silencing of Exocyst Genes in the Stigma Impairs the Acceptance of Compatible Pollen in Arabidopsis

Initial pollen-pistil interactions in the Brassicaceae are regulated by rapid communication between pollen grains and stigmatic papillae and are fundamentally important, as they are the first step toward successful fertilization. The goal of this study was to examine the requirement of exocyst subunits, which function in docking secretory vesicles to sites of polarized secretion, in the context of pollen-pistil interactions. One of the exocyst subunit genes, EXO70A1, was previously identified as an essential factor in the stigma for the acceptance of compatible pollen in Arabidopsis (Arabidopsis thaliana) and Brassica napus. We hypothesized that EXO70A1, along with other exocyst subunits, functions in the Brassicaceae dry stigma to deliver cargo-bearing secretory vesicles to the stigmatic papillar plasma membrane, under the pollen attachment site, for pollen hydration and pollen tube entry. Here, we investigated the functions of exocyst complex genes encoding the remaining seven subunits, SECRETORY3 (SEC3), SEC5, SEC6, SEC8, SEC10, SEC15, and EXO84, in Arabidopsis stigmas following compatible pollinations. Stigma-specific RNA-silencing constructs were used to suppress the expression of each exocyst subunit individually. The early postpollination stages of pollen grain adhesion, pollen hydration, pollen tube penetration, seed set, and overall fertility were analyzed in the transgenic lines to evaluate the requirement of each exocyst subunit. Our findings provide comprehensive evidence that all eight exocyst subunits are necessary in the stigma for the acceptance of compatible pollen. Thus, this work implicates a fully functional exocyst complex as a component of the compatible pollen response pathway to promote pollen acceptance.In flowering plants, sexual reproduction occurs as a result of constant communication between the male gametophyte and the female reproductive organ, from the initial acceptance of compatible pollen to final step of successful fertilization (for review, see Beale and Johnson, 2013; Dresselhaus and Franklin-Tong, 2013; Higashiyama and Takeuchi, 2015). In the Brassicaceae, the stigmas that present a receptive surface for pollen are categorized as dry and covered with unicellular papillae (Heslop-Harrison and Shivanna, 1977). Communication is initiated rapidly following contact of a pollen grain with a stigmatic papilla, as the role of the papillae is to regulate the early cellular responses leading to compatible pollen germination. The basal compatible pollen recognition response also presents a barrier to foreign pollen or is inhibited with self-incompatible pollen (for review, see Dickinson, 1995; Hiscock and Allen, 2008; Chapman and Goring, 2010; Indriolo et al., 2014b).The initial adhesive interaction between the pollen grain and the papilla cell in the Brassicaceae is mediated by the exine of the pollen grain and the surface of the stigmatic papilla (Preuss et al., 1993; Zinkl et al., 1999). A stronger connection results between the adhered pollen grain and the stigmatic papilla with the formation of a lipid-protein interface (foot) derived from the pollen coat and the stigmatic papillar surface (Mattson et al., 1974; Stead et al., 1980; Gaude and Dumas, 1986; Elleman and Dickinson, 1990; Elleman et al., 1992; Preuss et al., 1993; Mayfield et al., 2001). It is at this point that a Brassicaceae-specific recognition of compatible pollen is proposed to occur (Hülskamp et al., 1995; Pruitt, 1999), though the nature of this recognition system is not clearly defined. Two stigma-specific Brassica oleracea glycoproteins, the S-Locus Glycoprotein and S-Locus Related1 (SLR1) protein, play a role in compatible pollen adhesion (Luu et al., 1997, 1999), potentially through interactions with the pollen coat proteins, PCP-A1 and SLR1-BP, respectively (Doughty et al., 1998; Takayama et al., 2000). The simultaneous recognition of self-incompatible pollen would also take place at this stage (for review, see Dresselhaus and Franklin-Tong, 2013; Indriolo et al., 2014b; Sawada et al., 2014). Thus, this interface not only provides a strengthened bond between the pollen grain and stigmatic papilla, but likely facilitates the interaction of signaling proteins from both partners to promote specific cellular responses in the stigmatic papilla toward the pollen grain.One response regulated by these interactions is the release of water from the stigmatic papilla to the adhered compatible pollen grain to enable the pollen grain to rehydrate, germinate, and produce a pollen tube (Zuberi and Dickinson, 1985; Preuss et al., 1993). Upon hydration, the pollen tube emerges at the site of pollen-papilla contact and penetrates the stigma surface between the plasma membrane and the overlaying cell wall (Elleman et al., 1992; Kandasamy et al., 1994). Pollen tube entry into the stigmatic surface represents a second barrier, selecting compatible pollen tubes. Subsequently, the compatible pollen tubes traverse down to the base of the stigma, enter the transmitting tract, and grow intracellularly toward ovules for fertilization. Pollen-pistil interactions at these later stages are also highly regulated (for review, see Beale and Johnson, 2013; Dresselhaus and Franklin-Tong, 2013; Higashiyama and Takeuchi, 2015).EXO70A1, a subunit of the exocyst, was identified as a factor involved in early pollen-stigma interactions, where it is required in the stigma for the acceptance of compatible pollen and inhibited by the self-incompatibility response (Samuel et al., 2009). Stigmas from the Arabidopsis (Arabidopsis thaliana) exo70A1 mutant display constitutive rejection of wild-type-compatible pollen (Samuel et al., 2009; Safavian et al., 2014). This stigmatic defect was rescued by the stigma-specific expression of an Red Fluorescent Protein (RFP):EXO70A1 transgene (Samuel et al., 2009) or partially rescued by providing a high relative humidity environment (Safavian et al., 2014). In addition, the stigma-specific expression of an EXO70A1 RNA interference construct in Brassica napus ‘Westar’ resulted in impaired compatible pollen acceptance and a corresponding reduction in seed production compared with compatible pollinations with wild-type B. napus ‘Westar’ pistils (Samuel et al., 2009). From these studies, EXO70A1 was found to be a critical component in stigmatic papillae to promote compatible pollen hydration and pollen tube entry through the stigma surface. One of the functions of the exocyst is to mediate polar secretion (for review, see Heider and Munson, 2012; Zárský et al., 2013; Synek et al., 2014). Consistent with this, previous studies have observed vesicle-like structures in proximity to the stigmatic papillar plasma membrane in response to compatible pollen in both Brassica spp. and Arabidopsis species (Elleman and Dickinson, 1990, 1996; Dickinson, 1995; Safavian and Goring, 2013; Indriolo et al., 2014a). The secretory activity is predicted to promote pollen hydration and pollen tube entry. As well, consistent with the proposed inhibition of EXO70A1 by the self-incompatibility pathway (Samuel et al., 2009), a complete absence or a significant reduction of vesicle-like structures at the stigmatic papillar plasma membrane was observed in the exo70A1 mutant and with self-incompatible pollen (Safavian and Goring, 2013; Indriolo et al., 2014a).The exocyst is a well-defined complex in yeast (Saccharomyces cerevisiae) and animal systems, consisting of eight subunits, SEC3, SEC5, SEC6, SEC8, SEC10, SEC15, EXO70, and EXO84 (TerBush et al., 1996; Guo et al., 1999). Exocyst subunit mutants were first identified in yeast as secretory mutants displaying a cytosolic accumulation of secretory vesicles (Novick et al., 1980). Subsequent work defined roles for the exocyst in vesicle docking at target membranes in processes such as regulated secretion, polarized exocytosis, and cytokinesis to facilitate membrane fusion by Soluble NSF Attachment protein Receptor (SNARE) complexes (for review, see Heider and Munson, 2012; Liu and Guo, 2012). In plants, genes encoding all eight exocyst subunits have been identified, and many of these genes exist as multiple copies. For example, the Arabidopsis genome contains single copy genes for SEC6 and SEC8, two copies each for SECRETORY3 (SEC3), SEC5, SEC10, and SEC15, three EXO84 genes, and 23 EXO70 genes (Chong et al., 2010; Cvrčková et al., 2012; Vukašinović et al., 2014). Ultrastructural studies using electron tomography uncovered the existence of a structure resembling the exocyst in Arabidopsis (Otegui and Staehelin, 2004; Seguí-Simarro et al., 2004). Localization studies of specific Arabidopsis exocyst subunits also supported conserved roles in polarized exocytosis and cytokinesis in plants. Localization studies have shown EXO70, SEC6, and SEC8 at the growing tip of pollen tubes (Hála et al., 2008), EXO70A1 at the stigmatic papillar plasma membrane (Samuel et al., 2009), SEC3a, SEC6, SEC8, SEC15b, EXO70A1, and EXO84b at the root epidermal cell plasma membrane and developing cell plate (Fendrych et al., 2010, 2013; Wu et al., 2013; Zhang et al., 2013; Rybak et al., 2014), and SEC3a at the plasma membrane in the embryo and root hair (Zhang et al., 2013). Similar to the yeast exocyst mutants, vesicle accumulation has also been observed in the exo70A1 and exo84b mutants (Fendrych et al., 2010; Safavian and Goring, 2013). Taken together, these findings strongly support that plant exocyst subunits function in vivo in vesicle docking at sites of polarized secretion and cytokinesis (for review, see Zárský et al., 2013). In support of this, a recent study investigating Transport Protein Particle (TRAPP)II and exocyst complexes during cytokinesis in Arabidopsis has identified all eight exocyst components in immunoprecipitated complexes (SEC3a/SEC3b, SEC5a, SEC6, SEC8, SEC10, SEC15b, EXO70A1, EXO70H2, and EXO84b; Rybak et al., 2014).Several plant exocyst subunit genes have been implicated in biological processes that rely on regulated vesicle trafficking, where corresponding mutants have displayed a range of growth defects. At the cellular level, these phenotypes have been associated with decreased cell elongation and polar growth (Cole et al., 2005, 2014; Wen et al., 2005; Synek et al., 2006), defects in cytokinesis and cell plate formation (Fendrych et al., 2010; Wu et al., 2013; Rybak et al., 2014), and disrupted Pin-Formed (PIN) auxin efflux carrier recycling and polar auxin transport (Drdová et al., 2013). Several Arabidopsis subunit mutants display strong growth defects such as the sec3a mutant with an embryo-lethal phenotype (Zhang et al., 2013), sec6, sec8, and exo84b mutants with severely dwarfed phenotypes and defects in root growth (Fendrych et al., 2010; Wu et al., 2013; Cole et al., 2014), and exo70A1 with a milder dwarf phenotype (Synek et al., 2006). The Arabidopsis exo70A1 mutant has also been reported to have defects in root hair elongation, hypocotyl elongation, compatible pollen acceptance, seed coat deposition, and tracheary element differentiation (Synek et al., 2006; Samuel et al., 2009; Kulich et al., 2010; Li et al., 2013). Essential roles for other exocyst subunits include Arabidopsis SEC5a/SEC5b, SEC6, SEC8, and SEC15a/SEC15b in male gametophyte development and pollen tube growth (Cole et al., 2005; Hála et al., 2008; Wu et al., 2013), SEC8 in seed coat deposition (Kulich et al., 2010), SEC5a, SEC8, EXO70A1, and EXO84b in root meristem size and root cell elongation (Cole et al., 2014), and a maize (Zea mays) SEC3 homolog in root hair elongation (Wen et al., 2005). Finally, the Arabidopsis EXO70B1, EXO70B2, and EXO70H1 subunits have been implicated in plant defense responses (Pecenková et al., 2011; Stegmann et al., 2012; Kulich et al., 2013; Stegmann et al., 2013).Even with these detailed studies on the functions of exocyst subunits in plants, a systematic demonstration of the requirement of all eight exocyst subunits in a specific plant biological process is currently lacking. EXO70A1 was previously identified as an essential factor in the stigma for compatible pollen-pistil interactions in Arabidopsis and B. napus (Samuel et al., 2009), and we hypothesized that this protein functions as part of the exocyst complex to tether post-Golgi secretory vesicles to stigmatic papillar plasma membrane (Safavian and Goring, 2013). To provide support for the proposed biological role of the exocyst in the stigma for compatible pollen acceptance, we investigated the roles of the remaining seven subunits, SEC3, SEC5, SEC6, SEC8, SEC10, SEC15, and EXO84, in Arabidopsis stigmatic papillae. Given that some Arabidopsis exocyst subunits were previously determined to be essential at earlier growth stages, stigma-specific RNA-silencing constructs were used for each exocyst subunit, and the early postpollination stages were analyzed for these transgenic lines. Our collective data demonstrates that all eight exocyst subunits are required in the stigma for the early stages of compatible pollen-pistil interactions.     

烟草花粉萌发和花粉管生长期间柱头和花柱中的钙分布

烟草柱头表面有两层覆盖物,其中含有少量细小的钙颗粒.花粉落到柱头上后,储存在花粉外壁中的钙被释放到覆盖层中.当花粉管穿过覆盖层长入柱头细胞之间时,花粉管顶端的细胞壁中出现了大量的细小钙颗粒.开花后22 h观察时,在花柱引导组织中形成了钙的梯度分布:花柱上部引导组织中的钙较少,而下部连接子房处的花柱引导组织中含有较多的钙颗粒.去雄花开花后1 d时,花柱上部引导组织中的钙明显增多;3 d时,连柱头细胞中也出现了较多的钙颗粒.讨论了烟草花柱引导组织中钙梯度分布和花粉管生长的关系.     

芦芽山自然保护区紫啸鸫的繁殖生态观察

紫啸鸫 (Ｍｙｉｏｐｈｏｎｅｕｓｃａｅｒｕｌｅｕｓ)为山地溪边生活的鸟类。 1 997～ 1 999年的 5至 9月作者在芦芽山保护区对紫啸鸫的繁殖生态作了观察。现将结果报道如下。1　自然概况及工作方法芦芽山自然保护区位于山西省吕梁山北端 ,地处宁武、五寨、岢岚三县交界 ,东经 1 1 1°50′～ 1 1 2°5′3 0″,北纬 3 8°3 5′4 0″～ 3 8°4 5′之间。境内森林繁茂 ,灌木丛生 ;总面积 3 2 . 1 8万亩 ,主峰芦芽山海拔 2772ｍ ;年均温 4～ 7°Ｃ ,年降水 50 0～ 70 0ｍｍ ,无霜期 90～ 1 3 5天。工作过程中 ,我们事先选定三条调查路线 ,(圪洞…     

Pollen development in a submerged plant,Ottelia alismoides (L.) Pers. (Hydrocharitaceae)

Exine structure and its developmental program in a submerged plant,Ottella alismoides (L.) Per. were investigated with scanning and transmission electron microscopies. Verrucate protrusions initiate on microspore plasma membrane at early tetrad stage. The verrucate protrusions develop into spines during free microspore stage. A foot layer is formed by accumulation of lamellated structure. The pollen grains ofOttelia alismoides are inaperturate, not omniaperturate, because of the well-developed foot layer. The inaperturate pollen grains ofOttelia are characterized by the spinous protrusions and the granular foot layer.     

Pollen Deposition on and under the Water Surface

In the summers of 1974 and 1975 pollen deposition was studied in two bays of the Baltic Sea near Stockholm with roofed and unroofed samplers mounted on rafts and with samplers submerged to levels of 30 and 60 cm over the bottom. The unroofed traps show larger totals of pollen grains than the roofed samplers. Sufficient data could not be obtained to establish that the totals of pollen grains in the submerged samplers at level 30 cm were larger than the totals at level 60 cm. The differences in pollen rain in the two seasons can be attributed mainly to the meteorological conditions, viz, to the particularly dry and warm summer of 1975. In the raft samplers the percentages of redeposited arboreal pollen are lower than in the submerged ones. Transport by currents and redeposition influence the pollen spectra in the submerged samplers. The pollen spectra in samplers over and under the water surface depend mainly on the specific composition of the surrounding vegetation. Pollen transport over short distances is therefore of great importance. No evidence was found of long-distance pollen transport.     

Directional Guidance of Nicotiana alata Pollen Tubes in Vitro and on the Stigma

Pollen tubes navigate the route from stigma to ovule with great accuracy, but the cues that guide them along this route are not known. We reproduced the environment on the stigma of Nicotiana alata by immersing pollen in stigma exudate or oil close to an interface with an aqueous medium. The growth of pollen in this culture system mimicked growth on stigmas: pollen grains hydrated and germinated, and pollen tubes grew toward the aqueous medium. The rate-limiting step in pollen germination was the movement of water through the surrounding exudate or oil. By elimination of other potential guidance cues, we conclude that the directional supply of water probably determined the axis of polarity of pollen tubes and resulted in growth toward the interface. We propose that a gradient of water in exudate is a guidance cue for pollen tubes on the stigma and that the composition of the exudate must be such that it is permeable enough for pollen hydration to occur but not so permeable that the supply of water becomes nondirectional. Pollen tube penetration of the stigma may be the most frequently occurring hydrotropic response of higher plants.     

海草化学成分及其生物活性研究进展

海草为指生长于海洋和河口等近海水下一大类的单子叶高等植物统称。论文综述了世界范围海草分离的次生代谢产物及其生物或生理活性。     

山西庞泉沟自然保护区长尾雀繁殖习性观察

长尾雀 (Ｖｒａｇｕｓｓｉｂｉｒｉｃｕｓ)在山西庞泉沟自然保护区为留鸟。其繁殖习性国内报道尚少。 1 998～ 2 0 0 0年 4～ 8月 ,我们在庞泉沟自然保护区对该鸟的繁殖习性作了观察。现记述如下。1　观察点的自然概况庞泉沟自然保护区在山西省吕梁山脉中段 ,东经1 1 1°2 2′～ 33′和北纬 37°4 5′～ 5 5′之间 ;海拔 1 6 0 0～2 831ｍ ;高层乔木以华北落叶松 (Ｌａｒｉｘ ｐｒｉｎｃｉｐｉｓ -ｒｕｐｐｒｅｃｈｔｉｉ)、云杉 (Ｐｉｃｅａｓｐｐ .)为主 ;灌木以沙棘(Ｈｉｐｐｏｐｈａｅｒｈａｍａｉｃｌｅｓ)、刺梨 (Ｒｉｂｅｓｎｕｒｅ…     

Chemical Nature of Phagostimulants in Pollen Attractive to Honeybees

Honey bees display a powerful ability to recognize pollen from most plants as food and non-pollen materials as not being food. We sequentially extracted a mixed species blend of pollen with a range of non polar to polar solvents and tested the extracts for attractiveness and feeding enhancement by young bees. Both non polar and polar materials were independently attractive when added in trace quantities to a plain artificial diet. The attractants have little inherent nutritional value, as addition of phagostimulants to artificial diets did not increase the life spans of bees compared to phagostimulant-free diets. These data indicate that pollen phagostimulants consist not of a single or a few specific compounds, but rather are a suite of diverse components that additively or synergistically serve to exceed a threshold level of stimulation necessary for feeding.     

Pollen limitation and Allee effect related to population size and sex ratio in the endangered Ottelia acuminata (Hydrocharitaceae): implications for conservation and reintroduction

Small populations may suffer more severe pollen limitation and result in Allee effects. Sex ratio may also affect pollination and reproduction success in dioecious species, which is always overlooked when performing conservation and reintroduction tasks. In this study, we investigated whether and how population size and sex ratio affected pollen limitation and reproduction in the endangered Ottelia acuminata, a dioecious submerged species. We established experimental plots with increasing population size and male sex ratio. We observed insect visitation, estimated pollen limitation by hand‐pollinations and counted fruit set and seed production per fruit. Fruit set and seed production decreased significantly in small populations due to pollinator scarcity and thus suffered more severe pollen limitation. Although frequently visited, female‐biased larger populations also suffered severe pollen limitation due to few effective visits and insufficient pollen availability. Rising male ratio enhanced pollination service and hence reproduction. Unexpectedly, pollinator preferences did not cause reduced reproduction in male‐biased populations because of high pollen availability. However, reproductive outputs showed more variability in severe male‐biased populations. Our results revealed two component Allee effects in fruit set and seed production, mediated by pollen limitation in O. acuminata. Moreover, reproduction decreased significantly in larger female‐biased populations, increasing the risk of an Allee effect.