Pollenkitt – its composition, forms and functions

Two types of sticky pollen coat material exist in angiosperms, both produced by the anther tapetum. Pollenkitt is the most common adhesive material present around pollen grains of almost all angiosperms pollinated by animals, whereas tryphine seems to be restricted only to Brassicaceae. Tapetal cell protoplasts have different patterns of development according to the products formed during their development and degeneration. If tryphine is formed, the tapetal cell protoplasts lose their individuality at the microspore stage. If pollenkitt is formed, their contents degenerate at later stages. Cell content is totally reabsorbed, when ripe pollen is not surrounded by any gluing material. Current knowledge of pollenkitt formation, deposition on pollen grains and chemical composition are reviewed and discussed. Methods for detecting this viscous fluid are also presented. The many functions of pollenkitt, deduced from personal observations and the literature, act in the period between anther opening and pollen hydration on the stigma; they are: (1) to hold pollen in the anther until dispersal; (2) to enable secondary pollen presentation; (3) to facilitate pollen dispersal; (4) to protect pollen from water loss; (5) to protect pollen from ultra-violet radiation; (6) to maintain sporophytic proteins responsible for pollen–stigma recognition inside exine cavities; (7) to protect pollen protoplasts from fungi and bacteria; (8) to keep together pollen grains during transport; (9) to protect pollen from hydrolysis and exocellular enzymes; (10) to render pollen attractive to animals; (11) to render pollen visible to animal eyes; (12) to hide pollen from animal eyes; (13) to avoid predation of pollen through smell; (14) to enable adhesion to insect bodies; (15) to enable pollen packaging by bees and to form corbicules; (16) to provide a digestible reward for pollinators; (17) to enable pollen clumps to reach the stigma; (18) to allow self-pollination; (19) to facilitate adhesion to the stigma; (20) to facilitate pollen rehydration. Depending on the developmental program of the species, these functions may act during pollen presentation, in relation to pollinators, during pollen dispersal and when pollen reaches the stigma.     

羽叶薰衣草雄性不育的细胞学研究

用光镜和电镜观察羽叶薰衣草(Lavandula pinnata L.)雄性不育小孢子发育过程的细胞形态学特征.结果表明:羽叶薰衣草花药4枚,每枚花药通常具4个小孢子囊.花药壁发育为双子叶型,从外向内分为表皮、药室内壁、中层和绒毡层4层细胞.减数分裂形成的四分体为四面体及十字交叉型.小孢子的发育过程可分为造孢细胞期、减数分裂时期、小孢子发育早期、小孢子发育晚期.未观察到二胞花粉期和成熟花粉期.羽叶薰衣草花粉败育主要发生在单核花粉时期,细胞内物质解体并逐渐消失变成空壳花粉或花粉皱缩变形成为各种畸形的败育花粉.在此之前小孢子的发育正常.羽叶薰衣草小孢子不育机制体现在绒毡层过早解体、四分体时期以后各细胞中线粒体结构不正常、胼胝质壁与小孢子母细胞脱离、花药壁细胞中淀粉出现时间异常等. 壁发育为双子叶型,从外向内分为表皮、药室内壁、中层和绒毡层4层细胞.减数分裂形成的四分体为四面体及十字交叉型.小孢子的发育过程可分为造孢细胞期、减数分裂时期、小孢子发育早期、小孢子发育晚期.未观察到二胞花粉期和成熟花粉期.羽叶薰衣草花粉败育主要发生在单核花粉时期,细胞内物质解体并逐渐消失变成空壳花粉或花粉皱缩变形成为各种畸形的败育花粉.在此 前小孢子的发育正常.羽叶薰衣草小孢子不育机制体现在绒毡层过早解体、四分体时期以后各细胞中线粒体结构不正常、胼胝质壁与小孢子母细胞脱离、花药壁细胞中淀粉出现时间异常等. 壁发育为双子叶型,从外向内分为表皮、药室内壁、中层和绒毡层4层细胞.减数分裂形成的四分体为四     

The Men-10 cDNA encodes a novel form of proline-rich protein expressed in the tapetum of dioecious Silene latifolia

 The Men-10 gene is expressed specifically in the tapetum tissue that surrounds and nourishes the developing microspores in the dioecious plant species, Silene latifolia. Men-10 encodes a proline-rich protein that contains a predicted signal region, indicating that it may be secreted from the tapetal cells and function in the extracellular domain of the tapetum or be translocated to the developing microspores. Here we report the sequence and precise expression pattern of the Men-10 cDNA and demonstrate a high level of restriction fragment length polymorphism associated with the Men-10 locus. The possible classification of Men-10 amongst known groups of proline- and hydroxyproline-rich glycoproteins, such as the arabinogalactan proteins, is discussed. Received: 20 December 1997 / Revision accepted: 2 July 1998     

Biogenesis and function of the lipidic structures of pollen grains

 Pollen grains contain several lipidic structures, which play a key role in their development as male gametophytes. The elaborate extracellular pollen wall, the exine, is largely formed from acyl lipid and phenylpropanoid precursors, which together form the exceptionally stable biopolymer sporopollenin. An additional extracellular lipidic matrix, the pollen coat, which is particularly prominent in entomophilous plants, covers the interstices of the exine and has many important functions in pollen dispersal and pollen-stigma recognition. The sporopollenin and pollen coat precursors are both synthesised in the tapetum under the control of the sporophytic genome, but at different stages of development. Pollen grains also contain two major intracellular lipidic structures, namely storage oil bodies and an extensive membrane network. These intracellular lipids are synthesised in the vegetative cell of the pollen grain under the control of the gametophytic genome. Over the past few years there has been significant progress in elucidating the composition, biogenesis and function of these important pollen structures. The purpose of this review is to describe these recent advances within the historical context of research into pollen development. Received: 1 November 1997 / Revision accepted: 3 February 1998     

Efficient production of genetically engineered,male-sterile <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> using anther-specific promoters and genes derived from <Emphasis Type="Italic">Brassica oleracea</Emphasis> and <Emphasis Type="Italic">B. rapa</Emphasis>

Prevention of transgene flow from genetically modified crops to food crops and wild relatives is of concern in agricultural biotechnology. We used genes derived from food crops to produce complete male sterility as a strategy for gene confinement as well as to reduce the food purity concerns of consumers. Anther-specific promoters (A3, A6, A9, MS2, and MS5) were isolated from Brassica oleracea and B. rapa and fused to the β-glucuronidase (GUS) reporter gene and candidate genes for male sterility, including the cysteine proteases BoCysP1 and BoCP3, and negative regulatory components of phytohormonal responses involved in male development. These constructs were then introduced into Arabidopsis thaliana. GUS analyses revealed that A3, A6, and A9 had tapetum-specific promoter activity from the anther meiocyte stage. Male sterility was confirmed in tested constructs with protease or gibberellin insensitive (gai) genes. In particular, constructs with BoCysP1 driven by the A3 or A9 promoter most efficiently produced plants with complete male sterility. The tapetum and middle layer cells of anthers expressing BoCysP1 were swollen and excessively vacuolated when observed in transverse section. This suggests that the ectopic expression of cysteine protease in the meiocyte stage may inhibit programmed cell death. The gai gene also induced male sterility, although at a low frequency. This is the first report to show that plant cysteine proteases and gai from food crops are available as a novel tool for the development of genetically engineered male-sterile plants. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

RNAi-mediated male sterility of tobacco by silencing TA29

The superior performance of F₁ hybrids has a significant impact on agricultural productivity. For commercial application, the availability of an efficient system for obtaining male-sterile lines of crops is an essential prerequisite. Here we have investigated the use of RNA interference (RNAi) technology to silence a male-specific gene in the model host tobacco. TA29 is expressed exclusively in anthers at the time of microspore development. About 10 out of 13 tobacco lines transformed with a hairpin RNAi construct containing TA29 sequences were male sterile. Transgenic plants were phenotypically indistinguishable from non-transgenic plants. At the anthesis stage, pollen grains from transgenic, male-sterile plants were aborted and lysed in comparison to the round and fully developed pollen in non-transgenic plants. Microscopic analysis of anthers showed selective degradation of tapetum in transgenic plants with no microspore development. One week after self-pollination, the ovules of non-transgenic plants were double the size of those in transgenic plants, due to successful self-fertilization. Male sterile transgenic plants set seed normally, when cross-pollinated with pollen from non-transgenic plants, confirming no adverse effect on the female parts of the flower. These results show that silencing of male-specific genes by RNAi is potentially a useful tool for generating male-sterile lines for producing hybrid seed.     

Ontogeny of intruding non-periplasmodial tapetum in the wild chicory,Cichorium intybus (Compositae)

The tapetal development ofCichorium intybus L. is investigated using LM and TEM and discussed in relation to the development in other species. During the second meiotic division the tapetal cells become binucleate and lose their cell walls. They intrude the loculus at the time of microspore release from the meiotic callose walls, which means that a locular cavity is never present in this species. During pollen development they tightly junct the exine, especially near the tips of the spines. During the two-celled pollen grain stage they degenerate and most of their content turns into pollenkitt. Until anther dehiscence they keep their individuality, which means that these intruding tapetal cells never fuse to form a periplasmodium. The ultrastructural cytoplasmatic changes during this development are discussed in relation to possible functions.     

甜椒花药绒毡层的二型性及其组织化学研究

在甜椒（Capsicum annuum L.)中,靠近花粉中部的绒毡层自药隔产生,由较大的细胞组成,而花药外部区域的其余的绒毡层细胞较小,来自于初生壁层,前者的细胞具有大液泡和较大的细胞核,甲基绿－派罗宁和汞－溴酚蓝染色反应较后者弱,在造孢组织时期,二者液泡内都含有较大的球形的酸性磷酸酶颗粒,在以后的发育中,这种颗粒消失,在减数分裂时期,两种绒毡层的DNA,RNA和蛋白质合成活动增强,来自药隔的绒毡层积累了更多的DNA,绒毡层在解体时酸性磷本酶活性很高,两种不同的绒毡层退化过程相似,在全部发育过程中绒毡层内无淀粉粒。     

Ultrastructural aspects of cytoplasmic male sterility inPetunia hybrida

Summary Anther development of isogenic male fertile and cytoplasmic male sterile types ofPetunia hybrida cv. Blue Bedder is studied by electron microscopy. First deviation in sporogenesis of the sterile type, is observed during leptotene stage of the meiocytes. Initial aberration is represented by the presence of large vacuoles in the cytoplasm of the tapetal cells. These vacuoles reveal the first aspects of degeneration; no other ultrastructural differences are observed. Vacuolation is accompanied by the condensation of cytoplasmic organelles. The tapetal cells become distorted and ultrastructural aberrations in mitochondria do occur. The mitochondria elongate and contain several tubular cristae.Substantial evidence suggests, that cytoplasmic male sterility in petunia is encoded by the mitochondrial genome (Boeshore el al. 1983). However, before degeneration becomes manifest, no consistent ultrastructural differences in mitochondrial organization are observed.Abortion of the tapetum and the sporogenous tissue in cytoplasmic male sterile plants, generally follows a corresponding pattern. Ultimately, the cells are highly distorted, the nucleus is disrupted and the cytoplasm disorganized. Mitochondria and plastids degenerate and many lipid droplets are present.     

Reflective organelles in the anterior pigment epithelium of the iris of the European starling Sturnus vulgaris

The ultrastructure and chemical composition of reflective organelles in the anterior pigment epithelium of the iris of the European starling Sturnus vulgaris were examined. The reflective organelles produced a diffuse white reflectance at the iris mid-section which was visible only when the stroma was removed. The pigment granules were clear, angular, and birefringent under the light microscope. In electron micrographs the granules were irregular in shape and density, sometimes crystalline in appearance, but more often they were lost during sectioning or staining. Guanine was abundant in the modified pigment epithelium of the starling, but not in the pigment epithelia of other birds that lacked birefringent granules. Pteridines, such as xanthopterin and leucopterin, were present in small amounts. Pteridines were also present in the iris stroma which had no reflective organelles. The reflective organelles in the starling pigment epithelium resemble both the reflecting platelets of lower vertebrate chromatophores and the reflective granules in the tapeta of various vertebrates. Possible derivation of the organelles from these sources is discussed.