Ovules and seeds ofDirachma socotrana (Dirachmaceae)

Dirachma has a bitegmic, crassinucellate and anatropous ovule with a single median provascular tegumentary bundle. The seed coat is characterized by an exotesta and an endotegmic pigment layer. Although the fruit ofDirachma superficially resembles that of theGeraniaceae s. str., the characters of ovule and seed do not support a relationship with that family. Also a relationship withBarbeyaceae, as suggested by recentrbcL studies, is not supported by seed anatomical characters. The true relationships ofDirachma are difficult to assess on the basis of ovule and seed characters alone. TheRhamnaceae may be a closer relative.     

朱唇种子吸水特性及其在干旱胁迫下萌发特性

种子粘液质是植物在长期适应环境过程中形成的,该物质对于种子的扩散、定居、生存力的改善、萌发、幼苗生存乃至抵御有毒化学物质毒害等都具有重要的生态学意义。朱唇为唇形科鼠尾草属多年生草本植物,原产美洲热带地区,现已广泛栽植于世界各地。为了理解朱唇种子表面的粘液物质吸水特性和种子在干旱胁迫下的萌发特性,该研究以朱唇种子为材料,运用光学显微镜和扫描电子显微镜观察以及种子萌发试验的方法,对种子和粘液层的形态结构、粘液质对种子萌发的影响进行了研究。结果表明:朱唇种子为卵形,表面为负网状结构,千粒重为(1.611±0.0084)g,无粘液种子吸水倍数为3,粘液种子吸水倍数为25,粘液层吸水倍数为122。粘液和无粘液种子及粘液层的重量都随吸水时间的延长而增长,但脱水过程要远长于吸水过程。朱唇种子吸水2 h达到饱和,经过36 h可干燥失水恢复原重。不同浓度PEG对朱唇种子的萌发均有影响,发芽势随PEG浓度升高而显著降低。朱唇种子在5%PEG胁迫下发芽率最高达(90.00±8.66)%,20%PEG胁迫下发芽率最低为(76.67±10.41)%,低浓度PEG对朱唇种子萌发有一定促进作用。这说明朱唇种子为速萌型种子,其粘液质在种子吸水过程中起到举足轻重的作用,能保证短时间内有充足的水分供其萌发。     

Cortical microtubules mark the mucilage secretion domain of the plasma membrane in Arabidopsis seed coat cells

During their differentiation Arabidopsis thaliana seed coat cells undergo a brief but intense period of secretory activity that leads to dramatic morphological changes. Pectic mucilage is secreted to one domain of the plasma membrane and accumulates under the primary cell wall in a ring-shaped moat around an anticlinal cytoplasmic column. Using cryofixation/transmission electron microscopy and immunofluorescence, the cytoskeletal architecture of seed coat cells was explored, with emphasis on its organization, function and the large amount of pectin secretion at 7 days post-anthesis. The specific domain of the plasma membrane where mucilage secretion is targeted was lined by abundant cortical microtubules while the rest of the cortical cytoplasm contained few microtubules. Actin microfilaments, in contrast, were evenly distributed around the cell. Disruption of the microtubules in the temperature-sensitive mor1-1 mutant affected the eventual release of mucilage from mature seeds but did not appear to alter the targeted secretion of vesicles to the mucilage pocket, the shape of seed coat cells or their secondary cell wall deposition. The concentration of cortical microtubules at the site of high vesicle secretion in the seed coat may utilize the same mechanisms required for the formation of preprophase bands or the bands of microtubules associated with spiral secondary cell wall thickening during protoxylem development.     

Development and structure of the comose seeds ofHillia (Rubiaceae)

The hairs at the apical end of the seeds ofHillia are pluriseriate, multicellular structures. The cells making up a hair are elongated exotesta cells and, consequently, also have secondary thickenings identical (H. parasitica) or similar (H. costanensis) to those found on the exotesta cells on the main body of the seeds. Hair formation already starts in bud stage: at and around the chalazal region of an ovule, integument epidermis cells are grouped together to form ± elongated packets of 4–7 cells. The cells of each packet undergo further elongation and anticlinal division so that a hair on a mature seed may be up to c. 30 mm long. Basally, the seeds have a tail- to ± wing-like appendage, made up of only two cell layers, the exotesta of the ab- and adaxial side of the seed. This basal appendage shows the same anatomical structure as the wings of various anemochorous rubiaceous seeds. Although seed hairs of this kind are unique in theRubiaceae and — from the point of development and structure — not homologous to exotesta wings, the presence of a basal wing-like appendage suggests thatHillia, previously often placed into a tribe of its own (Hillieae), can be accommodated in theCinchoneae, a tribe in which winged, anemochorous seeds predominate. The tufts of hairs of the comose seeds ofHillia look superficially similar to those of certainAsclepiadaceae andApocynaceae (like theRubiaceae belonging to the orderGentianales). Comparisons based on literature data, however, reveal that there are striking differences in the position, development and structure of the hairs (produced at the micropylar end, initiated after fertilization, hairs unicellular, etc.).     

甜叶菊同源四倍体离体诱导及鉴定

用不同浓度秋水仙素溶液处理甜叶菊不定芽,诱导同源四倍体,并进行解剖学、染色体鉴定和流式细胞仪鉴定倍性。结果表明:(1)用0.20%的秋水仙素溶液浸泡甜叶菊不定芽12h,同源四倍体诱导率最高,可达32.14%。(2)同源四倍体植株与二倍体(对照)相比,其气孔、叶片等均表现巨大性,且叶片变厚、叶色浓绿、叶片皱缩。(3)对照植株染色体2n=2x=22,四倍体植株染色体2n=4x=44;流式细胞仪倍性鉴定结果显示,对照DNA相对含量为100,四倍体DNA相对含量为200。(4)该研究共鉴定出48株甜叶菊同源四倍体植株,为进行倍性植株的诱导奠定了技术基础,为进一步开展甜叶菊同源四倍体新品种的选育提供了实验材料。     

Seed coat anatomy ofCrossostylis (Rhizophoraceae): its evolutionary and systematic implications

The seed coat structure of all 13 species ofCrossostylis was studied to contribute to an understanding of species delimitation and relationships within the genus. The mature seed coat is relatively uniform and consistently constructed mainly by a well-developed exotesta and a well-developed fibrous exotegmen. The species differ in the thickness of the exotesta and exotegmen, the anatomy of exotestal cells, the presence and absence of persistent mesotesta, and so forth. On the basis of comparisons of these characters, close relationships are suggested in the species groups such as:Crossostylis banksiana andC. cominsii; C. biflora, C. raiateensis andC. multiflora; C. gandiflora, C. sebertii andC. imera; and five species in the Fiji Islands. These relationships except for those of Fijian five species are also supported by cladistics as their common characters are evaluated as synapomorphy. Species-level separation ofC. banksiana, C. pedunculata andC. raiateensis each from the closest species is doubted based on the results of seed coat structure.     

The role of COBRA‐LIKE 2 function,as part of the complex network of interacting pathways regulating Arabidopsis seed mucilage polysaccharide matrix organization

The production of hydrophilic mucilage along the course of seed coat epidermal cell differentiation is a common adaptation in angiosperms. Previous studies have identified COBRA‐LIKE 2 (COBL2), a member of the COBRA‐LIKE gene family, as a novel component required for crystalline cellulose deposition in seed coat epidermal cells. In recent years, Arabidopsis seed coat epidermal cells (SCEs), also called mucilage secretory cells, have emerged as a powerful model system for the study of plant cell wall components biosynthesis, secretion, assembly and de muro modification. Despite accumulating data, the molecular mechanism of COBL function remains largely unknown. In the current research, we utilized genetic interactions to study the role of COBL2 as part of the protein network required for seed mucilage production. Using correlative phenotyping of structural and biochemical characteristics, unique features of the cobl2 extruded mucilage are revealed, including: ‘unraveled’ ray morphology, loss of primary cell wall ‘pyramidal’ organization, reduced Ruthenium red staining intensity of the adherent mucilage layer, and increased levels of the monosaccharides arabinose and galactose. Examination of the cobl2cesa5 double mutant provides insight into the interface between COBL function and cellulose deposition. Additionally, genetic interactions between cobl2 and fei1fei2 as well as between each of these mutants to mucilage‐modified 2 (mum2) suggest that COBL2 functions independently of the FEI‐SOS pathway. Altogether, the presented data place COBL2 within the complex protein network required for cell wall deposition in the context of seed mucilage and introduce new methodology expending the seed mucilage phenotyping toolbox.     

Seed coat anatomy,karyomorphology, and relationships ofSimmondsia (Simmondsiaceae)

The development of the seed coat ofSimmondsia, whose relationships are extremely problematic, is documented, and its structure is compared to those of putatively related families Euphorbiaceae and Buxaceae. InSimmondsia, the young seed coat is composed of (1) the palisadal exotesta, (2) the thick aerenchymatous mesotesta which is further differentiated into the outer and the inner tissue of mesotesta, and the undifferentiated (3) endotesta and (4) tegmen. At maturity, only the palisadal exotesta composed of thick-walled and prismatic cells, as well as the outer tissue of mesotesta composed of elongate, thick-walled cells, are persistent, while all the remainder is crushed. These distinctive structural features of the exo- and mesotesta inSimmondsia are not found in Euphorbiaceae, but prevalent in Buxaceae. Evidence from seed coat anatomy and other sources supports the view thatSimmondsia has close affinities with Buxaceae, and be placed as a distinct family along with Buxaceae in Buxales.Simmondsia has 2n=52 as a tetraploid ofx=13, and probably represents a taxon adapted to desert areas by polyploidization in the order.     

Anatomy and ontogeny of Pterodon emarginatus (Fabaceae: Faboideae) seed.

The aim of this study was to describe the anatomy and ontogeny of Pterodon emarginatus seed using the usual techniques. The ovules are campilotropous, crassinucelate, and bitegmic. The following processes occur during integument development: anticlinal divisions and phenolic compound accumulations in the exotesta, whose cells become palisade; predominantly periclinal divisions and cell expansion in the mesotesta, where the rapheal bundle differentiates; differentiation of the hourglass-cell layer adjacent to the palisade; fusion of outer and inner integuments, which remain individualized structures only at the micropylar end; and intense pectin impregnation in the mesotesta thicker walls with lignification restricted to the xylem. At the hilar pole, the Faboideae seed characteristic structure develops, with double palisade layer, subhilar parenchyma, and tracheid bar. The younger nucellus shows thicker pectic cell walls and is consumed during seed formation. The endosperm is nuclear and, after cellularization, shows peripheral cells with dense lipid content; the seeds are albuminous. The axial embryo shows fleshy cotyledons, which accumulate lipid and protein reserves; starch is rare. Although the seed structure is characteristic of the Fabaceae, the inner integument coalesces into the outer integument without being reabsorbed.     

Mucilage secretion: an adaptive mechanism to reduce seed removal by soil erosion?

Diaspores of many plant species inhabiting open vegetation in semi‐arid environments secrete mucilage after wetting (myxospermy) that glues the diaspores to the ground and prevents movement when the mucilage dries. In the present study, we test whether mucilage secretion can be considered as a selective response to soil erosion in plant species inhabiting semi‐arid environments. We relate the amount and type of mucilage secretion by seeds of Helianthemum violaceum and Fumana ericifolia (Cistaceae) to the number of raindrop impacts needed to remove these seeds after gluing them with their own mucilage to the ground and also the time that these seeds resist water run‐off without detaching. We also compare the amount of seed mucilage production by plants growing in habitats without erosion and plants affected by severe erosion by fitting mixed effect models. Our results show an important phenotypic variation in the amount of mucilage secretion in both species, although it is suggested that the effect of mucilage secretion in the rate of seed removal by erosion is species‐ and mechanism‐dependent. For F. ericifolia, the amount of mucilage secreted by the seeds is directly proportional to their resistance to raindrop impacts and is positively related to the intensity of the erosive processes that the plants experience. Nevertheless, all the seeds resist the force of run‐off during 60 min, irrespective of the amount of mucilage they produce. In H. violaceum, mucilage secretion per se, and not the amount of mucilage produced by the seeds, has an effect on the rate of seed removal by erosive processes. Furthermore, cellulosic fibrils were found only in the mucilage of F. ericifolia but not in H. violaceum. Overall, our results only partially support the hypothesis that a selective response to soil erosion exists. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 241–251.     

Seed-coat anatomy of japanese species ofCorydalis andDicentra (Papaveraceae; Fumarioideae)

Development and structure of seed-coat were examined in 16 species ofCorydalis and two species ofDicentra. Neither the tegmen (developed ii) nor the testa (developed oi) is multiplicative during seed development. Mature seed-coat is consistent in all the species examined in having mechanical structure in the exo- or endotesta. Differences are found in (1) which of the integumentary layers develops into the main mechanical layer (exotesta or endotesta), (2) whether a mesotesta is differentiated or not, and (3) whether the endotegmen is persistent as a layer of thick-walled cells, is persistent only partially, or is thoroughly degenerated. Theses seed-coat characters distinguish six groups of species (i.e., four groups inCorydalis and two inDicentra), which represent well infrageneric taxa proposed on the other characters. Evidence from seed-coat anatomy further suggests thatDicentra spectabilis (subg.Hedycapnos) retains the primitive (endotestal) seed-coat of Fumarioideae.     

荒漠植物种子粘液的生态学意义

种子粘液是在种皮外层细胞的高尔基体内产生并分泌到胞腔内或细胞壁层的吸湿膨胀的一类果胶类多糖物质。具粘液种子的植物大多生长在荒漠地区,广泛存在于十字花科、菊科和车前科等类群中。粘液的存在对荒漠植物种子的扩散、萌发、防御以及幼苗的生长等都具有重要的生态学意义,是荒漠植物适应干旱少雨的生态环境的有效对策之一。对粘液种子的研究不仅可全面揭示荒漠植物的生态适应机制及其进化生态意义,还可为研究基因控制的糖类生物合成和分泌、细胞次生壁的生物合成及形态分化建立理想的模式体系。为此,在广泛查阅相关文献的基础上,该文综合分析了国内外种子粘液的研究进展,并重点探讨了以下几方面问题：（1）种子粘液的化学成分：（2）粘液及粘液种皮的形态特征：（3）粘液细胞分化与粘液生物合成的细胞学及基因调控机制以及粘液的释放方式：（4）种子粘液的生态学意义。在此基础上展望了今后的研究方向,以期为推动我国荒漠植物种子生态学的理论与应用研究及西部荒漠区的植物物种多样性保护和生态保育提供重要理论依据。     

Isozymes as molecular markers for diploid and tetraploid individuals ofNajas marina (Najadaceae)

The genetic variability of five natural populations ofNajas marina L., i.e. one diploid of subsp.marina (Europe), two of subsp.intermedia (Europe) and both a diploid (C. Africa) and a tetraploid (Middle East) of subsp.armata, has been estimated by means of electrophoretic studies. These populations differ in their morphology and karyotype. Emphasis is placed on the characteristics and status of a tetraploid cytotype from Merkaz Sappir (Israel). Almost all the variation observed is expressed in seed alcohol dehydrogenase (ADH). The differences are in a unique allele of theAdh-2 locus and in the formation of novel heteromeric isozymes.Adh genes in seeds can be used as a marker for the autotetraploid character. The other enzyme systems tested failed in this respect. The genetic variability based on 23 loci is rather low. Nevertheless, the autotetraploid population has a higher or equal ratio of polymorphic loci than the related diploids. Cluster analysis illustrated not only thatNajas marina subsp.marina has diverged much from subsp.intermedia and subsp.armata, but also showed the difference between the latter two taxa, as well as the intermediate position of the autotetraploid population.     

抱茎独行菜MUM4基因的克隆及分析

抱茎独行菜(Lepidium perfoliatum L.)为十字花科具典型粘液繁殖体植物,为探究该植物中种皮粘液质基因（MUCILAGE-MODIFIED4,MUM4,该基因在拟南芥中编码NDP-L-鼠李糖合成酶)的功能,通过生物信息学分析设计引物克隆得到抱茎独行菜MUM4基因,命名为LpMUM4。同源比对分析结果表明,LpMUM4与拟南芥AtMUM4基因具有很高的一致性。qRT-PCR结果表明,该基因在抱茎独行菜各组织中均有表达,在角果和根中的表达量最高,且其表达量随角果的发育表现出渐强的趋势。免疫组织化学定位分析表明,LpMUM4基因于角果发育的早期阶段在内珠被和外珠被都有表达,而在外珠被的表皮和亚表皮中表达量更高,至角果发育的最后阶段,其表达集中于表皮和亚表皮层,这可能与抱茎独行菜的外珠被发育成种皮及粘液质的生成有关。将LpMUM4基因转化拟南芥,该基因的过表达对位于粘液质合成途径中的上游基因AtTTG1具有显著的抑制作用。表型比对观察显示,转基因拟南芥与其野生型植株形态无显著差异,这可能是因为抱茎独行菜种皮的发育和粘液质的形成是一个多基因调控的复杂过程,某一基因的过表达或许不会引起明显的表型变化。     

Plant and bacterial mucilages of the maize rhizosphere: Comparison of their soil binding properties and histochemistry in a model system

Mucilages from the root tips of axenically-grown maize and from a bacterium (Cytophaga sp.) isolated from the rhizosheaths of field-grown roots, were immobilized by drying onto nylon blotting membrane. The mucilage plaques remained in place through repeated rewettings and histochemical treatments. Staining of the plaques showed that both mucilages included acidic groups, and 1,2 diols (the latter notably fewer in bacterial mucilage). Bacterial mucilage plaques stained strongly for protein, plant mucilage was unstained. Plaques of both mucilages bound soil particles strongly if soil was applied to wet mucilage and then dried. Bound soil was not lost with rewetting. Dry weight and densitometer measurements showed that bacterial mucilage bound about 10% more soil than the same surface area of root-cap mucilage. Pretreatment of plaques with periodate oxidation eliminated most soil binding by root-cap mucilage but this was completely reversible by reduction with borohydride. Soil binding to bacterial mucilage was unaffected by periodate but much diminished by borohydride pretreatment (partially restored by subsequent oxidation). Neither pretreatment with cationic dyes nor preincubation in pectinase, pectin methylesterase or protease affected subsequent soil binding by the mucilage plaques. Pretreatment of root-cap mucilage plaques with lectins specific for component sugars also did not alter soil binding. It is concluded that mucilages of both plant and bacterial origin can contribute to the adhesion and cohesion of maize rhizosheaths, but each by a different mechanism. Binding by root-cap mucilage depends on 1,2 diol groups of component sugars, that of bacterial mucilage does not, and is likely to be protein mediated. ei]Section editor: R O D Dixon     

Seed morphology of Rhododendron sichotense (Ericaceae): systematic implications

The size of Rhododendron sichotense seeds and exotesta cells from 20 populations were studied using a scanning electron microscope (SEM). The results of a correlation analysis showed that seed size depends on bioclimatic factors. As a species marker, we used the exotesta cell elongation coefficient. This characteristic was unresponsive to environmental variables, demonstrating its taxonomic significance. In the centre of the species range, the samples had an exotesta cell elongation coefficient that was typical for the species, but in samples from the far northern and southern parts of the range, where the distribution of R. sichotense meets that of of R. dauricum L. and R. mucronulatum Turcz., respectively, the value of the exotesta cell elongation coefficient was intermediate between these species. Therefore, the exotesta cell elongation coefficient can be recommended for use in the detection of hybridisation areas.     

荒漠植物种子粘液的生态学意义

种子粘液是在种皮外层细胞的高尔基体内产生并分泌到胞腔内或细胞壁层的吸湿膨胀的一类果胶类多糖物质。具粘液种子的植物大多生长在荒漠地区, 广泛存在于十字花科、菊科和车前科等类群中。粘液的存在对荒漠植物种子的扩散、萌发、防御以及幼苗的生长等都具有重要的生态学意义, 是荒漠植物适应干旱少雨的生态环境的有效对策之一。对粘液种子的研究不仅可全面揭示荒漠植物的生态适应机制及其进化生态意义, 还可为研究基因控制的糖类生物合成和分泌、细胞次生壁的生物合成及形态分化建立理想的模式体系。为此, 在广泛查阅相关文献的基础上, 该文综合分析了国内外种子粘液的研究进展, 并重点探讨了以下几方面问题: (1)种子粘液的化学成分; (2)粘液及粘液种皮的形态特征; (3)粘液细胞分化与粘液生物合成的细胞学及基因调控机制以及粘液的释放方式; (4)种子粘液的生态学意义。在此基础上展望了今后的研究方向, 以期为推动我国荒漠植物种子生态学的理论与应用研究及西部荒漠区的植物物种多样性保护和生态保育提供重要理论依据。     

<Emphasis Type="Italic">In vitro</Emphasis> induction and identification of autotetraploids of <Emphasis Type="Italic">Dioscorea zingiberensis</Emphasis>

Dioscorea zingiberensis is an important medicinal plant and a source of diosgenin in China. We report research on the induction, characteristics, and chemical assays of polyploid plants of D. zingiberensis. Immersing calli in 0.3% colchicine solution for 16 h prior to culture induced a high number of autotetraploid plants. The induction rate reached as high as 36.7% of treated calli. More than 50 lines of autotetraploid plants were obtained. All tetraploid plants showed typical polyploidy characteristics. Twenty selected tetraploid lines were transferred to the field for determination of morphological characteristics and for chemical assays. Six elite lines have been selected for further selection and breeding into new varieties for commercial production.     

Cellulose synthesis via the FEI2 RLK/SOS5 pathway and cellulose synthase 5 is required for the structure of seed coat mucilage in Arabidopsis

The seeds of Arabidopsis thaliana and many other plants are surrounded by a pectinaceous mucilage that aids in seed hydration and germination. Mucilage is synthesized during seed development within maternally derived seed coat mucilage secretory cells (MSCs), and is released to surround the seed upon imbibition. The FEI1/FEI2 receptor-like kinases and the SOS5 extracellular GPI-anchored protein were shown previously to act on a pathway that regulates the synthesis of cellulose in Arabidopsis roots. Here, we demonstrate that both FEI2 and SOS5 also play a role in the synthesis of seed mucilage. Disruption of FEI2 or SOS5 leads to a reduction in the rays of cellulose observed across the seed mucilage inner layer, which alters the structure of the mucilage in response to hydration. Mutations in CESA5, which disrupts an isoform of cellulose synthase involved in primary cell wall synthesis, result in a similar seed mucilage phenotype. The data indicate that CESA5-derived cellulose plays an important role in the synthesis and structure of seed coat mucilage and that the FEI2/SOS5 pathway plays a role in the regulation of cellulose synthesis in MSCs. Moreover, these results establish a novel structural role for cellulose in anchoring the pectic component of seed coat mucilage to the seed surface.