稻属植物胚的形态结构与二(异)型子叶

长久以来植物学界认定稻(Oryza sativa L.)是单子叶植物.作者从稻胚发育的研究中确认稻胚具二型子叶,并非单子叶.稻属其他种的胚胎形态与O.sativa是否相同?是否具二型子叶?根据扫描电子显微镜的观察结果,稻属(Oryza) 22个种和亚种的胚的形态结构可以分为两种类型.O.sativa等16个种胚具腹鳞和侧鳞,属第一类型;O. meyeriana (Zoll. et Mor. ex Steud.) Baill.ssp. tuberculata W. C. Wu et Y. G. Lu, G. C. Wang等6个种(亚种)胚缺腹鳞和侧鳞,属第二类型.O.sativa和O. meyeriana ssp. tuberculata的胚胎发育过程所出现的盾片原基、胚根鞘原基、胚芽鞘原基和生长锥均来自原胚,前二者发育成胚套,是外围子叶;胚芽鞘原基发育成围在生长锥外并盖住生长锥的空心的倒锥状胚芽鞘,是顶生子叶.第一类型与第二类型稻胚都具有二型子叶.第二类型稻胚在盾片原基发育过程中并不分化出腹鳞和侧鳞,因而造成第二类型稻胚缺腹鳞与侧鳞.稻的二型子叶源于原胚的背腹极性分化.     

玉米胚胎发育、萌发与胚的结构及子叶二型性

运用扫描电镜与半薄切片技术,观察了玉米(Zea mays L.)的胚发育过程,得到以下认识:第一、关于原胚.玉米合子细胞分裂形成的原胚分为胚柄、胚基与胚体三部分.胚柄短小,寿命短暂.胚基具有生长带,纵向伸长长度大,胚基的上部参与形成胚根鞘,其余部分干缩后附在胚根鞘末端.第二、玉米胚的背腹极性及二型子叶.原胚初期胚体出现背腹极性,腹面的细胞小,细胞质稠密,液泡较少;背面的细胞较大,细胞质稠密度略低,液泡较多.原胚后期胚体分化为腹部与背部,腹部从腹面的中央突起,背部在腹部的周围(从左至右侧)及整个胚体背面.进入幼胚时期,腹部分化为胚芽鞘、生长锥、胚轴、胚根和胚根鞘(大部分).期间,胚芽鞘原基和根原始细胞的分化都从胚体的中轴部位开始,然后向两侧和四周扩展,表现出胚体腹面形态的两侧对称性.原胚的背部形成盾片原基,盾片原基经历向左、右、上、下的迅速扩展和加厚的生长,将整个腹部所分化形成的构件藏于盾片的纵沟之中,最后盾片从纵沟的边缘长出的左、右侧鳞均向胚体的中轴线生长,完整显示出玉米胚腹面的两侧对称.玉米胚由腹部顶端形成胚芽鞘和生长锥的情况与水稻胚的胚芽鞘(顶生子叶)和生长锥的形成相同,玉米的胚芽鞘也是顶生子叶,盾片则是侧生子叶.玉米异型子叶的由来在于胚体的背腹极性.第三、玉米胚的真实形态结构及胚胎发育时期的划分.玉米胚是一个胚轴,其顶部是具胚芽鞘的胚芽,中部是具侧生子叶(盾片)的胚轴,下部是具胚根鞘的胚根.盾片从背面到腹面包住整个胚轴系统,在胚的腹面上可见从盾片边缘衍生的左、右侧鳞的边缘相迭,只在接缝线的上、下端留下蝌蚪状的小孔,使胚芽鞘和胚根鞘的末端稍露出.胚胎发育分为4个时期: 1.原胚期--从合子细胞分裂开始至分化背部与腹部为止;2.腹部迅速分化期;3.盾片快速生长期;4.侧鳞生长、胚套形成期.第四、获取垂直于胚腹面正中央纵切面是正确认识玉米胚形态的关键.     

稻胚发育的三维形态研究兼论胚各部分的形态本质

运用扫描电镜及塑料半薄切片技术,从水稻（ＯｒｙｚａｓａｔｉｖａＬ．）授粉后２ｄ开始至种子成熟,追踪观察了稻胚的三维形态发育,根据结果,对胚各部分的形态本质提出一些新的见解。（１）授粉后２ｄ的胚由胚柄、胚基和胚体组成。胚基为胚柄和胚体之间的过渡区,呈喇叭状,胚基与胚柄不能等同。２ｄ的胚未出现器官分化,属原胚;但胚背腹分化明显,即存在背腹极性。（２）授粉后第３至第５天幼胚的形态变化及器官分化至关重要。盾片和胚芽鞘在授粉后３ｄ的幼胚上同时出现,两者均直接由原胚分化,并非胚芽鞘从盾片发生。胚芽鞘原基经历这３ｄ的特殊形态演变,形成空心倒锥状的胚芽鞘,展现了禾本科特有的胚芽鞘的形态形成机理。３ｄ幼胚胚根的原形成层、基本分生组织及根冠分化;４ｄ幼胚小丘状生长锥形成,胚根的原表皮分化,茎根轴形成;５ｄ幼胚胚芽、胚轴与胚根初步形成。（３）稻胚具有二型子叶,胚套是胚的外围子叶,盾片是此子叶的一个主要部分（侧生子叶）,胚芽鞘是顶生子叶。     

8种耳叶苔属植物的孢子形态及壁层结构电镜观察

对8种耳叶苔属(Frullania)植物的孢子形态进行了电镜观察研究.其中,运用扫描电镜(SEM)观察了7种耳叶苔属植物的孢子形态及纹饰,所观察的孢子都为近球形或近多角形,无萌发孔,属于中型孢子(25～45 μm),表面纹饰为密集型疣状(颗粒状),其中4种具有明显的莲座状结构.运用透射电镜(TEM)观察了4种耳叶苔属植物的孢壁结构,结果显示,4种孢子的壁层超微结构相似:周壁为颗粒状物质,覆盖在外壁表面.外壁有多个数量不等的玫瑰状结构,周壁颗粒物质填充在内.内壁与外壁分层不明显,由外向内电子层密度逐渐增加.     

玉米胚胎发育、萌发与胚的结构及子叶二型性

运用扫描电镜与半薄切片技术,观察了玉米(Zea mays L.)的胚发育过程,得到以下认识：第一、关于原胚。玉米合子细胞分裂形成的原胚分为胚柄、胚基与胚体三部分。胚柄短小,寿命短暂。胚基具有生长带,纵向伸长长度大,胚基的上部参与形成胚根鞘,其余部分干缩后附在胚根鞘末端。第二、玉米胚的背腹极性及二型子叶。原胚初期胚体出现背腹极性,腹面的细胞小,细胞质稠密,液泡较少;背面的细胞较大,细胞质稠密度略低,液泡较多。原胚后期胚体分化为腹部与背部,腹部从腹面的中央突起,背部在腹部的周围(从左至右侧)及整个胚体背面。进入幼胚时期,腹部分化为胚芽鞘、生长锥、胚轴、胚根和胚根鞘(大部分)。期间,胚芽鞘原基和根原始细胞的分化都从胚体的中轴部位开始,然后向两侧和四周扩展,表现出胚体腹面形态的两侧对称性。原胚的背部形成盾片原基,盾片原基经历向左、右、上、下的迅速扩展和加厚的生长,将整个腹部所分化形成的构件藏于盾片的纵沟之中,最后盾片从纵沟的边缘长出的左、右侧鳞均向胚体的中轴线生长,完整显示出玉米胚腹面的两侧对称。玉米胚由腹部顶端形成胚芽鞘和生长锥的情况与水稻胚的胚芽鞘(顶生子叶)和生长锥的形成相同,玉米的胚芽鞘也是顶生子叶,盾片则是侧生子叶。玉米异型子叶的由来在于胚体的背腹极性。第三、玉米胚的真实形态结构及胚胎发育时期的划分。玉米胚是一个胚轴,其顶部是具胚芽鞘的胚芽,中部是具侧生子叶(盾片)的胚轴,下部是具胚根鞘的胚根。盾片从背面到腹面包住整个胚轴系统,在胚的腹面上可见从盾片边缘衍生的左、右侧鳞的边缘相迭,只在接缝线的上、下端留下蝌蚪状的小孔,使胚芽鞘和胚根鞘的末端稍露出。胚胎发育分为4个时期：1．原胚期——从合子细胞分裂开始至分化背部与腹部为止;2．腹部迅速分化期;3．盾片快速生长期;4．侧鳞生长、胚套形成期。第四、获取垂盲于胚腹面正中央纵切面是正确认识玉米胚形态的关键。     

Effects of submergence on development and gravitropism in the coleoptile of Oryza sativa L.

Caryopses of rice (Oryza sativa L. cv. Sasanishiki) were germinated in air or under water. In submerged seedlings a twofold increase in coleoptile growth rate and an inhibition of root growth was observed. The amount of starch in the amyloplasts of submerged coleoptiles was substantially reduced compared to the air-grown control plants and plastids had a proplastidic character. During the rapid elongation of coleoptiles under water, the osmotic concentration of the press sap remained constant, whereas in air-grown coleoptiles a decrease was measured. Determination of curvature of gravistimulated air-grown and submerged shoots was carried out by placing the coleoptiles horizontally in air of 98% relative humidity. Air-grown coleoptiles reached a vertical orientation within 5 h after onset of gravistimulation. In coleoptiles germinated under water the first signs of consistent negative gravitropic bending occurred after 4–5 h and curvature was complete after 24 h. During the first 5 h of gravistimulation the water-grown coleoptiles grew at an average rate of 0.39 mm·h^–1, whereas in air-grown coleoptiles a rate of 0.27 mm·h^–1 was measured. Concomitant with the delayed onset of gravitropic bending of the water-grown coleoptiles, a change in plastid ultrastructure and an increase in starch content was observed. We conclude that the gravitropic responsiveness of the rice coleoptile depends on the presence of starch-filled amyloplasts.We wish to thank H.-J. Ensikat for technical assistance with the scanning electron microscopy. Supported by the Bundesminister für Forschung und Technologie and the Deutsche Forschungsgemeinschaft.     

Phototropism of rice (Oryza sativa L.) coleoptiles: fluence-response relationships, kinetics and photogravitropic equilibrium

Phototropism of rice (Oryza sativa L.) coleoptiles induced by unilateral blue light was characterized using red-light-grown seedlings. Phototropic fluence-response relationships, investigated mainly with submerged coleoptiles, revealed three response types previously identified in oat and maize coleoptiles: two pulse-induced positive phototropisms and a phototropism that depended on stimulation time. The effective ranges of fluences and fluence rates were comparable to those reported for maize. Compared with oats and maize, however, curvature responses in rice were much smaller and coleoptiles straightened faster after establishing the maximal curvature. When stimulated continuously, submerged coleoptiles developed curvature slowly over a period of 6 h, whereas air-grown coleoptiles, which showed smaller phototropic responsiveness, established a photogravitropic equilibrium from about 4 h of stimulation. The plot of the equilibrium angle against log fluence rates yielded a bell-shaped optimum curve that spanned over a relatively wide fluence-rate range; a maximal curvature of 25° occurred at a fluence rate of 1 μmol · m⁻² · s⁻¹. This optimum curve apparently reflects the light sensitivity of the steady-state phototropic response. Received: 28 June 1996 / Accepted: 30 July 1996     

Search for and analysis of single nucleotide polymorphisms (SNPs) in rice (Oryza sativa, Oryza rufipogon) and establishment of SNP markers.

We searched for SNPs in 417 regions distributed throughout the genome of three Oryza sativa ssp. japonica cultivars, two indica cultivars, and a wild rice (O. rufipogon). We found 2800 SNPs in approximately 250,000 aligned bases for an average of one SNP every 89 bp, or one SNP every 232 bp between two randomly selected strains. Graphic representation of the frequency of SNPs along each chromosome showed uneven distribution of polymorphism-rich and -poor regions, but little obvious association with the centromere or telomere. The 94 SNPs that we found between the closely related cultivars 'Nipponbare' and 'Koshihikari' can be converted into molecular markers. Our establishment of 213 co-dominant SNP markers distributed throughout the genome illustrates the immense potential of SNPs as molecular markers not only for genome research, but also for molecular breeding of rice.     

Growth at reduced turgor: irreversible and reversible cell-wall extension of maize coleoptiles and its implications for the theory of cell growth

The relationship between steady-state elongation rate (G) and turgor pressure (P; G/P curve) was investigated using isolated segments of maize (Zea mays L.) coleoptiles incubated in osmotic solutions of a water potential range of 0 to -10 bar (polyethylene glycol 6000 as osmoticum). Short-term elongation measurements revealed curvilinear G/P curves with a steep slope at high turgor and a shallow slope at low turgor. Owing to a decrease of osmotic pressure and turgor, there was a tendency for straightening of the G/P curves during long-term elongation. An elongation rate of zero was adjusted by lowering the turgor by 4.5 bar at a constant osmotic pressure of 6.7 bar. Auxin increased — whereas abscisic acid decreased — the slope of the G/P curve but these hormones had no effect on the threshold turgor of growth (Y = 2.2 bar). It is concluded that extensibility of the growing cell walls represented by the yielding coefficient of Lockhart's growth equation is turgor-dependent and therefore decreases to a very low value as the turgor approaches Y. When the turgor was kept at Y, a constant segment length was maintained over at least 6 h. However, separation of reversible (l_rev) and irreversible (l_irr) components of total (in vivo) length (l_tot = l_rev + l_irr) W measuring segment length before and after freezing/thawing revealed that l_irr increased continuously and l_rev decreased continuously at constant l_tot. After a step-down in turgor the segments grew in l_irr although they shrank in l_tot over the whole turgor range of 0irr irreversible length - l_rev reversible length - l_tot total length (= l_irr + l_rev) - _i osmotic pressure of cell sap - _i water potential of tissue - _o water potential of incubation medium - ABA abscisic acid - G growth rate - m yielding coefficient - P turgor pressure - PEG polyethylene glycol 6000 - Y yield threshold Supported by Deutsche Forschungsgemeinschaft (SFB 206). We thank R. Hertel for helpful comments.     

Genome-wide Investigation of Intron Length Polymorphisms and Their Potential as Molecular Markers in Rice (Oryza sativa L.)

Intron length polymorphisms (ILPs) have been used as geneticmarkers in some studies. However, a systematic investigationand large-scale exploitation of ILP markers has not been reported.In this study, we performed a genome-wide search of ILPs betweentwo subspecies (indica and japonica) in rice using the draftgenomic sequences of cultivars 93-11 (indica) and Nipponbare(japonica) and 32 127 full-length cDNA sequences of Nipponbareobtained from public databases. We identified 13 308 putativeILPs. Based on these putative ILPs, we developed 5811 candidateILP markers via electronic-PCR with primers designed in flankingexons. We further conducted experiment to verify the candidateILP markers. Out of 215 candidate ILP markers tested on 93-11,Nipponbare and their hybrid, we successfully exploited 173 codominantILP markers. Further analyses on 10 rice accessions showed thatthese ILP markers were widely applicable and most (71.1%) exhibitedsubspecies specificity. This feature suggests that ILPs wouldbe useful for the studies of genome evolution and inter-subspeciesheterosis and for cross-subspecies marker-assisted selectionin rice. In addition, by testing 51 pairs of the ILP primerson five Gramineae plants and three dicot plants, we found anotherdesirable characteristic of rice ILP markers that they havehigh transferability to other plants.     

Development and mapping of 2240 new SSR markers for rice (Oryza sativa L.).

A total of 2414 new di-, tri- and tetra-nucleotide non-redundant SSR primer pairs, representing 2240 unique marker loci, have been developed and experimentally validated for rice (Oryza sativa L.). Duplicate primer pairs are reported for 7% (174) of the loci. The majority (92%) of primer pairs were developed in regions flanking perfect repeats > or = 24 bp in length. Using electronic PCR (e-PCR) to align primer pairs against 3284 publicly sequenced rice BAC and PAC clones (representing about 83% of the total rice genome), 65% of the SSR markers hit a BAC or PAC clone containing at least one genetically mapped marker and could be mapped by proxy. Additional information based on genetic mapping and "nearest marker" information provided the basis for locating a total of 1825 (81%) of the newly designed markers along rice chromosomes. Fifty-six SSR markers (2.8%) hit BAC clones on two or more different chromosomes and appeared to be multiple copy. The largest proportion of SSRs in this data set correspond to poly(GA) motifs (36%), followed by poly(AT) (15%) and poly(CCG) (8%) motifs. AT-rich microsatellites had the longest average repeat tracts, while GC-rich motifs were the shortest. In combination with the pool of 500 previously mapped SSR markers, this release makes available a total of 2740 experimentally confirmed SSR markers for rice, or approximately one SSR every 157 kb.     

Structure and distribution of lignin in primary and secondary cell walls of maize coleoptiles analyzed by chemical and immunological probes

Lignin is an integral constituent of the primary cell walls of the dark-grown maize (Zea mays L.) coleoptile, a juvenile organ that is still in the developmental state of rapid cell extension. Coleoptile lignin was characterized by (i) conversion to lignothiolglycolate derivative, (ii) isolation of polymeric fragments after alkaline hydrolysis, (iii) reactivity to antibodies against dehydrogenative polymers prepared from monolignols, and (iv) identification of thioacidolysis products typical of lignins. Substantial amounts of lignin could be solubilized from the coleoptile cell walls by mild alkali treatments. Thioacidolysis analyses of cell walls from coleoptiles and various mesocotyl tissues demonstrated the presence of guaiacyl-, syringyl- and (traces of)p-hydroxyphenyl units besidesp-coumaric and ferulic acids. There are tissue-specific differences in amount and composition of lignins from different parts of the maize seedling. Electron-microscopic immunogold labeling of epitopes recognized by a specific anti-guaiacyl/syringyl antibody demonstrated the presence of lignin in all cell walls of the 4-d-old coleoptile. The primary walls of parenchyma and epidermis were more weakly labeled than the secondary wall thickenings of tracheary elements. No label was found in middle lamellae and cell corners. Lignin epitopes appeared first in the tracheary elements on day 2 and in the parenchyma on day 3 after sowing. Incubation of coleoptile segments in H₂O₂ increased the amount of extractable lignin and the abundance of lignin epitopes in the parenchyma cell walls. Lignin deposition was temporally and spatially correlated with the appearance of epitopes for prolinerich proteins, but not for hydroxyproline-rich proteins, in the cell walls. The lignin content of coleoptiles was increased by irradiating the seedlings with white or farred light, correlated with the inhibition of elongation growth, while growth promotion by auxin had no effect. It is concluded that wall stiffness, and thus extension growth, of the coleoptile can be controlled by lignification of the primary cell walls. Primary-wall lignin may represent part of an extended polysaccharide-polyphenol network that limits the extensibility of the cell walls.Abbreviations G, S, H guaiacyl, syringyl andp-hydroxyphenyl constituents of lignin - HRGP hydroxyproline-rich glycoprotein - LTGA lignothioglycolic acid - PRP proline-rich protein Dedicated to Professor Benno Parthier on occasion of his 65th birthdayDeceased 7 November 1996