内蒙古西部额济纳盆地早白垩世孢粉植物群

本文首次报道了西部额济纳盆地井下中生代地层中的孢粉植物群,该微体植物群的牲是,裸子植物花粉占绝对优势,蕨类孢子次之,早期被子植物花粉偶见。根据特征分子的出现情况,将这套地层的时代归和早白垩世早期,约在凡兰吟期至早巴列姆期范围内。     

白皮松雌配子体愈伤组织的诱导和分化

白皮松雌配子体愈伤组织的诱导和分化顾淑荣,朱至清,赵敬芳（中国科学院植物研究所,１０００４４）陈正华（中国科学院遗传研究所,１００１０１）裸子植物的胚乳与被子植物的不同,被子植物的胚乳是双受精的产物,胚乳细胞是三倍牲的。而裸子植物是单受精的,它的胚乳...     

一道试题分析

裸子植物比蕨类植物更适于陆地生活的特征是( )。A.大都是高大的乔木B.受精脱离了水的限制C.有了根、茎、叶的分化D.胚珠有子房壁包被着分析:解答此题需要掌握蕨类植物和裸子植物的主要特征,还要善于比较分析两个植物类群的相互关系及它们与环境的关系。这个题较难,属于掌握层次的试题。在植物的进化过程中,裸子植物能取代蕨类植物,     

广西大瑶山裸子植物区系分析及其在林业中的意义

大瑶山是广西中部偏东最大的山脉,是广西植物最丰富且在植物学上也是著名的地区。本地区有野生裸子植物6科,11属,17种,4变种,占广西野生裸子植物属的61.11%,种的41.18%。本文通过对属种地理成分的分析,探讨了大瑶山裸子植物区系的性质,是一兼有热带和温带成分的亚热带区系。本文还讨论了大瑶山裸子植物主要种类的分布,以及在植被中的地位及其生产意义。     

植物界的一个新类群——原裸子植物

自植物界登陆以来,又经历了近四亿年的发展与演化,终于形成了今天气象万千、形态各异、生态类型多样并遍布全球的植被景观。在名目繁多的植物类群中,生存于中泥盆世至早石炭世(距今3.7—3.2亿年)的一个已经绝灭了的植物类群——原裸子植物纲,晚近才被确定下来,并日益受到人们的格外青睐。我国著名古植物学家徐仁、李星学和周志炎三教授,曾率先对这类植物作过简略介绍。原裸子植物在高等陆生植物的发展演化上占有显赫的地位,本文拟对这一植物类群再作一些较为系统的介绍。原裸子植物概念的形成原裸子植物的概念,是由美国古植物学家C.B.Beck首先提出的。1960年,他在研究北美晚泥盆世植物化石时,意外地发现一种古羊齿(Archaeopteris)的     

我国地方植物志出版情况简介(七)

在《广西植物》第21卷第4期381～382页刊登了我国地方植物志出版情况简介(六)之后,又有一些地方植物志陆续出版,为了及时反映我国地方植物志的出版状况,作者根据最近收集的资料,将这些信息简介如下,供大家参考,遗漏之处,还望广大读者多加批评指正。1.《湖南植物志》,第2卷(2000),含裸子植物和被子植物的杨梅科至芍药科。该志计划出7卷,包括蕨类植物、裸子植物和被子植物,其中蕨类植物按秦仁昌(1978)系统,裸子植物按郑万钧(1977)系统,被子植物按恩格勒Ａ.Ｅｎｇｌｅｒ(1964)系统。2.《广东植物志》,第4卷(2000),包括裸子植物中的10科和被…     

每期20题

1一个水池中生长着莲、香蒲、浮萍和金鱼藻等植物,这些水生植物组成了()。 A.水池植物群落B.水池生态系统 C.水池植物种群D.水池植物类群系? 2.在地球表面的气候条件中,决定植物群落地理分布的两个主要因素是()。 A.热量和水分B.热量和风力 c.日照和风力0.风力和水分 3.目前植物界中种类最多,最占优势的类群是A.植物化学组成B.植物形态结构c.植物化石D.植物地理分布(4)达尔文用什么理论解释下图代表的植物进化关A.用进废退C.神造说B.灾变D.自然选择彼子植物裸子植物 ^.藻类植物B.菌类植物 c.被子植物D.裸子植物 4.下列一级保护植物中…     

裸子植物和被子植物的基本区别

植物界大约有50万种植物,其中种子植物有近25万种。种子植物又包括裸子植物和被子植物两大类。这两类植物在植物教材中占有重要位置,但对于裸子植物和被子植物在形     

不同起源时间的植物叶凋落物在中亚热带的分解特性

选择9种起源时间不同的植物的凋落叶,采用分解袋法,在浙江千岛湖地区从2006年6月到2008年6月进行了分解试验,试图探索植物进化过程中凋落物分解特性的演变趋势.所选的9种植物分属于4个类群,按起源时间由早到晚依次为蕨类植物(芒萁和桫椤)、裸子植物(苏铁、水杉、杉木和马尾松)、双子叶植物(木荷和青冈)及单子叶植物(毛竹).每隔一个月取样,每种凋落物3次重复.结果表明:不同植物类群凋落物基质的氮(N)、木质素(Lignin)含量及Lignin/N比值与分解速率具有良好的相关性.起源时间越晚的植物凋落物的基质N含量越高,为单子叶植物>双子叶植物>裸子植物>蕨类植物.Lignin含量和Lignin/N比值的趋势一致,均为起源时间越晚而值越低,即蕨类植物>裸子植物>双子叶植物>单子叶植物.凋落物分解系数k值的范围在0.25～0.63之间,表现出毛竹>青冈>木荷>水杉>马尾松>杉木>苏铁>桫椤>芒萁的趋势.4个植物类群的凋落物分解速率的均值为单子叶植物>双子叶植物>裸子植物>蕨类植物.试验结果初步表明:植物凋落物分解的进化趋势是由分解缓慢逐渐演变为分解较快.     

裸子植物系统发育的几个问题

种子植物分为裸子植物和被子植物两大类。裸子植物现存种类不多,全世界仅有70     

OBSERVATIONS ON THE MICROBODIES IN THE GENUS TILLANDSIA (BROMELIACEAE)

Organelles morphologically similar to microbodies have been found in several tissues of atmospheric species of Tillandsia from different habitats. The presence of catalase was demonstrated by the DAB reaction thus confirming the microbody nature of these organelles. They are a feature of the Tillandsia species with normal photosynthetic carbon fixation and with CAM. Their size is consistently small. The nucleoid observed in the microbodies shows a characteristic morphology which has not been reported before within other plant microbodies. This nucleoid is composed of minute tubular structures, for which the authors here propose a three-dimensional arrangement.     

Isolation of microbodies from plant tissues

Specialized microbodies have previously been isolated and characterized from fatty seedling tissues (glyoxysomes) and leaves (leaf peroxisomes). We have now examined 11 other plant tissues, including tubers, fruits, roots, shoots, and petals, and find that all contain particulate catalase, a distinctive common enzyme component of microbodies. On linear sucrose gradients the catalase activity peaks sharply at a higher equilibrium density (1.20 to 1.25 gram per cm³ in the various tissues) than the mitochondria (1.17 to 1.20). Only small amounts of protein are recovered in the fractions containing catalase, although a definite band is visible in preparations from some tissues, e.g., potato. As in the preparations from castor bean endosperm and spinach leaves for which comparable data are provided, the distribution of glycolate oxidase and uricase follows closely that of catalase on the gradients. The preparations from potato lack glyoxylate reductase and the transaminases, typical enzymes of leaf peroxisomes, and the distinctive enzymes of glyoxysomes are missing. Nonspecialized microbodies with limited enzyme composition can thus be isolated from a variety of plant tissues.     

LOCALIZATION OF ENZYMES WITHIN MICROBODIES

Microbodies from rat liver and a variety of plant tissues were osmotically shocked and subsequently centrifuged at 40,000 g for 30 min to yield supernatant and pellet fractions. From rat liver microbodies, all of the uricase activity but little glycolate oxidase or catalase activity were recovered in the pellet, which probably contained the crystalline cores as many other reports had shown. All the measured enzymes in spinach leaf microbodies were solubilized. With microbodies from potato tuber, further sucrose gradient centrifugation of the pellet yielded a fraction at density 1.28 g/cm³ which, presumably representing the crystalline cores, contained 7% of the total catalase activity but no uricase or glycolate oxidase activity. Using microbodies from castor bean endosperm (glyoxysomes), 50–60% of the malate dehydrogenase, fatty acyl CoA dehydrogenase, and crotonase and 90% of the malate synthetase and citrate synthetase were recovered in the pellet, which also contained 96% of the radioactivity when lecithin in the glyoxysomal membrane had been labeled by previous treatment of the tissue with [¹⁴C]choline. When the labeled pellet was centrifuged to equilibrium on a sucrose gradient, all the radioactivity, protein, and enzyme activities were recovered together at peak density 1.21–1.22 g/cm³, whereas the original glyoxysomes appeared at density 1.24 g/cm³. Electron microscopy showed that the fraction at 1.21–1.22 g/cm³ was comprised of intact glyoxysomal membranes. All of the membrane-bound enzymes were stripped off with 0.15 M KCl, leaving the "ghosts" still intact as revealed by electron microscopy and sucrose gradient centrifugation. It is concluded that the crystalline cores of plant microbodies contain no uricase and are not particularly enriched with catalase. Some of the enzymes in glyoxysomes are associated with the membranes and this probably has functional significance.     

Fine-structural characterization of plant microbodies

Summary Morphology and distribution of the relatively less well known organelles of plants have been studied with the electron microscope in tissues fixed in glutaraldehyde and postfixed in osmium tetroxide. An organelle comparable morphologically to the animal microbody and similar to the plant microbody isolated by Mollenhauer et al. (1966) has been encountered in a variety of plant species and tissues, and has been studied particularly in bean and radish roots, oat coleoptiles, and tobacco roots, stems and callus. The organelle has variable shape and is 0.5 to 1.5 in the greatest diameter. It has a single bounding membrane, a granular to fibrillar matrix of variable electron density, and an intimate association with one or two cisternae of rough endoplasmic reticulum (ER). Microbodies are easily the most common and generally distributed of the less well characterized organelles of plant cells. It seems very probable that they contain the enzymes characteristic of animal lysosomes (containing hydrolases) or animal microbodies (containing catalase and certain oxidases). Spherosomes are also possible sites of enzyme activity but are not as common or as widely distributed as microbodies. For this reason it appears likely that the particles designated as plant lysosomes, spherosomes, peroxisomes, etc., in some of the cytochemical and biochemical studies on enzyme localization will prove to be microbodies.Variations in the morphology and ER associations of microbodies in tissues of bean and radish are described and discussed. Crystal-containing bodies (CCBs) are interpreted as a specialized type of microbody characteristic of metabolically less active cells. Stages in the formation of CCBs from microbodies of typical appearance are illustrated for Avena.The general occurrence of microbodies in meristematic and differentiating cells and their close association with the ER suggest that they may play active roles in cellular metabolism. The alterations in their morphology and numbers that are observed in certain differentiating cells suggest further that the enzyme complements and metabolic roles of microbodies might change during cellular differentiation. If so, microbodies could be the functional equivalent of both microbodies and lysosomes of animal cells.NASA Predoctoral Trainee.Public Health Service Postdoctoral Fellow.     

The widespread occurrence of plant cytosomes resembling animal microbodies

Summary Single membrane bounded organelles characterized by a physical association with endoplasmic reticulum have been observed in a wide range of cell types and plant species including Gymnosperm, Angiosperm, Pteridophyte, and Thallophyte (algae and fungi) tissues. The morphological similarity between these organelles and animal microbodies suggests that they are cytological homologues. Plant microbodies were observed both with and without dense internal inclusions but unlike animal microbodies could not be shown to contain uricase. Plant microbody membranes are resistant to degenerative influences and remain associated with a small portion of endoplasmic reticulum even in isolated cell fractions.     

Targeting and processing of a chimeric protein with the N-terminal presequence of the precursor to glyoxysomal citrate synthase.

Glyoxysomal citrate synthase in pumpkin is synthesized as a precursor that has a cleavable presequence at its N-terminal end. To investigate the role of the presequence in the transport of the protein to the microbodies, we generated transgenic Arabidopsis plants that expressed beta-glucuronidase with the N-terminal presequence of the precursor to the glyoxysomal citrate synthase of pumpkin. Immunogold labeling and cell fractionation studies showed that the chimeric protein was transported into microbodies and subsequently was processed. The chimeric protein was transported to functionally different microbodies, such as glyoxysomes, leaf peroxisomes, and unspecialized microbodies. These observations indicated that the transport of glyoxysomal citrate synthase is mediated by its N-terminal presequence and that the transport system is functional in all plant microbodies. Site-directed mutagenesis of the conserved amino acids in the presequence caused abnormal targeting and inhibition of processing of the chimeric protein, suggesting that the conserved amino acids in the presequence are required for recognition of the target or processing.     

The structure of microbodies and their associations with other organelles in zoosporangia ofEntophlyctis variabilis

Summary The ultrastructure of microbodies in developing zoosporangia ofEntophlyctis variabilis was studied by three dimensional reconstructions from serial sections and by cytochemical localization of catalase activity. The morphology of microbodies and the spatial association of microbodies with other organelles varied during fungal development. In incipient zoo-sporangia, granular dilations resembling microbodies arose from rough ER. Young, enlarging zoosporangia contained elongate, contorted microbodies continuous with ER and aligned along bundles of microtubules. Oval, paired microbodies, lying on each side of an ER cisternae, were found in all zoosporangia, but in older zoosporangia this configuration of microbodies predominated. Analysis of serial sections revealed that these oval, paired microbodies were sometimes continuous with each other, with ER, and also apparently with the ER cisterna interposed between them. Other paired, oval microbodies were clearly discrete. Constrictions were found along the length of elongate microbodies and at junctions between oval microbodies. These constrictions may represent stages in fragmentation of microbodies from pre-existing microbodies. These observations suggest that microbodies originated in three ways: 1. as local dilations in tubular ER, 2. as lateral buds from opposite sides of ER cisternae, and 3. as fragments from elongate microbodies.Microbodies were consistently spatially associated with ER, nuclear envelopes, and mitochondria. The cisterna of ER passing between paired microbodies sometimes extended into a branching, tubular system of ER which curved around the side of one microbody and lay between this microbody and the forming face of a dictyosome. The cytochemical localization of thiamine pyrophosphatase activity in this cisterna when it is not associated with dictyosomes suggests a role in metabolic control. These spatial associations indicate that the microbody assemblage with other organelles represents functional units where propinquity to other organelles and intraluminal continuities insure a system for transport of substrates and products.     

Ultrastructure of the vegetative cell ofBrassica napus pollen with particular reference to microbodies

Summary The ultrastructure of the vegetative cell ofBrassica napus tricellular pollen grains, just before anthesis with standard chemical fixation, is reported. The vegetative cell may be regarded as a highly differentiated and metabolically active fat-storage cell. It contains many mitochondria with a well developed internal membrane system, starchless plastids, microbodies, lipid bodies, dictyosomes and numerous vesicles thought to originate from the dictysomes. Rough endoplasmic reticulum organized in stacks of cisternae is also spatially associated with certain organelles, mainly lipid bodies, microbodies and plastids. There are also randomly distributed polyribosome areas. The microbodies are mainly polymorphic in shape and are often observed in contact with lipid bodies. The above spatial relationship implies that the microbodies may have a glyoxysomal function. In the late period of vegetative cell maturation, the microbodies are probably involved in the process of glyconeogenesis in which the conversion of lipid reserves to sugar takes place.Abbreviations VC vegetative cell - VN vegetative nucleus - SC sperm cell - M mitochondria - MB microbodies - L lipid body - P plastid - D dictyosomes     

A correlative ultrastructural and enzymatic study of cotyledonary microbodies following germination of fat-storing seeds

Summary Sunflower, cucumber, and tomato cotyledons, which contain microbodies in both the early lipid-degrading and the later photosynthetic stages of post-germinative growth, were processed for electron microscopy according to conventional procedures and examined 1, 4 and 7 days after germination. Homogenates of sunflower cotyledons were assayed for enzymes characteristic of glyoxysomes and leaf peroxisomes (both of which are defined morphologically as microbodies) at stages corresponding to the fixations for electron microscopy. The particulate nature of these enzymes was demonstrated by differential and equilibrium density centrifugation, making it possible to relate them to the microbodies seen in situ.One day after germination, the microbodies are present as small organelles among large numbers of protein and lipid storage bodies; the cell homogenate contains catalase but no detectable isocitrate lyase (characteristic of glyoxysomes) or glycolic acid oxidase (characteristic of leaf peroxisomes). 4 days after germination, numerous microbodies (glyoxysomes) are in extensive and frequent contact with lipid bodies. The microbodies often have cytoplasmic invaginations. At this stage the cells are rapidly converting lipids to carbohydrates, and the homogenate has high isocitrate lyase activity. 7 days after germination, microbodies (peroxisomes) are appressed to chloroplasts and frequently squeezed between them in the green photosynthetic cells. The homogenate at this stage has substantial glycolic acid oxidase activity but a reduced level of isocitrate lyase. It is yet to be determined whether the peroxisomes present at day 7 are derived from preexisting glyoxysomes or arise as a separate population of organelles.     

Glyoxysomal Malate Dehydrogenase in Pumpkin: Cloning of a cDNA and Functional Analysis of Its Presequence

Glyoxysomal malate dehydrogenase (gMDH) is an enzyme of theglyoxylate cycle that participates in degradation of storageoil. We have cloned a cDNA for gMDH from etiolated pumpkin cotyledonsthat encodes a polypep-tide consisting of 356 amino acid residues.The nucleotide and N-terminal amino acid sequences revealedthat gMDH is synthesized as a precursor with an N-terminal extrapeptide.The N-terminal presequence of 36 amino acid residues containstwo regions homologous to those of other micro-body proteins,which are also synthesized as large precursors. To investigatethe functions of the N-terminal presequence of gMDH, we generatedtransgenic Arabidopsis that expressed a chimeric protein consistingof rß-glucuroni-dase and the N-terminal region ofgMDH. Immunologi-cal and immunocytochemical studies revealedthat the chimeric protein was imported into microbodies suchas gly-oxysomes and leaf peroxisomes and was then subsequentlyprocessed. Site-directed mutagenesis studies showed that theconserved amino acids in the N-terminal presequence, Arg-10and His-17, function as recognition sites for the targetingto plant microbodies, and Cys-36 in the presequence is responsiblefor its processing. These results correspond to those from theanalyses of glyoxysomal citrate synthase (gCS), which was alsosynthesized as a large precursor, suggesting that common mechanismsthat can recognize the targeting or the processing of gMDH andgCS function in higher plant cells. (Received July 10, 1997; Accepted November 22, 1997)