The Fine Structure of Young Tracheary Xylem Elements Arising by Redifferentiation of Parenchyma in Wounded Coleus Stem

The dense granulation characteristic of parenchyma cells redifferentiatinginto tracheary xylem elements was found to be due to a concentrationof organelles and associated vesicles in the cytoplasmic bandswithin which the secondary-wall thickenings form. Among theseorganelles are mitochondria, plastid-like bodies, elements ofthe endoplasmic reticulum, and Golgi-structures. Numerous smallvesicles occur in the cytoplasm adjacent to developing wallbands and occasionally within the bands themselves. As the secondary-wall reticulations develop, they stain moreintensely with permanganate, becoming increasingly more electrondense. The evidence suggests that this is due to their progressivelignification. The electron density appears also in the primarywall at the bases of the bands, and extends through it betweenopposite bands of adjacent cells.     

类叶升麻(毛茛科)次生木质部管状分子的研究

利用扫描电子显微镜对毛良科类叶升麻（Artaea asiaticaHara）根和根状茎次生木质部中的管状分子进行观察．发观其管状分子类型丰富,主要有：管胞、管胞状导管、纤维导管和典型的导管分子,其中管胞、管胞状导管和纤维导管为在该类群中首次报道;在导管分子中．存在着梯状穿孔板、网状穿孔板、混合型穿孔板和单穿孔板．其中网状穿孔板和混合型穿孔板为在陔类群中的首次报道;对其导管分子上的侧壁穿孔板、多穿孔板和纹孔膜残余也进行了描述。根据类叶升麻次生木质部中多变的管状分子类型,认为以往积累的有关毛茛科植物管状分子类型及导管穿孔板类型是小个面的,因此以该性状为参考作出的有关某一个类群的原始性和进化性的推论也是不可靠的。同时探讨了不同类型管状分子作类叶升麻不同器官的分布与其生理功能和生态环境的关系,同时将该植物作为毛莨科的代表类群．与其它基邴类群植物导管分子进行了比较。     

Cell Wall Thickening of the Xylem Tracheary Elements in Different Zones of the Adventitious Root of Allium cepa L.

Cell wall thickness of the xylem tracheary elements was measuredin the proto- and metaxylem of the Allium cepa L. adventitiousroot. Measurements were taken in root fragments of known age(1, 3, 5, 7 and 9 d) located in either the basal or medio-apicalzone. Tracheary elements in the protoxylem matured within ashorter period of time than those in the metaxylem. Final cellwall thickness was greater in metaxylem than in protoxylem components.The cell wall thickening in the tracheary elements in both proto-and metaxylem was more rapid in the basal zone of the root thanin the medio-apical zone. Additionally, cell walls of the maturetracheary elements were thicker in the basal zone than in areasfurther from the bulb. Allium cepa, onion, root, cell wall, xylem maturation     

植物管状分子发育中的细胞凋亡

细胞凋亡在植物发育过程和防御机制中发挥着重要作用.植物细胞凋亡具有染色质固缩和边缘化、DNA片断化、核的降解、质膜内缩、大量囊泡的出现、细胞壁的修饰等特征,是由相关的基因、蛋白酶以及细胞色素C介导和调控的.本文根据国内外的研究报道,对两种管状分子(导管、筛管)发育过程中细胞凋亡的形态学变化以及机制进行分析,为进一步探讨细胞凋亡的途径和机制提供参考.     

国产球盖蕨科植物管状分子的比较研究

利用扫描电镜观察了国产球盖蕨科10种植物,鳞毛蕨科6种植物的管状分子,结果显示:它们的管状分子端壁和侧壁的形态及结构分别相同,且侧壁具有穿孔板。它们具有4种类型的管状分子:(1)梯状穿孔板,无穿孔板的二型性现象;(2)梯状穿孔板,具有二型性现象;(3)梯状-网状混合穿孔板;(4)大孔状穿孔板。穿孔板仅存在于端壁的管状分子为导管分子,而端壁和侧壁形态、结构相似,有或无穿孔板的管状分子为管胞,蕨类植物中的管状分子主要为管胞,这与传统观点不同。管状分子的形态特征表明:球盖蕨科是鳞毛蕨群的成员,但不是原始成员,可能属于其中较为进化的类群,与鳞毛蕨科有许多共同特征,但仍存在较大差异,所以将其作为独立的科是合理的,推测球盖蕨科中的鱼鳞蕨属是比较进化的属,柄盖蕨属相对原始,红腺蕨属的系统位置应介于二者之间。     

蹄盖蕨科5种植物管状分子的研究

采用扫描电镜观察了国产蹄盖蕨科3属5种植物的管状分子,发现安蕨属、拟鳞毛蕨属和蹄盖蕨属管状分子结构类似,具体可分为3种类型:(1)梯状穿孔板,无穿孔板二型性现象;(2)梯状穿孔板,有穿孔板二型性现象;(3)梯状-网状混合穿孔板.除长江蹄盖蕨不具有梯状穿孔板,有穿孔板二型性现象外,其余4种均具有上述3种类型.该结果支持安蕨属、拟鳞毛蕨属和蹄盖蕨属三者之间有亲密关系的观点,并在前人基础上提出了新的管胞定义:管胞是指维管植物木质部中存在的一类狭长中空,端部圆凸或尖削,不具有明显端壁,侧壁具有多个侧壁穿孔板,纹孔膜从缺失到不同程度存在的死细胞.     

The Development of the Runner-bean Leaf with Special Reference to the Relation between the Sizes of the Lamina and of the Petiolar Xylem: I. The Relation between Lamina Area and Petiolar Xylem

An investigation has been made of the relation between the sizesof the lamina and of the petiolar xylem of both mature and immatureleaves of the runner bean (Phaseolus multiflorus Willd.). The ratios xylem area/lamina area and the number of vessels/laminaarea are lowest for mature leaves. Immature leaves gave higherbut somewhat more variable values for these two ratios. There is a constant growth ratio between the lpminn area andthe xylem area, such that k is approximately o·61 inthe allometry formula. The significance of the results is briefly considered from thepoint of view that the xylem area is related to the water requirementsof the leaf.     

Factors affecting the growth of Eucalyptus delegatensis seedlings in inhibitory forest and grassland soils

In many highland forests of Eucalyptus delegatensis in Tasmania the establishment and healthy growth of eucalypts is promoted and maintained by fire. In the absence of fire, secondary succession from eucalypt forest to rainforest occurs, during which the eucalypts decline and die prematurely. On sites that are prone to radiation frost severe reduction or removal of a tree canopy allows a sward of tussock grasses to develop, in competition with which seedlings of eucalypts decline in growth and a high proportion dies.Factors of the soil that could contribute to these phenomena were investigated by means of pot experiments that used soils from:o     

Structure of Cellulose Microfibrils in Primary Cell Walls from Collenchyma

In the primary walls of growing plant cells, the glucose polymer cellulose is assembled into long microfibrils a few nanometers in diameter. The rigidity and orientation of these microfibrils control cell expansion; therefore, cellulose synthesis is a key factor in the growth and morphogenesis of plants. Celery (Apium graveolens) collenchyma is a useful model system for the study of primary wall microfibril structure because its microfibrils are oriented with unusual uniformity, facilitating spectroscopic and diffraction experiments. Using a combination of x-ray and neutron scattering methods with vibrational and nuclear magnetic resonance spectroscopy, we show that celery collenchyma microfibrils were 2.9 to 3.0 nm in mean diameter, with a most probable structure containing 24 chains in cross section, arranged in eight hydrogen-bonded sheets of three chains, with extensive disorder in lateral packing, conformation, and hydrogen bonding. A similar 18-chain structure, and 24-chain structures of different shape, fitted the data less well. Conformational disorder was largely restricted to the surface chains, but disorder in chain packing was not. That is, in position and orientation, the surface chains conformed to the disordered lattice constituting the core of each microfibril. There was evidence that adjacent microfibrils were noncovalently aggregated together over part of their length, suggesting that the need to disrupt these aggregates might be a constraining factor in growth and in the hydrolysis of cellulose for biofuel production.Growth and form in plants are controlled by the precisely oriented expansion of the walls of individual cells. The driving force for cell expansion is osmotic, but the rate and direction of expansion are controlled by the mechanical properties of the cell wall (Szymanski and Cosgrove, 2009). Expanding, primary cell walls are nanocomposite materials in which long microfibrils of cellulose, a few nanometers in diameter, run through a hydrated matrix of xyloglucans, pectins, and other polymers (Knox, 2008; Mohnen, 2008; Szymanski and Cosgrove, 2009; Scheller and Ulvskov, 2010). Native cellulose microfibrils are partially crystalline (Nishiyama, 2009; Fernandes et al., 2011). Formerly, primary wall cellulose was thought to have a unique crystal structure called cellulose IV₁ (Dinand et al., 1996), but NMR evidence suggests the presence of forms similar to the better characterized cellulose Iα and Iβ crystalline forms together with large quantities of less ordered cellulose (Wickholm et al., 1998; Sturcová et al., 2004; Wada et al., 2004). Nevertheless, cellulose is much more ordered than any other component of the primary cell wall (Bootten et al., 2004), in keeping with its key role of providing strength and controlling growth.The stiffness of the cell wall is greatest in the direction of the cellulose microfibrils, where growth is directional and the predominant microfibril orientation is usually transverse to the growth direction (Green, 1999; MacKinnon et al., 2006; Szymanski and Cosgrove, 2009). Expansion of the cell wall then requires either widening of the spacing between microfibrils (Marga et al., 2005) or slippage between them (Cosgrove, 2005), or both, and the microfibrils reorient toward the direction of growth (Anderson et al., 2010). Polymer cross bridges between microfibrils (McCann et al., 1990) are thought to resist these deformations of the cell wall nanostructure and, thus, to control the rate of growth. Until recently, most attention was focused on bridging xyloglucans, hydrogen bonded to microfibril surfaces (Scheller and Ulvskov, 2010). However, there is evidence that not all xyloglucans are appropriately positioned (Fujino et al., 2000; Park and Cosgrove, 2012a) and that other bridging polymers may be involved (Zykwinska et al., 2007). It has also been suggested that bundles of aggregated microfibrils, not single microfibrils, might be the key structural units in primary cell walls (Anderson et al., 2010), as in wood (Fahlén and Salmén, 2005; Fernandes et al., 2011). If so, single microfibrils could bridge between microfibril bundles. In summary, the growth of plant cells is not well understood, and we need more information on how cellulose orientation is controlled and on the nature of the bridging polymers, the cellulose surfaces to which these polymers bind, and the cohesion between microfibril surfaces that might mediate aggregation.Cellulose microfibrils are synthesized at the cell surface by large enzyme complexes having hexagonal symmetry, sometimes called “rosettes” (Somerville, 2006). Each complex contains multiple cellulose synthases that differ between primary cell walls and wood, although the appearance of the complexes is similar (Somerville, 2006; Atanassov et al., 2009). The simultaneous synthesis, from the same end, of all the chains in a native cellulose microfibril is why they are parallel (Nishiyama et al., 2002, 2003), in contrast to the entropically favored antiparallel structure found in man-made celluloses like rayon (Langan et al., 2001). The number of chains in a microfibril and the number of cellulose synthases in the synthetic complex are evidently related. It is commonly assumed that the number of chains is divisible by six, matching the hexagonal rosette symmetry, and 36-chain models (Himmel et al., 2007) bounded by the hydrophilic [110] and [1-10] crystal faces, as in algal celluloses (Bergenstråhle et al., 2008), have been widely adopted. The assembly and orientation of cellulose are connected, as several cellulose synthase mutants have phenotypes defective in cellulose orientation and plant form as well as depleted in cellulose content (Paredez et al., 2008). In certain other mutant lines, the crystallinity of the microfibrils appears to be affected (Fujita et al., 2011; Harris et al., 2012; Sánchez-Rodríguez et al., 2012).Therefore, a detailed understanding of the structure of primary wall cellulose microfibrils would help us to understand cellulose synthesis as well as the growth and structural mechanics of living plants (Burgert and Fratzl, 2009). Primary cell walls and their cellulose skeletons also affect food quality characteristics like the crispness of salad vegetables and apples (Malus domestica; Jarvis, 2011). When biofuels are produced from lignocellulosic biomass, lignification leads to recalcitrance (Himmel et al., 2007), but some of the cell types in Miscanthus spp., switchgrass (Panicum virgatum), and arable crop residues have only primary walls with no lignin, and recalcitrance then depends on the nature of the cellulose microfibrils (Beckham et al., 2011).A relatively detailed structure has recently been proposed for the microfibrils of spruce (Picea spp.) wood (Fernandes et al., 2011), which are 3.0 nm in diameter, allowing space for only about 24 cellulose chains. Evidence from x-ray diffraction supported a “rectangular” shape (Matthews et al., 2006) bounded by the [010] and [200] faces. There was considerable disorder increasing toward the surface, and the microfibrils were aggregated into bundles about 15 to 20 nm across, with some, but not all, of the lateral interfaces being resistant to water (Fernandes et al., 2011). Disordered domains are a feature of other strong biological materials such as spider silk (van Beek et al., 2002).Therefore, it is of interest whether any of these features of wood cellulose might also be found in the cellulose microfibrils of primary (growing) cell walls. It would be particularly useful to characterize the disorder known to be present in primary wall microfibrils, that is, to define how cellulose that is not measured as “crystalline” differs from crystalline cellulose. Many of the experiments leading toward a structure for wood cellulose were dependent on exceptionally uniform orientation of the cellulose microfibrils (Sturcová et al., 2004; Fernandes et al., 2011). However, in growing cell walls, the microfibrils are not uniformly oriented. When microfibrils are first laid down at the inner face of the primary cell wall, their orientation is normally transverse to the direction of growth, but as the cell wall expands, the microfibrils reorient so that the orientation distribution, integrated across the thickness of the expanded cell wall, becomes progressively closer to random (Cosgrove, 2005; MacKinnon et al., 2006).This technical problem does not apply to the cell walls of celery (Apium graveolens) collenchyma, which are similar in composition to other primary cell walls but have their microfibrils oriented relatively uniformly along the cell axis (Sturcová et al., 2004; Kennedy et al., 2007a, 2007b). Some structural information on celery collenchyma cellulose has already been derived from spectroscopic and scattering experiments (Sturcová et al., 2004; Kennedy et al., 2007a, 2007b), confirming the disorder expected in a primary wall cellulose. Some of these experiments were analogous to what has been done on spruce cellulose (Fernandes et al., 2011), but insufficient data are available to specify the number of chains in each primary wall microfibril, the nature and location of the disorder, and the presence or absence of direct contact between microfibrils. Here, we report x-ray and neutron scattering and spectroscopic experiments addressing these questions and leading to a proposed structure for primary wall cellulose microfibrils. Characterizing a structure containing so much disorder presented unusual challenges, but disorder appears to be central to the enigmatic capacity of primary wall cellulose to provide high strength and yet to permit and control growth.     

Proteomic Analysis of Microtubule Interacting Proteins over the Course of Xylem Tracheary Element Formation in Arabidopsis

Plant vascular cells, or tracheary elements (TEs), rely on circumferential secondary cell wall thickenings to maintain sap flow. The patterns in which TE thickenings are organized vary according to the underlying microtubule bundles that guide wall deposition. To identify microtubule interacting proteins present at defined stages of TE differentiation, we exploited the synchronous differentiation of TEs in Arabidopsis thaliana suspension cultures. Quantitative proteomic analysis of microtubule pull-downs, using ratiometric ¹⁴N/¹⁵N labeling, revealed 605 proteins exhibiting differential accumulation during TE differentiation. Microtubule interacting proteins associated with membrane trafficking, protein synthesis, DNA/RNA binding, and signal transduction peaked during secondary cell wall formation, while proteins associated with stress peaked when approaching TE cell death. In particular, CELLULOSE SYNTHASE-INTERACTING PROTEIN1, already associated with primary wall synthesis, was enriched during secondary cell wall formation. RNAi knockdown of genes encoding several of the identified proteins showed that secondary wall formation depends on the coordinated presence of microtubule interacting proteins with nonoverlapping functions: cell wall thickness, cell wall homogeneity, and the pattern and cortical location of the wall are dependent on different proteins. Altogether, proteins linking microtubules to a range of metabolic compartments vary specifically during TE differentiation and regulate different aspects of wall patterning.     

植物管状细胞栓塞后的重新充注研究进展

在植物吸收水分以后 ,水分运输对于植物正常的生长发育是非常重要的。在干旱和冬季反复冻融循环以后 ,植物体内的管状细胞容易充满水蒸气和空气 ,形成腔隙和栓塞。腔隙和栓塞的形成对水分在植物体内的运输造成了很大的障碍 ,从而影响了植物的生长与发育。当植物重新获得水分时 ,已形成腔隙和栓塞的管状细胞的重新充注能使一部分管状细胞的输水功能得到恢复 ,从而保证了一些器官的生理功能的正常进行。近些年来 ,人们对植物管状细胞的重新充注涉及到的许多植物组织和生理过程进行深入的研究 ,并提出了各种机理。鉴于植物管状细胞形成栓塞后重新充注对植物水分运输的重要生理作用 ,本文对重新充注的许多机理进行了综合评述     

Imaging Cell Wall Architecture in Single Zinnia elegans Tracheary Elements

The chemical and structural organization of the plant cell wall was examined in Zinnia elegans tracheary elements (TEs), which specialize by developing prominent secondary wall thickenings underlying the primary wall during xylogenesis in vitro. Three imaging platforms were used in conjunction with chemical extraction of wall components to investigate the composition and structure of single Zinnia TEs. Using fluorescence microscopy with a green fluorescent protein-tagged Clostridium thermocellum family 3 carbohydrate-binding module specific for crystalline cellulose, we found that cellulose accessibility and binding in TEs increased significantly following an acidified chlorite treatment. Examination of chemical composition by synchrotron radiation-based Fourier-transform infrared spectromicroscopy indicated a loss of lignin and a modest loss of other polysaccharides in treated TEs. Atomic force microscopy was used to extensively characterize the topography of cell wall surfaces in TEs, revealing an outer granular matrix covering the underlying meshwork of cellulose fibrils. The internal organization of TEs was determined using secondary wall fragments generated by sonication. Atomic force microscopy revealed that the resulting rings, spirals, and reticulate structures were composed of fibrils arranged in parallel. Based on these combined results, we generated an architectural model of Zinnia TEs composed of three layers: an outermost granular layer, a middle primary wall composed of a meshwork of cellulose fibrils, and inner secondary wall thickenings containing parallel cellulose fibrils. In addition to insights in plant biology, studies using Zinnia TEs could prove especially productive in assessing cell wall responses to enzymatic and microbial degradation, thus aiding current efforts in lignocellulosic biofuel production.The organization and molecular architecture of plant cell walls represent some of the most challenging problems in plant biology. Although much is known about general aspects of assembly and biosynthesis of the plant cell wall, the detailed three-dimensional molecular cell wall structure remains poorly understood. The highly complex and dynamic nature of the plant cell wall has perhaps limited the generation of such detailed structural models. This information is pivotal for the successful implementation of novel approaches for conversion of biomass to liquid biofuels, given that one of the critical processing steps in biomass conversion involves systematic deconstruction of cell walls. Therefore, a comprehensive understanding of the architecture and chemical composition of the plant cell wall will not only help develop molecular-scale models, but will also help improve the efficiency of biomass deconstruction.The composition and molecular organization of the cell wall is species and cell type dependent (Vorwerk et al., 2004). Thus, the development of a model plant system, which utilizes a single cell type, has enhanced our capacity to understand cell wall architecture. The ability to generate a population of single Zinnia elegans plant cells that were synchronized throughout cell wall deposition during xylogenesis was developed in the 1980s (Fukuda and Komamine, 1980). Mesophyll cells isolated from the leaves of Zinnia and cultured in the presence of phytohormones will transdifferentiate into tracheary elements (TEs), which are individual components of the xylem vascular tissue (Fukuda and Komamine, 1980). During this transdifferentiation process, TEs gradually develop patterned secondary wall thickenings, commonly achieving annular, spiral, reticulate, scalariform, and pitted patterns (Bierhorst, 1960; Falconer and Seagull, 1988; Roberts and Haigler, 1994). These secondary wall thickenings serve as structural reinforcements that add strength and rigidity to prevent the collapse of the xylem under the high pressure created by fluid transport. During the final stages of transdifferentiation, TEs accumulate lignin in their secondary walls and undergo programmed cell death, which results in the removal of all cell contents, leaving behind a “functional corpse” (Roberts and McCann, 2000; Fukuda, 2004).In broad terms, the primary cell wall of higher plants is mainly composed of three types of polysaccharides: cellulose, hemicelluloses, and pectins (Cosgrove, 2005). Cellulose is composed of unbranched β-1,4-Glc chains that are packed together into fibrils by intermolecular and intramolecular hydrogen bonding. Hemicelluloses and pectins are groups of complex polysaccharides that are primarily composed of xyloglucans/xylans and galacturonans, respectively. Hemicelluloses are involved in cross-linking and associating with cellulose microfibrils, while pectins control wall porosity and help bind neighboring cells together. The patterned deposits of secondary wall in Zinnia TEs primarily consist of cellulose microfibrils, along with hemicelluloses, and also lignin, a complex aromatic polymer that is characteristic of secondary walls and provides reinforcement (Turner et al., 2007). All the molecular components in the cell wall correspond to a multitude of different polysaccharides, phenolic compounds, and proteins that become arranged and modified in muro, yielding a structure of great strength and resistance to degradation.Currently, electron microscopy is the primary tool for structural studies of cell walls and has provided remarkable information regarding wall organization. Fast-freeze deep-etch electron microscopy in combination with chemical and enzymatic approaches have generated recent models of the architecture of the primary wall (McCann et al., 1990; Carpita and Gibeaut, 1993; Nakashima et al., 1997; Fujino et al., 2000; Somerville et al., 2004). Direct visualization of secondary wall organization has been focused toward the examination of multiple wall layers in wood cells (Fahlen and Salmen, 2005; Zimmermann et al., 2006). However, few studies have examined the secondary wall, so our knowledge regarding the higher order architecture of this type of wall is limited. Over the past few decades, atomic force microscopy (AFM) has provided new opportunities to probe biological systems with spatial resolution similar to electron microscopy techniques (Kuznetsov et al., 1997; Muller et al., 1999), with additional ease of sample preparation and the capability to probe living native structures. AFM has been successfully applied to studies of the high-resolution architecture, assembly, and structural dynamics of a wide range of biological systems (Hoh et al., 1991; Crawford et al., 2001; Malkin et al., 2003; Plomp et al., 2007), thus enabling the observation of the ultrastructure of the plant cell wall, which is of particular interest to us (Kirby et al., 1996; Morris et al., 1997; Davies and Harris, 2003; Yan et al., 2004; Ding and Himmel, 2006).To generate more detailed structural models, knowledge about the structural organization of the cell wall can be combined with spatial information about chemical composition. Instead of utilizing chromatography techniques to analyze cell wall composition by extracting material from bulk plant samples (Mellerowicz et al., 2001; Pauly and Keegstra, 2008), Fourier transform infrared (FTIR) spectromicroscopy can be used to directly probe for polysaccharide and aromatic molecules in native as well as treated plant material (Carpita et al., 2001; McCann et al., 2001). FTIR spectromicroscopy is not only able to identify chemical components in a specific system but also can determine their distribution and relative abundance. This technique also improves the sensitivity and spatial resolution of cellular components without the derivatization needed by chemical analysis using chromatography. Polysaccharide-specific probes, such as carbohydrate-binding modules (CBMs), can also be used to understand the chemical composition of the plant cell wall. CBMs are noncatalytic protein domains existing in many glycoside hydrolases. Based on their binding specificities, CBMs are generally categorized into three groups: surface-binding CBMs specific for insoluble cellulose surfaces, chain-binding CBMs specific for single chains of polysaccharides, and end-binding CBMs specific for the ends of polysaccharides or oligosaccharides. A surface-binding CBM with high affinity for the planar faces of crystalline cellulose (Tormo et al., 1996; Lehtio et al., 2003) has been fluorescently labeled and used to label crystals as well as plant tissue (Ding et al., 2006; Porter et al., 2007; Liu et al., 2009; Xu et al., 2009). The binding capacity of the CBM family has been further exploited for the detection of different polysaccharides, such as xylans and glucans, and can thus be used for the characterization of plant cell wall composition (McCartney et al., 2004, 2006).In this study, we used a combination of AFM, synchrotron radiation-based (SR)-FTIR spectromicroscopy, and fluorescence microscopy using a cellulose-specific CBM to probe the cell wall of Zinnia TEs. The Zinnia TE culture system proved ideal for observing the structure and chemical composition of the cell wall because it comprises a single homogeneous cell type, representing a simpler system compared with plant tissues, which may contain multiple cell types. Zinnia TEs were also advantageous because they were analyzed individually, and population statistics were generated based on specific conditions. Furthermore, cultured Zinnia TEs were used for the consistent production of cell wall fragments for analysis of the organization of internal secondary wall structures. In summary, we have physically and chemically dissected Zinnia TEs using a combination of imaging techniques that revealed primary and secondary wall structures and enabled the reconstruction of TE cell wall architecture.     

国产对囊蕨亚科（蹄盖蕨科）植物的管状分子

利用扫描电镜观察了国产蹄盖蕨科（Athyriaceae）对囊蕨亚科（Deparioideae）10种植物及双盖蕨属（Diplazium Sw．）3种植物根状茎的管状分子。结果显示,这些管状分子端壁和侧壁的形态及结构分别相同且侧壁具有穿孔板（多穿孔板）。根据穿孔板的形态特征,将该亚科的管状分子分为5种类型：（1）梯状穿孔板,无穿孔的二型性现象：（2）梯状穿孔板,有穿孔的二型性现象：（3）网状穿孔板：（4）梯状-网状混合的穿孔板：（5）大孔状穿孔板。按照纹孔膜残留的程度又可分为3种：部分区域有完整的纹孔膜、残留呈网状或线状以及很少或无纹孔膜残留。结合前人的研究资料,发现蕨类植物的管状分子与被子植物的导管分子在形态和输导机理上存在明显差异,管胞和导管分子不能仅仅根据纹孔膜的存在与否来确定,而应根据穿孔板存在于端壁还是侧壁进行判断,即穿孔板仅存在于端壁的管状分子为导管分子：端壁和侧壁形态及结构分别相同,有或无穿孔板的管状分子为管胞。由此可以推测蕨类植物和裸子植物中输导水分和矿物质的管状分子主要为管胞。单叶双盖蕨属（Triblemma（J．Sm．）Ching）与双盖蕨属管状分子的特征并不相似,显示了将单叶双盖蕨属从双盖蕨属独立出来归人对囊蕨亚科的合理性。根据管状分子的特征,推测假蹄盖蕨属（Athyriopsis Ching）和蛾眉蕨属（Lunathyrium Koidz．）可能是比较进化的属,而介蕨属（Dryoathyrium Ching）相对比较原始,单叶双盖蕨属的系统位置应介于假蹄盖蕨属与介蕨属之间。     

国产对囊蕨亚科(蹄盖蕨科)植物的管状分子

利用扫描电镜观察了国产蹄盖蕨科(Athyriaceae)对囊蕨亚科(Deparioideae)10种植物及双盖蕨属(Diplazium Sw.)3种植物根状茎的管状分子。结果显示, 这些管状分子端壁和侧壁的形态及结构分别相同且侧壁具有穿孔板(多穿孔板)。根据穿孔板的形态特征, 将该亚科的管状分子分为5种类型: (1)梯状穿孔板, 无穿孔的二型性现象; (2)梯状穿孔板, 有穿孔的二型性现象; (3)网状穿孔板; (4)梯状-网状混合的穿孔板; (5)大孔状穿孔板。按照纹孔膜残留的程度又可分为3种: 部分区域有完整的纹孔膜、残留呈网状或线状以及很少或无纹孔膜残留。结合前人的研究资料, 发现蕨类植物的管状分子与被子植物的导管分子在形态和输导机理上存在明显差异, 管胞和导管分子不能仅仅根据纹孔膜的存在与否来确定, 而应根据穿孔板存在于端壁还是侧壁进行判断, 即穿孔板仅存在于端壁的管状分子为导管分子; 端壁和侧壁形态及结构分别相同, 有或无穿孔板的管状分子为管胞。由此可以推测蕨类植物和裸子植物中输导水分和矿物质的管状分子主要为管胞。单叶双盖蕨属(Triblemma(J. Sm.) Ching)与双盖蕨属管状分子的特征并不相似, 显示了将单叶双盖蕨属从双盖蕨属独立出来归入对囊蕨亚科的合理性。根据管状分子的特征, 推测假蹄盖蕨属(Athyriopsis Ching)和蛾眉蕨属(Lunathyrium Koidz.)可能是比较进化的属, 而介蕨属 (Dryoathyrium Ching)相对比较原始, 单叶双盖蕨属的系统位置应介于假蹄盖蕨属与介蕨属之间。     

植物管状细胞栓塞后的重新充注研究进展

在植物吸收水分以后,水分运输对于植物正常的生长发育是非常重要的。在干旱和冬季反复冻融循环以后,植物体内的管状细胞容易充满水蒸气和空气,形成腔 隙和栓塞。腔隙和栓塞的形成对水分在植物体内的运输造成了很大的障碍,从而影响了植物的生长与发育。当植物重新获得水分时,已形成腔隙和栓塞的管状细胞的重新充注能使一部分管状细胞的输水功能得到恢复,从而保证了一些器官的生理功能的正常进行。近些年来,人们对植物管状细胞的重新充注涉及到的许多植物组织和生理过程进行深入的研究,并提出了各种机理。鉴于植物管状细胞形成栓塞后重新充注对植物水分运输的重要生理作用,本文对重新充注的许多机理进行了综合评述。     

Electron Microscopic Observations on the Fine Structure of Cell Walls of Chlamydia psittaci

L-cell cultures were infected with elementary bodies (EB) of meningopneumonitis organisms. Cell walls were prepared from reticulate bodies (RB), which are the intracellular developmental forms into which EB are converted, and from EB at appropriate times after infection. When fragmented EB cell walls were shadowcast with platinum palladium alloy, about one-half of the fragments were seen to be composed of hexagonally arrayed structures on the inner side of the cell wall. When EB cell walls were negatively stained with phosphotungstic acid, they all showed this fine structural array. These macromolecular units were estimated to be about 18 nm in diameter. RB cell walls, harvested at various times after infection, were similarly stained; about 20% of RB walls at 15 hr after infection showed traces of these regular structures, but only 2% of them had the structures at 24 hr. When RB cell walls prepared from penicillin-containing culture were examined, they were observed to be similar to RB without penicillin. When EB cell walls were treated with formamide at 160 C, and then centrifuged in a 10 to 40% potassium tartrate density gradient, hexagonal particles about 20 nm in diameter were obtained as a middle band in the gradient column. These particles were not obtained from RB cell walls harvested from cultures with or without penicillin. It is concluded that the particles are macromolecular subunits located on the inner side of the EB cell walls, that the subunits probably provide the structural rigidity found in the EB, and that their synthesis is inhibited by penicillin.