The cytoskeleton of Cobaea seed hairs:

The cell wall of Cobaea scandens seed hairs developed in a characteristic sequence, with the deposition of a cellulose thread onto a pectic swelling layer was the final event. The cellulose thread was intracellularly accompanied by a band of 10–18 microtubules. During the formation of the swelling layer the microtubules were homogeneously distributed; they ran circumferentially normal to the cell axis. When cellulose-thread formation started, the microtubules became arranged in a helical band. The density of the microtubules varied during the different phases of development. The highest density was observed before cellulosethread formation and ranged from 6–15 m·m^-2. The length of the microtubules, 20–30 m, was determined by direct measurements, as well as estimated from the total microtubular length in a given area and the counted free ends. With the indirect immunofluorescence technique the microtubules of the band stained inhomogeneously. Those which were located at the edges of the band fluoresced more intensely than those of the central part. Attempts to visualize actin filaments in the hair cells with rhodaminyl-conjugated phalloidin resulted in a homogeneous staining of the area of the microtubular band, indicating that actin filaments may be present in this region. Though, in thin sections and dry-cleaved cells, filamentous structures were observed between the microtubules, caution is expressed that the observed fluorescence was, indeed, due to actin filaments. The role of the filamentous structures is discussed with respect to formation and maintenance of the microtubular band. Microtubules apparently did not cross coated pits which were visualized in the plasma membrane through the dry-cleaving technique.Abbreviations IFT indirect immunofluorescence technique - RP rhodaminyl-conjugated phalloidin - SEM scanning electron microscopy     

Energetic approach to the folding of alpha/beta barrels

The folding of a polypeptide into a parallel (alpha/beta)8 barrel (which is also called a circularly permuted beta 8 alpha 8 barrel) has been investigated in terms of energy minimization. According to the arrangement of hydrogen bonds between two neighboring beta-strands of the central barrel therein, such an alpha/beta barrel structure can be folded into six different types: (1) left-tilted, left-handed crossover; (2) left-tilted, right-handed crossover; (3) nontilted, left-handed crossover; (4) nontilted, right-handed crossover; (5) right-tilted, left-handed crossover; and (6) right-tilted, right-handed crossover. Here "tilt" refers to the orientational relation of the beta-strands to the axis of the central beta-barrel, and "crossover" to the beta alpha beta folding connection feature of the parallel beta-barrel. It has been found that the right-tilted, right-handed crossover alpha/beta barrel possesses much lower energy than the other five types of alpha/beta barrels, elucidating why the observed alpha/beta barrels in proteins always assume the form of right tilt and right-handed crossover connection. As observed, the beta-strands in the energy-minimized right-tilted, right-handed crossover (alpha/beta)8-barrel are of strong right-handed twist. The value of root-mean-square fits also indicates that the central barrel contained in the lowest energy (alpha/beta)8 structure thus found coincides very well with the observed 8-stranded parallel beta-barrel in triose phosphate isomerase (TIM). Furthermore, an energetic analysis has been made demonstrating why the right-tilt, right-handed crossover barrel is the most stable structure. Our calculations and analysis support the principle that it is possible to account for the main features of frequently occurring folding patterns in proteins by means of conformational energy calculations even for very complicated structures such as (alpha/beta)8 barrels.     

Direct studies of dikaryotization in Schizophyllum commune

The growth, duplication and fate of multikaryotic hyphae bearing true clamp connections, as derived from compatible matings of Schizophyllum commune, were studied by phase contrast microscopy. The nuclei (N) of multikaryotic apices maintained a near central position during hyphal growth. True clamp connection formation occurred with near synchronous mitosis followed by septal synthesis across the clamp neck and main hyphal axis. Nuclear progeny after mitosis in a hexakaryon included 6 N in the apex, 1 N in the clamp and 5 N in the penultimate cell; the solitary nucleus in the clamp later entered the penultimate cell. Similar events occurred for clamp connection formation and mitosis in the trikaryon, quadrikaryon or pentakaryon, whether in the apex or primary branches. Nuclear content of the multikaryotic apex (2 N through 10 N) had no apparent effect on the rate of individual hyphal growth. Reduction of the nuclear number in a trikaryon occurred by long-term entrappment of a solitary nucleus in the clamp and subsequent outgrowth of the dikaryotic penultimate cell. Occasionally, more than one nucleus became entrapped in the clamp cell. The ephemeral nature of the multikaryon was indicated by the fact that older cultures appeared to be exclusively dikaryotic hyphae at the colony periphery.     

茯苓基本生物学特性研究

以11个不同来源的茯苓菌株为材料,研究了茯苓菌丝体、子实体和担孢子的形态特征及适宜的生长、发育条件。结果表明,茯苓菌丝体为少分枝、有隔膜、无锁状联合的多核菌丝,茯苓担孢子核相以双核为主,双核孢子,单核孢子和无核孢子分别占87.2%,4.7%和8.1%。配对试验结果表明,同一菌株及不同菌株原生质体分离株间的配对均能融洽生长,同一菌株担孢子间的配对均产生拮抗线,但其中有少数配对在交接区形成扇形区域,拮抗线随后消失,而不同菌株担孢子间的配对则全部形成稳定的栅栏型菌落,暗示茯苓担孢子中的两个细胞核是具遗传互补性,能形成独立个体的异双核,茯苓可能是一种次级同宗结合菌。     

Pit organs in axolotls: a second class of lateral line neuromasts

The lateral line system of axolotls (Ambystoma mexicanum) consists of mechanoreceptive neuromasts and electroreceptive ampullary organs. All neuromasts in salamanders are located superficially and are organized into lines that are homologous to canal neuromasts in fishes. Ampullary organs are confined to the head and generally are located adjacent to the lines of superficial neuromasts. Axolotls, however, also possess a third class of receptors; these form restricted patches on the head and are possibly homologous to the superficial pit organs in fishes. In order to test this hypothesis the morphology of the suspected pit organs was examined with scanning electron microscopy, and a number of their physiological properties were determined. Pit organs are approximately half the size of neuromasts and have fewer hair cells, although these hair cells do possess kinocilia and stereocilia like those of neuromasts. Pit organs also possess cupulae and exhibit a pattern of innervation identical to that of neuromasts. Pit organs and neuromasts also exhibit similar rates of spontaneous activity, are excited by weak water currents but not weak electric stimuli, and are not inhibited by magnesium ions. Pit organs appear to have slightly lower rates of spontaneous discharge than neuromasts, however, and have slightly lower displacement thresholds to low frequency wave stimuli. These data support the contention that the pit organs of axolotls constitute a second class of neuromasts homologous to the pit organs of fishes.     

人胚DA能神经元移植于帕金森氏病猴模型的TH免疫细胞化学的研究

为了对人胚黑质ＤＡ神经元移植治疗ＰＤ人的临床应用作出客观评估,将８－１２周人胚黑质细胞移植到用ＭＰＴＰ诱发的偏侧ＰＤ猴新纹状体内。实验动物分别存活２个月、５个月和１年后,用ＴＨ免疫细胞化学方法对被移植的人胚ＤＡ细胞的存活和与宿主间的突触联系进行检查。在光镜下可见被移植侧的新纹状体内有ＴＨ阳性细胞,它们成小群散在分布,每小群有３－１０个细胞。ＴＨ阳性细胞的轴突延伸到整个新纹状体,树突呈现出正常发育过     

The fine structure and cytology of the association between the parasitic red algaHolmsella australis and its red algal hostGracilaria furcellata

Summary Holmsella australis Noble andKraft ms. is a colourless red algal parasite, forming whitish pustules on its photosynthetic red algal host,Gracilaria furcellata Harvey. In the infected region, host cortical tissue continues to grow and enclose the expanding pustule. Filaments of both host and parasite grow apically, the cells being connected by primary pit connections (PCs). Secondary PCs form between cells of the same species, and in addition,H. australis initiates the formation of secondary PCs with cells ofG. furcellata. All three types of secondary PC are morphologically distinct. In hostparasite PCs the surface adjoining the host cell is similar in structure to a host-host PC, while that adjoining the parasite cell has the structure of a parasite-parasite PC. The plasma membrane is continuous between the cells of the unrelated host and parasite. In addition, a cap membrane is typically produced only on the host surface, though occasionally the parasite side is enclosed by a cap membrane as well. Cap membranes are absent from parasite-parasite PCs (making them intracellular), while host-host PCs are typically extracellular, both cells producing cap membranes. The presence or absence of a cap membrane in certain positions appears to vary, and suggests that cells may be able to regulate its presence. Since transport of nutrients would be expected to occur from host to parasite cells, and between parasite cells, the morphological evidence presented here suggests the PCs may be the pathway.     

高雄山虫草及其细脚拟青霉无性型

报道采自安徽省天堂寨自然保护区的高雄山虫草Cordyceps takaomontana及其无性型细脚拟青霉Paecilomyces tenuipes ,应用单子囊孢子分离鉴定和微循环产孢的方法确证了两者的对应关系,并修订了高雄山虫草的原始描述。双梭孢虫草C．bifusispora可能为高雄山虫草的同物异名。同时采集的具数个红色子座且有双梭形子囊孢子的虫草不是同一个种。     

Xylem structure and connectivity in grapevine (Vitis vinifera) shoots provides a passive mechanism for the spread of bacteria in grape plants

BACKGROUND AND AIMS: Bacterial leaf scorch occurring in a number of economically important plants is caused by the xylem-limited bacterium Xylella fastidiosa (Xf). In grapevine, Xf systemic infection causes Pierce's disease and is lethal. Traditional dogma is that Xf movement between vessels requires the digestion of inter-vessel pit membranes. However, Yersinia enterocolitica (Ye) (a bacterium found in animals) and fluorescent beads moved rapidly within grapevine xylem from stem into leaf lamina, suggesting open conduits consisting of long, branched xylem vessels for passive movement. This study builds on and expands previous observations on the nature of these conduits and how they affect Xf movement. METHODS: Air, latex paint and green fluorescence protein (GFP)-Xf were loaded into leaves and followed to confirm and identify these conduits. Leaf xylem anatomy was studied to determine the basis for the free and sometimes restricted movement of Ye, beads, air, paint and GFP-Xf into the lamina. KEY RESULTS: Reverse loading experiments demonstrated that long, branched xylem vessels occurred exclusively in primary xylem. They were observed in the stem for three internodes before diverging into mature leaves. However, this stem-leaf connection was an age-dependent character and was absent for the first 10-12 leaves basal to the apical meristem. Free movement in leaf blade xylem was cell-type specific with vessels facilitating movement in the body of the blade and tracheids near the leaf margin. Air, latex paint and GFP-Xf all moved about 50-60% of the leaf length. GFP-Xf was never observed close to the leaf margin. CONCLUSIONS: The open vessels of the primary xylem offered unimpeded long distance pathways bridging stem to leaves, possibly facilitating the spread of bacterial pathogens in planta. GFP-Xf never reached the leaf margins where scorching appeared, suggesting a signal targeting specific cells or a toxic build-up at hydathodes.     

第一磨牙窝沟封闭预防龋病的两年临床疗效观察

目的:评估窝沟封闭对预防第一磨牙窝沟龋的2年临床疗效。方法:选择贵阳市花溪区200名7-9岁经家长同意并签署窝沟封闭知情同意书的学生为实验组,进行第一磨牙窝沟封闭;因家长不同意而未进行窝沟封闭的200名同龄学生为对照组,两年内复查两组的龋病发病率和封闭剂的保留情况。结果:实验组窝沟封闭后第一年、第二年第一磨牙龋病的发生率分别为1.50%和1.01%,而对照组分别为4.00%和6.57%,第二年实验组的第一磨牙龋病发病率显著低于对照组,差异有统计学意义(P0.05)。实验组第一年、第二年的封闭剂完全保留率分别是85.5%和80.4%。结论:窝沟封闭作为一项健康干预措施,能有效降低学生的龋病发病率。