杨梅根结线虫病及其病原鉴定

本文报道对杨梅根结线虫病的研究及病原鉴定结果。该病症状为:病树根部形成大小不一的根结,内有乳白色囊状雌虫及棕色卵囊;后期根结腐烂,病树叶片黄化脱落,梢枯乃至死亡。病原鉴定确认,引起该病的根结线虫有3个种:爪哇根结线虫(Meloidogyne javanica)、南方根结线虫(M.incognita)和北方根结线虫(M. hapla)。爪哇根结线虫为优势种。     

Microtubule dynamics in mitosis in Aspergillus nidulans

Mitosis in Aspergillus nidulans is very rapid, requiring less than 5 min at 37 °C in germlings (Bergen and Morris, 1983). In this time the cytoplasmic microtubules (MTs) must disassemble, the mitotic spindle assemble, function and disassemble, and cytoplasmic MTs reassemble. It follows that cytoplasmic MTs must be extremely dynamic in this period and we were interested, in particular, in examining the processes of MT disassembly in prophase and reassembly in anaphase and telophase. We observed a diploid strain that expressed GFP-α-tubulin. We used a spinning disk confocal microscope that allowed rapid image capture, which proved necessary because microtubule dynamics were extremely rapid. We found, for the first time, that microtubule severing occurs in prophase in a filamentous fungus and that catastrophe rather than nucleation limits astral microtubule growth.     

Expression of the calcium-binding protein S100A4 is markedly up-regulated by osmotic stress and is involved in the renal osmoadaptive response

Proteomic analysis of Inner Medullary Collecting Duct (IMCD3) cells adapted to increasing levels of tonicity (300, 600, and 900 mosmol/kg H(2)O) by two-dimensional difference gel electrophoresis and mass spectrometry revealed several proteins as yet unknown to be up-regulated in response to hypertonic stress. Of these proteins, one of the most robustly up-regulated (22-fold) was S100A4. The identity of the protein was verified by high pressure liquid chromatography-mass spectrometry. Western blot analysis confirmed increased expression with increased tonicity, both acute and chronic. S100A4 protein expression was further confirmed by immunocytochemical analysis. Cells grown in isotonic conditions showed complete absence of immunostaining, whereas chronically adapted IMCD3 cells had uniform cytoplasmic localization. The protein is also regulated in vivo as in mouse kidney tissues S100A4 expression was many -fold greater in the papilla as compared with the cortex and increased further in the papilla upon 36 h of thirsting. Increased expression of S100A4 was also observed in the medulla and papilla, but not the cortex of a human kidney. Data from Affymetrix gene chip analysis and quantitative PCR also revealed increased S100A4 message in IMCD3 cells adapted to hypertonicity. The initial expression of message increased at 8-10 h following exposure to acute sublethal hypertonic stress (550 mosmol/kg H(2)O). Protein and message half-life in IMCD3 cells were 85.5 and 6.8 h, respectively. Increasing medium tonicity with NaCl, sucrose, mannitol, and choline chloride stimulated S100A4 expression, whereas urea did not. Silencing of S100A4 expression using a stable siRNA vector (pSM2; Open Biosystems) resulted in a 48-h delay in adaptation of IMCD3 cells under sublethal osmotic stress, suggesting S100A4 is involved in the osmoadaptive response. In summary, we describe the heretofore unrecognized up-regulation of a small calcium-binding protein, both in vitro and in vivo, whose absence profoundly delays osmoadaptation and slows cellular growth under hypertonic conditions.     

Microtubule nucleation

Microtubule nucleation is the process in which several tubulin molecules interact to form a microtubule seed. Microtubule nucleation occurs spontaneously in purified tubulin solutions, and molecular intermediates between tubulin dimers and microtubules have been identified. Microtubule nucleation is enhanced in tubulin solutions by the addition of gamma-tubulin or various gamma-tubulin complexes. In vivo, microtubule assembly is usually seeded by gamma-tubulin ring complexes. Recent studies suggest, however, that microtubule nucleation can occur in the absence of gamma-tubulin, and that gamma-tubulin may have other cell functions apart from being a major component of the gamma-tubulin ring complex.     

The functions of myosin II and myosin V homologs in tip growth and septation in Aspergillus nidulans

Because of the industrial and medical importance of members of the fungal genus Aspergillus, there is considerable interest in the functions of cytoskeletal components in growth and secretion in these organisms. We have analyzed the genome of Aspergillus nidulans and found that there are two previously unstudied myosin genes, a myosin II homolog, myoB (product = MyoB) and a myosin V homolog, myoE (product = MyoE). Deletions of either cause significant growth defects. MyoB localizes in strings that coalesce into contractile rings at forming septa. It is critical for septation and normal deposition of chitin but not for hyphal extension. MyoE localizes to the Spitzenkörper and to moving puncta in the cytoplasm. Time-lapse imaging of SynA, a v-SNARE, reveals that in myoE deletion strains vesicles no longer localize to the Spitzenkörper. Tip morphology is slightly abnormal and branching occurs more frequently than in controls. Tip extension is slower than in controls, but because hyphal diameter is greater, growth (increase in volume/time) is only slightly reduced. Concentration of vesicles into the Spitzenkörper before incorporation into the plasma membrane is, thus, not required for hyphal growth but facilitates faster tip extension and a more normal hyphal shape.     

Acetylation of Synaptosomal Protein: Inhibition by Veratridine

Abstract: Incubation of synaptosomes with [³H]acetate results in rapid labeling of protein. Labeling is decreased in the presence of veratridine, and the effect of veratridine is blocked by tetrodotoxin. Most of the radioactivity can be removed by base or acid hydrolysis, and is probably incorporated as acetate; it is this fraction that is affected by the veratridine. The data suggest that veratridine stimulates deacetylation of synaptosomal protein. This raises the question whether acetylation-deacetylation is involved in membrane function.     

The ultrastructure of mitosis inChroomonas salina (Cryptophyceae)

Summary A detailed account of the ultrastructure of mitosis in a member of theCryptophyceae is given for the first time. The initial indication of mitosis is the duplication of the flagellar bases. The nucleus migrates towards the anterior of the cell and its envelope and nucleolus break down. The chromatin which at interphase is in the form of scattered clumps, condenses into a solid mass through which run narrow tunnels. Each tunnel allows the passage of one to four microtubules. At metaphase the dense plate of chromatin is situated on the equator and the spindle has a rectangular shape. Individual chromosomes cannot be recognized and no morphologically differentiated kinetochores have been observed. The flagella remain functional, their bases stay at the anterior side of the nucleus and do not move to the poles. At anaphase two plates of chromatin separate and these move apart until they come to lie against the ER sheath surrounding the chloroplasts. The new nuclear envelope starts to form on the opposite side of the daughter nucleus. Cytokinesis may commence early in mitosis and consists of a constriction of the parent cell, starting from the posterior end, followed by separation of the two daughters. The present work supports earlier views that only one chromosome is evident during the nuclear division of these organisms. The mitosis is completely different from that of theDinophyceae with which theCryptophyceae were formerly linked.     

THE COMPLEX BINDING OF γ-AMINOBUTYRIC ACID TO A RAT BRAIN SYNAPTIC MEMBRANE PREPARATION

The association of γ-aminobutyric acid (GABA) with rat brain synaptic membranes is complex and involves more than one set of binding sites. This fact is suggested by the form of experimentally determined binding curves and confirmed by the destruction of one set of homogenous sites by covalent modifications with iodine. The difference in binding of GABA by two sets of membranes which have been exhaustively iodinated in the presence and absence of an excess of GABA corresponds to 1/6 of the binding expressed by uniodinated membranes after equilibration with 0.25 μm -GABA. This difference appears to be the result of the expression of a homogeneous set of independent sites, each of which contains an iodinatable'residue that is protected by bound GABA. Examination of the factors leading to the retention of radioactive ligand by a synaptic membrane preparation is suggestive of a method for determining the maximum number of binding sites for a given ligand and for evaluating solution space without displacing the bound species or adding a presumably inert tracer. Three additional measurements of retention of high ligand concentration are shown to be sufficient for the determination. Employment of the method facilitates the investigation of the interaction of the membrane preparations with individual agonists and antagonists.     

The role of microtubules in rapid hyphal tip growth of Aspergillus nidulans

The filamentous fungus Aspergillus nidulans grows by polarized extension of hyphal tips. The actin cytoskeleton is essential for polarized growth, but the role of microtubules has been controversial. To define the role of microtubules in tip growth, we used time-lapse microscopy to measure tip growth rates in germlings of A. nidulans and in multinucleate hyphal tip cells, and we used a green fluorescent protein-alpha-tubulin fusion to observe the effects of the antimicrotubule agent benomyl. Hyphal tip cells grew approximately 5 times faster than binucleate germlings. In germlings, cytoplasmic microtubules disassembled completely in mitosis. In hyphal tip cells, however, microtubules disassembled through most of the cytoplasm in mitosis but persisted in a region near the hyphal tip. The growth rate of hyphal tip cells did not change significantly in mitosis. Benomyl caused rapid disassembly of microtubules in tip cells and a 10x reduction in growth rate. When benomyl was washed out, microtubules assembled quickly and rapid tip growth resumed. These results demonstrate that although microtubules are not strictly required for polarized growth, they are rate-limiting for the growth of hyphal tip cells. These data also reveal that A. nidulans exhibits a remarkable spatial regulation of microtubule disassembly within hyphal tip cells.