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Journal ArticleDOI

An ultrastructural basis for hyphal tip growth in pythium ultimum

01 Mar 1970-American Journal of Botany (John Wiley & Sons, Ltd)-Vol. 57, Iss: 3, pp 245-266
About: This article is published in American Journal of Botany.The article was published on 1970-03-01. It has received 216 citations till now. The article focuses on the topics: Hyphal tip & Pythium ultimum.
Citations
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Journal ArticleDOI
TL;DR: The findings are consistent with the hypothesis that vesicles produced by the endomembrane system in the subapical region become concentrated in the apex where they are incorporated at the expanding surface.
Abstract: Hyphal tips of fungi representing Oomycetes, Zygomycetes, Ascomycetes, Basidiomycetes, and Deuteromycetes were examined by light and electron microscopy and compared with respect to their protoplasmic organization. In all fungi studied, there is a zone at the hyphal apex which is rich in cytoplasmic vesicles but nearly devoid of other cell components. Some vesicle profiles are continuous with the plasma membrane at the apices of these tip-growing cells. The subapical zones of hyphae contain an endomembrane system which includes smooth-surfaced cisternae associated with small clusters of vesicles. The findings are consistent with the hypothesis that vesicles produced by the endomembrane system in the subapical region become concentrated in the apex where they are incorporated at the expanding surface. Septate fungi (Ascomycetes, Basidiomycetes, and Deuteromycetes) have an apical body (Spitzenkorper) which is associated with growing hyphal tips. In electron micrographs of these fungi, an additional specialized region within the accumulation of apical vesicles is shown for the first time. This region corresponds on the bases of distribution among fungi, location in hyphae, size, shape and boundary characteristics to the Spitzenkorper seen by light microscopy. This structure is not universally associated with tip growth, whereas apical vesicles are widespread among tip-growing systems.

429 citations

Journal ArticleDOI
TL;DR: It is demonstrated that fungal ROS production is critical in maintaining a mutualistic fungus–plant interaction.
Abstract: Although much is known about the signals and mechanisms that lead to pathogenic interactions between plants and fungi, comparatively little is known about fungus-plant mutualistic symbioses. We describe a novel role for reactive oxygen species (ROS) in regulating the mutualistic interaction between a clavicipitaceous fungal endophyte, Epichloe festucae, and its grass host, Lolium perenne. In wild-type associations, E. festucae grows systemically in intercellular spaces of leaves as infrequently branched hyphae parallel to the leaf axis. A screen to identify symbiotic genes isolated a fungal mutant that altered the interaction from mutualistic to antagonistic. This mutant has a single-copy plasmid insertion in the coding region of a NADPH oxidase gene, noxA. Plants infected with the noxA mutant lose apical dominance, become severely stunted, show precocious senescence, and eventually die. The fungal biomass in these associations is increased dramatically, with hyphae showing increased vacuolation. Deletion of a second NADPH oxidase gene, noxB, had no effect on the E. festucae-perennial ryegrass symbiosis. ROS accumulation was detected cytochemically in the endophyte extracellular matrix and at the interface between the extracellular matrix and host cell walls of meristematic tissue in wild-type but not in noxA mutant associations. These results demonstrate that fungal ROS production is critical in maintaining a mutualistic fungus-plant interaction.

407 citations


Cites result from "An ultrastructural basis for hyphal..."

  • ...In older leaves, most of the hyphae had unusual branching and the cells were highly vacuolated, a morphology indicative of tip growth (Grove et al., 1970; Barelle et al., 2003), but some hyphae were similar in growth pattern and morphology to those found in younger leaves....

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Journal ArticleDOI
TL;DR: The results support the hypothesis that mycelial growth involves the duplication of a ‘growth unit’ which consists of a tip and a certain mean length of hypha.
Abstract: Growth of Mucor hiemalis, Geotrichum candidum, Aspergillus nidulans, Neurospora crassa and Penicillium chrysogenum was studied by time lapse photography. The total hyphal length of the mycelium of each species increased at an exponential rate; in M. hiemalis exponential growth continued until the mycelium had a total hyphal length in excess of 10 mm. After spore germination there was an initial phase of discontinuous tip production followed by a phase of ‘continuous’ tip production. The hyphal length and number of tips possessed by a mycelium increased exponentially at approximately the same specific growth rate. The amplitude of the oscillations in the length of the hyphal growth unit of a mycelium decreased progressively during mycelial growth and eventually the growth unit attained a more or less constant value. The results support the hypothesis that mycelial growth involves the duplication of a ‘growth unit’ which consists of a tip and a certain mean length of hypha.

293 citations

Journal ArticleDOI
TL;DR: The results obtained allowed us to assess the importance of knowing the carrier and removal status of canine coronavirus, as a source of infection for other animals, not necessarily belonging to the same breeds.

271 citations

Book ChapterDOI
01 Jan 1971
TL;DR: The Golgi apparatus in its most familiar form is that part of the cell’s endomembrane system consisting of regions of stacked cisternae (dictyosomes) which lack ribosomes, a complex structure with unique functions in compartmentalizing products of synthesis and producing exocytotic vesicles whose membranes are capable of fusing with plasma membrane.
Abstract: The Golgi apparatus in its most familiar form is that part of the cell’s endomembrane system1 consisting of regions of stacked cisternae (dictyosomes) which lack ribosomes. It is a complex structure with unique functions in compartmentalizing products of synthesis, serving as a site of cytomembrane differentiation and producing exocytotic vesicles whose membranes are capable of fusing with plasma membrane. Unlike semiautonomous organelles such as chloroplasts and mitochondria, the function of the Golgi apparatus in secretion depends on functional continuity with other components of the endomembrane system.

227 citations

References
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Journal ArticleDOI
TL;DR: The stain reported here differs from previous alkaline lead stains in that the chelating agent, citrate, is in sufficient excess to sequester all lead present, and is less likely to contaminate sections.
Abstract: Aqueous solutions of lead salts (1, 2) and saturated solutions of lead hydroxide (1) have been used as stains to enhance the electron-scattering properties of components of biological materials examined in the electron microscope. Saturated solutions of lead hydroxide (1), while staining more intensely than either lead acetate or monobasic lead acetate (l , 2), form insoluble lead carbonate upon exposure to air. The avoidance of such precipitates which contaminate surfaces of sections during staining has been the stimulus for the development of elaborate procedures for exclusion of air or carbon dioxide (3, 4). Several modifications of Watson's lead hydroxide stain (1) have recently appeared (5-7). All utilize relatively high pH (approximately 12) and one contains small amounts of tartrate (6), a relatively weak complexing agent (8), in addition to lead. These modified lead stains are less liable to contaminate the surface of the section with precipitated stain products. The stain reported here differs from previous alkaline lead stains in that the chelating agent, citrate, is in sufficient excess to sequester all lead present. Lead citrate, soluble in high concentrations in basic solutions, is a chelate compound with an apparent association constant (log Ka) between ligand and lead ion of 6.5 (9). Tissue binding sites, presumably organophosphates, and other anionic species present in biological components following fixation, dehydration, and plastic embedding apparently have a greater affinity for this cation than lead citrate inasmuch as cellular and extracellular structures in the section sequester lead from the staining solution. Alkaline lead citrate solutions are less likely to contaminate sections, as no precipitates form when droplets of fresh staining solution are exposed to air for periods of up to 30 minutes. The resultant staining of the sections is of high intensity in sections of Aralditeor Epon-embedded material. Cytoplasmic membranes, ribosomes, glycogen, and nuclear material are stained (Figs. 1 to 3). STAIN SOLUTION: Lead citrate is prepared by

24,137 citations

Journal ArticleDOI
TL;DR: More rapid than previous techniques, this method gives blocks which do not fracture unduly on trimming and provides sections of soft tissues at 1 μ for phase contrast microscopy, as well as ultrathin sections which cut as easily with glass knives as sections of methacrylate.
Abstract: Fixed tissue is dehydrated with tertiary butyl alcohol overnight. The following day it is cleared in toluene, infiltrated and embedded in Araldite resin-hardener-accelerator mixture without dibutyl...

3,197 citations

Journal ArticleDOI
TL;DR: Results strongly suggest that new membrane is synthesized in the rough ER and subsequently transferred to the smooth ER in rat hepatocytes during a period of rapid cell differentiation.
Abstract: The development of the endoplasmic reticulum of rat hepatocytes was studied during a period of rapid cell differentiation, i.e., from 3 days before to 8 days after birth. Before birth, the ER increases in volume, remaining predominantly rough surfaced; after birth, the increase continues but affects mainly the smooth-surfaced part of the system. These changes are reflected in variations of the RNA/protein and PLP/protein ratios of microsomal fractions: the first decreases, while the second increases, with age. The analysis of microsomal membranes and of microsomal lipids indicates that the PLP/protein ratio, the distribution of phospholipids, and the rate of P32 incorporation into these phospholipids show little variation over the period examined and are comparable to values found in adult liver. Fatty acid composition of total phosphatides undergoes, however, drastic changes after birth. During the period of rapid ER development in vivo incorporation of leucine-C14 and glycerol-C14 into the proteins and lipids of microsomal membranes is higher in the rough-than in the smooth-surfaced microsomes, for the first hours after the injection of the label; later on (∼10 hr) the situation is reversed. These results strongly suggest that new membrane is synthesized in the rough ER and subsequently transferred to the smooth ER.

530 citations

Journal ArticleDOI

378 citations