Isolation of Sordaria fimicola from Maize Stalks

Sordaria fimicola, which does not appear to have been isolated from maize before, was isolated from stalks in the field throughout the growing season. The fungus occurred at low frequencies and was confined largely to the nodes. Although it was repeatedly isolated from maize stalks it appears to be an opportunistic inhabitant. In a greenhouse study it could not be re-isolated from maize seedling roots although a reduction in dry weight accumulation, root length and plant height was recorded.     

An Endogenous Rhythm of Spore Discharge in Sordaria fimicola

The sporulation process in Sordaria fimicola has been studiedunder controlled conditions, with particular reference to discharge.Discharge occurred with a circadian periodicity for the greaterpart of the sporulation life of the culture, with peaks at about18.00 hours in either light or darkness. The consistency ofthis phenomenon was confirmed by an analysis of previous work.Fluctuations in light intensity, temperature, relative humidity,carbon dioxide concentration, and vibration were eliminatedas far as possible, as causes of this periodicity. Minor fluctuationsin discharge rate with a period of less than 24 h were probablyrandom. The general nature of the periodicity was shown to be consistentwith some aspects of endogenous rhythms in other organisms.However, spore discharge in S. fimicola is very sensitive tolight, and it is readily entrained to discharge out of phasewith the natural period. The rate of development of two stages of spore formation (delimitationand maturation) were determined, and these were related to therate and periodicity of discharge. From the data it was impossibleto establish at which stage of sporulation the periodicity arose.     

The fine structure of ascospore shape and development inCeratocystis fimbriata

Ascospore development inCeratocystis fimbriata Ell. & Halst. commenced in an eight-nucleate ascus. A single vesicle formed along the periphery of the ascus from fragments of ascospore delimiting membranes, surrounded all eight nuclei and eventually invaginated, first forming pouches with open ends, then finally enclosing each of the eight nuclei in a separate sac, thus delimiting ascospores. Pairing of the ascospores followed and brim formation occurred at the contact area between two ascospores. Osmiophilic bodies contributed to the formation of brim-like appendages by fusing to the ascospore walls. Additional brims were observed at opposite ends of the ascospores giving them a double-brimmed appearance.Abbreviations AV ascus vesicle - DM delimiting membrane - EV electron translucent bodies - G granules - M mitochondria - N nucleus - OB osmiophilic bodies - PMV plasmamembrane vesicles - PW primary wall - SW secondary wall     

Sporopollenin formation in the ascospore wall of Neurospora crassa

Chemical extraction procedures have shown that sporopollenin is a major component of the ascospore wall of Neurospora crassa and Neurospora tetrasperma. The sporopollenin is about 12% total dryweight of ascospores, and is localised in the ribbed perispore layer. Radioactive β-carotene is efficiently incorporated into the sporopollenin, and it is suggested that carotenoids are the natural precursors that are polymerised in the perispore. However, three carotenoid-deficient mutants of N. crassa produced perispores of normal appearance and properties.     

Effects of Airspeed and Humidity Changes on Spore Discharge in Sordaria fimicola

An improved experimental system is described for studying therate of spore discharge in Sordaria fimicola subjected to anair-stream of controlled rate and relative humidity. Under nearlysaturated conditions the rate of air-flow does not seem to affectthe rate of discharge. Reduction of the R.H. from 95 per centto 70 per cent or 35 per cent leads to an immediate but temporaryincrease in discharge rate. 70 per cent R.H. seems only to affectactual discharge, but prolonged exposure to 35 per cent R.H.interferes as well with earlier stages in spore development.It is suggested that the immediate effect on discharge is physicalrather than biochemical. There is evidence that the perithecialwall plays some part in the control of spore discharge.     

Revisiting the Life Cycle of Dung Fungi,Including Sordaria fimicola

Dung fungi, such as Sordaria fimicola, generally reproduce sexually with ascospores discharged from mammalian dung after passage through herbivores. Their life cycle is thought to be obligate to dung, and thus their ascospores in Quaternary sediments have been interpreted as evidence of past mammalian herbivore activity. Reports of dung fungi as endophytes would seem to challenge the view that they are obligate to dung. However, endophyte status is controversial because surface-sterilization protocols could fail to kill dung fungus ascospores stuck to the plant surface. Thus, we first tested the ability of representative isolates of three common genera of dung fungi to affect plant growth and fecundity given that significant effects on plant fitness could not result from ascospores merely stuck to the plant surface. Isolates of S. fimicola, Preussia sp., and Sporormiella sp. reduced growth and fecundity of two of three populations of Bromus tectorum, the host from which they had been isolated. In further work with S. fimicola we showed that inoculations of roots of B. tectorum led to some colonization of aboveground tissues. The same isolate of S. fimicola reproduced sexually on inoculated host plant tissues as well as in dung after passage through sheep, thus demonstrating a facultative rather than an obligate life cycle. Finally, plants inoculated with S. fimicola were not preferred by sheep; preference had been expected if the fungus were obligate to dung. Overall, these findings make us question the assumption that these fungi are obligate to dung.     

The fine structure of akinete formation and germination in Cylindrospermum

Summary Akinete formation and germination were studied in a species of Cylindrospermum using the electron microscope. The differentiation of a vegetative cell into an akinete is characterized by cell enlargement, sheath condensation, deposition of several spore envelope layers, including a dense fibrillar layer and deposition of large cyanophycin granules. The mature akinete in addition to the multilayered envelope retains internally a large number of cyanophycin granules, a photosynthetic thylakoid system, polyhedral bodies, lipid deposits and nucleoplasmic regions. Germination of the akinete can take place in several modes differing in detail. Most frequently the spore envelope remains intact and the germling which may or may not have divided emerges through a pore at one end of the envelope. The photosynthetic thylakoid system appears to increase by the fusion of small vesicles found in the cytoplasm. Alpha-granules are numerous and cyanophycin is nearly absent in the germling.     

Pattern formation and the fine structure of the developing cell wall in colonies of Pediastrum boryanum

A single-layered disc of peripheral pronged cells and central prongless cells impart the typical gear shape to colonies of Pediastrum, while the walls of each cell have a characteristic reticulate triangular pattern. The two-layered wall forms in the cells during colony formation following zoospore aggregation and adhesion. The uniformly thin outer layer reflects contours resulting from differential thickening in the reticulate pattern of the inner, thicker, more fibrillar and granular wall layer. The reticulate pattern thus imparted to the outer wall layer persists in empty zoosporangia following the release of zoospores. Columns of electron-dense material extend through the outer wall layer except at the ridges and centers of the reticulum. Following mitosis and cleavage, the resulting zoospores are extruded within a vesicle membrane consisting of the inner wall layer. Separation of this membrane from the parent cell occurs in material of the inner layer adjacent to the outer wall. Vesicles containing swarming zoospores also contain a granular material which appears to become associated with the aggregating and adhering cells of new colonies. Microtubules occur in zoospores prior to adherence but are absent during wall deposition.     

Inherited differences in crossing over and gene conversion frequencies between wild strains of Sordaria fimicola from "Evolution Canyon".

Recombination generates new combinations of existing genetic variation and therefore may be important in adaptation and evolution. We investigated whether there was natural genetic variation for recombination frequencies and whether any such variation was environment related and possibly adaptive. Crossing over and gene conversion frequencies often differed significantly in a consistent direction between wild strains of the fungus Sordaria fimicola isolated from a harsher or a milder microscale environment in "Evolution Canyon," Israel. First- and second-generation descendants from selfing the original strains from the harsher, more variable, south-facing slope had higher frequencies of crossing over in locus-centromere intervals and of gene conversion than those from the lusher north-facing slopes. There were some significant differences between strains within slopes, but these were less marked than between slopes. Such inherited variation could provide a basis for natural selection for optimum recombination frequencies in each environment. There were no significant differences in meiotic hybrid DNA correction frequencies between strains from the different slopes. The conversion analysis was made using only conversions to wild type, because estimations of conversion to mutant were affected by a high frequency of spontaneous mutation. There was no polarized segregation of chromosomes at meiosis I or of chromatids at meiosis II.     

The fine structure of the epidermal cell wall in azuki bean epicotyl

Journal of Plant Research - The arrangement of microfibrils in the wall of epidermal cells in the epicotyl of the azuki bean plant has been observed. The outer and inner tangential walls have a...     

Inherited and environmentally induced differences in mutation frequencies between wild strains of Sordaria fimicola from "Evolution Canyon".

We have studied whether there is natural genetic variation for mutation frequencies, and whether any such variation is environment-related. Mutation frequencies differed significantly between wild strains of the fungus Sordaria fimicola isolated from a harsher or a milder microscale environment in "Evolution Canyon," Israel. Strains from the harsher, drier, south-facing slope had higher frequencies of new spontaneous mutations and of accumulated mutations than strains from the milder, lusher, north-facing slope. Collective total mutation frequencies over many loci for ascospore pigmentation were 2.3, 3.5 and 4.4% for three strains from the south-facing slope, and 0.9, 1.1, 1.2, 1.3 and 1.3% for five strains from the north-facing slope. Some of this between-slope difference was inherited through two generations of selfing, with average spontaneous mutation frequencies of 1.9% for south-facing slope strains and 0.8% for north-facing slope strains. The remainder was caused by different frequencies of mutations arising in the original environments. There was also significant heritable genetic variation in mutation frequencies within slopes. Similar between-slope differences were found for ascospore germination-resistance to acriflavine, with much higher frequencies in strains from the south-facing slope. Such inherited variation provides a basis for natural selection for optimum mutation rates in each environment.     

Absence of interference in association with gene conversion in Sordaria fimicola, and presence of interference in association with ordinary recombination

From the analysis of large samples of gene conversion asci in the g locus of Sordaria fimicola, it was found that neither the conversion event itself nor conversion-associated recombination of flanking markers cause either chiasma or chromatid interference with crossing over in a neighboring interval. The presence of more than one kind of crossover event, one causing interference the other not, is considered. The existence of two kinds of gene loci, one of single-cistron composition and the other of multiple-cistron composition, is discussed in relation to reciprocal recombination within a locus.     

The fine structure of secretion in Hyalophysa chattoni: formation of the attachment peduncle and the chitinous phoretic cyst wall.

The settling tomite stage of the apostome Hyalophysa chattoni secretes a phoretic cyst wall composed of chitin, mucopolysaccharides, and protein. Within 1 1/2 h after settling, an electron-dense proteinaceous cyst layer (the outer layer) is formed from secretions originating at the base of the kineties and from the thick pellicular layer between the kineties. The inner cyst layer, composed primarily of chitin (acidic and neutral polysaccharides are also present), is secreted across the entire cell surface. Cyst wall formation is completed within 6 h. The fine structure of endocyst secretion resembles stages in the secretion of chitin by fungi, yeasts, and arthropods. A proteinaceous attachment peduncle is secreted to anchor the cell to a shrimp host and is formed by the release of electrondense dense secretory bodies from the cell's ventral surface.     

The fine structure of the pollen wall inStrelitzia reginae (Musaceae)

The pollen wall ofStrelitzia reginae (Musaceae) consists of a nearly unsculptured, very thin, highly reduced, but coherent exine, and a thick intine (with an outer, channeled layer and an inner, largely homogeneous layer). After short, incomplete acetolysis the exine covers the remaining, severely shrinked protoplast as a folded, but unaltered “skin”, while the intine has totally disappeared. After extended acetolysis only the coherent, skin-like exine remains. Thus, the term “exine-less pollen” sometimes used for similar sporoderm structures in other genera ofZingiberales is misleading and should be substituted by the term “skin-like exine”. Surprisingly, the peculiar pollen wall ultrastructure ofStrelitzia and some otherZingiberales is very similar to that of some genera of theLaurales, an example for convergent evolution within the angiosperms.