Beryllium toxicity inNeurospora crassa

InNeurospora crassa,0.44 mM Be²⁺ caused half-maximal inhibition of growth and this inhibition could be fully counteracted by the addition of 2.5 mM Ca²⁺ to the medium. Mn²⁺ and Mg²⁺ were less effective in reversing the growth inhibition caused by Be²⁺ and the order of effectiveness was Ca²⁺ > Mn2+ > Mg²⁺. Fe3+ and Zn²⁺ were ineffective in reversing Be²⁺ toxicity. Pyruvate, malate and succinate also reversed the growth inhibition caused by Be²⁺ inN. crassa. Pyruvate restored growth by a mechanism not involving control of Be²⁺ accumulation in the mould. The rate of utilisation of glucose by the mycelia grown in the presence of Be²⁺ was reduced, while that of pyruvate was not affected. The results indicate that the primary metabolic lesion in Be²⁺ toxicity inN. crassa is probably a block at some step(s) in the glycolytic sequence.     

Paedogenetic conidiation inNeurospora crassa

Under conditions of growth limitation the germ tubes ofNeurospora crassa macroconidia may convert to functional conidiophores with developing chains of viable, new conidia. The induction of this paedogenetic conidiation in liquid culture does not require exposure to high temperature, as reported for conidia of some other ascomycetous fungi, but it is induced at normal growth temperatures within 12–15 h by germination of the conidia in a dilute, nutrient-poor incubation medium. The inoculum density, temperature of incubation, presence or absence of white light, and genetic strain ofN. crassa also influence the kinetics of conidium formation.     

Intra-chromosomal position interference inNeurospora crassa

Multiple-point crosses where 20 pairs of regions (ten loosely linked markers) for the study of contiguous exchanges involving two linkage groups, capable of being investigated at a time, were utilized. In order to find out the effect of a chelating agent on interference, crosses were treated with different molar concentrations of ethylene-diamine tetraacetic acid (EDTA). All marker strains were standardized before use by inbreeding with a wild-type of known parentage.Since tests based on Coefficient of Coincidence and on Poisson distribution for finding out the position interference are rather unsatisfactory, a method based onContingency Chi-square test for detecting the intensity and nature of interference is described.Data obtained from 1813 analyzable ordered tetrads show that positive interference is absent in the control crosses. It is present among certain regions in crosses when treated with 4×10^–5M and 10×10^–5M EDTA but it vanishes again in crosses when treated with 20×10^–5M EDTA. Negative interference is present in the control crosses but it varies among pairs of regions on the two linkage groups. The localization and intensity of interference are alterable with EDTA treatment. The data are discussed in the light of certain concepts invoking to explain the mechanism that involves a genetic exchange.     

Calcium and tip growth inNeurospora crassa

Summary We examined the ionic regulation of tip growth inNeurospora crassa by a combination of electrophysiology and confocal microscopy. To determine if transmembrane ionic fluxes are required for tip growth, we voltage clamped the membrane from –200 to +50 mV. In this voltage range, transmembrane ionic fluxes would either reverse (e.g., K⁺) or change dramatically (e.g., Ca²⁺ influx) but had no effect on hyphal growth rates. Therefore, ionic fluxes (including Ca²⁺ influx) may not be required for tip growth. However, intracellular Ca²⁺ may still play an obligatory role in tip growth. To assess this possibility, we first increased cytosolic Ca²⁺ directly by ionophoresis. Elevated Ca²⁺ induced subapical branch initiation, often multiple tips. At hyphal tips, fluorescence ratio imaging using fluo-3 and fura-red revealed a pronounced tip-high Ca²⁺ gradient within 10 m of the tip in growing hyphae which was not observed in nongrowing hyphae. Injection of the Ca²⁺ chelator 1,2-bis(ortho-aminophenoxy)ethane-N,N,N,N-tetrapotassium acetate consistently inhibited growth concomitantly with a depletion of intracellular Ca²⁺ and dissipation of the tip-high gradient. We conclude that Ca²⁺ plays a regulatory role in tip initiation and the maintenance of tip growth. Because plasma membrane ionic fluxes do not play a role in tip growth, we suggest that the tip-high Ca²⁺ gradient is generated from intracellular Ca²⁺ stores in the ascomyceteN. crassa.Abbreviations BAPTA 1,2-bis(ortho-aminophenoxy)ethane-N,N,N,N-tetrapotassium acetate - [Ca²⁺]_i intracellular Ca²⁺ concentration - fluo-3 2,7-dichloro-6-hydroxy-3-oxo-9-xanthenyl-4-methyl-2,2-(ethylenedioxy)dianiline-N,N,N,N-tetraacetic acid     

Rate of total RNA synthesis inNeurospora crassa

The rate of synthesis of total RNA inneurospora crassa has been determined under two different conditions of exponential growth. The values obtained were compared with the previously reported rates of stable RNA synthesis: at the higher growth rate the synthesis of stable RNA accounts for a larger fraction of total RNA synthesis than at the lower grwoth rate.     

Protein oxidation related to morphogenesis inNeurospora crassa

Hyphae ofNeurospora crassa exposed to the air adhere to each other, form aerial hyphae, and conidiate. During these morphogenic events, the carbonyl content in purified total protein was determined as a measurement of protein oxidation. A peak of protein carbonyl content coincided in time with hyphal adhesion, with initiation of aerial hyphae growth, and with the onset of conidia formation. These results suggest increased generation of reactive oxygen species at the start of each morphogenic process and a reversion of the hyperoxidant states with the appearance of new structures.     

Fluence response relationship of carotenogenesis inNeurospora crassa

The fluence response of the blue light induced carotenoid synthesis inNeurospora is biphasic. Using fluence rates between 0.3 and 40 Wm^-2, increasing illumination times beyond 16 min (at 20°C) result in a second rise of the amount of carotenoids synthesized in the subsequent dark period. On altering the temperature, the transition point to the second phase of the response is shifted to shorter/longer illumination periods with increasing/decreasing temperature, respectively. The transition point can also be shifted by administering high fluence rates of near UV light: The start of the second phase is already triggered after an irradiation time of 2 min. The findings suggest that elements of the transduction sequence become depleted and senstivity recovers in a temperature-dependent process. The biphasic response and the effects of UV light are discussed in relation to the transduction mechanism and to the ecological significance.Presented in part at the meeting of the Deutsche Botanische Gesellschaft, September 1978, Marburg, Federal Republic of Germany     

The structure and development of septa inNeurospora crassa

Summary Electron microscopy of septa ofNeurospora crassa has shown that microfibrillar material is a major structural component. These microfibrils are arranged in a predominantly tangential orientation and in young (24 hours) mycelium can often be seen in unextracted septal preparations. In older (5 days) mycelium they are overlain with amorphous material, which can be removed by treatment with Pronase, or by chemical extractions. The structure of septa is described and compared with that of the lateral hyphal wall.Developing septa are typically surrounded by vesicles, and sometimes by alignments of cytoplasmic tubules. Electron and light microscopic autoradiography have shown that N-acetylglucosamine is quickly and specifically incorporated into developing septa, and there is no evidence for its prior incorporation into any cytoplasmic site. Glucose is also incorporated into septa, but less specifically. From the autoradiographic results and from experiments with chemical and enzymic extractions it is suggested that chitin is a major component of the septum. A model of the septum is constructed from these data.     

Effects of chelating agents on crossing-over inNeurospora crassa

Screening methods were adapted to find out effective concentrations of the chelating agents, ethylenediamine tetraacetic acid and 8-hydroxy quinoline which produced modifications in the cross-over frequencies. Final crosses were designed to study the close and distantly placed regions on either side of the centromeres. Eleven regions were studied using tetrads, and eight regions using randomly selected ascospores.The magnitude and intensity of modification in the cross-over values vary from region to region, but an overall increase in the cross-over frequency was observed.Significant departures in cross-over values were found between the various treated crosses with respect to a number of regions.The mode of action of the chelating agents was not easy to formulate, but implications attached to it have been discussed.     

Fatty acid control of cyclic AMP levels inNeurospora crassa

Several saturated, monosaturated, and polyunsaturated fatty acids produce rapid increases in cyclic AMP levels in the fungusNeurospora crassa when added to the growth medium at 10–50 M. The time courses of cyclic AMP increase resembled those previously shown to be induced by other agents, reaching peak cyclic AMP levels at about 2 min after fatty acid addition. These fatty acids had little or no influence on adenylate cyclase fromNeurospora crassa in vitro. On the basis of previous evidence that uncouplers of oxidative phosphorylation increase cyclic AMP levels and that fatty acids can act as uncouplers, we suggest that the fatty acids in vivo may act to increase cyclic AMP levels by acting as uncouplers of oxidative phosphorylation. In agreement with this suggestion, two fatty acids were shown to produce decreased ATP-ADP ratios inNeurospora at concentrations producing cyclic AMP increases.     

The effect of copper on histidine biosynthesis inNeurospora crassa

The inhibition of growth of a wild strain ofNeurospora crassa by Cu²⁺ is counteracted by histidine, histidine methyl ester, histidinol and Mn²⁺. In the presence of Cu²⁺, the total free amino acid content decreased by 30%. The decreased free amino acid pools of arginine, histidine and tyrosine were restored on the addition of Mn²⁺. Histidinol phosphate phosphatase showed a decrease in activity in the presence of Cu²⁺. This inhibition was reversed on the addition of excess Mn²⁺. The data suggest that copper toxicity in the mould is due to suppression of histidine biosynthesis.     

Carbon starvation mediated changes in carbohydrate metabolism inNeurospora crassa

Carbon starvation conditions were found to increase the activities of gluconeogenic enzymes such as malic enzyme, cytosolic malate dehydrogenase and isocitrate lyase along with proteases and inhibition in glucose catabolic enzymes such as G6P dehydrogenase and FDP aldolase inNeurospora crassa