Wall and hyphal growth

Wall and hyphal growth

116 WALL AND HYPHAL GROWTH The group held a meeting on 'Wall and hyphal growth' at Queen Elizabeth College, London University on 5-7 April 1978. Eigh...

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116

WALL AND HYPHAL GROWTH The group held a meeting on 'Wall and hyphal growth' at Queen Elizabeth College, London University on 5-7 April 1978. Eighteen people contributed to the sympos ium and a further 33 read papers during the open paper sessions. Approximately 225 people attended the symposium; of the 203 who registered for the meeting, 110 were members of the society and 31 came from overseas (representing America, Canada, Denmark, Italy, France, Switzerland, Holland, Israel and Eire). The fact that less than 60 of the people attending the symposium were in residence illustrates the value of London as a venue for such meetings. One of the most encouraging aspects of the meeting was the large number of young mycologists in the audience; I estimate that about 50 Ph.D. students attended the symposium! Professor L.E. Hawker" was the guest of honour of the Society at a symposium dinner held at the London Embassy Hotel; 94 people attended this function. The proceedings ofthe symposium will be published by Cambridge University Press and will form the second symposium volume published by the Society. The group wishes to record its appreciation to the Royal Society, the British Council, G.D. Searle Ltd., and Glaxo Research Ltd. for their help in sponsoring this meeting. A. Trinci ·Professor Hawker has written to the President 'It was most enjoyable to attend last week's meeting and meet so many old friends including yourself. I would have liked an opportunity to thank the members for entertaining me to dinner an unexpected honour which was much appreciated... with again many thanks for the welcome I had'. Abstracts of Papers read during the Open Paper Sessions on 5th April 1978 at Queen Elizabeth College. The Effects of 5 F1uorocytosine on HyphaI Nuclei of Candida albicans W.H. Wain and A.M. Polak·, National Heart Hospital, Westmoreland Street and Cardiothoracic Institute, 2 Beaumont Street, London, and ·Phlrmaceutical Research Division, F. Hoffmann La Roche, 124 Grenzacherstrasse, 4002 Basel, Switzerland. In experiments with yeasts ,S Ftuorocytosine (5FC) was shown to cause numerous biochemical effects. These included xenob iotic synthesis (5FC :'.5FU .. 5 FdUMP) ; enzyme inhibition (thymidylate synthetase) ; incorporation inhibition (3H-thymidine" DNA; 3:Zp04" RNA); quantity inhibition (DNA. RNA and carbohydrate); concentration increase (carbohydrate per cell); decreased cell division and increased cell volume . A significant number of these can be explained by an inhibition of DNA synthesis and consequent unbalanced growth. Some of these phenomena have been demonstrated in the hyphaI phase of Candida albicans, with continued hyphal elongation during inhibition of DNA synthesis. This communication presents a significant decrease in the number of nuclei per hypha treated with 5 fluorocytosine when there was no significant alteration in hyphal growth. Hyphal branching and apical growth in relation to wall composition and enzymes in Mucor

hiemalis: S. Lucek & B.E. Plunkett, Botany Department, Birkbeck CoUege, Malet St., London WCl. The mean branch density (number of primary branches per unit length of leading hypha, sample of 60 internodes) of Mucor hiemalis is increased by 6-azauracil (6AU) and decreased by 8-azaguanine (8AG) and other N.A. base analogues. At suitable concentrations for these morphological effects some redu ct ion of hyphal growth rate occurs . The paramorphogenic effe ct s are reversible by transfer to analogue-free media (6AU, 8AG) or the addit ion of the normal base (6AU only) . Enhanced hyphal wall hexosamine and reduced " chitinase" activity correlate with diminished growth. On the other hand, specific act ivity of intracellular protease dramatically rises with increased branching and falls with diminished branching.

117 Growth of Geotrichum candidum on ethanol K. AlIermann, I. Kier, J. Olsen & F. Floto, Institute of Plant Physiology, University of Copenhagen, f/). Farimagsgade 2A, DK·13S3 Copenhagen. Geotrichum candidum is able to grow on a synthetic medium which contained ethanol as the only carbon source. The growth rate on ethanol was 0.21 h-i at 25°C (doubling time, 3.3 h) compared with a growth rate of 0.39 h-i (doubling time, 1.8 h) when glucose was the carbon source. The isozymes of alcoholdehydrogenase (ADH) from cultures grown on glucose and ethanol have been characterized by polyacrylamide electrophoresis and by the reaction with cinnamylalcohol. The effect of pH on ADH-activity in the oxidative and in the reductive assay has been measured. The pH-optimum for the activity in both assays is 7.0 to 7.5 at which pH the activity in the reductive assay is about 6 times higher than in the oxidative assay. In ethanol grown cultures the cinnamylalcohol/ethanol ratio is higher at pH 9.0 (ca. 0.9) than at pH 7.0 (ca. 0.3). Carbon-limited continuous cultivation of Geotrichum candidum

J.R. Andersen & 1. Schneider, Institute of Plant Physiology, University of Copenhagen, 0sterfarimagsgade 2A, DK·13S3 Copenhagen. Geotrichum candidum was grown in a 1 I glucose-limited chemostat culture. In addition to glucose the medium contained only a few mineral salts; no trace elements or vitamins were added. Steady states were obtained at dilution rates from 0.03 to 0.45 h-i. The yield (Y) of organism from glucose was not constant. Y was lowest at the lowest specific growth rates studied, due to a relatively higher degree of maintenance energy. The growth form was filamentous at all specific growth rates studied. Spore formation only occurred at low dilution rates. Pellet formation was sometimes a problem, but only in old cultures at high dilution rates. Wallgrowth caused some deviation from simple Monod-kinetics. Spiral growth of mould colonies and its implications for the growth of hyphal tips M.F. Madelin, Department of Botany, University of Bristol, Woodland Rd., Bristol BSS lUG Sordaria fimicola on 0.02% malt extract agar displayed spiralling of the colony in a clockwise direction (viewed from above the agar plate). Only hyphae at the agar surface contributed to this spiral aspect. The direction of curvature of individual hyphae was related to their supporting surface; hyphae curved to the right as they advanced over it. This sustained departure from straight growth is attributed to a displacement of the plastic apex of the hypha as a result of its own axial rotation. Experiments with other species suggest that spiral growth of individual vegetative hyphae is not uncommon in fungi. Models of tip growth P.T. Saunders, Department of Mathematics, Queen Elizabeth College, Campden Hill Rd., London W8 7 AH Most models of tip growth make no predictions concerning the shape of the tip, which for simplicity is generally assumed to be hemispherical. If the wall is considered as an elastic membrane whose shape is determined by internal pressures, then assumptions about the distribution of the pressure and the variation in wall rigidity lead directly to predictions of shape. In particular, uniform hydrostatic pressure and uniform isotropic elasticity of the wall of the extension zone imply that the tip should be a paraboloid of revolution. which is in reasonable accord with observations. Variations in growth among wild-type isolates of Aspergillus nidulans. C.R Caten & lean M. Lawrence, Department of Genetics, University of Binningham,

Birmingham BIS 2IT Independent isolates of Aspergillus nidulans differ in radial growth (r) and in maximum growth yield with 1% (w/v) glucose as carbon source. Hybridization of isolates indicated that this natural variation in both growth parameters is determined by polygenic systems, although a single gene having a major effect on r above 35°C was detected. Disruptive selection for r among the progeny of single crosses produced strains with higher and lower growth rates than any of the natural isolates. Slow selections had higher specific growth rates (jJ.) and higher growth yields than fast selections.

118 Hyphal interaction and aggregation in Doratomyces purpureofuscus A. Breton, Laboratoire de phytomorphogenese, Clermont-Ferrand L'edification des corernies depend d'interactions s'exercant au sein de l'organisme ou de I'organe. Des phenomenes de concurrence permettent d'expliquer les interactions intervenant entre mycelium vegetatif et coremies, et au sein des structures agregees ou elles contrdlent la morphogenese des rhizoides et revolution des filaments ascendents. En outre diverses experiences montrent que Ie developpement des coremies isolees, ou leur regeneration apres decapitation ou ablation des rhizoides, necessite la presence d'un mycelium vivant ala base de la coremie. Des relations entre les hyphes vegetatives et Ia corernie d'etablissent par Ie biais d'anastornoses. Un facteur intramyeelien, constitue d'une ou plusieurs petites molecules thermostables, controle l'agregation et en assure le maintien. Effect of lysine starvation on the growth of Neurospora crassa M.H. Fletcher&. A.PJ. Trinci, Microbiology Department, Queen Elizabeth College, Carnpden Hill Road, London W.8. Protein and DNA synthesis were inhibited about 3 h after the onset oflysine starvation of cultures of an auxotrophic strain of Neurospora crassa. However, the dry weight of these cultures continued to increase for a further 3 h; thus growth was 'unbalanced'. A temporary period (3 h) of lysine starvation has been used to induce synchronization of mycelial cultures. These cultures showed stepwise increases in DNA and protein but not in RNA, carbohydrate or dry weight. Ultrastructures of the septum in Dimargaris cristalligena P. Jeffries &. T.W.K. Young, University of Edinburgh and Chelsea College Hyphae of Dimargaris cristalligena (Dimargaritaceae) have complex septa. The septum comprises a cross-wall possessing a flared, central pore, occluded by a plug which usually appears to bear a globose body on each side of the cross-wall. The cross-wall consists of electronlucent material which is continuous with a similar layer in the hyphal wall. The septal plug and associated bodies are composed of electrondense material. The plasmalemma passes through the pore, around the rim of the plug. Endoplasmic reticulum is frequently associated with the septal complex. These septa are compared with those found in the Kickxellales and Harpellales, Spore wall development in some British rust fungi A.P. Bennell, Royal Botanic Garden, Edinburgh EH3 SLB Teliospores characterised by verrucose (Puccinia calcitrapaet, tuberculate (Puccinia smyrnii) and echinulate iTranzschelia anemones) ornaments, are shown by electron microscopy to follow similar sequence of development. The ornamentation results from a differential deposition of secondary wall components into invaginations of the cytoplasm in the young spore. The shape and size of the mature spore ornaments is determined by the configuration of these invaginations, which subsequently exsert revealing the protruberances, as further centripetal secondary walling occurs and the outer, primary wall degenerates. This ontogeny contrasts with that of pitted and reticulate-walled teliospores. Biochemical studies on walls of Oomycetes B. Vaziri, Botany Department, The University, Whiteknights, Reading. Wall-bound proteins and glucan linkage patterns are known to differ between Oornycetes, but there is no information on the taxonomic value of such differences. Thin-layer chromatography has been used to characterise over sixty isolates of Saprolegniaceae and Pythiaceae. Attention will be concentrated on a comparison of thin-layer chromatography and results from the amino acid analyser for heterothallic and homothallic eccentric Achlya species. Computed dendrograms suggest that both techniques are of value in distinguishing between isolates, but that the data pose other taxonomic problems. The zygophore surface of Mucorales B.E. Jones, Department of Microbiology, University of Aberdeen, Marischal College, Aberdeen AB9 lAS Competent sexual reproduction in heterothallic Mucorales requires the cohesion of opposite mating-type ( (+) and (-) ) zygophores, This cell-cellfusion is specific to the zygopnores, so it is probable that their surfaces differ from those of vegetative and asexual thalli. Zygophore-specific antigens have been detected by raising antisera in rabbits to (+) and

119 (-) zygophores of Mucor mucedo. The binding of antibodies to cell surfaces was detected by indirect immunofluorescence using fluorescein conjugated anti-rabbit (goat) IgG. There was no difference between affinities for (+) or (-) surfaces by the two antisera. The effect of inhibitors on wall deposition in the coenocytic fungus Saprolegnia G.W. Beakes, Department of Plant Biology, Ridley Building, The University, Newcastle upon Tyne Streptomycin inhibits all stages in the life cycle of Saprolegnia. In liquid culture no alteration in hyphal wall thickness of lomasome abundance is observed. However, in colonies induced to sporulate streptomycin appears to stimulate wall formation. At high antibiotic concentrations the hyphal compartment became partitioned by fine strands of wall-like material as portions of cytoplasm began to lyse. At sub-lethal concentrations thickened walls, abundant lomasomes and abnormal peg-like wall ingrowths were observed in sporangia, encysted zoospores, oogonia and oospores. These effects will be contrasted with those produced by cycloheximide, chloramphenicol, EDTA and excess divalent cations. Fungal spore discharge F. Floto, Institute of Plant Physiology, University of Copenhagen, (/). Farirnagsgade 2A, DK-1353 Copenhagen By placing a fruit body of a fungus on a modified microphone it is possible to registrate the recoil resulting from the discharge of a single spore. In ascomycetes it was observed that spores from an ascus may be discharged singly or all at a time. Basidiospores are discharged with much less energy than ascospores. Oscilloscopic traces of discharging basidiospores may be interpreted as showing the following series of events: 1. The drop is spreading on the surface of the spore thus running away from the sterigma and forcing the spore against the sterigma. 2. Breaking of the drop forces the spore away from the sterigma at the same time at the sterigma is straightening. 3. The hilum breaks and the spore flies away with the attached drop. In this theory the surface tension of the drop before discharge stores the energy utilized during the discharge. . Submerged culture of Agaricus bisporus in a synthetic medium G.A. Diitsch, Institut rur P1anzen biologie Physiologie, Zollikerstrasse 107, CH-8008, ZUrich The medium us.d to grow A. bisporus in submerged, stirred culture contained inorganic salts and a hexose (fructose, glucose or mannose). Of the nine vitamins tested, only thiamine seemed to be essential. Tween 80 had a strong growth promoting effect. The organism was grown at a pH of 5.3 and a temperature of 28°C. Under these conditions homogenous filamentous growth was obtained. The organism had a doubling time of 0.7 to 0.9 days. Metabolism, ceD growth and control of cap morphogenesis in Coprinus cinereus D. Moore, Botany Department, University of Manchester In the developing cap of the Coprinus cinereus carpophore four enzymes which contribute to arginine synthesis are derepressed (while remaining at low level in the stipe) and a fifth, urease, is repressed (while remaining at high activity in the stipe). The outcome is an accumulation of arginine and urea. This occurs at a time when hymenial cells, particularly paraphyses, are increasing greatly in size and it is thought that a causal connextion exists between the two events; i.e. that the cell enlargement is driven by the osmotic influx of water and that this is in tum a response to the accumulation of urea. Inactivation of extracellular laccase during fruit body development of Agaricusbisporus D.A. Wood, Microbiology Department, Glasshouse Crops Research Institute, Rustington, Litdehampton, Sussex BN16 3PU. Extracellular laccase activity of Agaricus bisporus increases during mycelial growth and declines rapidly during fruit body enlargement. Extracts of high and low enzyme activity remained stable on prolonged incubation and did not cross activate or inhibit on mixing. No activity changes occurred after dialysis, ultrafiltration or gel filtration. Molecular weight, pH optima and immunoelectrophoretic profiles were identical but differences were found in gel electrophoretic and precipitin band formation with high and low forms. Specific activity estimated by two separate methods was three fold greater in the high activity form. The mechanism of inactivation will be discussed.

120 Intracellular protease activity and differentiation in Agaricus bisporus D.A. Wood, Microbiology Department, Glasshouse Crops Research Institute, Rustington, Littlehampton, Sussex BNI6 3PU Sporophore formation in basidiomycetes is associated with large changes in protein composition and with increasing vacuolation of stipe and cap hyphae. To determine whether these changes are correlated with protein metabolism intracellular protease activity of A . bisporus sporophores was monitored during development . Specific activity of proteases active at pH 7.0 and 9.0 increased up to 20 fold with late stage stipe tissue showing the greatest activity . Acid phosphatase and t}D-N-acetylglucosaminidase did not show similar large activity changes. The properties and function of these proteases will be discussed. Abnormal cell wall growth in Cryptococcus induced by xylose: an ultrastructural and enzymic approach V. Notario &; J.R. Villanueva, Microbiology Department, Faculty of Sciences, University of Salamanca, Spain Xylose, when used as the sole carbon source, induced morphogenetic changes in Cryptococcus species. All species grown on xylose formed spherical cells which were two to three times larger than the normal, oval cells; much of this increase in size could be attributed to the thicker (xlO) walls formed by xylose grown cells. The walls of xylose grown cells contained higher concentrations of xylose and glucuronic acid than normal walls. Although small buds were formed, cell division was completely inhibited in cultures grown on xylose. I}xylosidase, xylanase and 1,3-{3-glucanase were found in cell-free extracts and filtrates of cultures grown on xylose. The role of these enzymes in morphogenesis will be discussed. Wall biochemistry during microcyle conidiation G. Deans &; J. Smith, Department of Applied Microbiology, Strathclyde University, Glasgow GI IXW Changes in the structural wall components occur during microcycle conidiation. In particular, the a-glucan fraction builds up during giant cell formation and is then re-utilised during conidiation. The relationship of the changes in wall components to synthetic and lytic enzyme activities will be discussed. Nucleic acid and protein biosynthesis during microcyle sporulation in A spergillus niger D.R. Berry, D.8. Duncan &; J.E. Smith, Department of Applied Microbiology, University of Strathc1yde, George Street, Glasgow GI lXW The biosynthesis of DNA, RNA and protein has been studied throughout microcycle sporulation in Aspergillus niger. Both chemical analysis and pulse labelling techniques indicate that the period of maximum formation of these macromolecules occurs during giant spore formation rather than conidiophore outgrowth. Fractionation of RNA by acrylamide gel electrophoresis and chromatography on Sigmacell 38 indicated that rRNA, tRNA and mRNA are being synthesised during giant spore formation . Results obtained using inhibitors of RNA and protein synthesis which indicated that the formation required for conidiophore production was transcribed during giant spore formation are in agreement with these observations. Lysis of growing blastospores of Candida albicans by echinocandin: a cytological approach A. Cassone, Institute of Microbiology, University of Rome and Rachel Mason, Sub-Department of Otemical Microbiology, University of Cambridge Echinocandin, a new antifungal agent , provoked the lysis of either budding blastospores or elongating hyphae of Candida albicans. Lysis occurred at the apex of the bud and at the tip of the germ-tube suggesting that the drug was unbalancing the process of wall growth. Early events (5 to 10 min) in osmotically-protected cells treated with lytic doses of echinocandin were marked by the appearance of convoluted membranou s bodies (MLBs) often closely lining the growing cell wall and sometimes fusing with the plasmamembrane of the emerging bud. Concomitantly, a progressive thinning of the cell wall associated with the profound derangement of its ultrastructural organization was observed. Post-lytic events (30 to 60 min) showed the presence of MLBs in the nucleus, mithocondria and vacuole. Complete cytoplasmic degeneration often ensued by 120 to 160 min.

121 Growth and cell division of a novel budding yeast, Sterigmatomyces halophilus I. Salmon & R.K. Poole, Microbiology Department, Queen Elizabeth College, Campden Hill Road, London W8 7AH Sterigmatomyces halophilus has an unusual mode of growth, daughter cells being formed remote from mother cells on fine projections (sterigma), which can be mechanically disrupted permitting separation of the cells. Rate zonal separation on sucrose equivolumetric gradients has allowed the fractionation of exponential cultures into various size classes, enabling the cell cycle to be studied. Measurements of DNA per cell in successive fractions indicates that DNA replication must occur either very early (i.e. in the unbudded mother cell) or very late in the cycle (i.e. just preceeding cytokinesis). St. halophilus may provide unique opportunities for investigating the spatial and temporal sequence of events in the cell cycle. Conidiogenic loss of apical polarity G. Turian, T.e. Ton-That & L. Najim, Laboratoire de Microbiologie generale, Universitl! de Geneve, Suisse Vegetative apical polarity may be differentiated by neutral red which turns to yellow in the tips of germ tubes of Neurospora crassa whilst the club-shaped tips of conidiophores (microcycled from heat shocked macroconidia) are stained red. In the depolarized tips of conidiophores, vesicles are distributed around the periphery whilst mitochondria are distributed uniformly throughout the tip. In vegetative hyphae of Monilia [ructigena nutritionally shifted-down, the depolarization process appears to be initiated by the disintegration of the "Spitzenkorper" into microvesicles. This process is accompanied by the peripheral spreading below the plasticizing wall of the previously apically located dense-cored vesicles and followed by the mitochondrial invasion of the clubbed, conidiogenic apices. Hyphal branching and growth acceleration in young Neurospora colonies AJ. Clutterbuck, Department of Genetics, University of Glasgow It has been suggested that hyphal tips branch when excess cytoplasmic growth cannot be taken up by faster tip extension. The evidence against this hypothesis is that Neurospora hyphae grown from single conidia first branch at the tips when growing at 300 urn if'1, although they later accelerate to 3000 urn if'1. Nor is acceleration of tip extension limiting since branches from fast growing mature hyphae accelerate more rapidly than those from younger, slower ones, but both rebranch at similar points. However, many mutants with reduced hyphal extension rates branch excessively. Therefore, either branching follows an endogenous rhythm which is modified in these mutants or branching occurs where extension is limited by unknown factors in young hyphae. The effect of rubratoxin on growth and morphology of Aspergillus niger M.O. Moss & F. Badii, Department of Microbiology, University of Surrey, GuiIdford, Surrey GU2 5XH The rubratoxins are toxic nonadrides produced by Penicillium rubrum which show some antifungal activity. Aspergillus niger and A. tamarii are particularly sensitive. A concentration of I mg/rnl completely inhibits both the germination of the conidiospores and subsequent growth of A. niger, whereas 0.5 mg/rnl inhibits growth but not germination and concentrations as low as 10 ug/rnl cause swelling, distortion and increased branching of the mycelium. Despite the reduction of growth in the presence of low concentrations of rubratoxin, glucose disappears from the medium at a comparable rate to the control and appears to be converted into metabolites such as pigments rather than biomass. Hyphal growth units in Pythium M.W. Dick, Botany Department, The University, Whiteknights, Reading The applicability and limitations of hyphal growth units (G) for characterising the juvenile mycelia of non-septate fungi have received little attention. Data are provided for over twenty oogonium-producing Py thium species using zoospore cyst inocula. Certain Pythium species possess deciduous spherical zoosporangia which can be germinated directly and which, on other occasions, can be included to produce zoospore cysts. Such species provide convenient material for assessing the variation of G values in relation to the volume of the progenitor inoculum within and between clones. The results are compared with values obtained for linear growth rates of mature mycelia in every case.

122 Variability of chitin content in relation to mycelial dry weight in aero-aquatic fungi P.J. Fisher & J. Webster, Department of Biological Sciences, University of Exeter, Hatherly Laboratories, Prince of Wales Road, Exeter EX4 4PS Colorime tric determination of chit in content of nine aero- aquat ic hyphom ycete s showed th at the conversion fact or (CF) value s (chitin content per unit dry weight of mycelium) varied with the age of mycelium , nutrient concentra tion of the medium and initial oxygen concentration of the water. CF values often decreased with age of my celium and also with lowered ox ygen concentration s. Consequently , for estimation of fun gal biomass in tissues , thi s technique is of limited value. High quality, linear growth, sporulation and carotenogenesis in Verticilliurn agaricinum L.R-G. Valadon & M. Osman, Royal Holloway College, London University Near-UV is very effective in increasing linear growt h, sporu la tio n and caro te no id production in V. agaricinum: Blue light has been shown to reverse the near-UV light effe ct and the pigment syste m 'mycochrome' has been proposed to account for conidiation in certain fungi. The light-minu s-dark difference spec trum for V. agaricinum, having two dip s a t 395 and 420 nm, is different from the 'my cochrorne' system which has a trough at 300 nm and a maximum at 400 nrn, However , since high irradiance reactions are part of the system in V. agaricinurn then phytochrome is probably involved, and it will be shown that ')'-carotene (C40 ) is the immediate precursor of neur osporaxanthin (C35). Selective destruction and alteration of hyphae of Polyporusarcularius G. Valla, Universite Claude Bernard, Lyon I, 43 Bid. du II Novembre 1918, F 69621, Villeurbanne Procedures for carrying out micro surgical operations with a ruby-biola ser on growing hyphae are described. The method presented can be applied to the separation, de stru ction and even alterati on of the hyphal compartments, without transferring the hyphae. Separation of an apical co mpart ment from its intercalary compartment is accompanied by a sudden but brief de crease of its elongation rate which late r assumes the previous rate . The duplication cycle is not modified by this treatment. Destruction of the apical compartment produced no apparent effe ct on intercalary compartments. Treatment of the tips of the hyphae induced severe and permanent drops in their rate s of elongation associated with the initiation of several bran ches along the treated compar tment. A colorimetric assay for chitinase activity O.A. Aribisala, Nigerian Institute of Oceanography and Marine Research, Lagos The enzyme activity of chitinase from Vibrio aleinolyticus has been assayed using 3,4dinitrophenyl-tetra-N-acetyl -chitotetraoside (3d4-DNP-TNAC) as chromogenic substrate. The pH and temperature optima were 5.5 and 56 C. The apparent K m value was about 7.5 pM. Hydrol ysis of the 3,4-DNP-TNAC was inhibited by chit in. Deoxyribonucleic acid differential synthesis during microeycle conidiation in Neurospora F. Grange & G. Turian, Laboratoire de Microbiologie generate, Universite de Geneve, Suisse In microcycle conidiation of N. crassa, obtained in submerged shaken cultures after a heat shock at 46°C for 15 hours , the syn thesis of DNA (measured by pulse-labeling) starts to increase one hour after the shift-down a t 25°C. Of the two peaks of synthesis observed, the second always paralleled the onset of conid iation. This second peak of DNA synthesis is apparently committed to the conidiation process which can be completed without further DNA synthesis as demonstrated by time-dependent effect of DNA synthesis inhibitors (hydroxyurea and 5-fluorodeoxyuridine).