[Melanin pigments of fungi under extreme environmental conditions (review)].

This review is dedicated to the research on the functions of melanin pigments in fungi. The participation of melanin pigments in protection from environmental factors is considered. Data on the biosynthetic pathways and types of melanin pigments in fungi are presented.

[Fungal anthraquinones (review)].

The review is devoted to the characteristics of anthraquinones--a group of pigments of quinoid nature often found in fungi. The distribution of anthraquinones in fungi, the routes of their biosynthesis, and their biological activity are considered.

[Comparative analysis of respiratory activity in the wild type strain of Neurospora crassa and its photoreceptor complex mutants].

Cell respiratory activity of protoplasts obtained from the wild type of Neurospora crassa and photoreceptor complex WCC--white collar 1 (wc-1) and white collar 2 (wc-2)--mutants of Neurospora crassa strains was investigated. Respiration inhibition by KCN in the presence of 25 mM succinate was similar in all strains and did not exceed 83-85% against control. The significant induction of KCN-resistant respiratory pathway occurred under 1% glucose oxidation in wc-1 and wc-2 mutants if compared with the wild type strains. The inhibitors of the main (cytochrome) pathway of electron transfer in mitochondria-1 mM KCN and antimycin A (4 microg/ml)--blocked the respiration rate of the protoplasts from N. crassa wild type by 75%, while the cell respiration of wc-1 and wc-2 strains was suppressed by approximately 50%. The specific inhibitor of alternative oxidase--10 mM salicylhydroxamic acid (SHAM)-in combination with the blockers of mitochondrial electron transfer chain caused the total suppression of respiratory activity of protoplasts in all studied strains. It is supposed that an increase of KCN-resistance in WCC mutants under glucose oxidation is connected with alternative oxidase activation as the result of failure in reception and signal transduction of active oxygen species.

[A comparative investigation of adaptation to oxidative stress factors a strain of mycelial fungus Paecilomyces lilacinus from Chernobyl Atomic Energy Station and strains of the same species from territories with basic level of radioactive pollution].

An oxidative stress resistance in Paecilomyces lilacinus strain from Chernobyl Atomic Energy Station (ChAES) as well as in P. lilacinus strains from zones with control level of radioactive pollution has been studied. It was shown that radial growth rate of the colony of the ChAES strain in a range of glucose concentrations 0.002%; 0.2%; 0.5%; 1.0% showed maximum on the medium with 0.2% glucose. It was 1.5 times higher than growth rate of the control strains. Adaptation slowdown reaction has been found as a result of the first 10-30 min H2O2 treatment most profound in the ChAES (No 1941) strain. Under 10(-3) mol/l H2O2 growth of No 1941 resumed with 20% loss in growth rate. Cessation of growth of the control strain (No 10) was observed under these conditions. It has been shown that in the strain from ChAES zone adaptation to low glucose content in the medium (0.2%) was coupled with an increased resistance to oxidative stress.

[Stress factor-induced changes in the activity of antioxidant protective mechanisms in the wild type strain of Neurospora crassa and in its photoreceptor complex mutants].

The effect of stress factors (changes in oxygen content, temperature, and illumination) on superoxide dismutase (SOD) and catalase activity, as well as on the content of thiol and disulfide groups in low-molecular-weight compounds and proteins of Neurospora crassa mycelium was studied in the wild type strain and white collar-1 (wc-1) and white collar-2 (wc-2) mutants. Environmental stress factors induced the activation of both SOD and catalase, as well as an increase in the thiol level in the wild type strain of Neurospora crassa. In the wc-1 and wc-2 mutants, an increase in catalase activity and in the total thiol level was revealed; however, activation of superoxide dismutase was not observed. A decrease in the formation of disulfide bonds in the proteins of wc-1 and wc-2 mutants (as compared with the wild type strain) was recorded. These results indicate disrupted transduction in the WCC mutants of stress factor signals that promote ROS (reactive oxygen species) formation.

[Reactive oxygen species and the strategy of the antioxidant defense in fungi: a review].

The level of reactive oxygen species (ROS) in the cell regulates the growth and differentiation of the fungal organism. This review considers the pathways of generation of the primary ROS and the defense methods used by fungi and yeasts against them as well as the involvement of thiol compounds in the antioxidant defense of the fungal cell. It is demonstrated that the adaptation of fungi to oxidative stress is tightly connected with the redox-dependent changes in the activities of antioxidant defense components.

[Oxidative stress and cell differentiation in Neurospora crassa].

Environmental stress factors induce oxidative stress in fungi by increasing the intracellular concentrations of reactive oxygen species (ROS). In the mycelium, ROS act as signal molecules needed for cytodifferentiation at certain stages of the development of fungi. Generation of ROS in cells induces the activation of antioxidant protective mechanisms. The purpose of this communication is to analyze the role of ROS in light signal transduction, mediated in Neurospora crassa cells by the White Collar Complex.

[A comparative study of the components of the antioxidant defense system during growth of the mycelium of a wild-type Neurospora crassa strain and mutants, white collar-1 and white collar-2].

A comparative study of the changes in the components of the antioxidant defense system (ADS), the activity of superoxide dismutase (SOD) and catalase and the level of extractable SH-groups, during the growth of wild-type and mutant (white collar-1 and white colar-2) Neurospora crassa strains was performed. Oxidative stress developing during spore germination and upon the transition to a stationary growth phase was accompanied in all strains by an increase in the level of extractable SH-groups and SOD activity, whereas the total catalase activity decreased during growth. However, in contrast to the wild-type strain, the activity of the catalase in the mutant strains wc-1 and wc-2 slightly increased upon the transition to the stationary phase. In the wc-2 mutant, SOD activity and the level of extractable SH-groups in the exponential growth phase were always lower than in the wild-type and wc-2 strains. The role of wc-1 and wc-2 genes in the level regulation of reactive oxygen species is discussed.

[Photoreceptor apparatus of a fungus Neurospora crassa].

Light governs living functions of ascomycete fungus Neurospora crassa by controlling expression of the genes responsible for differentiation of reproductive structures, synthesis of secondary metabolites and the circadian oscillator activity. Illumination also influences electrogenic processes in cell membrane and the activity and molecular organization of some enzymes. The major but, probably, not the sole photoreceptor pigment in Neurospora cells is WCC, a heterodimeric complex formed by PAS-domain-containing polypeptides WC-1 and WC-2, which are the products of genes white collar-1 and white collar-2. Mutation of any of these genes arrests most of the organism's responses to light. The photoreceptor belongs to a recently discovered vast group of non-homologous light-sensitive proteins, whose molecules bind flavin coenzymes as the photosensor chromophores. The photosignal transduction is started by excitation and photochemical activity of excited FAD molecule non-covalently bound by LOV-domain (a specialized version of PAS-domain) in WC-1 protein. The presence in both WC-1- and WC-2-proteins of "zinc fingers" (the GATA recognizing sequences) suggested that these motives might act as transcription factors. The critical analysis of photoinduction mechanism has shown, however, that promoters of light-sensitive genes do not contain a common cis-acting element, what makes to look for alternative mechanisms underlying photoregulated gene activity.

[The effect of hydrogen peroxide on the growth of microscopic mycelial fungi isolated from habitats with different levels of radioactive contamination].

The effect of hydrogen peroxide ( 10(-9)-10(-1) M) on the mycelial growth of the fungi Alternaria alternata, Cladosporium cladosporioides, Mucor hiemalis, and Paecilomyces lilacinus has been studied. The growth of fungi isolated from habitats with a background level of radioactive contamination was stopped by H2O2 concentrations equal to 10(-3) and 10(-2) M, whereas the growth of fungi that were isolated from habitats with high levels of radioactive contamination was only arrested by 10(-1) M H2O2. The response of the different fungi to hydrogen peroxide was of three types: (1) a constant growth rate of fungal hyphae at H2O2 concentrations between 10(-9) and 10(-4) M and a decrease in this rate at 10(-3) M H2O2, (2) a gradual decrease in the growth rate as the H2O2 concentration was increased, and (3) an increase in the growth rate as the H2O2 concentration was increased from 10(-7) to 10(2)-5 M. The melanin-containing species A. alternata and C. cladosporioides exhibited all three types of growth response to hydrogen peroxide, whereas the light-pigmented species M. hiemalis and P. lilacinus showed only the first type of growth response. A concentration of hydrogen peroxide equal to 10(-1) M was found to be lethal to all of the fungi studied. The most resistant to hydrogen peroxide was found to be the strain A. alternata 56, isolated from the exclusion zone of the Chernobyl Nuclear Power Plant.

[Participation of beta-carotene in antioxidant defense of bacterial cells]. / Uchastie beta-karotina v antioksidantnoi zashchite bakteral'noi kletki.

The effect of recombinant beta-carotene on the resistance of E. coli culture to menadione and paraquat was studied. The presence of beta-carotene in the E. coli cell significantly prevented an increase in the activity of superoxide dismutase induced by redox mediators but had no effect on the culture growth. The findings suggested the involvement of beta-carotene in the cell defense against oxidative stress.

[Initial stages of trisporic acid synthesis in Blakeslea trispora]. / Nachal'nye étapy sinteza trisporovykh kislot u Blakeslea trispora.

Biotransformation of beta-carotene with enzyme preparations isolated from the mycelium of Blakeslea trispora resulted in the formation of its hydroxylated metabolite and apocarotenals, products of oxidative degradation of this compound. By spectral, chromatographic, and chemical properties, the beta-carotene derivative was identified as 4-hydroxy-beta-carotene (isocryptoxanthine). One of the products of oxidative degradation of beta-carotene, beta-apo-13-carotenone, underwent modification in the presence of enzyme preparations from Blakeslea trispora with the formation of trisporic acid precursors. It should be emphasized that beta-apo-13-carotenone transformation proceeded more rapidly than beta-carotene oxidation by carbon in the 4-position. Our findings suggest that under conditions of oxidative stress, oxidative degradation of beta-carotene into beta-apo-13-carotenone leads to the formation of considerable amounts of trisporic acids.

[Superoxide dismutase and catalase activities in carotenoid-synthesizing fungi Blakeslea trispora and Neurospora crassa under the oxidative stress]. / Aktivnost' superoksiddismutazy i katalazy u karotinoidsinteziruiushchikh gribov Blakeslea trispora i Neurospora crassa v usloviiakh okislitel'nogo stressa.

The addition of menadione into the medium during cultivation of Neurospora crassa in the dark activated its constitutive superoxide dismutase. Exposure to light not only activated superoxide dismutase and catalase, but also increased the content of neurosporaxanthin. Superoxide dismutase activity in the mixed (+/-) mycelium of Blakeslea trispora synthesizing beta-carotene in the dark was much lower than that in Neurospora crassa. The superoxide dismutase activity further decreased in oxidative stress. The catalase activity decreased with an increase in the content of beta-carotene. Our results indicate that neurosporaxanthin possesses photoprotective properties in Neurospora crassa. In Blakeslea trispora (+/-) fungi, this compound acts as a major antioxidant during inactivation of enzymes that detoxify reactive oxygen species.

[Cyclic nucleotides and membrane electrogenesis in cell differentiation in Neurospora crassa]. / Tsiklicheskie nukleotidy i membrannyi élektrogenez v iavleniiakh kletochnoi differentsirovki u Neurospora crassa.

Significance of membrane electrogenic system and cyclic nucleotides for developmental regulation in lower eukaryotes was studied in Neurospora crassa. Despite of their morphological uniformity, hyphal cells were differentiated by their electrophysiological parameters--membrane potential and input resistance. The cells maintained regulated electric communication through septal pores. Such electric communication allowed the apical "cell" to compensate the energy requirements for membrane transport by means of the electrogenic mechanism of proximal zone. The photoinduced gene expression related to differentiation of reproductive structures has been shown to be mediated via cAMP. The changes of electric parameters observed in illuminated hyphal cells were controlled by the same photoregulation mechanism but were not involved in direct control of photoinduced gene expression.

[Effect of the cyclic nucleotide level on the degree of carotenoid pigment formation in the mycelial cells of Neurospora crassa]. / Vliianie urovnia tsiklicheskikh nukleotidov na intensivnost' obrazovaniia karotinoidnykh pigmentov v kletkakh mitseliia Neurospora crassa.

The relation between the content of cyclic nucleotides and the rate of formation of carotenoid pigments in the Neurospora crassa mycelium cells was investigated. Light derepression of the carotenoid synthesis during the photoinduction lag-period induced a transient decrease of the cAMP content. The intracellular cAMP content was in negative correlation with the constitutive level of carotenoid pigments. The cGMP content remained unchanged during the photoinduction lag-period and showed no correlation with the constitutive level of carotenoids in N. crassa cells.

[Influence of light on membrane potential of Neurospora crassa cells]. / Vliianie sveta na membrannyi potentsial kletok Neurospora crassa.

In experiments with left atrial and right ventricular tissues fast sodium current (INa) was decreased by substituting sucrose for sodium in Tyrode's solution and with antiarrhythmic drugs--INa blockers (lidocaine, diphenylhydantoine and ethmozine). It was shown that INa decrease results in the growth of refractoriness (R) of the cardiac tissues. The hypothesis is advanced that the R growth caused by INa decrease is one of the mechanisms of selective sensitiveness of ischemic heart tissues to antiarrhythmic drugs--INa blockers.

[Photoinduction of carotenoid synthesis by Neurospora crassa on different structural and functional states of nitrate reductase]. / Fotoinduktsiia sinteza karotinoidov u Neurospora crassa pri raznom strukturnom i funktsinal'nom sostoianii nitratreduktazy.

In order to clarify the role of nitrate reductase as a potential photoreceptor, the ability of N. crassa mycelial cells for light-dependent accumulation of carotenoid pigments has been studied. The repression of the nitrate reductase synthesis by ammonium ions has been found not to influence the rate of the photoinduced carotenogenesis. The mutant experiments have shown that damage to the structural integrity of the nitrate reductase molecule, e, g., disintegrated synthesis of the protein fragment of the enzyme molecule (mutants nit-2 and nit-3) or the molybdenum coenzyme (mutant nit-1) does not affect the activity of the photoregulatory system of N. crassa. Thus, nitrate reductase is not a necessary component of the photoregulatory mechanism of N. crassa responsible for the synthesis of carotenoids.