Responses of two ecotypes of <Emphasis Type="Italic">Medicago ciliaris</Emphasis> to direct and bicarbonate-induced iron deficiency conditions

Our study investigates the effect of iron deficiency on morpho-physiological and biochemical parameters of two Medicago ciliaris ecotypes (Mateur TN11.11 and Soliman TN8.7). Iron deficiency was imposed by making plants grow, either in an iron free or by the addition of CaCO₃/NaHCO₃ to the Hoagland nutrient solution. Our results showed that both true and bicarbonate Fe-deficiency induced the characteristic iron-chlorosis symptoms, although the intensity of the symptoms was ecotype-dependent. This variability in tolerance to iron deficiency was also displayed by other morphological parameters such as root biomass and chlorophyll concentration. Besides, iron chlorosis induced an increase in biochemical parameters: the iron reducing capacity (measured in vivo on root segments and in vitro on plasma membrane enriched vesicles) and rhizosphere acidification by enhancement of H⁺-ATPase activity were more pronounced in Mateur ecotype. These findings suggest that Soliman ecotype was more sensitive than Mateur one to iron chlorosis.     

Radiation induced biochemical mutation in Colletotrichum gloeosporioides penz. causing anthracnose of guava (psidium guajava L)

With the aid of radioactive phosphorus and gamma rays from Cobalt⁶⁰, a number of biochemical mutants were obtained which showed deficiency for amino acids like methionine, leucine and cystine and vitamins like biotin and thiamine. These biochemical mutants could not be distinguished from the wild type when grown on complete or otherwise suitably supplemented media. Pathogenicity tests of some of these biochemical mutants showed that all the five mutants tested are pathogenic on guava variety Allahabad Safeda, though these showed deficiency for different growth factors.     

Genetic and biochemical studies of phosphomannose isomerase deficient mutants ofSaccharomyces cerevisiae

Summary Three mannose-negative mutants ofSaccharomyces cerevisiae have been isolated. These mutants showed growth inhibition when mannose was added to a growth medium containing glycerol or fructose. Crosses between wild type mutants showed segregation of 2⁺/2⁻. Crosses between the mutants themselves showed that they were closely linked. Two mutants (XM3 and D2) showed characteristics of allelic structural alteration of phosphomannoseisomerase. Mutant D4 had a deficiency of phosphomannoseisomerase activity, but with a normal thermostability. Revertants from D4 had a normal thermostability.     

The effects of recessive lethal Notch mutations of Drosophila melanogaster on flavoprotein enzyme activities whose inhibitions cause Notch-like phenocopies

The biochemical action of the Notch locus whose mutants cause morphological aberrations in flies, viz., notches of wings and bristle multiplication, has been analyzed (1) by the addition to the food medium of enzyme inhibitors causing phenocopies of Notch and (2) by comparison of enzyme activity patterns of Notch mutants with different degrees of phenotypic expression. Notch phenocopies were induced by inhibitors of enzyme activities in two biochemical pathways: (1) the de novo pyrimidine synthesis by 5-methylorotate (inhibitor of dihydroorotate dehydrogenase) and (2) the choline shunt by amobarbital (inhibits choline dehydrogenase) and methoxyacetate (inhibits sarcosine dehydrogenase). The inhibition of de novo pyrimidine synthesis prevents the production of deoxyuridine-5-phosphate, the substrate for the synthesis of thymidine-5-phosphate via thymidylate synthase, whereas the inhibition of the choline shunt prevents the production of HCHO groups and glycine, both of which are involved in the synthesis of 5,10-methylenetetrahydrofolate, which is a cofactor of thymidylate synthase. It was already known that the inhibition of the latter enzyme in vivo induces Notch phenocopies. Notch mutants with a strong morphological expression show low enzyme activities for dihydroorotate dehydrogenase and choline dehydrogenase. Both are flavoprotein enzymes linked to the respiratory chain. The correspondence between the low enzyme activities in Notch mutants with a strong morphological expression and the phenocopying effect of antimetabolites on these enzymes in the two biochemical pathways involved strongly suggests that the morphological effects of Notch on flies are a consequence of lowered activities of choline dehydrogenase and dihydroorotate dehydrogenase.     

Sake brewing characteristics of a new type of cerulenin-resistant sake yeast mutant

Several new types of cerulenin-resistant mutants of sake yeast were isolated. These mutants showed respiratory deficiency and could grow on media containing a higher concentration of antibiotics than could the parent. Sakes brewed by the mutants produced less succinate than by both the parent yeast and the mutants with respiratory deficiency induced by ethidium bromide. In addition, the acidity of these mutants was decreased. Since low acidity is favourable in both sake and wine, these mutants might be applicable for both sake and wine brewing.     

Altered mechanoreceptor response in Drosophila bang-sensitive mutants

Bang-sensitive mutants of Drosophila melano gaster (bas ¹, bss^MW1, eas², tko^25t) display seizure followed by paralysis when subjected to mechanical shock. However, no physiological or biochemical defect has been found to be common to all of these mutants. In order to observe the effects of bang-sensitive mutations upon an identified neuron, and to study the nature of mechanically induced paralysis, we examined the response of a mechanosensory neuron in these mutants. In each single mutant and the double mutant bas ¹ bss^MW1, the frequency of action potentials in response to a bristle displacement was reduced. This is the first demonstration of a physiological defect common to several of the bang-sensitive mutations. Adaptation of spike frequency, cumulative adaptation to repeated stimulation (fatigue) and the time course of recovery from adaptation were also examined. Recovery from adaptation to a conditioning stimulus was examined in two mutants (bas ¹ and bss ^MW1), and initial recovery from adaptation was greater in both mutants. Quantification of receptor potentials was complicated by variability inherent in extracellular recording conditions, but examination of the waveform and range of amplitudes did not indicate clear mutant defects. Therefore the differences observed in the spike response may be due to an alteration of the transfer from receptor potentials to action potential production. DNA sequence analysis of tko and eas has indicated that they encode apparently unrelated biochemical products. Our results suggest that these biochemical lesions lead to a common physiological defect in mechanoreceptors. Although this defect does not provide a straightforward explanation for bang sensitivity, the altered cellular process may lead to bang sensitivity through its action in different parts of the nervous system.Abbreviations APA anterior post-alar - ANP anterior notopleural - bas bang-sensitive - bss bang-senseless - eas easily-shocked tko technical knockout     

Isolation and Characterization of Sex-Linked Female-Sterile Mutants in DROSOPHILA MELANOGASTER with Special Attention to Eggshell Mutants

To study genes that function mainly or exclusively during oogenesis, we have isolated and analyzed female-sterile mutations, with special emphasis on those that affect eggshell formation. Following treatment that induced 61 to 66% lethals, 8.1% of the 1071 X chromosomes tested carried recessive female sterility mutations (87 isolates), and 8.0% carried partial female-sterile mutations (86 isolates), respectively. In addition, three dominant female steriles were recovered. Some of the mutants had very low fecundity, and others laid morphologically normal eggs that failed to develop. A third category included 29 mutants that laid eggs with morphological abnormalities: 26 were female steriles, two were partial female steriles and one was fertile. Mutants of this third category were characterized in some detail and compared with 40 previously isolated mutants that laid similarly abnormal eggs. Approximately 28–31 complementation groups with morphological abnormalities were detected, some of which were large allelic series (11, 9, 7, 6 and 5 alleles). Twenty-four groups were mapped genetically or cytogenetically, and 21 were partially characterized by ultrastructural and biochemical procedures. Of the latter, one group showed clear deficiency of yolk proteins, and nine showed prominent ultrastructural defects in the chorion (at least eight accompanied by deficiencies in characterized chorion proteins). At least six groups with clear-cut effects were found at loci not previously identified with known chorion structural genes.     

Functional and regulatory analysis of the <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> CAX2 cation transporter

The vacuolar sequestration of metals is an important metal tolerance mechanism in plants. The Arabidopsis thaliana vacuolar transporters CAX1 and CAX2 were originally identified in a Saccharomyces cerevisiae suppression screen as Ca²⁺/H⁺ antiporters. CAX2 has a low affinity for Ca²⁺ but can transport other metals including Mn²⁺ and Cd²⁺. Here we demonstrate that unlike cax1 mutants, CAX2 insertional mutants caused no discernable morphological phenotypes or alterations in Ca²⁺/H⁺ antiport activity. However, cax2 lines exhibited a reduction in vacuolar Mn²⁺/H⁺ antiport and, like cax1 mutants, reduced V-type H⁺-ATPase (V-ATPase) activity. Analysis of a CAX2 promoter -glucoronidase (GUS) reporter gene fusion confirmed that CAX2 was expressed throughout the plant and strongly expressed in flower tissue, vascular tissue and in the apical meristem of young plants. Heterologous expression in yeast identified an N-terminal regulatory region in CAX2, suggesting that Arabidopsis contains multiple cation/H⁺ antiporters with shared regulatory features. Furthermore, despite significant variations in morphological and biochemical phenotypes, cax1 and cax2 lines both significantly alter V-ATPase activity, hinting at coordinate regulation among transporters driven by H⁺ gradients and the V-ATPase.     

Multiple biochemical effects of a series of X-ray induced mutations at the albino locus in the mouse

Further studies of the four radiation-induced lethal albino mutations causing glucose 6-phosphatase deficiency in the mouse have shown that there is also a deficiency of tyrosine aminotransferase in the newborn albino mutants. These two enzymes can be induced in fetal and newborn heterozygous or homozygous normal littermate controls by injection of glucagon or dibutyryl cyclic AMP, but not in the albino mutants. Microsomal NADH-cytochrome c reductase was found to be increased in the albino mutants. The multiple biochemical abnormalities in the albino mutants, in addition to the lack of gene dosage effect in the heterozygotes, suggest the involvement of genes other than the structural genes for particular enzymes. When a new radiation-induced lethal albino mutation was tested against the four original alleles, complementation resulted, and double heterozygotes were found to be viable, with normal enzyme levels.Supported by grants from the National Institutes of Health, 5 R01 AM 11448-05, 5R01 HD-00193-17, 5T01 GM00110-09, GM19100, and by a grant from the American Cancer Society, VC-64N.     

Isolation,Characterization, and Antifungal Susceptibility of Melanin-Deficient Mutants of <Emphasis Type="Italic">Scedosporium prolificans</Emphasis>

Scedosporium prolificans mutants lacking the ability to synthesize melanin were selected after ultraviolet light (UV) irradiation. UV exposure of S. prolificans conidia resulted in a high frequency of melanin-deficient (mel⁻) mutants. Stable and non-stable morphological variants were found in the population: reversion of the mutant phenotype was always to the wild-type phenotype. Based on their morphological differences, these variants were classified into five different groups that were phenotypically characterized. The mel⁻ mutants plus the wild-type strain were examined for in vitro susceptibility to antifungal agents with different and/or the same mechanism of action. There was no apparent difference in minimum inhibitory concentrations when comparing the wild-type and the mel⁻ mutants. Therefore, melanin does not appear to confer protection against the more important antifungal agents in S. prolificans. Received: 30 April 2002 / Accepted: 10 July 2002     

Possible Anti-tumor Promoting Properties of Marine Algae and In Vivo Activity of Wakame Seaweed Extract

The cAMP pathway and the Ras pathway are the two major pathways to sexual development in the fission yeast Schizosaccharomyces pombe. To understand the с AMP pathway or the related pathway, we analyzed mutants that display a phenotype similar to cyrl-, that is, hyper-sporulation. Nine mutants termed sam (sporulation abnormal mutant), which are highly inclined to sexual development despite the presence of nitrogen sources, were partially characterized. Cyclic AMP was detected in all nine sam mutant cells, and over-expression of the adenylyl cyclase gene (cyrl) failed to suppress the hyper-sporulation phenotype of these sam mutants, suggesting that none of the sam mutants were likely to be allelic to cyrl. Epistatic tests of sam mutants showed that they were divided into two dominant and seven recessive mutants. Dominants were able to make spores in sam/sam⁺ heterodiploid cells upon abundant nutrients. Both two dominant mutants bypassed the inability to make spores in rasl deficient diploid cells, suppressed the deficiency to execute sporulation in byr2 deficient diploid cells, but failed to suppress the byr1 deficiency. Two dominant mutations seem not to occur within the byr2 gene.     

Galactokinase-deficient mutants of Tetrahymena thermophila: Selection and characterization

Summary We have isolated a series of mutants of Tetrahymena thermophila which are resistant to inhibition of growth by the galactose analog, 2-deoxygalactose. These mutants were obtained after mutagenesis with nitrosoguanidine and the induction of cytogamy to permit the recovery of recessive mutations induced in the germline micronucleus. Resistance to 2-deoxygalactose is correlated with a decreased rate of growth in galactose minimal medium and greatly reduced levels of galactokinase. The resistant phenotype of the mutants is apparently due to the galactokinase deficiency, which prevents the accumulation of toxic phosphorylated metabolites of 2-deoxygalactose. Genetic analyses reveal that the 2-deoxygalactose resistance alleles segregate as single Mendelian loci. The galactokinase-deficient strains described here represent the first mutants in this organism for which the biochemical basis of the mutant phenotype is known. These mutants, as well as others isolated similarly, should be of value in the elucidation of the mechanisms governing galactokinase gene regulation and in improving techniques of selection for other recessive mutations in Tetrahymena.     

A genetic interaction between RAP1 and telomerase reveals an unanticipated role for RAP1 in telomere maintenance

RAP1 is one of the components of shelterin, the capping complex at chromosome ends or telomeres, although its role in telomere length maintenance and protection has remained elusive. RAP1 also binds subtelomeric repeats and along chromosome arms, where it regulates gene expression and has been shown to function in metabolism control. Telomerase is the enzyme that elongates telomeres, and its deficiency causes a premature aging in humans and mice. We describe an unanticipated genetic interaction between RAP1 and telomerase. While RAP1 deficiency alone does not impact on mouse survival, mice lacking both RAP1 and telomerase show a progressively decreased survival with increasing mouse generations compared to telomerase single mutants. Telomere shortening is more pronounced in Rap1^?/? Terc^?/? doubly deficient mice than in the single‐mutant Terc^?/? counterparts, leading to an earlier onset of telomere‐induced DNA damage and degenerative pathologies. Telomerase deficiency abolishes obesity and liver steatohepatitis provoked by RAP1 deficiency. Using genomewide ChIP sequencing, we find that progressive telomere shortening owing to telomerase deficiency leads to re‐localization of RAP1 from telomeres and subtelomeric regions to extratelomeric sites in a genomewide manner. These findings suggest that although in the presence of sufficient telomere reserve RAP1 is not a key factor for telomere maintenance and protection, it plays a crucial role in the context of telomerase deficiency, thus in agreement with its evolutionary conservation as a telomere component from yeast to humans.     

Dietary thyroid hormone replacement ameliorates hearing deficits in hypothyroid mice

Thyroid hormone (TH) insufficiency causes variable hearing impairment and mental deficiency in humans. Rodents lacking TH have congenital hearing deficiency that has been attributed to physiologic, morphologic, and developmental abnormalities of the auditory system. We examined four genetically defined strains of hypothyroid mice for development of hearing and response to TH replacement initiated during late gestation and continued through six weeks of age. Auditory brain stem response studies showed variable hearing impairment in homozygous mutants of each strain at three weeks of age relative to normal littermates. Mutants from three of the strains still had hearing deficiencies at six weeks of age. TH-enriched diet significantly improved hearing in three-week-old mutants of each strain relative to untreated mutants. Differences in the level of hearing impairment between the Prop1 ^df and Pit1 ^dw mutants, which have defects in the same developmental pathway, were determined to be due to genetic background modifier genes. Further physiologic and morphologic studies in the Cga ^tm1Sac strain indicated that poor hearing was due to cochlear defects. We conclude that TH supplement administered during the critical period of hearing development in mice can prevent deafness associated with congenital hypothyroidism of heterogeneous genetic etiology.     

Lack of mutagenic effect of vinyl chloride monomer in the mammalian spot test

The kinetics of the killing effect of ethanol was studied at 6–30% concentrations. Ploidy of cells, deficiency of the excision-repair system or holding under no-growth conditions did not influence survival.Ethanol at 24% increased, in the strain, the number of respiration-deficient cells from a spontaneous level of 0.4% up to nearly half of all survivors.Genetic analysis showed the mitochondrial nature of induced respiration-deficient mutants (or rho^?).The influence of yeast resistance to some antibiotics was studied on rho^? mutagenesis, both spontaneous and induced by ethanol. Neomycin-resistant strains were characterized by a significantly lower level of these mutations than were neomycin-sensitive strains.     

Significance of Pyruvate Carboxylase in Sugar Metabolism of Agrobacterium tumefaciens

Mutants, which fail to grow on glucose medium but can grow on succinate medium, were isolated by treatment with N-methyl-N′-nitro-N-nitrosoganidine from the wild-type strain of Agrobacterium tumefaciens, and were found to lose growth on several hexoses and three-carbon intermediates. The revertant mutants, which recovered the ability to grow on glucose medium, simultaneously regained the ability to grow on hexoses and three-carbon intermediates. By comparison of biochemical properties of the wild-type, the mutants and the revertant mutants, two mutant strains were characterized to be pyruvate carboxylase-deficient. Then, we concluded that these mutants might be induced by a single mutation at a genetic locus of pyruvate carboxylase and that the deficiency in the enzyme gave a pleiotropic effect on the ability to grow on hexoses and three-carbon intermediates. Some properties of pyruvate carboxylase of this bacterium were also presented.     

Non-specific, general and multiple stress resistance of growth-restricted Bacillus subtilis cells by the expression of the σB regulon

Bacillus subtilis cells respond almost immediately to different stress conditions by increasing the production of general stress proteins (GSPs). The genes encoding the majority of the GSPs that are induced by heat, ethanol, salt stress or by starvation for glucose, oxygen or phosphate belong to the σ^B-dependent general stress regulon. Despite a good understanding of the complex regulation of the activity of σ^B and knowledge of a very large number of general stress genes controlled by σ^B, first insights into the physiological role of this non-specific stress response have been obtained only very recently. To explore the physiological role of this regulon, we and others identified σ^B-dependent general stress genes and compared the stress tolerance of wild-type cells with mutants lacking σ^B or general stress proteins. The proteins encoded by σ^B-dependent general stress genes can be divided into at least five functional groups that most probably provide growth-restricted B. subtilis cells with a multiple stress resistance in anticipation of future stress. In particular, sigB mutants are impaired in non-specific resistance to oxidative stress, which requires the σ^B-dependent dps gene encoding a DNA-protecting protein. Protection against oxidative damage of membranes, proteins or DNA could be the most essential component of σ^B-mediated general stress resistance in growth-arrested aerobic Gram-positive bacteria. Other general stress genes have both a σ^B-dependent induction pathway and a second σ^B-independent mechanism of stress induction, thereby partially compensating for a σ^B deficiency in a sigB mutant. In contrast to sigB mutants, null mutations in genes encoding those proteins, such as clpP or clpC, cause extreme sensitivity to salt or heat.     

Phytotron cultivation of early barley mutants

Conclusions The authors have tried to gather data which permit some information on the between and within locus reactions of induced early barley mutants to different photo- and thermoperiods. Eight mutant cases, showing rather drastic earliness in field cultivation and representing three different gene loci, were examined in phytotron experiments according to routine methods of cultivation. One of the mutants, mat-a ⁸, has been released as an original Swedish barley variety under the name of Svalöf's Mari. In a previous publication (Dormling et al., 1966) this mutant was compared to its parent variety, Svalöf's Bonus, under 30 different climatic conditions. In the present investigation three photoperiods (24, 16 and 8 hours of artificial light) were combined with three suitable thermoperiods (20-15°, 20-10° and 15-10°C).The results indicate that photoperiodic insensitivity, with regard to ear formation and heading capacity, as well as kernel production, is of rather frequent occurrence in connection with drastically early mutants in barley. Four out of eight induced mutants give a more or less pronounced insensitivity. Three of the four insensitive mutants represent locus a, one belongs to locus b. Of the two c-mutants none was insensitive; both were on the contrary pronounced long-day types.Photo- and thermoperiods interact in various ways. This is especially clear in the c-mutants just mentioned, which have a high generative productivity and efficiency at continuous light and high thermoperiods. They produce no grain but considerable vegetative matter at 8 hours of light, independently of thermoperiod, as well as at 16 hours of light with high temperatures. In fact, mutants of loci a and c differ strikingly with regard to their relations to the climatic conditions applied. The insensitive mutant b ¹³ is remarkably similar to the mutant a ¹², but its resemblance to the sensitive mutants b ⁷ and b ¹⁰ of the same locus is evidenced by its high average internode number.It ought to be pointed out here that the mutants of the three gene loci analysed in this study can be distinguished phenotypically with regard to morphological as well as physiological properties, in the field as well as in phytotron cultivation. The c-mutants are especially characteristic. However, there also seem to be clear differences in reaction between the allelic mutants of a locus. In fact, all eight mutants studied seem to react more or less differently.The insensitive mutant a ⁸, which has been released into practice, is also widely used in recombination work, and successful segregates have been isolated. The characteristics of a ⁸, which make the mutant valuable in practice, are also found in phytotron experimentation, specially with regard to earliness, generative efficiency and yield. Also the semidwarf habit and the insensitivity to changes in photo- and thermoperiods readily show up.This investigation has been generously supported by the Swedish Research Council of Forestry and Agriculture.     

Recombinational repair of alkylation lesions in phage T4

Summary Treatment of bacteriophage T4 by ethyl methanesulfonate (EMS)¹ caused more than a doubling in recombination between two rII markers. The functions of genes 47, 46, 32, 30, uvsX and y are known to be required for genetic recombination, and mutants defective in these genes were found to be more sensitive to inactivation by EMS than wild-type phage. This suggests that a recombinational pathway involving the products of these genes may be employed in repairing EMS induced lethal lesions. Genes 45 and denV are apparently not involved in recombination, and mutants defective in these genes were not EMS-sensitive. Gene 47, 46 and y mutants which were defective in the repair of EMS induced lethal lesions had no detectable deficiency in their ability to undergo EMS-induced mutation. This implies that recombinational repair of EMS lesions does not contribute substantially to EMS mutatenesis. The results obtained here with EMS are in general similar to the results reported in the preceding paper with MNNG, suggesting that the lesions caused by both of these monofunctional alkylating agents may be eliminated by similar recombinational repair processes.