The cytoplasmic Cu,Zn superoxide dismutase of saccharomyces cerevisiae is required for resistance to freeze-thaw stress. Generation of free radicals during freezing and thawing

Enhancing freeze-thaw tolerance in baker's yeast: strategies and perspectives

Frozen dough technology is important in modern bakery operations, facilitating the transportation of dough at low temperatures to downstream sales points. However, the freeze-thaw process imposes significant stress on baker's yeast, resulting in diminished viability and fermentation capacity. Understanding the mechanisms underlying freeze-thaw stress is essential for mitigating its adverse effects on yeast performance. This review delves into the intricate mechanisms underlying freeze-thaw stress, focusing specifically on Saccharomyces cerevisiae, the primary yeast used in baking, and presents a wide range of biotechnological approaches to enhance freeze-thaw resistance in S. cerevisiae. Strategies include manipulating intracellular metabolites, altering membrane composition, managing antioxidant defenses, mediating aquaporin expression, and employing adaptive evolutionary and breeding techniques. Addressing challenges and strategies associated with freeze-thaw stress, this review provides valuable insights for future research endeavors, aiming to enhance the freeze-thaw tolerance of baker's yeast and contribute to the advancement of bakery science.

Comparison of liquid nitrogen-free slow freezing protocols toward enabling a practical option for centralized cryobanking of ovarian tissue

Geographically distributed ovarian tissue cryobanks remain limited due to the high facility and staff costs, and cold transportation to centers is associated with ischemia-induced tissue damage that increases with transport distance. It is ideal to perform the cryopreservation procedure at a tissue removal site or local hospital before shipment to cost-effective centralized cryobanks. However, conventional liquid nitrogen-based freezers are not portable and require expensive infrastructure. To study the possibility of an ovarian tissue cryopreservation network not dependent on liquid nitrogen, we cryopreserved bovine ovarian tissue using three cooling techniques: a controlled rate freezer using liquid nitrogen, a liquid nitrogen-free controlled rate freezer, and liquid nitrogen-free passive cooling. Upon thawing, we evaluated a panel of viability metrics in frozen and fresh groups to examine the potency of the portable liquid nitrogen-free controlled and uncontrolled rate freezers in preserving the ovarian tissue compared to the non-portable conventional controlled rate freezer. We found similar outcomes for reactive oxygen species (ROS), total antioxidant capacity (TAC), follicular morphology, tissue viability, and fibrosis in the controlled rate freezer groups. However, passive slow cooling was associated with the lowest tissue viability, follicle morphology, and TAC, and the highest tissue fibrosis and ROS levels compared to all other groups. A stronger correlation was found between follicle morphology, ovarian tissue viability, and fibrosis with the TAC/ROS ratio compared to ROS and TAC alone. The current study undergirds the possibility of centralized cryobanks using a controlled rate liquid nitrogen-free freezer to prevent ischemia-induced damage during ovarian tissue shipment.

Comparative effects of a calcium chelator (BAPTA-AM) and melatonin on cryopreservation-induced oxidative stress and damage in ovarian tissue

Oncology treatments cause infertility, and ovarian tissue cryopreservation and transplantation (OTCT) is the only option for fertility preservation in prepubertal girls with cancer. However, OTCT is associated with massive follicle loss. Here, we aimed to determine the effect of supplementation of slow freezing and vitrification media with BAPTA-AM and melatonin alone and in combination on ovarian tissue viability, reactive oxygen species (ROS) levels, total antioxidant capacity (TAC), and follicular morphology and viability. Our results indicated that BAPTA-AM and melatonin can significantly improve ovarian tissue viability and the TAC/ROS ratio and reduce ROS generation in frozen-thawed ovarian tissues in slow freezing and vitrification procedures. BAPTA-AM was also found to be less effective on TAC compared to melatonin in vitrified ovarian tissue. While supplementation of slow freezing and vitrification media with BAPTA-AM and/or melatonin could increase the percentage of morphologically intact follicles in cryopreserved ovarian tissues, the differences were not significant. In conclusion, supplementation of cryopreservation media with BAPTA-AM or melatonin improved the outcome of ovarian tissue cryopreservation in both vitrification and slow freezing methods. Our data provide some insight into the importance of modulating redox balance and intracellular Ca2+ levels during ovarian tissue cryopreservation to optimize the current cryopreservation methods.

Specific antioxidant enzymes are involved in the freeze-thawing response of industrial baker's yeasts

In this study, the biochemical basis of resistance to slow freezing and thawing (F-T) stress was explored in two baker yeast industrial strains of Saccharomyces cerevisiae that presented differential tolerance to freezing in order to be in the frozen bakery industry. Strain Y8, used commercially in sweet baking doughs, exhibited greater stress tolerance than Y9, a strain employed in regular doughs. Survival of Y8 was higher than that of Y9 (30% vs 12%) after F-T or other reactive oxygen species (ROS) inducing stresses compared to their non-stressed controls. The superior F-T tolerance of Y8 was related to its lower ROS accumulation capacity, determined by fluorometry in cell-free extracts and in vivo, by fluorescence microscopy upon F-T, being Y8 ROS accumulation 2-fold lower than that of Y9. That, in turn, could be positively associated with Y8's higher constitutive activities of cytosolic catalase (CAT) and superoxide dismutase by a significant activation (25%) of Y8 CAT after F-T. That would complement the protective effects of other protectant molecules like trehalose, present at high concentration in this strain.

Freeze–thaw condition limits the fermentation process and accelerates the aerobic deterioration of oat (Avena sativa) silage in the Qinghai-Tibet Plateau

The objective of this study is to determine the effect of freeze–thaw condition on the fermentation characteristics, microbial community, and aerobic stability of oat (Avena sativa) silage in the Qinghai-Tibet Plateau. Oat forage was harvested at milk ripening stage, ensiled in vacuum-sealed bags, and then stored at (1) a constant temperature of 20°C, as a control (20 group) or (2) subjected to freeze–thaw condition (alternating 20 and −5°C every 12 h; S group). The quality and microbial community in the silage were measured after 1, 3, 7, 14, and 60 days of ensiling, and the aerobic stability was measured after 60 days of ensiling at room temperature or at the two treatment temperatures. The results showed that the higher the pH, the lower the concentration of lactic acid and the ratio of lactic acid/acetic acid of the samples under freeze–thaw condition, as compared to those stored at 20°C. The dry matter content of 20 groups was significantly higher than S group (p < 0.05). While ash, neutral detergent fiber (NDF), acid detergent fiber (ADF), crude protein (CP), and water-soluble carbohydrates (WSC) had no significant difference between two groups. Lactobacillus spp., Leuconostoc spp., and Weissella spp. were the most prevalent bacterial genera in all groups. The abundance of Lactobacillus spp. in the 20 group was the highest on day 3 of ensiling (p < 0.05), and it reached the peak on day 14 in the S group, but the abundance in the S group did not exceed 50% during whole fermentation process. The abundance of Enterobacterales and the count of Escherichia coli in the S group was significantly higher than 20 group (p < 0.05). Interestingly, the lactic acid concentration was significant correlated with Lactobacillus spp. in 20 group, while correlated with Leuconostoc spp. in S group. The aerobic stability of the S group was lower than that of the 20 group (p < 0.05). The present study indicates that the freeze–thaw condition led to insufficient fermentation degree of silage by limiting the fermentation of Lactobacillus spp. and severely reduced the aerobic stability of oat silage.

Disruption of YCP4 enhances freeze-thaw tolerance in Saccharomyces cerevisiae

OBJECTIVE

This study aimed to identify genes related to freeze-thaw tolerance and elucidate the tolerance mechanism in yeast Saccharomyces cerevisiae as an appropriate eukaryote model.

RESULTS

In this study, one tolerant strain exposed to freeze-thaw stress was isolated by screening a transposon-mediated mutant library and the disrupted gene was identified to be YCP4. In addition, this phenotype related to freeze-thaw tolerance was confirmed by deletion and overexpressing of this corresponding gene. This mutant strain showed a freeze-thaw tolerance by reducing the intracellular level of reactive oxygen species and the activation of the MSN2/4 and STRE-mediated genes such as CTT1 and HSP12.

CONCLUSIONS

Disruption of YCP4 in S. cerevisiae results in increased tolerance to freeze-thaw stress.

Preservation of non-Saccharomyces yeasts: Current technologies and challenges

There is a recent and growing interest in the study and application of non-Saccharomyces yeasts, mainly in fermented foods. Numerous publications and patents show the importance of these yeasts. However, a fundamental issue in studying and applying them is to ensure an appropriate preservation scheme that allows to the non-Saccharomyces yeasts conserve their characteristics and fermentative capabilities by long periods of time. The main objective of this review is to present and analyze the techniques available to preserve these yeasts (by conventional and non-conventional methods), in small or large quantities for laboratory or industrial applications, respectively. Wine fermentation is one of the few industrial applications of non-Saccharomyces yeasts, but the preservation stage has been a major obstacle to achieve a wider application of these yeasts. This review considers the preservation techniques, and clearly defines parameters such as culturability, viability, vitality and robustness. Several conservation strategies published in research articles as well as patents are analyzed, and the advantages and disadvantages of each technique used are discussed. Another important issue during conservation processes is the stress to which yeasts are subjected at the time of preservation (mainly oxidative stress). There is little published information on the subject for non-Saccharomyces yeast, but it is a fundamental point to consider when designing a preservation strategy.

Evaluation of quality and gene expression of goat embryos produced in vivo and in vitro after cryopreservation

In the present study, we aimed to identify morphological and molecular changes of in vivo and in vitro-produced goat embryos submitted to cryopreservation. In vivo embryos were recovered by transcervical technique from superovulated goats, whereas in vitro produced embryos were produced from ovaries collected at a slaughterhouse. Embryos were frozen by two-steps slow freezing method, which is defined as freezing to -32 °C followed by transfer to liquid nitrogen. Morphological evaluation of embryos was carried out by assessing blastocoel re-expansion rate and the total number of blastomeres. The expression profile of candidate genes related to thermal and oxidative stress, apoptosis, epigenetic, and implantation control was measured using RT-qPCR based SYBR Green system. In silico analyses were performed to identify conserved genes in goat species and protein-protein interaction networks were created. In vivo-produced embryos showed greater blastocoel re-expansion and more blastomere cells (P < 0.05). The expression level of CTP2 and HSP90 genes from in vitro cryopreserved embryos was higher than their in vivo counterparts. Unlikely, no significant difference was observed in the transcription level of SOD gene between groups. The high similarity of CPT2 and HSP90 proteins to their orthologs among mammals indicates that they share conserved functions. In summary, cryopreservation negatively affects the morphology and viability of goat embryos produced in vitro and changes the CPT2 and HSP90 gene expression likely in response to the in vitro production process.

Stress and ageing in yeast

There has long been speculation about the role of various stresses in ageing. Some stresses have beneficial effects on ageing-dependent on duration and severity of the stress, others have negative effects and the question arises whether these negative effects are causative of ageing or the result of the ageing process. Cellular responses to many stresses are highly coordinated in a concerted way and hence there is a great deal of cross-talk between different stresses. Here the relevant aspects of the coordination of stress responses and the roles of different stresses on yeast cell ageing are discussed, together with the various functions that are involved. The cellular processes that are involved in alleviating the effects of stress on ageing are considered, together with the possible role of early stress events on subsequent ageing of cells.

Screening and Genetic Network Analysis of Genes Involved in Freezing and Thawing Resistance in DaMDHAR-Expressing Saccharomyces cerevisiae Using Gene Expression Profiling

The cryoprotection of cell activity is a key determinant in frozen-dough technology. Although several factors that contribute to freezing tolerance have been reported, the mechanism underlying the manner in which yeast cells respond to freezing and thawing (FT) stress is not well established. Therefore, the present study demonstrated the relationship between DaMDHAR encoding monodehydroascorbate reductase from Antarctic hairgrass Deschampsia antarctica and stress tolerance to repeated FT cycles (FT2) in transgenic yeast Saccharomyces cerevisiae. DaMDHAR-expressing yeast (DM) cells identified by immunoblotting analysis showed high tolerance to FT stress conditions, thereby causing lower damage for yeast cells than wild-type (WT) cells with empty vector alone. To detect FT2 tolerance-associated genes, 3′-quant RNA sequencing was employed using mRNA isolated from DM and WT cells exposed to FT (FT2) conditions. Approximately 332 genes showed ≥2-fold changes in DM cells and were classified into various groups according to their gene expression. The expressions of the changed genes were further confirmed using western blot analysis and biochemical assay. The upregulated expression of 197 genes was associated with pentose phosphate pathway, NADP metabolic process, metal ion homeostasis, sulfate assimilation, β-alanine metabolism, glycerol synthesis, and integral component of mitochondrial and plasma membrane (PM) in DM cells under FT2 stress, whereas the expression of the remaining 135 genes was partially related to protein processing, selenocompound metabolism, cell cycle arrest, oxidative phosphorylation, and α-glucoside transport under the same condition. With regard to transcription factors in DM cells, MSN4 and CIN5 were activated, but MSN2 and MGA1 were not. Regarding antioxidant systems and protein kinases in DM cells under FT stress, CTT1, GTO, GEX1, and YOL024W were upregulated, whereas AIF1, COX2, and TRX3 were not. Gene activation represented by transcription factors and enzymatic antioxidants appears to be associated with FT2-stress tolerance in transgenic yeast cells. RCK1, MET14, and SIP18, but not YPK2, have been known to be involved in the protein kinase-mediated signalling pathway and glycogen synthesis. Moreover, SPI18 and HSP12 encoding hydrophilin in the PM were detected. Therefore, it was concluded that the genetic network via the change of gene expression levels of multiple genes contributing to the stabilization and functionality of the mitochondria and PM, not of a single gene, might be the crucial determinant for FT tolerance in DaMDAHR-expressing transgenic yeast. These findings provide a foundation for elucidating the DaMDHAR-dependent molecular mechanism of the complex functional resistance in the cellular response to FT stress.

The roles of reactive oxygen species and antioxidants in cryopreservation

Cryopreservation has facilitated advancement of biological research by allowing the storage of cells over prolonged periods of time. While cryopreservation at extremely low temperatures would render cells metabolically inactive, cells suffer insults during the freezing and thawing process. Among such insults, the generation of supra-physiological levels of reactive oxygen species (ROS) could impair cellular functions and survival. Antioxidants are potential additives that were reported to partially or completely reverse freeze-thaw stress-associated impairments. This review aims to discuss the potential sources of cryopreservation-induced ROS and the effectiveness of antioxidant administration when used individually or in combination.

Flavanols protect the yeast Saccharomyces cerevisiae against heating and freezing/thawing injury

AIMS

The aim of the study was to check whether two flavanols ((-)-epigallocatechin gallate and (+)-catechin) can ameliorate oxidative stress (OS) accompanying and contributing to the lethal effects of heating (50°C) and freezing-thawing on the yeast Saccharomyces cerevisiae.

METHODS AND RESULTS

The flavanols studied increased yeast survival during heating and freezing-thawing, estimated by the colony forming assay. They improved also such indices of OS as increased production of reactive oxygen species, decrease of total antioxidant activity of yeast cell extracts and increase in the level of protein carbonyls.

CONCLUSIONS

Amelioration of OS by flavanols increases the survival of the yeast subjected to high temperature and freezing-thawing.

SIGNIFICANCE AND IMPACT OF THE STUDY

Flavanols may be considered as means of enhancing yeast survival under extreme temperature conditions and probably in other conditions involving OS.

Mitochondrial Superoxide Dismutase and Yap1p Act as a Signaling Module Contributing to Ethanol Tolerance of the Yeast Saccharomyces cerevisiae

There are two superoxide dismutases in the yeast Saccharomyces cerevisiae-cytoplasmic and mitochondrial enzymes. Inactivation of the cytoplasmic enzyme, Sod1p, renders the cells sensitive to a variety of stresses, while inactivation of the mitochondrial isoform, Sod2p, typically has a weaker effect. One exception is ethanol-induced stress. Here we studied the role of Sod2p in ethanol tolerance of yeast. First, we found that repression of SOD2 prevents ethanol-induced relocalization of yeast hydrogen peroxide-sensing transcription factor Yap1p, one of the key stress resistance proteins. In agreement with this, the levels of Trx2p and Gsh1p, proteins encoded by Yap1 target genes, were decreased in the absence of Sod2p. Analysis of the ethanol sensitivities of the cells lacking Sod2p, Yap1p, or both indicated that the two proteins act in the same pathway. Moreover, preconditioning with hydrogen peroxide restored the ethanol resistance of yeast cells with repressed SOD2 Interestingly, we found that mitochondrion-to-nucleus signaling by Rtg proteins antagonizes Yap1p activation. Together, our data suggest that hydrogen peroxide produced by Sod2p activates Yap1p and thus plays a signaling role in ethanol tolerance.

IMPORTANCE

Baker's yeast harbors multiple systems that ensure tolerance to high concentrations of ethanol. Still, the role of mitochondria under severe ethanol stress in yeast is not completely clear. Our study revealed a signaling function of mitochondria which contributes significantly to the ethanol tolerance of yeast cells. We found that mitochondrial superoxide dismutase Sod2p and cytoplasmic hydrogen peroxide sensor Yap1p act together as a module of the mitochondrion-to-nucleus signaling pathway. We also report cross talk between this pathway and the conventional retrograde signaling cascade activated by dysfunctional mitochondria.

Yeast petites and small colony variants: for everything there is a season

The yeast petite mutant was first found in the yeast Saccharomyces cerevisiae. The colony is small because of a block in the aerobic respiratory chain pathway, which generates ATP. The petite yeasts are thus unable to grow on nonfermentable carbon sources (such as glycerol or ethanol), and form small anaerobic-sized colonies when grown in the presence of fermentable carbon sources (such as glucose). The petite phenotype results from mutations in the mitochondrial genome, loss of mitochondria, or mutations in the host cell genome. The latter mutations affect nuclear-encoded genes involved in oxidative phosphorylation and these mutants are termed neutral petites. They all produce wild-type progeny when crossed with a wild-type strain. The staphylococcal small colony variant (SCV) is a slow-growing mutant that typically exhibits the loss of many phenotypic characteristics and pathogenic traits. SCVs are mostly small, nonpigmented, and nonhaemolytic. Their small size is often due to an inability to synthesize electron transport chain components and so cannot generate ATP by oxidative phosphorylation. Evidence suggests that they are responsible for persistent and/or recurrent infections. This chapter compares the physiological and genetic basis of the petite mutants and SCVs. The review focuses principally on two representatives, the eukaryote S. cerevisiae and the prokaryote Staphylococcus aureus. There is, clearly, commonality in the physiological response. Interestingly, the similarity, based on their physiological states, has not been commented on previously. The finding of an overlapping physiological response that occurs across a taxonomic divide is novel.

Oxidative markers in cryopreservation medium from frozen-thawed embryos: a possible tool for improved embryo selection in in vitro fertilization?

PURPOSE

The present study evaluated the association between oxidative parameters in embryo cryopreservation medium and laboratory and clinical outcomes.

METHODS

This prospective laboratory study was conducted in an IVF unit in a university-affiliated hospital with 91 IVF patients undergoing a frozen-thawed embryo transfer cycle. Following thawing, 50 μL of embryo cryopreservation medium was retrieved from each cryotube and tested by the thermochemiluminescence (TCL) assay. TCL amplitudes after 50 (H1), 150 (H2), and 280 s (H3) were recorded in counts per second (CPS) and the TCL ratio determined for comparison with implantation and pregnancy rates.

RESULTS

A total of 194 embryos were transferred in 85 frozen-thaw cycles. Twenty-one pregnancies (24.7 %) occurred. Implantation and overall and clinical pregnancy rates were higher when the median TCL H1 amplitude was <32 CPS compared to ≥32 CPS (14.6 vs. 5.3 %, 37.5 vs. 17 %, 28.1 vs. 9.4 %, respectively). No pregnancies occurred when the H1 amplitude was ≥40 CPS. Logistic regression multivariate analysis found that only the median TCL H1 amplitude was associated with the occurrence of pregnancy (OR = 2.93, 95 % CI 1.065-8.08). The TCL ratio inversely correlated with the duration of embryo cryopreservation (r = -0.37).

CONCLUSIONS

The results indicate that thawed embryos may express oxidative processes in the cryopreservation medium, and higher oxidative levels are associated with lower implantation rates. These findings may aid in the improved selection of frozen-thawed embryos for IVF.

Cu/Zn-superoxide dismutase and glutathione are involved in response to oxidative stress induced by protein denaturing effect of alachlor in Saccharomyces cerevisiae

Alachlor is a widely used pre-emergent chloroacetanilide herbicide which has been shown to have many harmful ecological and environmental effects. However, the mechanism of alachlor-induced oxidative stress is poorly understood. We found that, in Saccharomyces cerevisiae, the intracellular levels of reactive oxygen species (ROS) including superoxide anions were increased only after long-term exposure to alachlor, suggesting that alachlor is not a pro-oxidant. It is likely that alachlor-induced oxidative stress may result from protein denaturation because alachlor rapidly induced an increased protein aggregation, leading to upregulation of SSA4 and HSP82 genes encoding heat shock proteins (Hsp) of Hsp70 and Hsp90 family, respectively. Although only SOD1 encoding Cu/Zn-superoxide dismutase (SOD), but not SOD2 encoding Mn-SOD, is essential for alachlor tolerance, both SODs play a crucial role in reducing alachlor-induced ROS. We found that, after alachlor exposure, glutathione production was inhibited while its utilization was increased, suggesting the role of glutathione in protecting cells against alachlor, which becomes more important when lacking Cu/Zn-SOD. Based on our results, it seems that alachlor primarily causes damages to cellular macromolecules such as proteins, leading to an induction of endogenous oxidative stress, of which intracellular antioxidant defense systems are required for elimination.

Comparative effects of adding β-mercaptoethanol or L-ascorbic acid to culture or vitrification-warming media on IVF porcine embryos

The aims of the present study were to; (1) determine the effects of supplementation with two antioxidants during in vitro culture (IVC) on embryo development and quality; and (2) test the effects of adding the antioxidants to vitrification-warming media on the cryotolerance of in vitro-produced (IVP) porcine blastocysts. In Experiment 1, presumptive zygotes were cultured without antioxidants, with 50 µM β-mercaptoethanol (β-ME) or with 100 µM L-ascorbic acid (AC). After culture, blastocyst yield, quality and cryotolerance were evaluated in each treatment group. In Experiment 2, survival rates (3 and 24 h), total cell number, apoptosis index and the formation of reactive oxygen species (ROS) in blastocysts vitrified-warmed with 100 µM AC or 50 µM β-ME or without antioxidants added to the vitrification medium were compared. Antioxidant addition during IVC had no effect on embryo development, total cell number or the apoptosis index, and culturing embryos in the presence of β-ME had no effects on cryotolerance. In contrast, ROS levels and survival rates after vitrification-warming were significantly improved in embryos cultured with AC. Furthermore, addition of AC into vitrification-warming media enhanced embryo survival and embryo quality after warming. In conclusion, our results suggest that supplementing culture or vitrification media with 100 µM AC improves the quality and cryosurvival of IVP porcine blastocysts.

Assessment of ethylene diurea-induced protection in plants against ozone phytotoxicity

Urbanization, industrialization and unsustainable utilization of natural resources have made tropospheric ozone (03) one of the world's most significant air pollutants. Past studies reveal that 0 3 is a phytotoxic air pollutant that causes or enhances food insecurity across the globe. Plant sensitivity, tolerance and resistance to 0 3 involve a wide array of responses that range from growth to the physiological, biochemical and molecular. Although plants have an array of defense systems to combat oxidative stress from 0 3 exposure, they still suffer sizable yield reductions. In recent years, the ground-level 0 3 concentrations to which crop plants have been exposed have caused yield loses that are economically damaging. Several types of chemicals have been applied or used to mitigate the effects produced by 0 3 on plants. These include agrochemicals (fungicides, insecticides, plant growth regulators), natural antioxidants, and others. Such treatments have been effective to one degree to another, in ameliorating Or generated stress in plants. Ethylene diurea (EDU) has been the most effective protectant used and has also served as a monitoring agent for assessing plant yield losses from 0 3 exposure. In this review, we summarize the data on how EDU has been used, the treatment methods tested, and application doses found to be both protective and toxic in plants. We have also summarized data that address the nature and modes of action (biophysical and biochemical) of EDU. In general, the literature discloses that EDU is effective in reducing ozone damage to plants, and indicates that EDU should be more widely used on 0 3 sensitive plants as a tool for biomonitoring of 0 3 concentrations. Biomonitoring studies that utilize EDU are very useful for rural and remote areas and in developing countries where 0 3 monitoring is constrained from unavailability of electricity. The mechanism(s) by which EDU prevents 0 3 toxicity in plants is still not completely known. EDU possesses great utility for screening plant sensitivity under field conditions in areas that experience high 0 3 concentrations, because EDU prevents 0 3 toxicity only in 0 3 sensitive plants. Ozone-resistant plants do not respond positively to EDU applications. However, EDU application dose and frequency must be standardized before it can be effectively and widely used for screening 0 3 sensitivity in plants. EDU acts primarily by enhancing biochemical plant defense and delaying Or induced senescence, thereby reducing chlorophyll loss, and maintaining physiological efficiency and primary metabolites; these actions enhance growth, biomass and yield of plants. We believe that future studies are needed to better address the EDU dose response relationship for many plant species, and to screen for new cultivars that can resist 0 3 stress. Although some research on the physiological and biochemical mechanisms of action of EDU have been performed, the new 'omics' tools have not been utilized to evaluate EDUs mechanism of action. Such data are needed, as is gene expression and proteome profiling studies on EDU-treated and -untreated plants.

Nitric oxide-mediated antioxidative mechanism in yeast through the activation of the transcription factor Mac1

The budding yeast Saccharomyces cerevisiae possesses various defense mechanisms against environmental stresses that generate reactive oxygen species, leading to growth inhibition or cell death. Our recent study showed a novel antioxidative mechanism mediated by nitric oxide (NO) in yeast cells, but the mechanism underlying the oxidative stress tolerance remained unclear. We report here one of the downstream pathways of NO involved in stress-tolerance mechanism in yeast. Our microarray and real-time quantitative PCR analyses revealed that exogenous NO treatment induced the expression of genes responsible for copper metabolism under the control of the transcription factor Mac1, including the CTR1 gene encoding high-affinity copper transporter. Our ChIP analysis also demonstrated that exogenous NO enhances the binding of Mac1 to the promoter region of target genes. Interestingly, we found that NO produced under high-temperature stress conditions increased the transcription level of the CTR1 gene. Furthermore, NO produced during exposure to high temperature also increased intracellular copper content, the activity of Cu,Zn-superoxide dismutase Sod1, and cell viability after exposure to high-temperature in a manner dependent on Mac1. NO did not affect the expression of the MAC1 gene, indicating that NO activates Mac1 through its post-translational modification. Based on the results shown here, we propose a novel NO-mediated antioxidative mechanism that Mac1 activated by NO induces the CTR1 gene, leading to an increase in cellular copper level, and then Cu(I) activates Sod1. This is the first report to unveil the mechanism of NO-dependent antioxidative system in yeast.

Understanding the cellular mechanism of recovery from freeze-thaw injury in spinach: possible role of aquaporins, heat shock proteins, dehydrin and antioxidant system

Recovery from reversible freeze-thaw injury in plants is a critical component of ultimate frost survival. However, little is known about this aspect at the cellular level. To explore possible cellular mechanism(s) for post-thaw recovery (REC), we used Spinacia oleracea L. cv. Bloomsdale leaves to first determine the reversible freeze-thaw injury point. Freeze (-4.5°C)-thaw-injured tissues (32% injury vs <3% in unfrozen control) fully recovered during post-thaw, as assessed by an ion leakage-based method. Our data indicate that photosystem II efficiency (Fv/Fm) was compromised in injured tissues but recovered during post-thaw. Similarly, the reactive oxygen species (O2 (•-) and H2 O2 ) accumulated in injured tissues but dissipated during recovery, paralleled by the repression and restoration, respectively, of activities of antioxidant enzymes, superoxide dismutase (SOD) (EC. 1.14.1.1), and catalase (CAT) (EC.1.11.1.6) and ascorbate peroxidase (APX) (EC.1.11.1.11). Restoration of CAT and APX activities during recovery was slower than SOD, concomitant with a slower depletion of H2 O2 compared to O2 (•-) . A hypothesis was also tested that the REC is accompanied by changes in the expression of water channels [aquaporines (AQPs)] likely needed for re-absorption of thawed extracellular water. Indeed, the expression of two spinach AQPs, SoPIP2;1 and SoδTIP, was downregulated in injured tissues and restored during recovery. Additionally, a notion that molecular chaperones [heat shock protein of 70 kDa (HSP70s)] and putative membrane stabilizers [dehydrins (DHNs)] are recruited during recovery to restore cellular homeostasis was also tested. We noted that, after an initial repression in injured tissues, the expression of three HSP70s (cytosolic, endoplasmic reticulum and mitochondrial) and a spinach DHN (CAP85) was significantly restored during the REC.

Increased oxidative stress tolerance results in general stress tolerance in Candida albicans independently of stress-elicited morphological transitions

A selection of tert-butylhydroperoxide (tBOOH)-tolerant Candida albicans mutants showed increased tolerances to 19 different stress conditions. These mutants are characterized by a constitutively upregulated antioxidative defense system and, therefore, adaptation to oxidative stress may play an important role in gaining general stress tolerance in C. albicans. Although C. albicans cells may undergo morphological transitions under various stress treatments, this ability shows considerable stress-specific and strain-specific variability and, hence, it is independent of mounting stress cross protections.

Effect of dietary antioxidants on the cytostatic effect of acrylamide during copper-deficiency in Saccharomyces cerevisiae

Yeast grown on a copper deficient medium was used to study acrylamide toxicity, obviating the need for genetic manipulation and accompanying compensatory effects.

Superoxide radicals have a protective role during H2O2 stress

H₂O₂-stressed yeast cells increase superoxide radical production, dependent on the mitochondrial respiratory chain. This is protective during H₂O₂ stress at low levels; however, higher superoxide levels are deleterious. This hormesis may further elucidate the role of reactive oxygen species in oxidative stress and aging.

Reactive oxygen species (ROS) consist of potentially toxic, partly reduced oxygen species and free radicals. After H₂O₂ treatment, yeast cells significantly increase superoxide radical production. Respiratory chain complex III and possibly cytochrome b function are essential for this increase. Disruption of complex III renders cells sensitive to H₂O₂ but not to the superoxide radical generator menadione. Of interest, the same H₂O₂-sensitive mutant strains have the lowest superoxide radical levels, and strains with the highest resistance to H₂O₂ have the highest levels of superoxide radicals. Consistent with this correlation, overexpression of superoxide dismutase increases sensitivity to H₂O₂, and this phenotype is partially rescued by addition of small concentrations of menadione. Small increases in levels of mitochondrially produced superoxide radicals have a protective effect during H₂O₂-induced stress, and in response to H₂O₂, the wild-type strain increases superoxide radical production to activate this defense mechanism. This provides a direct link between complex III as the main source of ROS and its role in defense against ROS. High levels of the superoxide radical are still toxic. These opposing, concentration-dependent roles of the superoxide radical comprise a form of hormesis and show one ROS having a hormetic effect on the toxicity of another.

The nature and mechanism of superoxide production by the electron transport chain: Its relevance to aging

Most biogerontologists agree that oxygen (and nitrogen) free radicals play a major role in the process of aging. The evidence strongly suggests that the electron transport chain, located in the inner mitochondrial membrane, is the major source of reactive oxygen species in animal cells. It has been reported that there exists an inverse correlation between the rate of superoxide/hydrogen peroxide production by mitochondria and the maximum longevity of mammalian species. However, no correlation or most frequently an inverse correlation exists between the amount of antioxidant enzymes and maximum longevity. Although overexpression of the antioxidant enzymes SOD1 and CAT (as well as SOD1 alone) have been successful at extending maximum lifespan in Drosophila, this has not been the case in mice. Several labs have overexpressed SOD1 and failed to see a positive effect on longevity. An explanation for this failure is that there is some level of superoxide damage that is not preventable by SOD, such as that initiated by the hydroperoxyl radical inside the lipid bilayer, and that accumulation of this damage is responsible for aging. I therefore suggest an alternative approach to testing the free radical theory of aging in mammals. Instead of trying to increase the amount of antioxidant enzymes, I suggest using molecular biology/transgenics to decrease the rate of superoxide production, which in the context of the free radical theory of aging would be expected to increase longevity. This paper aims to summarize what is known about the nature and mechanisms of superoxide production and what genes are involved in controlling the rate of superoxide production.

A new simple method for isolating multistress-tolerant semidominant mutants of Saccharomyces cerevisiae by one-step selection under lethal hydrogen peroxide stress condition

Tolerance of microorganisms to diverse stresses (i.e., multistress tolerance) is a very useful property with industrial applications. We have developed a simple method for isolating multistress-tolerant semidominant mutants of the budding yeast Saccharomyces cerevisiae by one-step selection under lethal hydrogen peroxide (H(2)O(2)) stress condition, which we named the lethal concentration of H(2)O(2) (LCH) method. This method involves simply isolating colonies after plating of mutagenized S. cerevisiae cells, which are cultivated overnight in liquid media, on agar plates containing a lethal concentration of H(2)O(2) for the wild-type strain. Phenotypic and genetic analyses of the ten strains isolated by this method revealed that two strains exhibiting stress tolerance to H(2)O(2), ethanol, heat shock, salt, organic solvent, freeze-thaw, chronological aging, and high concentrations of glucose possess semidominant and distinct single-gene mutations designated as MLT1-1 (multistress tolerance) and MLT2-1, which are responsible for multistress tolerance. From these results, we expect this method to confer multistress tolerance on industrial yeasts.

Changes in reactive oxygen species begin early during replicative aging of Saccharomyces cerevisiae cells

Increased reactive oxygen species (ROS) are a feature of aging cells, but little is known about when ROS generation begins as cells age. Here we show how ROS change in Saccharomyces cerevisiae cells throughout their early replicative life span using the fluorescent ROS indicator dihydroethidium (DHE), which has some specificity for the superoxide anion. Cells in a particular age range were heterogeneous with respect to their ROS burden. Surprisingly, some cells as young as 5-7 generations acquired a greatly increased level of ROS detected by DHE relative to virgin cells. By 12 generations 50% of cells had a substantial ROS burden despite being only halfway through their life span. In contrast to the wild type, cells of a sir2 mutant had lower levels of ROS reacting with DHE. Daughters from older mothers had low ROS levels, and this asymmetric distribution of ROS was SIR2-independent. Mitochondrial fragmentation also began to occur in cells after 4 generations and increased markedly as cells aged. Daughter cells regenerated normal tubular mitochondria despite the fragmentation of mitochondria in the mother cells, whereas daughters of the sir2 mutant had fragmented mitochondria at all ages.

Cryopreservation and oxidative stress in reproductive cells

In spite of the optimisation of cryopreservation protocols, post-thawing trauma to mammalian gametes cannot be completely avoided. Based on recent literature, cellular cryodamage in reproductive cells has been extensively characterised in terms of changes in the cell structure, whereas biochemical alterations have been poorly investigated. The present paper reviews the current knowledge about the involvement of oxidative stress in frozen-thawed cells by considering the most relevant studies in sperm and oocytes. Recognising that spermatozoa are highly susceptible to oxidative damage induced by cryopreservation, the need for further research is highlighted in order to understand whether changes in the redox state have a role in the reduced developmental potential of cryopreserved human reproductive cells.

Cytosolic superoxide dismutase (SOD1) is critical for tolerating the oxidative stress of zinc deficiency in yeast

Zinc deficiency causes oxidative stress in many organisms including the yeast Saccharomyces cerevisiae. Previous studies of this yeast indicated that the Tsa1 peroxiredoxin is required for optimal growth in low zinc because of its role in degrading H₂O₂. In this report, we assessed the importance of other antioxidant genes to zinc-limited growth. Our results indicated that the cytosolic superoxide dismutase Sod1 is also critical for growth under zinc-limiting conditions. We also found that Ccs1, the copper-delivering chaperone required for Sod1 activity is essential for optimal zinc-limited growth. To our knowledge, this is the first demonstration of the important roles these proteins play under this condition. It has been proposed previously that a loss of Sod1 activity due to inefficient metallation is one source of reactive oxygen species (ROS) under zinc-limiting conditions. Consistent with this hypothesis, we found that both the level and activity of Sod1 is diminished in zinc-deficient cells. However, under conditions in which Sod1 was overexpressed in zinc-limited cells and activity was restored, we observed no decrease in ROS levels. Thus, these data indicate that while Sod1 activity is critical for low zinc growth, diminished Sod1 activity is not a major source of the elevated ROS observed under these conditions.

Insufficiency of copper ion homeostasis causes freeze-thaw injury of yeast cells as revealed by indirect gene expression analysis

Saccharomyces cerevisiae is exposed to freeze-thaw stress in commercial processes, including frozen dough baking. Cell viability and fermentation activity after a freeze-thaw cycle were dramatically decreased due to freeze-thaw injury. Because this type of injury involves complex phenomena, the injury mechanisms are not fully understood. We examined freeze-thaw injury by indirect gene expression analysis during postthaw incubation after freeze-thaw treatment using DNA microarray profiling. The results showed that genes involved in the homeostasis of metal ions were frequently contained in genes that were upregulated, depending on the freezing period. We assessed the phenotype of deletion mutants of the metal ion homeostasis genes that exhibited freezing period-dependent upregulation and found that the strains with deletion of the MAC1 and CTR1 genes involved in copper ion homeostasis exhibited freeze-thaw sensitivity, suggesting that copper ion homeostasis is required for freeze-thaw tolerance. We found that supplementation with copper ions during postthaw incubation increased intracellular superoxide dismutase activity and intracellular levels of reactive oxygen species were decreased. Moreover, cell viability was increased by supplementation with copper ions. These results suggest that insufficiency of copper ion homeostasis may be one of the causes of freeze-thaw injury.

Hydrogen peroxide-induced response in E. coli and S. cerevisiae: different stages of the flow of the genetic information

Adaptation to oxidative stress is a major topic in basic and applied research. Cell response to stressful changes is realized through coordinated reorganization of gene expression. E. coli and S. cerevisiae are extremely amenable to genetic or molecular biological and biochemical approaches, which make these microorganisms suitable models to study stress response at a molecular level in prokaryotes and eukaryotes, respectively. The main focus of this review is (i) to discuss transcriptional control of global response to hydrogen peroxide in E. coli and S. cerevisiae, (ii) to summarize recent literature data on E. coli and S. cerevisiae adaptive response to oxidative stress at different stages of the flow of the genetic information: from transcription and translation to functionally active proteins and (iii) to discuss possible reasons for a lack of correlation between the expression of certain antioxidant genes at different levels of cellular organization.

Role of oxidative stress in C. jejuni inactivation during freeze-thaw treatment

Campylobacter jejuni represents one of the leading causes of bacterial enteritis throughout the world. Poultry is an important source of C. jejuni. Despite hygiene measures taken in the production chain, C. jejuni is frequently isolated from poultry meat. C. jejuni is a microaerophilic pathogen, affected by oxidative stress. Freeze-thaw treatment induces cell death by several mechanisms, including oxidative stress. In this article, we investigate the role of oxidative stress in C. jejuni sensitivity during and after a freeze-thaw treatment. This treatment results in dead and sublethally injured cells. The latter population might have an increased sensitivity to oxidative stress. To test this, cells were stored for another 24 h at 4 degrees C under aerobic conditions and compared to cells that were not treated. C. jejuni survival was measured in different media (water, BHI broth, chicken juice, and chicken fillets) to test the environment protective effect. Different strains were tested, including sodB (encoding the superoxide dismutase) and cj1371 (encoding a periplasmic protein) mutants. Cell death was particularly important in water but similar in BHI, chicken juice, and chicken fillets. The sodB mutant was more sensitive to freeze-thaw treatment, suggesting that the killing mechanism involves production of superoxide anions. On the contrary, the cj1371 mutant was more sensitive to storage at 4 degrees C, suggesting that it does not play a role in the detoxification of reactive oxygen species. Storage at 4 degrees C after freeze-thaw treatment increases cell death of oxidative stress-sensitive populations. Sensitization to oxidative stress, freeze-thaw treatment, and further storage at 4 degrees C could be a way to reduce C. jejuni populations on carcasses.

Yeast responses to stresses associated with industrial brewery handling: Figure 1

During brewery handling, production strains of yeast must respond to fluctuations in dissolved oxygen concentration, pH, osmolarity, ethanol concentration, nutrient supply and temperature. Fermentation performance of brewing yeast strains is dependent on their ability to adapt to these changes, particularly during batch brewery fermentation which involves the recycling (repitching) of a single yeast culture (slurry) over a number of fermentations (generations). Modern practices, such as the use of high-gravity worts and preparation of dried yeast for use as an inoculum, have increased the magnitude of the stresses to which the cell is subjected. The ability of yeast to respond effectively to these conditions is essential not only for beer production but also for maintaining the fermentation fitness of yeast for use in subsequent fermentations. During brewery handling, cells inhabit a complex environment and our understanding of stress responses under such conditions is limited. The advent of techniques capable of determining genomic and proteomic changes within the cell is likely vastly to improve our knowledge of yeast stress responses during industrial brewery handling.