A new currency for mutualism? Fungal endophytes alter antioxidant activity in hosts responding to drought

Fungal endophytes have significant effects on host performance including but not limited to changes in reproductive output, as well as, biotic and abiotic stress tolerance. The ultimate mechanisms for resistance to herbivory have been documented in a number of fungal-plant symbiota and involve the production of alkaloids by the fungus. Alkaloids have thus been defined as a currency responsible for increased host resistance to herbivory. We provide support for the hypothesis that another currency may be responsible for increased host tolerance to abiotic stress resulting from endophyte colonization; namely antioxidants. We report comparatively higher activity of antioxidants in endophyte colonized hosts resulting from abiotic stress and propose antioxidants are another currency via which mutualistic interactions between fungal endophytes and their hosts can occur. We recognize fungal endophyte interactions are diverse and complex and include antagonisms, commensalisms, and mutualisms.     

Biodiversity of fungal endophyte communities inhabiting switchgrass (Panicum virgatum L.) growing in the native tallgrass prairie of northern Oklahoma

This study was conducted to explore fungal endophyte communities inhabiting native switchgrass plants from the tallgrass prairie of northern Oklahoma. The primary focus was to isolate these endophytes in pure culture from surface-sterilized plant tissues and provide taxonomic identifications based on comparative analysis of ITS rDNA gene sequences. From these data, we evaluated the biodiversity of these potentially beneficial endosymbionts from this rapidly disappearing habitat of the Great Plains. While important from a strictly conservationist standpoint, this survey further allowed us to identify candidate endophytes for introduction into commercial switchgrass cultivars for biomass enhancement. A total of 210 whole plant samples were collected at early vegetative, full reproductive and senescence stages. Fungal endophytes were isolated, identified to species level when possible, and grouped into communities based on plant part, collection month and part of the prairie from which the plants were collected. Species diversity for each community was estimated by Shannon diversity index, and differences in diversity indices were compared using a t-test. The presence of fungal species representing at least 18 taxonomic orders suggests a high level of diversity in switchgrass endophyte communities. The fungal communities from shoot tissue had significantly higher species diversity than communities from the root tissue. The abundance of taxa assigned to the order Hypocreales (to which mutualistic, clavicipitaceous endophytes of cool-season grasses belong) found in shoot (64%) and root tissues (39%) throughout the growing season suggests great potential for utilizing these endophytes for enhancing biomass production and stress resistance of this important bioenergy crop.     

Effects of fungal endophytes on grass and non-grass litter decomposition rates

The influence of clavicipitaceous fungal endophytes on grass decomposition rates has been studied through field and laboratory experiments. However, the effects of endophytes on decomposition rates of non-grass species are unclear. This paper reviews research data related to the effects of fungal endophytes on decomposition rates of three litter types: grass, non-grass leaf litter (including spruce needle litter) and non-grass twigs and wood. We discuss how fungal endophytes are involved in, or regulate decomposition rates and may change lifestyles from fungal endophytes to saprotrophs. Classical morphology and molecular approaches together with digestion enzyme studies provide evidence to suggest that some endophyte species switch their ecological roles and adopt a new life style as saprotrophs. We also explore the main mechanisms that explain how fungal endophytes may decelerate decomposition rates and whether it is directly driven by alkaloids. Further research on the role of fungal endophytes in decomposition rates of both grass and non-grass litter is needed, especially those addressing the direct and indirect mechanisms by which endophytes affect decomposition rates.     

Diabetes,Oxidative Stress and Physical Exercise

Oxidative stress, an imbalance between the generation of reactive oxygen species and antioxidant defense capacity of the body, is closely associated with aging and a number of diseases including cancer, cardiovascular diseases, diabetes and diabetic complications. Several mechanisms may cause oxidative insult in diabetes, although their exact contributions are not entirely clear. Accumulating evidence points to many interrelated mechanisms that increase production of reactive oxygen and nitrogen species or decrease antioxidant protection in diabetic patients. In modern medicine, regular physical exercise is an important tool in the prevention and treatment of diseases including diabetes. Although acute exhaustive exercise increases oxidative stress, exercise training has been shown to up regulate antioxidant protection. This review aims to summarize the mechanisms of increased oxidative stress in diabetes and with respect to acute and chronic exercise.Key Words: Diabetes, physical activity, antioxidants, reactive oxygen species     

Symbiotic interactions as drivers of trade-offs in plants: effects of fungal endophytes on tall fescue

Studying the controls on biomass allocation trade-offs in plants are important since they affect harvestable product yields and are critical to understanding symbiotic interactions. Epichloae fungal endophytes associate with cool-season grasses, growing systemically within the plant inter-cellular spaces and are transmitted through seeds. We explore the endophytes influence on the relationship between the plant reproductive and vegetative aboveground biomass (reproductive effort: RE) and on the trade-off between two components of the reproductive biomass, number and weight of panicles (RPN), using tall fescue as a model system. Naturally endophyte-colonized, manipulatively endophyte-free, and naturally endophyte-free plants from Northern European wild-populations together with the cultivar Kentucky-31 were grown under different environmental conditions (nutrients x water). The endophyte had an effect on the RPN (E+: 6.19, ME-: 4.68 and E-: 4.40) which indicates how reproductive biomass is partitioned into number and mass of panicles, but not on RE (≈0.06). As expected, wild plants showed higher reproductive effort (≈0.06) compared to the cultivar KY-31 (0.05), irrespective of endophyte presence. Endophyte-colonized plants had lighter panicles than endophyte-free plants, a pattern that was clear among low-yielding plants. Similarly, the trade-off between RPN and RE was higher for endophyte-colonized plants. This was again evident among plants with low RE indicating that colonized plants split the yield into either greater number of panicles and/or lighter panicles. The effect of vertically transmitted endophytes has earlier been studied as ratios (e.g. RE); however, our study shows that this approach may hide size-dependent endophyte effects on these relationships. Our study reveals that Neotyphodium endophyte affects trade-offs in tall fescue plants in a complex manner, and is influenced by a number of biological and abiotic factors.     

The endophytic mycobiota of Arabidopsis thaliana

Fungal endophytes are receiving increasing attention as resources to improve crop production and ecosystem management. However, the biology and ecological significance of these symbionts remains poorly understood, due to a lack of model systems for more efficient research. In this work, we have analyzed the culturable endophytic mycobiota associated, in the wild, with leaves and siliques of the model plant A. thaliana. We have studied the effect of biotic and abiotic factors in the frequency of fungal endophytes in plant specimens, and in the species composition of the endophytic community. Our results indicate that the frequency of Arabidopsis plants hosting endophytes depends on the time of the year and the phenological stage of the plant, and that the probability of endophyte colonization increases as the life cycle of the plant progresses. The diversity of the endophytic assemblages of natural A. thaliana populations was high, and precipitation and temperature were the two main factors determining the diversity and species composition of the communities. We propose A. thaliana and its endophytes as a model system for an integral approach to the principles governing the endophytic lifestyle, taking advantage of the molecular tools and the abundant knowledge accessible from the host plant.     

Phyllosticta capitalensis, a widespread endophyte of plants

Phyllosticta capitalensis is an endophyte and weak plant pathogen with a worldwide distribution presently known from 70 plant families. This study isolated P. capitalensis from different host plants in northern Thailand, and determined their different life modes. Thirty strains of P. capitalensis were isolated as endophytes from 20 hosts. An additional 30 strains of P. capitalensis from other hosts and geographic locations were also obtained from established culture collections. Phylogenetic analysis using ITS, ACT and TEF gene data confirmed the identity of all isolates. Pathogenicity tests with five strains of P. capitalensis originating from different hosts were completed on their respective host plants. In all cases there was no infection of healthy leaves, indicating that this endophyte does not cause disease on healthy, unstressed host plants. That P. capitalensis is often isolated as an endophyte has important implications in fungal biology and plant health. Due to its endophytic nature, P. capitalensis is commonly found associated with lesions of plants, and often incorrectly identified as a species of quarantine importance, which again has implications for trade in agricultural and forestry production.     

Comparative analysis of the biodiversity of fungal endophytes in insect-induced galls and surrounding foliar tissue

Insect-induced galls are abnormal plant growths that can provide food and shelter to their inhabitants, resulting in stressed plant tissue that may alter the conditions for the colonization or proliferation of endophytic fungi. We investigated the effect gall formation has on fungal endophyte communities and diversity. Using three closely-related gall-forming aphid species that specialize on poplars, we characterized fungal endophyte diversity in galls and surrounding petiole and leaf lamina tissue. A total of 516 fungal endophyte samples were isolated from 272 tissue samples (32 leaves, 31 petioles, and 209 galls), resulting in 23 distinct morphotypes. Despite sharing a common host plant and often forming spatially contiguous galls, the endophyte profiles within the galls of each aphid species were distinct, not only from the galls of the other species, but also from surrounding plant tissue. These results suggest that insect galls can affect the composition of fungal endophyte species in plant tissues, by altering either the colonization or proliferation of their endophytic mycobiota. Likewise, fungal endophytes may be important in the ecology and evolution of insect galls.     

Oxidant Stress in Hemodialysis Patients: What Are the Determining Factors?

Oxidant stress contributes to morbidity in hemodialysis patients. Three possible causes of oxidant stress have been suggested: the uremic state, the dialyzer membrane, and bacterial contaminants from the dialysate. Oxidant stress occurs in uremia before dialysis therapy is initiated, as evidenced by increased production of reactive oxygen species, increased levels of oxidized plasma proteins and lipids, and decreased antioxidant defenses. It has been proposed that increased production of reactive oxygen species during hemodialysis is also an important contributor to oxidant stress. Hemodialysis is associated with a transient increase in production of reactive oxygen species, particularly with cellulose membranes. In addition, surveys have shown widespread contamination of dialysate by endotoxin, which may cross membranes and prime production of reactive oxygen species by phagocytic cells. Recent studies, however, show a decrease in protein oxidation from pre- to post-dialysis and a normalization of neutrophil reactive oxygen species production. Taken together, these data suggest that uremia, per se, is the most important cause of oxidant stress in hemodialysis patients. Dialysate quality may also contribute to oxidant stress, but evidence that the dialyzer membrane plays a role is weak.     

Oxidative stress in hemodialysis: Causative mechanisms,clinical implications,and possible therapeutic interventions

Oxidative stress (OS) is the result of prooxidant molecules overwhelming the antioxidant defense mechanisms. Hemodialysis (HD) constitutes a state of elevated inflammation and OS, due to loss of antioxidants during dialysis and activation of white blood cells triggering production of reactive oxygen species. Dialysis vintage, dialysis methods, and type and condition of vascular access, biocompatibility of dialyzer membrane and dialysate, iron administration, and anemia all can play a role in aggravating OS, which in turn has been associated with increased morbidity and mortality. Oral or intravenous administration of antioxidants may detoxify the oxidative molecules and at least in part repair OS‐mediated tissue damage. Lifestyle interventions and optimization of a highly biocompatible HD procedure might ameliorate OS development in dialysis.     

Reactive Oxygen Species Production by the Spermatozoa of Patients With Idiopathic Infertility: Relationship to Seminal Plasma Antioxidants

Purpose

We attempted to determine reactive oxygen species production by the spermatozoa of patients with idiopathic infertility and healthy donors, and observe whether increased production was due to decreased seminal plasma reactive oxygen species scavengers.

Materials and Methods

Reactive oxygen species production by spermatozoa and seminal plasma antioxidants was assayed in 18 patients with idiopathic infertility and 10 controls. Reactive oxygen species formation and seminal plasma antioxidants were measured by luminol and lucigenin dependent chemoluminescence, and enzymatic methods, respectively.

Results

Higher reactive oxygen species production was observed in 16 of the 18 patients (88.8%, p <0.0001 versus controls). Seminal plasma superoxide dismutase, catalase, glutathione peroxidase and total sulfhydryl group levels in infertile patients were significantly lower than in controls.

Conclusions

Decreased seminal plasma antioxidant activity and increased reactive oxygen species production can be responsible for idiopathic male infertility.     

Implications of oxidative stress in senescence

After a short review of the literature concerning the paradox of oxygen and the participation of the oxidative stress created by the prevalence of its reactive radical species over the antioxidant enzymes, the main experimental arguments favoring the hypothesis of the implication of free radicals in senescence will be exposed. The amplification of degrading processes of lipid peroxidation and altering of the protein thiol groups in the presence of reactive oxygen species will be outlined. Both the aging of mitochondria due to the alteration of the electron transport chain and the oxidative attack on the mitochondrial DNA and the activation of the apoptosis as programmed cell death phenomenon in the presence of free radicals of oxygen, nitrogen and carbon will be given a particular interest. Finally, the implication of radical species in the production of some cardiovascular degenerative diseases of elderly patients will be discussed, together with the protective role of antioxidant compounds and diet, as factors that confine the progressive degradation of the senescent human body.     

Neotyphodium fungal endophyte in tall fescue (Schedonorus phoenix): a comparison of three Northern European wild populations and the cultivar Kentuky-31

Pooideae grasses may be colonized by systemic fungal endophytes. The fitness of endophyte depends entirely on resources and seed transmission from the host plant, while colonized plants may gain increased survival, growth, and reproduction relative to their uncolonized conspecifics. Most research of endophyte-grass interactions have been carried out on few cultivars of tall fescue (Schedonorus phoenix) and their symbiont Neotyphodium coenophialum. Lack of studies using wild populations of tall fescue across the species natural distribution range, however, limits the understanding of the ecological and evolutionary role of the symbiosis in nature. We performed a common garden experiment in Southern Finland with three wild, tall fescue populations from northern Europe and the forage cultivar Kentucky-31 (KY-31). For each population, we used naturally endophyte-colonized, naturally endophyte-colonized but endophyte removed (decolonized), and naturally uncolonized plants to separate effects due to the host genotype from the endophyte. We evaluated growth variables and survival in four environmental treatments of varying water and nutrients. Supply of water and nutrients increased plant biomass and reproductive effort in all populations. This effect was higher for KY-31 plants which produced on average 55 % more seeds than wild plants, indicating better adaptation to high resource environments. However, the higher incidence of Claviceps sp. and the low winter survival indicated KY-31 tall fescue is mal-adapted to Northern European conditions. Naturally colonized plants had greater plant biomass (≈12 %), reproductive effort (≈22 %) and seed mass (≈29 %) than naturally uncolonized and decolonized plants. Nonetheless, endophyte colonization did not affect plant survival, and the effects of endophyte colonization on tiller number, panicle/tiller ratio and Claviceps sp. incidence depended on the population origin. In the wild populations, endophyte removal only reduced the number of tillers (≈29 % lower), while the difference between naturally colonized and naturally uncolonized plants was not significant. Our results show that endophyte symbiont increases tall fescue performance in general, but the differences between wild populations and cultivars indicate adaptation to local habitats and agronomic management, respectively. The comparison of naturally endophyte-colonized and decolonized plants suggests certain plant genotype-endophyte combinations found within populations result from local selection pressures.     

Free radicals, antioxidants, and neurologic injury: possible relationship to cerebral protection by anesthetics.

Oxygen-centered free radicals cause brain injury associated with trauma and stroke. These reactive oxygen species may be detoxified by endogenous antioxidants, but cell death occurs after antioxidants become depleted. General anesthetics penetrate into brain parenchyma, where they may abrogate oxidative injury to neurons by several mechanisms that prevent the initiation of free radical chain reactions or terminate the propagation of highly reactive radicals. First, general anesthetics may inhibit free radical generation because these drugs slow cerebral utilization of oxygen and glucose, inhibit oxidative metabolism in neutrophils, and prevent redox changes in hemoglobin. Second, antioxidant anesthetics, such as thiopental and propofol, directly scavenge reactive oxygen species and inhibit lipid peroxidation. Finally, anesthetics may prevent the elevation of extracellular glutamate concentration and inhibit the activation of excitatory glutamatergic receptors that augment oxidative stress after ischemia.     

Dietary Factors in the Prevention and Treatment of Nonmelanoma Skin Cancer and Melanoma

BACKGROUND: The endogenous antioxidant system of the skin scavenges reactive oxygen species and combats ultraviolet induced oxidative skin damage. Supporting this cutaneous defense system with topical or oral antioxidants may provide a successful strategy for the treatment and prevention of skin cancer. OBJECTIVE: Review evidence regarding treatment and prevention of melanoma and nonmelanoma skin cancers through dietary and topical antioxidants, vitamins, and herbal supplements. METHODS: Literature review. RESULTS: Review of the literature demonstrates that the administration of synthetic retinoids has not proved beneficial for otherwise healthy patients with nonmelanoma skin cancer. Selenium supplementation has reduced the incidence of several internal malignancies but not of nonmelanoma skin cancer. Synergistic use of beta-carotene with vitamins C and E has demonstrated prophylaxis against reactive oxygen radicals involved in nonmelanoma skin cancer and reduced sunburn reactions significantly. 1,25-dihydroxyvitamin D3 analog CB1093 has demonstrated promise as a therapeutic agent in the regression of the early stages of melanoma in specific cell lines. CONCLUSION: Delivery of exogenous antioxidants in combination appears to be a more successful strategy for enhancing the cutaneous antioxidant system than the administration of isolated antioxidants alone. Vitamin D analogs may have a role in the medical therapy of melanoma. However, avoiding exposure to ultraviolet light appears to be the only true panacea against the development of melanoma and NMSC.     

Non-systemic fungal endophytes in Festuca rubra plants infected by Epichloë festucae in subarctic habitats

Epichloë festucae is an endophytic fungus that infects systemically the aerial tissues of the host grass Festuca rubra. This fungus is transmitted vertically from the mother plant to seeds. Hypothetically, the presence of E. festucae could affect the infection of a plant by other fungal species. This could occur if E. festucae metabolites produced in planta interfere negatively with other fungal infections; or alternatively, if the modulation of plant defenses by the endophyte favour further fungal infections. We have analyzed the presence of culturable non-systemic endophytes in plants of F. rubra infected (E+) and not infected (E?) by E. festucae in two subarctic habitats, meadows and riverbanks in Northern Finland. The observed non-systemic endophyte infection frequencies were similar among E+ and E? plants from riverbanks, and E+ plants from meadows. In contrast to these, the infection frequency was significantly lower in E? plants from meadows. This result suggests that the presence of E. festucae is not a main factor determining the presence of non-systemic endophytes in plants. Instead, plant genetic characteristics related to compatibility with E. festucae and other endophytes in the more stable meadow populations might play a role in these fungus–fungus–plant interactions. As a result of the survey, 18 different taxa of non-systemic endophytes were identified in plants of F. rubra. All were ascomycetes except for one basidiomycete. Three endophytic taxa could not be ascribed to a genus, but sequence data indicated that they were conspecific with other unidentified endophytes that have been isolated in cold biomes at different locations.     

Diversity and significance of fungal endophytes from living stems of naturalized trees from Argentina

Fungal endophytes inhabit healthy tissues of all terrestrial taxa studied to date; however, fungi associated with woody tissue have been frequently overlooked. Here, we examined endophytes associated with healthy living stems of tree species exotic to Argentina (Broussonetia papyrifera, Celtis occidentalis and Ligustrum lucidum) in a natural reserve. To achieve this objective, fungi were induced to develop within the wood by drying sections of branches. For comparison purposes, a study of the organisms present on superficial and inner bark was carried out. Fifty-seven strains belonging to 12 different taxa, dominated by the anamorphic states of ascomycetes, were obtained from the 180 cultured chips. Coprinellus micaceus, Lecythophora hoffmannii and Rhizopus microsporus are cited for the first time as endophytes. Only two taxa appeared on more than one tree species. Assemblages of fungi obtained from each tree species were different and the fungal endophytes isolated were very different from those previously recorded for leaves of the same hosts in the same area. Thus, it is probable that the endophytes exhibit host- and tissue-specificity. Considering three main factors: 1. the invasive nature of two of the selected hosts, 2. the evaluation of woody tissue and 3. the taxonomic identity of the fungal isolations, hypotheses concerning ecological implications are here discussed. In this sense, Broussonetia papyrifera and Ligustrum lucidum could be considered as sources of potential inoculum for native plants, especially in protected areas, and the high diversity of fungal species living within the tissues of the hosts studied suggests their potential as important fungal reservoirs to be taken into account in conservation issues.     

Oxidative stress in relation to surgery: is there a role for the antioxidant melatonin?

During and after surgical procedures, there is a well defined physiological stress response that involves activation of inflammatory, endocrine, metabolic, and immunological mediators. Oxidative stress, which is defined to be a situation where the production of reactive oxygen/nitrogen species exceeds the mechanisms required to detoxify them, is believed to be an integrated part of the surgical stress response. Oxidative stress per se may be associated with complications such as myocardial injury, sepsis, pulmonary edema, kidney and liver failure, and increased mortality. Melatonin is a potent antioxidant and in many studies melatonin has been shown to be more effective than some "classical" antioxidants (e.g., vitamins E and C) in protecting against oxidative/nitrosative stress. There are numerous experimental studies in which the antioxidant properties of melatonin have been proven. In preliminary studies in newborns with asphyxia, sepsis, or respiratory distress syndrome, melatonin has proven to be a highly potent antioxidant. This review summarizes the results of animal and human studies wherein melatonin was shown to modulate oxidative stress; this discussion emphasizes the stress response related to surgery.     

Fungal endophytes: an untapped source of biocatalysts

Horizontally transmitted endophytes are an ecological group of fungi that infect living plant tissues and survive in them without causing any disease symptoms. Even as facets of the endophyte-plant symbiotic relationship are being uncovered, there is an increasing appreciation of the different growth substrates exploited by endophytes and the vast repertoire of secreted enzymes of these fungi. These attributes exemplify the striking biodiversity of fungal endophytes and should motivate bioprospecting these organisms to identify novel biocatalysts that might help address challenges in medicine, food security, energy production and environmental quality.     

Total antioxidant capacity—Relevance,methods and clinical implications

Oxidative stress is pre-empted by an adequate level of antioxidants, which scavenge oxidants when they are produced in excess by different sources, including leukocytes and immature spermatozoa. Enzymatic antioxidants, such as superoxide dismutase, catalase and glutathione peroxidase, and several non-enzymatic antioxidants (proteins, vitamins and minerals), working as oxidant scavengers and cofactors of enzymatic antioxidants have been identified in seminal plasma. The total antioxidant capacity (TAC) is a diagnostic test that can be utilised in the male infertility workup. TAC measures the amount of total antioxidants in seminal plasma. Therefore, it provides an assessment of the reductive potential in seminal plasma. Several studies have investigated the diagnostic application of TAC in various andrology conditions. There is substantial evidence in the literature to show that infertile patients have lower seminal TAC in comparison with fertile men. Moreover, there is a positive correlation between TAC and seminal parameters, such as sperm concentration, motility and morphology. Evaluation of TAC together with reactive oxygen species (ROS) and sperm DNA fragmentation index (DFI) may be beneficial in the diagnosis of male infertility.