Mutation in a homolog of yeast Vps53p accounts for the heat and osmotic hypersensitive phenotypes in Arabidopsis hit1-1 mutant

Previously, the growth of Arabidopsis hit1-1 (heat-intolerant) mutant was found to be inhibited by both heat and water stress (Wu et al. in J Plant Physiol 157:543–547, 2000). In order to determine the genetic mutation underlying the hit1-1 phenotype, map-based cloning of HIT1 gene was conducted. Transformation of the hit1-1 mutant with a HIT1 cDNA clone reverts the mutant to the heat tolerance phenotype, confirming the identity of HIT1. Sequence analysis revealed the HIT1 gene encodes a protein of 829 amino acid residues and is homologous to yeast (Saccharomyces cerevisiae) Vps53p protein. The yeast Vps53p protein has been shown to be a tethering factor that associates with Vps52p and Vps54p in a complex formation involved in the retrograde trafficking of vesicles to the late Golgi. An Arabidopsis homolog of yeast Vps52p has previously been identified and mutation of either the homolog or HIT1 by T-DNA insertion resulted in a male-specific transmission defect. The growth of yeast vps53Δ null mutant also shows reduced thermotolerance, and expression of HIT1 in this mutant can partially complement the defect, supporting the possibility of a conserved biological function for Vps53p and HIT1. Collectively, the hit1-1 is the first mutant in higher plant linking a homolog of the vesicle tethering factor to both heat and osmotic stress tolerance.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Transcriptomic and biochemical effects of pycnogenol in ameliorating heat stress-related oxidative alterations in rats

BackgroundHeat stress is a condition that is due to extreme heat exposure. It occurs when the body cannot keep its temperature healthy in response to a hot climate and associated with oxidative stress. Testicular hyperthermia can induce apoptosis of sperm cells, affect sperm production and decrease sperm concentration, leading to sperm disorder, for this reason, we examined the protective impact of pycnogenol that it has a wide range of biological benefits, including antioxidant, anti-inflammatory and anti-cancer activities against the oxidative alterations that happen in testicular and brain tissues due to heat stress in rats.Study designForty-eight Wistar male rats, approximately around 6 weeks age were allocated randomly into four groups (12 in each) of control, HS (subjected to heat stress and supplemented orally with 50 mg of pycnogenol/kg b. w./day dissolved in saline for 21 days), and pycnogenol (rats supplemented orally with 50 mg of pycnogenol/kg b. w./day dissolved in saline for 21 days).ResultsData revealed a promising role of pycnogenol as an antioxidant, natural product to successfully reverse the heat-induced oxidative alterations in testicular and brain tissues of rats through significant upregulation of superoxide dismutase-2, catalase, reduced glutathione, and anti-apoptotic gene, while downregulating pro-apoptotic, and heat shock protein70. Pycnogenol treatment also reversed the reproductive hormone level and spermatogenesis to their normal values.ConclusionPycnogenol as a natural protective supplement could recover these heat stress-induced oxidative changes in testes and hypothalamus.     

Stress tolerance in a yeast sterol auxotroph: role of ergosterol, heat shock proteins and trehalose

The role of ergosterol in yeast stress tolerance, together with heat shock proteins (hsps) and trehalose, was examined in a sterol auxotrophic mutant of Saccharomyces cerevisiae. Ergosterol levels paralleled viability data, with cells containing higher levels of the sterol exhibiting greater tolerances to heat and ethanol. Although the mutant synthesised hsps and accumulated trehalose upon heat shock to the same levels as the wild-type cells, these parameters did not relate to stress tolerance. These results indicate that the role of ergosterol in stress tolerance is independent of hsps or trehalose.     

Mitigation of adverse effects of heat stress on Vicia faba by exogenous application of magnesium

The effects of magnesium (Mg) supplementation on the growth performance, oxidative damage, DNA damage, and photosynthetic pigment synthesis, as well as on the activity level of carbonic anhydrase (CA), ribulose-1,5-bisphosphate carboxylase (Rubisco), and antioxidant enzymes were studied in Vicia faba L. plants exposed to heat stress (HS) and non-heat-stress (non-HS) conditions. Seeds were grown in pots containing a 1:1 mixture of sand and peat, with Mg treatments. The treatments consisted of (i) 0 Mg and non-HS (ambient temperature; control); (ii) 50 mM Mg; (iii) HS (38 °C); and (iv) 50 mM Mg and HS (38 °C). HS was imposed by placing potted plants in an incubator at 38 °C for 48 h. Growth attributes, total chlorophyll (Total Chl), and CA, and Rubisco activity decreased in plants subjected to HS, whereas accumulation of organic solutes [proline (Pro) and glycine betaine (GB)]; superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activity; DNA damage; electrolyte leakage (EL); and malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) content all increased. Application of Mg, however, significantly enhanced further proline (Pro), glycinebetaine (GB), SOD, POD, and CAT activity, and decreased DNA damage, EL, and MDA and H₂O₂ concentrations. These results suggest that adequate supply of Mg is not only essential for plant growth and development, but also improves plant tolerance to HS by suppressing cellular damage induced by reactive oxygen species through the enhancement of the accumulation of Pro and GB, and the actions of antioxidant enzymes.     

Ultradian rhythm of trehalose levels coupled to heat resistance in continuous cultures of the yeast Saccharomyces cerevisiae

Heat resistance appears to cycle in concert with energy metabolism in continuous culture of the yeast Saccharomyces cerevisiae. To study the mechanism of this oscillation, the authors first examined if heat shock proteins (Hsps) are involved. Neither the protein levels of major Hsps nor the expression of the β-galactosidase gene as a reporter under the control of the promoter carrying heat-shock element oscillated during the metabolic oscillation. The level of trehalose in yeast cycled with the same periodicity, as did energy metabolism. This oscillation was not found in a GTS1-deleted mutant that also did not show cyclic changes in heat resistance. These results suggest that heat resistance oscillation is induced by fluctuations in trehalose level and not by an oscillatory expression of Hsps. The increase in trehalose began at the start of the respiro-fermentative phase and the decrease began after the elevation of the cyclic adenosine monophosphate (cAMP) level. The authors hypothesize that the synthesis of trehalose parallels the activation of the glycolytic pathway and that trehalose is degraded by trehalase activated by cAMP coupled with the metabolic oscillation in the continuous culture of yeast.     

Influence of magnesium ions on heat shock and ethanol stress responses of Saccharomyces cerevisiae

This study has highlighted the role of magnesium ions in the amelioration of the detrimental effects of ethanol toxicity and temperature shock in a winemaking strain of Saccharomyces cerevisiae. Specifically, results based on measurements of cellular viability and heat shock protein synthesis together with scanning electron microscopy have shown that, by increasing the bioavailability of magnesium ions, physiological protection is conferred on yeast cells. Elevating magnesium levels in the growth medium from 2 to 20 mM results in repression of certain heat shock proteins following a typical heat shock regime (30–42°C shift). Seed inocula cultures prepropagated in elevated levels of magnesium (i.e. ‘preconditioned’) also conferred thermotolerance on cells and repressed the biosynthesis of heat shock proteins. Similar results were observed in response to ethanol stress. Extra- and intracellular magnesium may both act in the physiological stress protection of yeast cells and this approach offers potential benefits in alcoholic fermentation processes. The working hypothesis based on our findings is that magnesium protects yeast cells by preventing increases in cell membrane permeability elicited by ethanol and temperature-induced stress.     

Ultradian rhythm of trehalose levels coupled to heat resistance in continuous cultures of the yeast Saccharomyces cerevisiae

Heat resistance appears to cycle in concert with energy metabolism in continuous culture of the yeast Saccharomyces cerevisiae. To study the mechanism of this oscillation, the authors first examined if heat shock proteins (Hsps) are involved. Neither the protein levels of major Hsps nor the expression of the β-galactosidase gene as a reporter under the control of the promoter carrying heat-shock element oscillated during the metabolic oscillation. The level of trehalose in yeast cycled with the same periodicity, as did energy metabolism. This oscillation was not found in a GTS1-deleted mutant that also did not show cyclic changes in heat resistance. These results suggest that heat resistance oscillation is induced by fluctuations in trehalose level and not by an oscillatory expression of Hsps. The increase in trehalose began at the start of the respiro-fermentative phase and the decrease began after the elevation of the cyclic adenosine monophosphate (cAMP) level. The authors hypothesize that the synthesis of trehalose parallels the activation of the glycolytic pathway and that trehalose is degraded by trehalase activated by cAMP coupled with the metabolic oscillation in the continuous culture of yeast.     

Molecular events associated with acquisition of heat tolerance by the yeast Saccharomyces cerevisiae

Abstract: The heat shock response is an inducible protective system of all living cells. It simultaneously induces both heat shock proteins and an increased capacity for the cell to wisthstand potentially lethal temperatures (an increased thermotolerance). This has lead to the suspicion that these two phenomena must be inexorably linked. However, analysis of heat shock protein function in Saccharomyces cerevisiae by molecular genetic techniques has revealed only a minority of the heat shock proteins of this organism having appreciable influences on thermotolerance. Instead, physiological perturbations and the accumulation of trehalose with heat stress may be more important in the development of thermotolerance during a preconditioning heat shock. Vegetative S. cerevisiae also acquires thermotolerance through osmotic dehydration, through treatment with certain chemical agents and when, due to nutrient limitation, it arrests growth in the GI phase of the cell cycle. There is evidence for the activities of the cAMP-dependent protein kinase and plasma membrane ATPase being very important in thermotolerance determination. Also, intracellular water activity and trehalose probably exert a strong influence over thermotolerance through their effects on stabilisation of membranes and intracellular assemblies. Future investigations should address the unresolved issue of whether the different routes to thermotolerance induction cause a common change to the physical state of the intracellular environment, a change that may result in an increased stabilisation of cellular structures through more stable hydrogen bonding and hydrophobic interactions.     

Clearance of yeast prions by misfolded multi-transmembrane proteins

Accumulation of misfolded proteins in the endoplasmic reticulum (ER) induces the stress response to protect cells against toxicity by the unfolded protein response (UPR), heat shock response (HSR), and ER-associated degradation pathways. Here, we found that over-production of C-terminally truncated multi-transmembrane (MTM) mutant proteins triggers HSR, but not UPR, and clearance of yeast prions [PSI⁺] and [URE3]. One of the mutant MTM proteins, Dip5ΔC-v82, produces a disabled amino-acid permease. Fluorescence microscopy analysis revealed abnormal accumulation of Dip5ΔC-v82 in the ER. Importantly, the mutant defective in the GET pathway, which functions for ER membrane insertion of tail-anchored proteins, failed to translocate Dip5ΔC-v82 to the ER and disabled Dip5ΔC-v82-mediated prion clearance. These findings suggest that the GET pathway plays a pivotal role in quality assurance of MTM proteins, and entraps misfolded MTM proteins into ER compartments, leading to loss-of-prion through a yet undefined mechanism.     

Induction of barotolerance by heat shock treatment in yeast

In Saccharomyces cerevisiae, heat shock treatment provides protection against subsequent hydrostatic pressure damage. Such an induced hydrostatic pressure resistance (barotolerance) closely resembles the thermotolerance similarly induced by heat shock treatment. The parallel induction of barotolerance and thermotolerance by heat shock suggests that hydrostatic pressure and high temperature effects in yeast may be tightly linked physiologically.     

Effect of feeding Saccharomyces Cerevisiae on performance of dairy cows during summer heat stress

Effects of feeding a culture of Saccharomyces cerevisiae to lactating cows on their lactational performance during heat stress were determined. Multiparous Holstein cows (n = 723) calving during the summer months from two dairy farms were randomly assigned to a diet containing no yeast culture (control; n = 361) or 30 g/d of a S. cerevisiae yeast culture (YC; n = 362) fed from 20 to 140 d in milk (DIM). Cows were milked twice daily and the production of milk and milk components was measured every 2 weeks. Dry matter (DM) intakes from 6 pens were measured daily and pen temperature and humidity were evaluated hourly from June to November. Rectal temperature was measured in 88 cows (22/treatment/farm), once weekly, and blood was sampled from a subset of 120 cows at 58 and 100 DIM for measurements of plasma glucose, nonesterified fatty acids, 3-OH-butyrate, insulin, and urea N concentrations. Daily temperature, humidity and the temperature-humidity index in the study pens did not differ between treatments, and rectal temperature of cows in the control and YC treatments differed with days postpartum. Intake of DM was similar between diets, but cows fed YC produced 1.2 kg/d more milk, more milk true protein, solids-not-fat and lactose than that produced by control cows. However, energy-corrected milk yield, and concentrations of true protein, solids-not-fat and lactose did not differ between treatments. Feeding YC did not influence plasma metabolites, insulin, or body condition score of cows, but urea N concentrations were reduced. Feeding a yeast culture of S. cerevisiae improved yields of milk and milk components in heat-stressed multiparous Holstein cows.     

Influence of selenium sources on age-related and mild heat stress-related changes of blood and liver glutathione redox cycle in broiler chickens (Gallus domesticus)

Selenium is an essential trace element that up-regulates a major component of the antioxidant defense mechanism by controlling the body's glutathione (GSH) pool and its major Se-containing antioxidant enzyme, glutathione peroxidase (GPX). Evidence has emerged suggesting that organic selenium, natural seleno-amino acids found in plants, grains and selenized yeast, maintains the antioxidant defense system more efficiently than inorganic selenium. Inorganic selenium is a pro-oxidant, whereas organic selenium possesses antioxidant properties itself. As a pro-oxidant, inorganic selenium is not suitable for animals or humans. Therefore, we examined the GSH–GPX system in broiler chickens and determined that organic selenium was indeed more beneficial than inorganic selenium. Chickens fed the organic selenium as Sel-Plex^®, a selenized yeast, had elevated GPX activity in both blood and liver in a thermoneutral environment and after heat distress. More importantly, the ability to reduce the oxidized glutathione (GSSG to 2 GSH) was enhanced and facilitated by maintenance of glutathione reductase activity. Organic selenium-fed chickens were less affected by mild heat distress than inorganic selenium-fed chickens, and this assessment was based upon less induction of heat shock protein 70 (hsp70) in organic selenium-fed chickens. Our results clearly show that heat distress, a potent inducer of oxidative stress and hsp70, can be partially ameliorated by feeding organic selenium. We attribute this observation to an enhanced GSH–GPX antioxidant system in organic selenium-fed chickens.     

Thermal acclimation of broiler birds by intermittent heat exposure

Heat stress impairs the performance of broilers which increases the economic losses. Effect of duration of heat exposure on performance and acclimatory responses in broiler birds was investigated. At 21 d of age 160 Hubbard birds (80 males+80 females) were equally distributed into 5 treatments (T). The T1, T2, T3 and T4 were acclimated by daily exposure to heat (38±1 °C, 62±2% RH) for 1, 2, 3 and 4 h/d, respectively, for 14 d. T0 was the non-acclimated control (kept at 22±2 °C, 65±2% RH). At 36 d of age the thermotolerance of all birds was evaluated under simulated heat wave conditions by exposing them to an acute heat stress (43±1 °C, 55±3% RH) for 4 h. Body weight (BW), average daily gain (ADG) and average daily feed intake (ADFI) were not affected in T2 and T3, while T3 and T4 showed significant reductions in BW, ADG and ADFI compared to the control. Daily changes in ADFI/kg of metabolic BW (ADFI/BW^0.75), rectal temperature (Tr), rate of increase in rectal temperature (RITr) and evaporative water loss (EWL) showed biphasic patterns of acclimatory responses. The 2 phases were distinctly differentiated by plateau days. Phase 1 characterized by a sharp decline in ADFI/BW^0.75 followed by a gradual increase until the plateau, while Tr, RITr and EWL increased sharply followed by gradual decreases until the plateau. Beyond the plateau (phase 2), homeostatic responses in ADFI/BW^0.75, Tr, RITr and EWL were observed toward the end of the study. Acclimated birds were able to withstand the simulated heat wave with 0% mortality, lower Tr, and longer survival time compared to the control. In conclusion, acclimation could protect birds from acute heat waves and associated heat stress mortality until marketing age. However, applicability of these results towards the industry needs further investigations.     

Phosphorylation of the GTS1 gene product of the yeast Saccharomyces cerevisiae and its effect on heat tolerance and flocculation

The GTS1 gene from the yeast Saccharomyces cerevisiae showed pleiotropic effects on yeast phenotypes, including an increase of heat tolerance in stationary-phase cells and an induction of flocculation. Here, we found that the GTS1 product, Gts1p, was partially phosphorylated at some serine residue(s) in cells grown on glucose. Studies using mutants of protein kinase A (PKA) and CDC25, the Ras-GTP exchange activator, showed that PKA positively regulated the phosphorylation level of Gts1p. Overexpression of Gts1p in a mutant with attenuated PKA activity did not show any increase of heat tolerance and partially decreased flocculation inducibility, suggesting that phosphorylation of Gts1p is required for induction of these phenomena.