Ambient Growth Temperature Research Articles

Warm temperature-triggered developmental reprogramming requires VIL1-mediated, genome-wide H3K27me3 accumulation in Arabidopsis.

Changes in ambient temperature immensely affect developmental programs in many species. Plants adapt to high ambient growth temperature in part by vegetative and reproductive developmental reprogramming, known as thermo-morphogenesis. Thermo-morphogenesis is accompanied by massive changes in the transcriptome upon temperature change. Here, we show that transcriptome changes induced by warm ambient temperature require VERNALIZATION INSENSITIVE 3-LIKE 1 (VIL1), a facultative component of the Polycomb repressive complex PRC2, in Arabidopsis. Warm growth temperature elicits genome-wide accumulation of H3K27me3 and VIL1 is necessary for the warm temperature-mediated accumulation of H3K27me3. Consistent with its role as a mediator of thermo-morphogenesis, loss of function of VIL1 results in hypo-responsiveness to warm ambient temperature. Our results show that VIL1 is a major chromatin regulator in responses to high ambient temperature.

Morpho-physiological characterization of two wheat genotypes with contrasting trait of heat tolerance

Various biotic and abiotic stresses adversely affect crop yield across the globe. Wheat is cool-season cereal crop and sensitive to rise in ambient growth temperature. Ninety genotypes were screened under heat stress and non-heat stress locations. Low heat susceptibility index of <0.5 for HD2189, N5643, Kenphad39, HD2501, NI179, NI5439, HS240, HD2428 and HD2687 indicated that they are heat tolerant and high susceptibility index of >1.5 for PBN142, NI9947, HD2320, GW190, HD2135, NI917 and Batavia indicated that they are heat susceptible. Based on grain yield and heat susceptibility index, two genotypes namely HD2189 and Batavia with contrasting response to heat stress were selected for the further studies. Their morphological and physiological characterization was carried out at seedling stage using 22°C as control and 33°C as heat stress. Under heat stress conditions, reduction for seedling growth traits, relative water content (RWC) and membrane thermostability (MTS) was less in HD2189 (25.3%, 10.2%, 13%) compared to Batavia (55.3%, 34.4%, 30%). HD2189 maintained lower canopy temperature with depression values in the range of 3.75 to 8°C compared to Batavia (2.82 to 5.10°C). The conversion of source to sink was better for HD2189 as displayed by translocated dry matter (TDM), translocation efficiency (TE), contribution of plant assimilates (CPA), longer duration of grain filling, grain yield and yield components under high temperature. Trend for electron transport rate of PSII (ETRII) and effective quantum yield (YII) for both the varieties at 22°C and 33°C was similar. However, Batavia plants were adjusting through non-regulated heat dissipation indicating damage to the photosynthetic apparatus whereas HD2189 showed higher regulated heat dissipation. Thus, genotype HD2189 showed heat tolerance at seedling and adult plant stages compared to Batavia.

Cold-inducible expression of an Arabidopsis thaliana AP2 transcription factor gene, AtCRAP2, promotes flowering under unsuitable low-temperatures in chrysanthemum

Flowering time is regulated by biotic and abiotic stresses and affected by the ambient temperature. For chrysanthemum, a low ambient growth temperature can cause a flowering delay, which limits the annual commercial production. Therefore, it is important to improve the low-temperature flowering capability of chrysanthemum through genetic modifications. Here, we isolated a natural variation of a CRT/DRE-binding factor (CBF/DREB) 3 gene, CRAP2, from the Arabidopsis thaliana accession Condara (190AV) that encodes a stop codon at position 151 of the CBF3 protein. Unlike AtCBF3, the overexpression AtCRAP2 in Arabidopsis did not cause detectable growth retardation nor delayed flowering and it conferred cold tolerance. The cold-inducible expression of AtCRAP2 in chrysanthemum promoted flowering under short-day conditions with a low 15 °C nighttime temperature. RNA-sequencing of rd29A:AtCRAP2 and qRT-PCR assays of flowering time-related genes and AtCRAP2 expressed at an ambient temperature revealed that AtCRAP2 positively affected SOC1 and FTL3, thereby promoting flowering under low temperature stress and short-day conditions. These results indicate that DREB genes can be used in the genetic engineering of crop plants without accompanying negative effects by modifying the encoded proteins’ C termini.

Contribution of major FLM isoforms to temperature-dependent flowering in Arabidopsis thaliana.

FLOWERING LOCUS M (FLM), a component of the thermosensory flowering time pathway in Arabidopsis thaliana, is regulated by temperature-dependent alternative splicing (AS). The main splicing variant, FLM-β, is a well-documented floral repressor that is down-regulated in response to increasing ambient growth temperature. Two hypotheses have been formulated to explain how flowering time is modulated by AS of FLM. In the first model a second splice variant, FLM-δ, acts as a dominant negative isoform that competes with FLM-β at elevated ambient temperatures, thereby indirectly promoting flowering. Alternatively, it has been suggested that the induction of flowering at elevated temperatures is caused only by reduced FLM-β expression. To better understand the role of the two FLM splice forms, we employed CRISPR/Cas9 technology to specifically delete the exons that characterize each splice variant. Lines that produced repressive FLM-β but were incapable of producing FLM-δ were late flowering. In contrast, FLM-β knockout lines that still produced FLM-δ flowered early, but not earlier than the flm-3 loss of function mutant, as would be expected if FLM-δ had a dominant-negative effect on flowering. Our data support the role of FLM-β as a flower repressor and provide evidence that a contribution of FLM-δ to the regulation of flowering time in wild-type A. thaliana seems unlikely.

Fabrication of Sb-doped p-type ZnO Thin Films by Pulsed Laser Deposition

In this work, antimony (Sb)-doped p-type ZnO thin films on c-plane sapphire substrates have been fabricated by pulsed laser deposition, with Sb2O3 used as the dopant source. The effects of ambient gas or growth temperature on the fabrication process were investigated. The nitrogen ambient was found to be essential to achieve the p-type conduction. The Hall-effect measurements at room temperature indicated that the ZnO thin films doped with 3 at.% Sb and grown at 600 °C under N2 atmosphere exhibited p-type behavior with a hole concentration of 1.17×1017 cm−3, hole mobility of 0.63 cm2/V·s, and resistivity of 84.51 Ω·cm. X-ray diffraction and scanning electron microscopy revealed good crystallization and homogenous surface morphology of the ZnO:Sb thin films. The optical transmission spectrum of the ZnO:Sb thin films indicated that the energy band gap value was around 2.9 eV. Post-growth annealing at 650 oC converted the p-type conduction to n-type. This result implied that Sb-doping and annealing treatment were dominant factors determining native and extrinsic defects in the ZnO thin films, and thus controlling their electrical conductivity properties.

SHORT VEGETATIVE PHASE Up-Regulates TEMPRANILLO2 Floral Repressor at Low Ambient Temperatures.

Plants integrate day length and ambient temperature to determine the optimal timing for developmental transitions. In Arabidopsis (Arabidopsis thaliana), the floral integrator FLOWERING LOCUS T (FT) and its closest homolog TWIN SISTER OF FT promote flowering in response to their activator CONSTANS under long-day inductive conditions. Low ambient temperature (16°C) delays flowering, even under inductive photoperiods, through repression of FT, revealing the importance of floral repressors acting at low temperatures. Previously, we have reported that the floral repressors TEMPRANILLO (TEM; TEM1 and TEM2) control flowering time through direct regulation of FT at 22°C. Here, we show that tem mutants are less sensitive than the wild type to changes in ambient growth temperature, indicating that TEM genes may play a role in floral repression at 16°C. Moreover, we have found that TEM2 directly represses the expression of FT and TWIN SISTER OF FT at 16°C. In addition, the floral repressor SHORT VEGETATIVE PHASE (SVP) directly regulates TEM2 but not TEM1 expression at 16°C. Flowering time analyses of svp tem mutants indicate that TEM may act in the same genetic pathway as SVP to repress flowering at 22°C but that SVP and TEM are partially independent at 16°C. Thus, TEM2 partially mediates the temperature-dependent function of SVP at low temperatures. Taken together, our results indicate that TEM genes are also able to repress flowering at low ambient temperatures under inductive long-day conditions.

Fabrication of Sb-doped p-type ZnO Thin Films by Pulsed Laser Deposition

In this work, antimony (Sb)-doped p-type ZnO thin films on c-plane sapphire substrates have been fabricated by pulsed laser deposition, with Sb2O3 used as the dopant source. The effects of ambient gas or growth temperature on the fabrication process were investigated. The nitrogen ambient was found to be essential to achieve the p-type conduction. The Hall-effect measurements at room temperature indicated that the ZnO thin films doped with 3 at.% Sb and grown at 600 °C under N2 atmosphere exhibited p-type behavior with a hole concentration of 1.17×1017 cm−3, hole mobility of 0.63 cm2/V·s, and resistivity of 84.51 Ω·cm. X-ray diffraction and scanning electron microscopy revealed good crystallization and homogenous surface morphology of the ZnO:Sb thin films. The optical transmission spectrum of the ZnO:Sb thin films indicated that the energy band gap value was around 2.9 eV. Post-growth annealing at 650 oC converted the p-type conduction to n-type. This result implied that Sb-doping and annealing treatment were dominant factors determining native and extrinsic defects in the ZnO thin films, and thus controlling their electrical conductivity properties.

Global convergence in leaf respiration from estimates of thermal acclimation across time and space.

Recent compilations of experimental and observational data have documented global temperature-dependent patterns of variation in leaf dark respiration (R), but it remains unclear whether local adjustments in respiration over time (through thermal acclimation) are consistent with the patterns in R found across geographical temperature gradients. We integrated results from two global empirical syntheses into a simple temperature-dependent respiration framework to compare the measured effects of respiration acclimation-over-time and variation-across-space to one another, and to a null model in which acclimation is ignored. Using these models, we projected the influence of thermal acclimation on: seasonal variation in R; spatial variation in mean annual R across a global temperature gradient; and future increases in R under climate change. The measured strength of acclimation-over-time produces differences in annual R across spatial temperature gradients that agree well with global variation-across-space. Our models further project that acclimation effects could potentially halve increases in R (compared with the null model) as the climate warms over the 21st Century. Convergence in global temperature-dependent patterns of R indicates that physiological adjustments arising from thermal acclimation are capable of explaining observed variation in leaf respiration at ambient growth temperatures across the globe.

Control of flowering by ambient temperature.

The timing of flowering is a crucial decision in the life cycle of plants since favourable conditions are needed to maximize reproductive success and, hence, the survival of the species. It is therefore not surprising that plants constantly monitor endogenous and environmental signals, such as day length (photoperiod) and temperature, to adjust the timing of the floral transition. Temperature in particular has been shown to have a tremendous effect on the timing of flowering: the effect of prolonged periods of cold, called the vernalization response, has been extensively studied and the underlying epigenetic mechanisms are reasonably well understood in Arabidopsis thaliana. In contrast, the effect of moderate changes in ambient growth temperature on the progression of flowering, the thermosensory pathway, is only starting to be understood on the molecular level. Several genes and molecular mechanisms underlying the thermosensory pathway have already been identified and characterized in detail. At a time when global temperature is rising due to climate change, this knowledge will be pivotal to ensure crop production in the future.

Oxygen isotopes and MgCO3 in brachiopod calcite and a new paleotemperature equation

Modern brachiopods and their ambient seawater, compiled from 34 localities, covering shallow-waters from the poles to the tropics were analyzed for their oxygen isotopic compositions, and SrCO3 and MgCO3 contents. If the routine seawater δ18O composition and the ‘MgCO3 effect’ on oxygen isotopes are considered in calculations, calcification temperatures are concordant with measured ambient seawater temperatures. The SrCO3 contents of modern brachiopods appear to be unrelated to ambient growth temperatures, while their MgCO3 contents exhibit some relationship with temperature and growth rate, controlled, in part, by ambient productivity or clearance rates or local environment, and by taxonomic affinity such as presence or absence of caeca.Linear least-squares regression analysis yields a new oxygen isotope paleotemperature equation for brachiopod calcite, which makes adjustment for shell MgCO3 contents, and covers habitats with water temperatures ranging from −2° to +32°C:T°C=16.192–3.468δc–δSW–MgcN=319,R2=0.98.The Mg-effect adjustment is based on the change in shell-calcite δ18O by +0.17‰ per mol% MgCO3 (Jiménez-López et al., 2004). This adjustment is critical to the determination of calcification temperatures for modern articulated brachiopods, especially the ones from cold and warm water habitats, and/or the ones with exceptionally low or high MgCO3 contents, which otherwise may be offset (lower or higher) by as much as 7°C. Furthermore, this adjustment may be critical for fossil brachiopods and other marine calcitic invertebrates with variable MgCO3 contents, and when using their δ18O and ∆47 for determining ancient seawater δ18O compositions and temperatures.

Temperature-dependent regulation of flowering by antagonistic FLM variants

The appropriate timing of flowering is crucial for plant reproductive success. It is therefore not surprising that intricate genetic networks have evolved to perceive and integrate both endogenous and environmental signals, such as carbohydrate and hormonal status, photoperiod and temperature. In contrast to our detailed understanding of the vernalization pathway, little is known about how flowering time is controlled in response to changes in the ambient growth temperature. In Arabidopsis thaliana, the MADS-box transcription factor genes FLOWERING LOCUS M (FLM) and SHORT VEGETATIVE PHASE (SVP) have key roles in this process. FLM is subject to temperature-dependent alternative splicing. Here we report that the two main FLM protein splice variants, FLM-β and FLM-δ, compete for interaction with the floral repressor SVP. The SVP-FLM-β complex is predominately formed at low temperatures and prevents precocious flowering. By contrast, the competing SVP-FLM-δ complex is impaired in DNA binding and acts as a dominant-negative activator of flowering at higher temperatures. Our results show a new mechanism that controls the timing of the floral transition in response to changes in ambient temperature. A better understanding of how temperature controls the molecular mechanisms of flowering will be important to cope with current changes in global climate.

Electrical, optical and structural properties of Al-doped ZnO thin films grown on GaAs(111)B substrates by pulsed laser deposition

We report on the characteristics of Al-doped ZnO thin films (AZO) grown on GaAs(111)B substrates using pulsed laser deposition. The influence of ambient gas composition, overall pressure, and growth temperature on the electrical, structural and optical properties of 100nm-thin films grown from a ZnO target with 2wt.% Al were investigated. Growth in a 1Pa pure O2 ambient was found to be superior to films grown in Ar ambient or vacuum with respect to their electrical properties. As-grown AZO films showed a low resistivity on the order of 10−4Ωcm. Post-deposition annealing in-situ showed no improvement of the transport properties, irrespective of annealing temperature and ambient gas. At high substrate temperatures, the interaction with the GaAs(111)B substrate seemed to affect the growth and conductivity of the AZO films.

Acclimation of photosynthesis in a boreal grass (Phalaris arundinacea L.) under different temperature, CO<sub>2</sub>, and soil water regimes

The aim of this work was to study the acclimation of photosynthesis in a boreal grass (Phalaris arundinacea L.) grown in controlled environment chambers under elevated temperature (ambient + 3.5°C) and CO2 (700 μmol mol−1) with varying soil water regimes. More specifically, we studied, during two development stages (early: heading; late: florescence completed), how the temperature response of light-saturated net photosynthetic rate (Psat), maximum rate of ribulose-1,5-bisphosphate carboxylase/oxygenase activity (Vcmax) and potential rate of electron transport (Jmax) acclimatized to the changed environment. During the early growing period, we found a greater temperature-induced enhancement of Psat at higher measurement temperatures, which disappeared during the late stage. Under elevated growth temperature, Vcmax and Jmax at lower measurement temperatures (5–15°C) were lower than those under ambient growth temperature during the early period. When the measurements were done at 20–30°C, the situation was the opposite. During the late growing period, Vcmax and Jmax under elevated growth temperature were consistently lower across measurement temperatures. CO2 enrichment significantly increased Psat with higher intercellular CO2 compared to ambient CO2 treatment, however, elevated CO2 slightly decreased Vcmax and Jmax across measurement temperatures, probably due to down-regulation acclimation. For two growing periods, soil water availability affected the variation in photosynthesis and biochemical parameters much more than climatic treatment did. Over two growing periods, Vcmax and Jmax were on average 36.4 and 30.6%, respectively, lower with low water availability compared to high water availability across measurement temperatures. During the late growing period, elevated growth temperature further reduced the photosynthesis under low water availability. Vcmax and Jmax declined along with the decrease in nitrogen content of leaves as growing period progressed, regardless of climatic treatment and water regime. We suggest that, for grass species, seasonal acclimation of the photosynthetic parameters under varying environmental conditions needed to be identified to fairly estimate the whole-life photosynthesis.

Compound‐specific differences in 13C of soluble carbohydrates in leaves and phloem of 6‐month‐old Eucalyptus globulus (Labill)

Movement of photoassimilates from leaves to phloem is an important step for the flux of carbon through plants. Fractionation of carbon isotopes during this process may influence their abundance in heterotrophic tissues. We subjected Eucalyptus globulus to 20, 25 and 28 °C ambient growth temperatures and measured compound-specific δ(13)C of carbohydrates obtained from leaves and bled phloem sap. We compared δ(13)C of sucrose and raffinose obtained from leaf or phloem and of total leaf soluble carbon, with modelled values predicted by leaf gas exchange. Changes in δ(13)C of sucrose and raffinose obtained from either leaves or phloem sap were more tightly coupled to changes in c(i)/c(a) than was δ(13)C of leaf soluble carbon. At 25 and 28 °C, sucrose and raffinose were enriched in (13)C compared to leaf soluble carbon and predicted values - irrespective of tissue type. Phloem sucrose was depleted and raffinose enriched in (13)C compared to leaf extracts. Intermolecular and tissue-specific δ(13)C reveal that multiple systematic factors influence (13)C composition during export to phloem. Predicting sensitivity of these factors to changes in plant physiological status will improve our ability to infer plant function at a range of temporal and spatial scales.

Ambient temperature signaling in plants: An emerging field in the regulation of flowering time

Plants show remarkable developmental plasticity to survive in a continually changing environment. One example is their capability to adjust flowering time in response to environmental changes. Ambient growth temperature, which is strongly affected by global temperature changes, has a profound effect on flowering time. However, those effects have been largely ignored in research. Recent molecular genetic studies ofArabidopsis as a model system have implicated several genes, and have identified a molecular mechanism underlying the responses of plants to changes in ambient temperature. Here, we describe recent discoveries related to ambient temperature signaling and the control of flowering time inArabidopsis. We also discuss current perspectives on how plants sense and respond to such changes.

Intrinsically disordered protein from a pathogenic mesophile Mycobacterium tuberculosis adopts structured conformation at high temperature

Compared to eukaryotes, the occurrence of "intrinsically disordered" or "natively unfolded" proteins in prokaryotes has not been explored extensively. Here, we report the occurrence of an intrinsically disordered protein from the mesophilic human pathogen Mycobacterium tuberculosis. The Histidine-tagged recombinant Rv3221c biotin-binding protein is intrinsically disordered at ambient and physiological growth temperatures as revealed by circular dichroism and Fourier transform infrared (FTIR) spectroscopic studies. However, an increase in temperature induces a transition from disordered to structured state with a folding temperature of approximately 53 degrees C. Addition of a structure inducing solvent trifluoroethanol (TFE) causes the protein to fold at lower temperatures suggesting that TFE fosters hydrophobic interactions, which drives protein folding. Differential Scanning Calorimetry studies revealed that folding is endothermic and the transition from a disordered to structured state is continuous (higher-order), implying existence of intermediates during folding process. Secondary structure analysis revealed that the protein has propensity to form beta-sheets. This is in conformity with FTIR spectrum that showed an absorption peak at wave number of 1636 cm(-1), indicative of disordered beta-sheet conformation in the native state. These data suggest that although Rv3221c may be disordered under ambient or optimal growth temperature conditions, it has the potential to fold into ordered structure at high temperature driven by increased hydrophobic interactions. In contrast to the generally known behavior of other intrinsically disordered proteins folding at high temperature, Rv3221c does not appear to oligomerize or aggregate as revealed through numerous experiments including Congo red binding, Thioflavin T-binding, turbidity measurements, and examining molar ellipticity as a function of protein concentration. The amino acid composition of Rv3221c reveals that it has 24% charged and 54.9% hydrophobic amino acid residues. In this respect, this protein, although belonging to the class of intrinsically disordered proteins, has distinct features. The intrinsically disordered state and the biotin-binding feature of this protein suggest that it may participate in many biochemical processes requiring biotin as a cofactor and adopt suitable conformations upon binding other folded targets.

Heat stress in wheat ( Triticum aestivum L.): Effects on grain growth and quality traits

Heat stress effects on grain dry mass and quality were studied in spring wheat genotypes ( Triticum aestivum L.). Three cultivars were chosen with respect to heat tolerance: Lavett (genotype 1), selected for temperate growing conditions and two CIMMYT cultivars, Ciano-79 (genotype 2) and Attila (genotype 3), respectively heat sensitive and heat tolerant varieties for warm environments. Plants were grown in pots at two different day/night temperatures (18/13 and 25/20 °C) in climate-controlled glasshouses and exposed to a 3-day heat shock during the grain-filling phase. To investigate its effect on quality and yield the following traits were included: grain dry mass, flour protein concentration, glutenin macro polymer (GMP) fraction, glutenin particle size, and particle size distribution. The magnitude in which a heat shock during grain filling affects quality and yield depends on the heat tolerance of genotypes and the preceding ambient growth temperature. As expected, the responses to heat varied between and within genotypes; on the one hand grain size and dry mass decreased, on the other hand, protein related traits were improved. In genotype 1 (Lavett) a negative correlation was found between flour protein concentration and grain dry mass. However, in genotype 3 (Attila) flour protein concentration remained quite stable under a wide range of grain dry mass in response to the treatments. Genotype 2 (Ciano-79) showed an intermediate response. These big differences in genotypic response do have a potential significant impact for maintaining quality under adverse conditions. In all genotypes the effect of heat stress was larger when plants were grown at 18/13 °C compared to 25/20 °C; especially, grain dry mass was decreased while flour protein and GMP protein fraction, GMP quantity, as well as particle size were significantly increased. The results show that genetic differences in stability of quality and yield in wheat under heat stress can be induced by a short heat-shock treatment during the grain-filling phase. It is concluded that an evaluation of quality and yield responses of wheat genotypes to short spells of heat, could considerably be improved by a heat-shock treatment during the early grain-filling phase.

Low-temperature-induced desaturation of fatty acids and expression of desaturase genes in the cyanobacterium Synechococcus sp. PCC 7002.

Changes in response to temperature of lipid classes, fatty acid composition and mRNA levels for acyl-lipid desaturase genes were studied in the marine unicellular cyanobacterium, Synechococcus sp. PCC 7002. The degree of unsaturation of C18 fatty acids increased in cells grown at lower temperature for all lipid classes, and omega 3 desaturation occurred specifically in cells grown at low temperature. While the level of 18:1(9) fatty acids declined, desaturation at the omega 3 position of C18 fatty acids increased gradually during a 12-h period after a temperature shift-down to 22 degrees C. However, the mRNA levels of the desA (delta 12 desaturase), desB (omega 3 desaturase) and desC (delta 9 desaturase) genes increased within 15 min after a temperature shift-down to 22 degrees C; the desaturase gene mRNA levels also rapidly declined within 15 min after a temperature shift-up to 38 degrees C. Therefore, the elevation of mRNA levels for the desaturase genes is not the rate-limiting event for the increased desaturation of membrane lipids after a temperature shift-down. The rapid, low-temperature-induced changes in mRNA levels occurred even when cells were grown under light-limiting conditions for which the growth rates at 22 degrees C and 38 degrees C were identical. These studies indicate that the ambient growth temperature, and not some other growth rate-related process, regulates the expression of acyl lipid desaturation in this cyanobacterium.

Diversity of flowering responses in wild Arabidopsis thaliana strains.

Although multiple environmental cues regulate the transition to flowering in Arabidopsis thaliana, previous studies have suggested that wild A. thaliana accessions fall primarily into two classes, distinguished by their requirement for vernalization (extended winter-like temperatures), which enables rapid flowering under long days. Much of the difference in vernalization response is apparently due to variation at two epistatically acting loci, FRI and FLC. We present the response of over 150 wild accessions to three different environmental variables. In long days, FLC is among those genes whose expression is most highly correlated with flowering. In short days, FRI and FLC are less important, although their contribution is still significant. In addition, there is considerable variation not only in vernalization response, but also in the response to differences in day length or ambient growth temperature. The identification of accessions that flower relatively early or late in specific environments suggests that many of the flowering-time pathways identified by mutagenesis, such as those that respond to day length, contribute to flowering-time variation in the wild. In contrast to differences in vernalization requirement, which are mainly mediated by FRI and FLC, it seems that variation in these other pathways is due to allelic effects at several different loci.

The Effect of Sodium Azide on Basic and Induced Thermotolerance in Saccharomyces cerevisiae

The action mechanism of the mitochondrial inhibitor sodium azide on thermotolerance in Saccharomyces cerevisiae was studied. At ambient growth temperature, pretreatment with sodium azide was shown to improve the thermotolerance of parent cells and the hsp104 mutant. Treating with the inhibitor during a mild heat shock suppressed the development of induced thermotolerance due to the inhibition of heat shock protein (Hsp104) synthesis. Treating with the inhibitor immediately before lethal heat shock produced a variety of effects on thermotolerance depending on whether the yeast metabolism was oxidative or fermentative. The conclusions are: (1) the protective effect of sodium azide on the thermotolerance of S. cerevisiae cells grown on glucose-containing medium is not related to Hsp104 functioning, and (2) the mechanisms of basic and induced thermotolerance differ considerably.