Single Stress Conditions Research Articles

Automated Imaging, Tracking, and Analytics Pipeline for Differentiating Environmental Effects on Root Meristematic Cell Division.

Exposure of plants to abiotic stresses, whether individually or in combination, triggers dynamic changes to gene regulation. These responses induce distinct changes in phenotypic characteristics, enabling the plant to adapt to changing environments. For example, iron deficiency and heat stress have been shown to alter root development by reducing primary root growth and reducing cell proliferation, respectively. Currently, identifying the dynamic temporal coordination of genetic responses to combined abiotic stresses remains a bottleneck. This is, in part, due to an inability to isolate specific intervals in developmental time where differential activity in plant stress responses plays a critical role. Here, we observed that iron deficiency, in combination with temporary heat stress, suppresses the expression of iron deficiency-responsive pPYE::LUC (POPEYE::luciferase) and pBTS::LUC (BRUTUS::luciferase) reporter genes. Moreover, root growth was suppressed less under combined iron deficiency and heat stress than under either single stress condition. To further explore the interaction between pathways, we also created a computer vision pipeline to extract, analyze, and compare high-dimensional dynamic spatial and temporal cellular data in response to heat and iron deficiency stress conditions at high temporal resolution. Specifically, we used fluorescence light sheet microscopy to image Arabidopsis thaliana roots expressing CYCB1;1:GFP, a marker for cell entry into mitosis, every 20 min for 24 h exposed to either iron sufficiency, iron deficiency, heat stress, or combined iron deficiency and heat stress. Our pipeline extracted spatiotemporal metrics from these time-course data. These metrics showed that the persistency and timing of CYCB1;1:GFP signal were uniquely different under combined iron deficiency and heat stress conditions versus the single stress conditions. These metrics also indicated that the spatiotemporal characteristics of the CYCB1;1:GFP signal under combined stress were more dissimilar to the control response than the response seen under iron deficiency for the majority of the 24-h experiment. Moreover, the combined stress response was less dissimilar to the control than the response seen under heat stress. This indicated that pathways activated when the plant is exposed to both iron deficiency and heat stress affected CYCB1;1:GFP spatiotemporal function antagonistically

Cumulative effects of drought–flood abrupt alternation on the photosynthetic characteristics of rice

The photosynthetic characteristics of crops under drought–flood abrupt alternation (DFAA) provide a foundation for the precise modeling of yield formation. However, current modeling practices are largely based on single water stress conditions or continuously well-watered conditions that differs considerably from the actual rice growing conditions in South China where DFAA occurs. This study aims to investigate the cumulative effects of DFAA on the photosynthetic characteristics of rice. The experiments were conducted in 2017 and 2018, and six DFAA groups with different combinations of drought and flooding were tested during the jointing–heading stage of rice. Three additional treatments were also used to compare the photosynthetic characteristics of rice under different water conditions, namely, those under continuous well-watered (CW), continuous drought (CD), and continuous flooded (CF) conditions. The results showed that there was photosynthetic inhibition after the DFAA stress, followed by recovery and compensation. Interestingly, two different kinds of interaction between the prior drought and the subsequent flooding were observed: the antagonistic effect of the preceding drought on the subsequent-flood-induced photosynthetic inhibition and the synergistic effect of the subsequent flooding on the preceding-drought-induced photosynthetic inhibition. In addition, the antagonistic effect on gs was more pronounced in DFAA groups that experienced prior mild or long-term drought, and the synergistic effect on gs was more deleterious in DFAA groups with severe subsequent flooding. These cumulative effects of DFAA were affected by the leaf-to-air vapor pressure difference (VPDleaf) and probably resulted in different leaf water use strategies in rice. This research increases our knowledge of the effects of the interaction between drought and flooding on rice photosynthesis and highlights the need to consider these complex interactions in future yield modeling and production practices.

Neural network-based fingerprinting of monoclonal antibody aggregation using biolayer interferometry.

Aggregates are widely accepted to be a critical quality attribute (CQA) for biotherapeutics and believed to impact product immunogenicity. Monitoring of aggregates is typically performed using multiple orthogonal tools as any single tool is unable to offer comprehensive characterization of aggregate species over the entire size and morphology range that they can exist in. Researchers have attempted to categorize monoclonal antibody (mAb) aggregates into six classes based on their respective physicochemical properties. In this study, we have developed model based on artificial neural network (ANN) to predict the stress history of mAb contributing to the aggregate formation, based on binding sensogram profiles obtained with biolayer interferometry (BLI). It was observed that each class of mAb aggregates exhibited unique binding profiles that were characteristic fingerprint of that class. The proposed model uses principal components extracted from the mAb-Fcγ receptor binding sensogram (106 profiles from 9 stressed mAb samples) as inputs while the unique identification codes in the form of binary coded numbers are used as model outputs. The latter served as a fingerprint for each class of mAb aggregates generated by subjecting to specific stress conditions. The ANN was trained using Levenberg-Marquardt algorithm with Bayesian regularization, using 86 sensogram profiles, in the ratio of 80:10:10 for internal training, validation, and testing. The trained ANN accurately identified each single stress condition that the samples were subjected to based on their binding sensogram profiles. The model was also able to predict stress history for samples that had been subjected to more than one kind of stress with reasonable accuracy. The proposed approach therefore can be effectively employed for control of product quality in biopharmaceutical industry as well as for prediction of stress history of a sample.

Co-overexpression of AVP1 and OsSIZ1 in Arabidopsis substantially enhances plant tolerance to drought, salt, and heat stresses

Abiotic stresses such as water deficit, salt, and heat are major environmental factors that negatively affect plant growth, development, and productivity. Previous studies showed that overexpression of the Arabidopsis vacuolar H+-pyrophosphatase gene AVP1 increases salt and water deficit stress tolerance and overexpression of the rice SUMO E3 ligase gene OsSIZ1 improves heat and water deficit stress tolerance in transgenic plants. In this report, the effects of co-overexpression of AVP1 and OsSIZ1 in Arabidopsis on abiotic stress tolerance were studied. It was found that AVP1/OsSIZ1 co-overexpressing plants performed significantly better than AVP1-overexpressing plants and OsSIZ1-overexpressing plants, and produced 100% more seed than wild-type plants under single stress or multiple stress conditions. The increased stress tolerance in AVP1/OsSIZ1 co-overexpressing plants was substantially larger than the increased stress tolerance in AVP1-overexpressing plants and OsSIZ1-overexpressing plants under every abiotic stress condition tested. This research provides the proof-of-concept that crop yields might be substantially improved using this approach.

Additional oxidative stress reroutes the global response of Aspergillus fumigatus to iron depletion

BackgroundAspergillus fumigatus has to cope with a combination of several stress types while colonizing the human body. A functional interplay between these different stress responses can increase the chances of survival for this opportunistic human pathogen during the invasion of its host. In this study, we shed light on how the H2O2-induced oxidative stress response depends on the iron available to this filamentous fungus, using transcriptomic analysis, proteomic profiles, and growth assays.ResultsThe applied H2O2 treatment, which induced only a negligible stress response in iron-replete cultures, deleteriously affected the fungus under iron deprivation. The majority of stress-induced changes in gene and protein expression was not predictable from data coming from individual stress exposure and was only characteristic for the combination of oxidative stress plus iron deprivation. Our experimental data suggest that the physiological effects of combined stresses and the survival of the fungus highly depend on fragile balances between economization of iron and production of essential iron-containing proteins. One observed strategy was the overproduction of iron-independent antioxidant proteins to combat oxidative stress during iron deprivation, e.g. the upregulation of superoxide dismutase Sod1, the thioredoxin reductase Trr1, and the thioredoxin orthologue Afu5g11320. On the other hand, oxidative stress induction overruled iron deprivation-mediated repression of several genes. In agreement with the gene expression data, growth studies underlined that in A. fumigatus iron deprivation aggravates oxidative stress susceptibility.ConclusionsOur data demonstrate that studying stress responses under separate single stress conditions is not sufficient to understand how A. fumigatus adapts in a complex and hostile habitat like the human body. The combinatorial stress of iron depletion and hydrogen peroxide caused clear non-additive effects upon the stress response of A. fumigatus. Our data further supported the view that the ability of A. fumigatus to cause diseases in humans strongly depends on its fitness attributes and less on specific virulence factors. In summary, A. fumigatus is able to mount and coordinate complex and efficient responses to combined stresses like iron deprivation plus H2O2-induced oxidative stress, which are exploited by immune cells to kill fungal pathogens.

Regulation of reactive oxygen and nitrogen species by salicylic acid in rice plants under salinity stress conditions.

This study investigated the regulatory role of exogenous salicylic acid (SA) in rice and its effects on toxic reactive oxygen and nitrogen species during short-term salinity stress. SA application (0.5 and 1.0 mM) during salinity-induced stress (100 mM NaCl) resulted in significantly longer shoot length and higher chlorophyll and biomass accumulation than with salinity stress alone. NaCl-induced reactive oxygen species production led to increased levels of lipid peroxidation in rice plants, which were significantly reduced following SA application. A similar finding was observed for superoxide dismutase; however, catalase (CAT) and ascorbate peroxidase (APX) were significantly reduced in rice plants treated with SA and NaCl alone and in combination. The relative mRNA expression of OsCATA and OsAPX1 was lower in rice plants during SA stress. Regarding nitrogenous species, S-nitrosothiol (SNO) was significantly reduced initially (one day after treatment [DAT]) but then increased in plants subjected to single or combined stress conditions. Genes related to SNO biosynthesis, S-nitrosoglutathione reductase (GSNOR1), NO synthase-like activity (NOA), and nitrite reductase (NIR) were also assessed. The mRNA expression of GSNOR1 was increased relative to that of the control, whereas OsNOA was expressed at higher levels in plants treated with SA and NaCl alone relative to the control. The mRNA expression of OsNR was decreased in plants subjected to single or combination treatment, except at 2 DAT, compared to the control. In conclusion, the current findings suggest that SA can regulate the generation of NaCl-induced oxygen and nitrogen reactive species in rice plants.

Optimization of seawater-based triacylglycerol accumulation in a freshwater green alga, Chlorella kessleri, through simultaneous imposition of lowered-temperature and enhanced-light intensity

Triacylglycerols (TG), the major components of crop oils used for the production of food oils and biodiesel fuel, accumulate in algal species under single environmental stress conditions including nitrogen-starvation. In a freshwater green alga, Chlorella kessleri, its TG content reached 24.7% in dry cell weight in 72h, on cultivation in 3-fold diluted seawater (1/3 SW), through the synergetic stimulating effects of hyperosmosis and nutrient-limitation. These observations would indicate the importance of combinatory stresses for strong induction of TG accumulation [Hirai et al. 2016]. We here searched for novel stresses in C. kessleri to elevate the seawater-based TG accumulation level through their additional actions. A higher light intensity (moderate light, ML) caused a small, but definite increase of TG, whereas a lowered growth temperature (LT) led to a large, but temporal increase of it until 48h, followed by severe degradation. The decrease of TG in LT cells was abolished on simultaneous imposition of ML. C. kessleri cells were then cultured in 1/3 SW under combinatory conditions of ML/LT, the TG content consequently increasing to as high as 48.5% in dry cells. These results indicated the validity of combinatory stresses for strong induction of algal TG accumulation. As to the fatty acid composition of TG, C. kessleri was intermediate between palm and the other three major oil crops including rapeseed. The rapid and abundant accumulation of TG with fatty acid composition suitable for industrial use demonstrated the great potential of development of the industrial algal TG production system with the use of the combinatory stresses in C. kessleri. TG of C. kessleri was also characteristic to contain C18 acids as representing 81mol% of its constituent fatty acids or 90% of fatty acids at its sn-2 position, which suggested a peculiar TG synthetic pathway in this oleaginous alga.

Natural variation reveals contrasting abilities to cope with alkaline and saline soil among different Medicago truncatula genotypes

Abiotic stress conditions cause extensive losses to agricultural production worldwide. Salinity and alkalinity affect plant growth, photosynthesis and availability of nutrients including Fe. Many studies have described the response mechanisms of plants to single abiotic stress conditions. However, in the field, crops and other plants are routinely subjected to a combination of different abiotic stresses. Salinity and alkalinity are wide-spread in Tunisia, where Medicago truncatula occurs as a native species. We established a growth system to study the combined effects of salinity and alkalinity conditions in laboratory conditions. We screened 11 Tunisian M. truncatula lines from the SARDI collection based on their phenotypic responses to the double stress. Salinity and alkalinity affected germination rates, shoot and root dry weights, pigment contents and root morphology parameters. We were able to select among the 11 investigated lines four sensitive and tolerant lines with different abilities to respond to the double stress. Tolerant and sensitive genotypes (two lines each) differed in root flavin contents, root flavin staining patterns and concentrations of root flavins in the nutrient solution. Root architecture, flavin root localization in epidermal cells and flavin secretion are relevant tolerance mechanisms for salt and alkaline stress in M. truncatula. Pairs of contrasting lines from close origins were identified that will be useful tools to identify genes for the tolerance mechanisms.

Differences and commonalities of plant responses to single and combined stresses.

In natural or agricultural environments, plants are constantly exposed to a wide range of biotic and abiotic stresses. Given the forecasted global climate changes, plants will cope with heat waves, drought periods and pathogens at the same time or consecutively. Heat and drought cause opposing physiological responses, while pathogens may or may not profit from climate changes depending on their lifestyle. Several studies have been conducted to find stress-specific signatures or stress-independent commonalities. Previously this has been done by comparing different single stress treatments. This approach has been proven difficult since most studies, comparing single and combined stress conditions, have come to the conclusion that each stress treatment results in specific transcriptional changes. Although transcriptional changes at the level of individual genes are highly variable and stress-specific, central metabolic and signaling responses seem to be common, often leading to an overall reduced plant growth. Understanding how specific transcriptional changes are linked to stress adaptations and identifying central hubs controlling this interaction will be the challenge for the coming years. In this review, we will summarize current knowledge on plant responses to different individual and combined stresses and try to find a common thread potentially underlying these responses. We will begin with a brief summary of known physiological, metabolic, transcriptional and hormonal responses to individual stresses, elucidate potential commonalities and conflicts and finally we will describe results obtained during combined stress experiments. Here we will concentrate on simultaneous application of stress conditions but we will also touch consequences of sequential stress treatments.

Soybean Na+/H+ antiporter GmsSOS1 enhances antioxidant enzyme activity and reduces Na+ accumulation in Arabidopsis and yeast cells under salt stress

Our previous work revealed that the soybean GmsSOS1 enhances salt tolerance in Arabidopsis. In this work, we studied the physiological mechanisms by which the GmsSOS1 confers salt and oxidative stress tolerance in Arabidopsis and yeast cells. Under salt stress condition, the GmsSOS1-expressing Arabidopsis plants displayed larger leaf area, lower leaf relative electrolytic leakage, less accumulation of H2O2, superoxide anion radicals (O2−), and malondialdehyde compared with wild type. In consistent with these observations, the activities of antioxidant enzymes catalase, ascorbate peroxide, and peroxidase in the GmsSOS1-expressing plants were higher than those in wild type under salt stress. Combined salt and oxidative stresses caused more damage and higher accumulation of H2O2 and Na+ than single stress condition in both wild type and the GmsSOS1-expressing plants. However, the GmsSOS1-expressing Arabidopsis plants could maintain significantly lower levels of H2O2 and Na+ and exhibited better growth than wild type under either single or combined stress. The GmsSOS1 complemented the yeast plasma membrane-localized Na+/H+ antiporter and enhanced salt tolerance by reducing Na+ accumulation in yeast cells. Our results suggest that the soybean GmsSOS1 can alleviate the primary Na+ toxicity by limiting Na+ accumulation and mitigate the secondary oxidative stress through improving antioxidant enzyme activity.

Synergistic effect of multiple stress conditions for improving microalgal lipid production

This increasing consumption of fossil fuels and emission of greenhouse gases causes climate change. Thus, the development of alternative energy sources such as biofuel is necessary. Microalgae have been spotlighted as renewable energy resources because the potential for producing biofuels from CO2. However, the unit cost for the production of algae-based biofuel must be reduced for commercialization compared to the petroleum. The optimization of culture conditions of microalgal strains is crucial to increase lipid production for economically viable biofuels. We rapidly analyzed the combined effect of various stress conditions (nitrogen starvation, temperature, pH, and salt concentration) on the lipid production in various strains using a multiplex microfluidic system, enabling multiple operations from cell culture to lipid extraction of different strains. We found the lipid productivity was enhanced by 25 to 54% under combinations of two stress condition compared to the single stress condition. However, the combination of more than three stress conditions reduced the lipid productivities of all microalgal strains because of more stressful environment to the cells compared to the combinations of two stress conditions. We further validated the synergistic effect of combined stress conditions in flask culture with the increases in lipid productivities by up to 106% compared to the single stress condition. We also observed that fatty acids composition, which influences the quality of algal biofuels, was changed according to the combination of stress conditions. In particular, C. protothecoides can be good candidate for production of high quality of biodiesel, because it has high CN, IV and low CFPP which is suitable for high quality of biodiesel. These results indicate that combination of multiple stress conditions can be efficient strategy for the optimization of microalgal cultivation to produce algal biofuels with high quality and economic feasibility.

The combined effects of nitrate with high temperature and high light intensity on coral bleaching and antioxidant enzyme activities

The frequency and severity of coral bleaching events have increased in recent decades. Regionally, human-attributed nutrient pollution, particularly nitrate, has increased in coastal areas due to inflow from rivers and groundwater. The combined effects of increased nitrate concentrations with high temperature or high light on bleaching events and reactive oxygen species levels (ROS) were tested. Coral fragments of Montipora digitata were incubated for 3 and 6 days at different light intensities (200 and 600 μmol m−2 s−1), temperatures (27 and 32 °C), and nitrate concentrations (<1 and 10 μM). Quantum yields of the photosynthetic electron transport system were significantly decreased under high-temperature conditions. Because there were strong correlations between zooxanthellae density and antioxidant enzyme activities (superoxide dismutase and catalase), we hypothesized that a decrease in zooxanthellae occurred due to oxidative stresses. Our results show that enrichment of nitrate can accelerate coral bleaching under high light or high temperature conditions compared with single stress conditions. If the concentration of nitrate increases damage to coral reefs in coastal areas could significantly increase under high temperature or high light stress.

Drought and UV-B radiation effect on photosynthesis and antioxidant parameters in soybean and maize

Drought and ultraviolet-B (UV-B) radiation are the most adverse factors for plant growth and productivity. The aim of this study was to compare the effects and interaction of drought and UV-B radiation in the seedlings of maize and soybean. The relative leaf water content was the main factor resulting in reduced growth in response to drought. The anthocyanin and phenol levels were increased under UV-B radiation. Drought and UV-B radiation caused great membrane damage, as assessed by lipid peroxidation and osmolyte leakage. Catalase, peroxidase, superoxide dismutase and hydrogen peroxide were observed under both stress conditions. Proline increased primarily in drought-stressed seedlings and may be the drought-induced factor with a protective role in response to UV-B. The total dry matter of both plant species was decreased due to the chlorophyll content and photosynthetic rate decreased under single and combined stress conditions. UV-B radiation had more adverse effects on growth of maize and soybean seedlings than drought by the physiological and biochemical parameters measured.

Elicitor Mixtures Significantly Increase Bioactive Compounds, Antioxidant Activity, and Quality Parameters in Sweet Bell Pepper

Sweet bell peppers are greatly appreciated for their taste, color, pungency, and aroma. Additionally, they are good sources of bioactive compounds with antioxidant activity, which can be improved by the use of elicitors. Elicitors act as metabolite-inducing factors (MIF) by mimic stress conditions. Since plants rarely experience a single stress condition one by one but are more likely to be exposed to simultaneous stresses, it is important to evaluate the effect of elicitors on plant secondary metabolism as mixtures. Jasmonic acid (JA), hydrogen peroxide (HP), and chitosan (CH) were applied to fruits and plants of bell pepper as mixtures. Bioactive compounds, antioxidant activity, and quality parameters were evaluated. The assessed elicitor cocktail leads to an increase in the variables evaluated (P≤ 0.05) when applied to mature fruits after harvest, whereas the lowest values were observed in the treatment applied to immature fruits. Therefore, the application of the elicitor cocktail to harvested mature fruits is recommended in order to improve bioactive compounds and the antioxidant activity of sweet bell peppers.

A step towards understanding plant responses to multiple environmental stresses: a genome‐wide study

In natural habitats, especially in arid areas, plants are often simultaneously exposed to multiple abiotic stresses, such as salt, osmotic and heat stresses. However, most analyses of gene expression in stress responses examine individual stresses. In this report, we compare gene expression in individual and combined stresses. We show that combined stress treatments with salt, mannitol and heat induce a unique pattern of gene expression that is not a simple merge of the individual stress responses. Under multiple stress conditions, expression of most heat and salt stress-responsive genes increased to levels similar to or higher than those measured in single stress conditions, but osmotic stress-responsive genes increased to lower levels. Genes up-regulated to higher levels under multiple stress condition than single stress conditions include genes for heat shock proteins, heat shock regulators and late embryogenesis abundant proteins (LEAs), which protect other proteins from damage caused by stresses, suggesting their importance in multiple stress condition. Based on this analysis, we identify candidate genes for engineering crop plants tolerant to multiple stresses.

Simultaneous application of heat, drought, and virus to Arabidopsis plants reveals significant shifts in signaling networks.

Considering global climate change, the incidence of combined drought and heat stress is likely to increase in the future and will considerably influence plant-pathogen interactions. Until now, little has been known about plants exposed to simultaneously occurring abiotic and biotic stresses. To shed some light on molecular plant responses to multiple stress factors, a versatile multifactorial test system, allowing simultaneous application of heat, drought, and virus stress, was developed in Arabidopsis (Arabidopsis thaliana). Comparative analysis of single, double, and triple stress responses by transcriptome and metabolome analysis revealed that gene expression under multifactorial stress is not predictable from single stress treatments. Hierarchical cluster and principal component analyses identified heat as the major stress factor, clearly separating heat-stressed from non-heat-stressed plants. We identified 11 genes differentially regulated in all stress combinations as well as 23 genes specifically regulated under triple stress. Furthermore, we showed that virus-treated plants displayed enhanced expression of defense genes, which was abolished in plants additionally subjected to heat and drought stress. Triple stress also reduced the expression of genes involved in the R-mediated disease response and increased the cytoplasmic protein response, which was not seen under single stress conditions. These observations suggested that abiotic stress factors significantly altered turnip mosaic virus-specific signaling networks, which led to a deactivation of defense responses and a higher susceptibility of plants. Collectively, our transcriptome and metabolome data provide a powerful resource to study plant responses during multifactorial stress and allow identifying metabolic processes and functional networks involved in tripartite interactions of plants with their environment.

Compensation phenomena found in Acidithiobacillus ferrooxidans after starvation stress

Acidithiobacillus ferrooxidans showed the compensate growth and oxidation after re-feeding with sufficient ferrous materials after starvation. Compensatory phenomena were first detected in chemoautotrophic organisms. Starvation stress of Acidithiobacillus ferrooxidans was achieved via culturing in low concentrations of iron. During compensation, growth and ferrous oxidation took place faster than in controls. In addition, some genes related to ferrous oxidation (such as rus) and carbon assimilation (cbbR, csoS3) were expressed in different patterns in the low energy environments. Their expression patterns can account for this increased growth and oxidation. Other groups of genes (cspAB, feoAB, fur) were suppressed in response to starvation stress. The presence of pyrite and joint cold stress can render compensation nearly undetectable. This may be why the compensation phenomena observed under these conditions was not the same as that observed under single starvation stress conditions. Gene expression reflected a possible mechanism of tolerance to starvation in Acidithiobacillus ferrooxidans, which would allow the organism to adapt and survive in ferrous-limited environments.

Physiological Response of Different Wine Yeasts to Hyperosmotic Stress

The physiological and cellular responses of different types of wine yeast strains (industrial strains AWRI R2 and Freddo and newly selected strain Saccharomyces cerevisiae B) to hyperosmotic stress (sorbitol as the osmoticum) were studied. A modified model synthetic medium was used to better understand the protection that trehalose provides wine yeasts under single-stress conditions. Exposing cells in the midexponential growth phase to 1.7 M sorbital enhanced production of glycerol and increased glycerol-3-phosphate dehydrogenase activity in all three wine yeasts, especially in industrial strain AWRI R2. However, dramatic accumulation of trehalose and an increase in trehalose-6-phosphate synthase activity were found only in Freddo and S. cerevisiae B. Strains Freddo and S. cerevisiae B also showed higher tolerance to hyperosmotic stress than AWRI R2. The survival rate of strains Freddo and S. cerevisiae B was >90% during stress treatment but was ~50% for strain AWRI R2. Glycerol was the main osmolyte used by wine yeast under hyperosmotic stress. The accumulation of trehalose was strain-dependent and endogenous trehalose correlated with acquisition of tolerance to hyperosmotic stress. A preliminary application of heat shock (leading to trehalose accumulation) was given to strain AWRI R2 before hyperosmotic stress treatment. Pretreatment with heat shock improved its osmotolerance markedly and the accumulation of trehalose played an important role. Results suggest that when glycerol is induced, trehalose could enhance osmotolerance of wine yeasts significantly. Trehalose was an important osmoprotectant.

Effects of stress, corticosterone, and epinephrine administration on learning in place and response tasks

These experiments examined the effects of prior stress, corticosterone, or epinephrine on learning in mazes that can be solved efficiently using either place or response strategies. In a repeated stress condition, rats received restraint stress for 6 h/day for 21 days, ending 24 h before food-motivated maze training. In two single stress conditions, rats received a 1-h episode of restraint stress ending 30 min or 24 h prior to training. Single stress ending 30 min prior to training resulted in a significant interaction of stress and learning on the two tasks, with significant enhancement of learning in the response task and non-significant impairment in the place task. Neither acute nor chronic stress significantly altered learning in either task when the stress ended 24 h before training. Thus, the anterograde effects of stress on maze learning ended within a single day. Two stress-related hormones, corticosterone and epinephrine, were tested for effects on learning parallel to those of acute stress. When administered 30 min prior to training, a corticosterone dose (40 mg/kg) that enhanced memory on a spontaneous alternation task did not significantly enhance or impair learning in either task. Two doses of epinephrine that modulate memory in other settings were used to test the effects of epinephrine on learning. Pre-training injections of 0.03 mg/kg epinephrine impaired place learning, while 0.1 mg/kg epinephrine impaired response learning. The epinephrine results mimicked those seen with acute stress on the place task, but were opposite those seen after acute stress on the response task. Thus, corticosterone does not appear to be a major factor mediating the effects of acute stress on place and response learning and epinephrine is, at most, a partial contributor to these effects.

A Two-Step Clustering for 3-D Gene Expression Data Reveals the Main Features of the Arabidopsis Stress Response.

Summary We developed an integrative approach for discovering gene modules, i.e. genes that are tightly correlated under several experimental conditi ons and applied it to a threedimensional Arabidopsis thaliana microarray dataset. The dataset consists of approximately 23000 genes responding to 9 abiotic stress conditions at 6-9 different points in time. Our approach aims at finding relatively small and dense modules lending themselves to a specific biological interpretation. In order to detect g ene modules within this dataset, we employ a two-step clustering process. In the first step, a k-means clustering on one condition is performed, which is subsequently used in the second step as a seed for the clustering of the remaining conditions. To validate the significance of the obtained modules, we performed a permutation analysis and determined a null hypothesis to compare the module scores against, providing a p-value for each module. Significant modules were mapped to the Gene Ontology (GO) in order to determine the participating biological processes. As a result, we isolated modules showing high significance wi th respect to the p-values obtained by permutation analysis and GO mapping. In these modules we identified a number of genes that are either part of a general stress response with similar characteristics under different conditions (coherent modules), or part of a more specific stress response to a single stress condition (single response modules). We also found genes clustering within several conditions, which are, however, not part of a coherent module. These genes have a distinct temporal response under each condition. We call the modules they are contained in individual response modules(IR).