The Role of Behavior in Temperature Acclimation and Tolerance in Ectotherms

A review of field and laboratory investigations suggests thatmany ectothermic vertebrates can exploit the spatiotemporaldistribution of environmental temperatures to maximize energyutilization and to enhance survivability. Diel and seasonalcycles in thermal preference, acclimation rate, thermal toleranceand heat-hardening may well be adapted to temporal variationsin environmental temperature. In addition, many ectoiherms behaviorallyexploit thermal heterogeneity in the environment. Such behavioraladaptations are synergistic with various degrees of physiologicalregulation. Voluntary brief exposures to temperatures that wouldbe lethal upon prolonged exposure can result in heat-hardening.Heat-hardening, distinct from acclimation to high temperature,is a short-term increase in thermal tolerance while toleranceacclimation is a longer lasting response within normal rangesof environmental temperatures; both are reversible nongeneticresponses. The physiological and ecological significance ofbehaviorally mediated heat-hardening may be greater than previouslyrealized and suggest new approaches for future study.     

Thermal Tolerance Limits of Diamondback Moth in Ramping and Plunging Assays

Thermal sensitivity is a crucial determinant of insect abundance and distribution. The way it is measured can have a critical influence on the conclusions made. Diamondback moth (DBM), Plutella xylostella (L.) (Lepidoptera: Plutellidae) is an important insect pest of cruciferous crops around the world and the thermal responses of polyphagous species are critical to understand the influences of a rapidly changing climate on their distribution and abundance. Experiments were carried out to the lethal temperature limits (ULT₀ and LLT₀: temperatures where there is no survival) as well as Upper and Lower Lethal Temperature (ULT₂₅ and LLT₂₅) (temperature where 25% DBM survived) of lab-reared adult DBM population to extreme temperatures attained by either two-way ramping (ramping temperatures from baseline to LT₂₅ and ramping back again) or sudden plunging method. In this study the ULT₀ for DBM was recorded as 42.6°C and LLT₀ was recorded as −16.5°C. DBM had an ULT₂₅ of 41.8°C and LLT₂₅ of −15.2°C. The duration of exposure to extreme temperatures had significant impacts on survival of DBM, with extreme temperatures and/or longer durations contributing to higher lethality. Comparing the two-way ramping temperature treatment to that of direct plunging temperature treatment, our study clearly demonstrated that DBM was more tolerant to temperature in the two-way ramping assay than that of the plunging assay for cold temperatures, but at warmer temperatures survival exhibited no differences between ramping and plunging. These results suggest that DBM will not be put under physiological stress from a rapidly changing climate, rather access to host plants in marginal habitats has enabled them to expand their distribution. Two-way temperature ramping enhances survival of DBM at cold temperatures, and this needs to be examined across a range of taxa and life stages to determine if enhanced survival is widespread incorporating a ramping recovery method.     

Thermal Limits in Relation to Acclimation in the Neotropical Millipede Gymnostreptus olivaceus (Diplopoda,Spirostreptidae)

The neotropical millipede, Gymnostreptus olivaceus, lives at ambient temperatures of about 20ºC. Its thermal tolerance was tested after acclimation to lower and higher temperatures as occurs under winter and summer conditions in the south and southeast regions of Brazil. An increase in tolerance to low temperatures was found in adapted specimens. The ecological aspects of this capability are discussed.     

Induction of Freezing Tolerance in Spinach during Cold Acclimation

Spinach (Spinacia oleracea L.) seedlings, grown in soil or on an agar medium in vitro, became cold acclimated when exposed to a constant 5°C. Plants subjected to cold acclimation, beginning 1 week postgermination, attained freezing tolerance levels similar to that achieved by seedlings that were cold acclimated beginning 3 weeks after sowing. Seedlings at 1 week of age had only cotyledonary leaves, while 3-week-old seedlings had developed true leaves. Plants grown in vitro were able to increase in freezing tolerance, but were slightly less hardy than soil-grown plants. These results suggest that spinach, a cool-season crop that begins growth in early spring when subzero temperatures are likely, can undergo cold acclimation at the earliest stages of development following germination. Axenic seedlings, grown in vitro, were used to develop a noninjurious radiolabeling technique. Leaf proteins were radiolabeled to specific activities of 10⁵ counts per minute per microgram at 25°C or 5 × 10⁴ counts per minute per microgram at 5°C over a 24 hour period. The ability to radiolabel leaf proteins of in vitro grown plants to high specific activities at low temperature, without injury or microbial contamination, will facilitate studies of cold acclimation.     

Role of Abscisic Acid in Thermal Acclimation of Plants

Abscisic acid (ABA) is a stress hormone that confers resistance to abiotic stressors, including drought, salt, cold, and heat. In general, antioxidant capacity and heat shock proteins (HSPs) mainly mediate ABA to enhance thermal acclimation in plants, but sugar metabolism and signaling also play critical roles in this response in the presence of ABA. Indeed, ABA accelerates sugar metabolism and transports more carbohydrates to spikelets under heat stress, which is beneficial to plants surviving under stressful conditions. Few studies have summarized the interactions among sucrose metabolism, signaling, and hormones in plants during heat stress, but this topic will likely attract more attention in the future. This article reviews the antioxidant capacity, HSPs, sugar metabolism, hormone crosstalk, and their interactions involved in ABA-induced heat tolerance in plants. Clarifying the underlying mechanisms will be invaluable for breeding heat-resistant cultivars and for developing new tissue culture techniques that reduce heat damage in plants.     

Exogenous Abscisic Acid Mimics Cold Acclimation for Cacti Differing in Freezing Tolerance

The responses to low temperature were determined for two species of cacti sensitive to freezing, Ferocactus viridescens and Opuntia ficus-indica, and a cold hardy species, Opuntia fragilis. Fourteen days after shifting the plants from day/night air temperatures of 30/20[deg]C to 10/0[deg]C, the chlorenchyma water content decreased only for O. fragilis. This temperature shift caused the freezing tolerance (measured by vital stain uptake) of chlorenchyma cells to be enhanced only by about 2.0[deg]C for F. viridescens and O. ficus-indica but by 14.6[deg]C for O. fragilis. Also, maintenance of high water content by injection of water into plants at 10/0[deg]C reversed the acclimation. The endogenous abscisic acid (ABA) concentration was below 0.4 pmol g-1 fresh weight at 30/20[deg]C, but after 14 d at 10/0[deg]C it increased to 84 pmol g-1 fresh weight for O. ficus-indica and to 49 pmol g-1 fresh weight for O. fragilis. Four days after plants were sprayed with 7.5 x 10-5 M ABA at 30/20[deg]C, freezing tolerance was enhanced by 0.5[deg]C for F. viridescens, 4.1[deg]C for O. ficus-indica, and 23.4[deg]C for O. fragilis. Moreover, the time course for the change in freezing tolerance over 14 d was similar for plants shifted to low temperatures as for plants treated with exogenous ABA at moderate temperatures. Decreases in plant water content and increases in ABA concentration may be important for low-temperature acclimation by cacti, especially O. fragilis, which is widely distributed in Canada and the United States.     

Quantification of the Role of Acclimation Temperature in Temperature Tolerance of Fishes

The relative effect of acclimation temperature on temperature tolerance was estimated from a geometrical partitioning of the temperature tolerance polygon of a fish species into three distinct zones relative to four key tolerance temperatures. This approach yields a middle tolerance zone which is independent of acclimation temperature bounded by upper and lower acclimation dependent zones. Acclimation dependent and independent temperature tolerance zones can be quantified by either areal or linear methods. Both methods were applied to quantify the effect of acclimation temperature in 21 species of temperate fishes for which temperature tolerance polygons were available. Temperature tolerance polygon areas of these 21 species ranged from 468 to 1380°C² and are linearly related (r ²=0.93, p<0.001) to ultimate incipient upper lethal temperatures. Although areal and linear partitioning methods yielded similar acclimation independent and dependent tolerances, estimates from the areal method incorporates additional information concerning the shape of the temperature tolerance polygon, in particular lower and upper lethal temperature plateaus. Mean combined acclimation dependent and independent tolerance areas of these 21 species were not different, indicating that acclimation effectively doubles the temperature tolerance polygon. Mean lower acclimation dependent area was nearly three times greater than mean upper acclimation dependent area, suggesting that acclimation plays a larger role in tolerance of low rather than high temperatures. Among these 21 species, temperature tolerance of brook charr and sheepshead minnow were the least and most affected by acclimation temperature, respectively.     

Enhanced Tolerance to Ascochyta Blight in Chickpea Plants via Low Temperature Acclimation

Russian Journal of Plant Physiology - Low temperature (LT) and Ascochyta blight are two major stresses in chickpea (Cicer arietinum L.) cultivation. After exposure to LT treatments (acclimation,...     

Water Relations and Low-Temperature Acclimation for Cactus Species Varying in Freezing Tolerance

Opuntia ficus-indica and Opuntia streptacantha are widely cultivated cacti that can tolerate temperatures no lower than -10[deg]C, whereas Opuntia humifusa, which is native to southern Canada and the eastern United States, can tolerate -24[deg]C. As day/night air temperatures were decreased from 30/20 to 10/0[deg]C, the osmotic pressure increased 0.10 MPa for O. ficus-indica and O. streptacantha but 0.38 MPa for O. humifusa. The increases in osmotic pressures were due mostly to the synthesis of fructose, glucose, and sucrose. In addition, O. humifusa produced a substantial amount of mannitol during exposure to low temperatures. Substantial accumulation of sugars and mannitol in cells of O. humifusa may help prevent intracellular freeze dehydration and ice formation as well as provide noncolligative protection to its membranes. Mucilage was slightly higher in all three species at the lower temperatures. Extracellular nucleation of ice occurred closer to the equilibrium freezing temperature for plants at 10/0[deg]C compared with 30/20[deg]C, which could make the cellular dehydration more gradual and, thus, less damaging. Results from nuclear magnetic resonance indicated a restricted mobility of intracellular water at the lower temperatures, especially for O. humifusa, which is consistent with its lower water content and higher levels of low molecular weight solutes.     

Extensive Heterogeneity and Intrinsic Variation in Spatial Genome Organization

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Extensive cis-Regulatory Variation Robust to Environmental Perturbation in Arabidopsis

cis- and trans-acting factors affect gene expression and responses to environmental conditions. However, for most plant systems, we lack a comprehensive map of these factors and their interaction with environmental variation. Here, we examined allele-specific expression (ASE) in an F1 hybrid to study how alleles from two Arabidopsis thaliana accessions affect gene expression. To investigate the effect of the environment, we used drought stress and developed a variance component model to estimate the combined genetic contributions of cis- and trans-regulatory polymorphisms, environmental factors, and their interactions. We quantified ASE for 11,003 genes, identifying 3318 genes with consistent ASE in control and stress conditions, demonstrating that cis-acting genetic effects are essentially robust to changes in the environment. Moreover, we found 1618 genes with genotype x environment (GxE) interactions, mostly cis x E interactions with magnitude changes in ASE. We found fewer trans x E interactions, but these effects were relatively less robust across conditions, showing more changes in the direction of the effect between environments; this confirms that trans-regulation plays an important role in the response to environmental conditions. Our data provide a detailed map of cis- and trans-regulation and GxE interactions in A. thaliana, laying the ground for mechanistic investigations and studies in other plants and environments.     

Genotypic Variation for Drought Tolerance in Beta vulgaris

Insufficient soil moisture during summer months is now the majorcause of sugar beet yield losses in the UK. However, selectionfor increased drought tolerance has not been a breeding priorityuntil recently. Genetic variation for drought tolerance is anessential prerequisite for the development of more stress-tolerantvarieties, but commercial sugar beet varieties seem to havesimilar yield responses to drought. The objective of this studywas to assess the degree of genotypic variation for droughttolerance within a wide range of sugar beet germplasm and genebankaccessions within Beta. Thirty sugar beet genotypes were screenedunder field drought conditions, and putative drought tolerantand sensitive lines (in terms of yield reduction in polythene-coveredvs. irrigated plots) were identified. Significant genotype xwater treatment interactions were found for dry matter yieldand relative leaf expansion rate. Genotypic differences fordrought susceptibility index were also significant. Differentialsensitivity of seedling shoot growth to water deficit was examinedby comparing 350 genebank accessions in a simple growth chamberscreen. Methods of data management were devised to highlightlines for entry into subsequent field tests. The results ofthe field and seedling screens indicate that there is variationfor tolerance to water deficits within sugar beet and relatedtypes, and that there are lines that show greater drought tolerancethan selected commercial varieties. Divergent lines showingcontrasting behaviour should aid in the identification of keymorpho-physiological traits that confer drought tolerance.     

Acclimation and Selection for Increased Resistance to Thermal Stress in Drosophila Buzzatii

Direct selection for increased resistance to a heat shock (41.9° for 90 min) was carried out using two replicate lines of Drosophila buzzatii that were derived from a large base population. Selected individuals were first acclimated to high temperature before selection, while control individuals were acclimated but not selected, and selection was performed every second generation. Resistance to heat shock with acclimation increased in selected lines. Without acclimation, a correlated smaller increase in heat-shock resistance was suggested. Survival of males was higher than that of females in all lines when tested with acclimation, but with direct exposure to high temperatures, survival of females was greater than that of males both in selection and control lines but not in the base population. From analysis of reciprocal cross progeny between lines, one selection line was found to possess a dominant autosomal factor that significantly increased resistance of males much more than resistance of females. Also suggestive was recessive traits on the X chromosome in both selection lines that increased thermotolerance. No cytoplasmic effects were found. After accounting for other effects, survival of F(1) flies was intermediate, suggesting that additive variation is present for one or more of the autosomes.     

Variation in Drought Tolerance of Different Stylosanthes Accessions

Twenty genotypes of Stylosanthes consisting four species were evaluated under rain fed condition employing biochemical and physiological attributes to select drought tolerant lines. Relative water content measured at 50 % flowering stage of the plants showed significant variations among the lines which ranged from 32.11 in S. scabra RRR94-86 to 83.33 % in S. seabrana 2539. The results indicated that S. scabra genotypes were more tolerant to drought over other lines as evidenced by high leaf thickness, proline accumulation, content of sugars and chlorophyll, and nitrate reductase activity.     

Cross Tolerance to Environmental Stressors: Effects of Hypoxic Acclimation on Cardiovascular Responses of Channel Catfish (Ictalurus punctatus) to a Thermal Challenge

Hypoxia and temperature are two major, interactive environmental variables that affect cardiovascular function in fishes. The purpose of this study was to determine if acclimation to hypoxia increases thermal tolerance by measuring cardiovascular responses to increasing temperature in two groups of channel catfish. The hypoxic group was acclimatized to moderate hypoxia (50% air saturation, a P_O2 of approximately 75 Torr) at a temperature of 22 °C for 7 days. The normoxic (i.e. control) group was maintained the same, but under normoxic conditions (a P_O2 of approximately 150 Torr). After acclimation, fish were decerebrated, fitted with dorsal aorta cannulae, and then exposed to increasing temperature while cardiovascular variables were recorded. The endpoint (critical thermal maximum, CTMax) was defined as a temperature at which heart rate and blood pressure sharply decreased, indicating cardiovascular collapse. Fish acclimatized to moderate hypoxia had higher resting heart rate than controls. Hypoxic acclimatized fish had a significantly higher CTMax. Acclimation to hypoxia increases the cardiovascular ability of channel catfish to withstand an acute temperature increase.     

Overexpression of WsSGTL1 Gene of Withania somnifera Enhances Salt Tolerance,Heat Tolerance and Cold Acclimation Ability in Transgenic Arabidopsis Plants

Background

Sterol glycosyltrnasferases (SGT) are enzymes that glycosylate sterols which play important role in plant adaptation to stress and are medicinally important in plants like Withania somnifera. The present study aims to find the role of WsSGTL1 which is a sterol glycosyltransferase from W. somnifera, in plant’s adaptation to abiotic stress.

Methodology

The WsSGTL1 gene was transformed in Arabidopsis thaliana through Agrobacterium mediated transformation, using the binary vector pBI121, by floral dip method. The phenotypic and physiological parameters like germination, root length, shoot weight, relative electrolyte conductivity, MDA content, SOD levels, relative electrolyte leakage and chlorophyll measurements were compared between transgenic and wild type Arabidopsis plants under different abiotic stresses - salt, heat and cold. Biochemical analysis was done by HPLC-TLC and radiolabelled enzyme assay. The promoter of the WsSGTL1 gene was cloned by using Genome Walker kit (Clontech, USA) and the 3D structures were predicted by using Discovery Studio Ver. 2.5.

Results

The WsSGTL1 transgenic plants were confirmed to be single copy by Southern and homozygous by segregation analysis. As compared to WT, the transgenic plants showed better germination, salt tolerance, heat and cold tolerance. The level of the transgene WsSGTL1 was elevated in heat, cold and salt stress along with other marker genes such as HSP70, HSP90, RD29, SOS3 and LEA4-5. Biochemical analysis showed the formation of sterol glycosides and increase in enzyme activity. When the promoter of WsSGTL1 gene was cloned from W. somnifera and sequenced, it contained stress responsive elements. Bioinformatics analysis of the 3D structure of the WsSGTL1 protein showed functional similarity with sterol glycosyltransferase AtSGT of A. thaliana.

Conclusions

Transformation of WsSGTL1 gene in A. thaliana conferred abiotic stress tolerance. The promoter of the gene in W.somnifera was found to have stress responsive elements. The 3D structure showed functional similarity with sterol glycosyltransferases.     

大绒鼠冷驯化和脱冷驯化能量代谢特征的变化

通过测定冷驯化(5℃)到脱冷驯化(30℃)条件下,大绒鼠(Eothenomys miletus)的体重、摄入能、静止代谢率(RMR)、非颤抖性产热(NST)和血清瘦素含量等参数,探讨了血清瘦素浓度与能量收支的关系。结果表明,冷驯化可致大绒鼠体重下降,RMR、NST、摄入能升高,血清瘦素浓度降低;脱冷驯化后大绒鼠体重增加,RMR、NST、摄入能降低,血清瘦素浓度增加。血清瘦素含量与体重呈正相关,与RMR、NST、摄入能呈负相关。表明大绒鼠的体重、摄入能和产热能力具有较强的可塑性,且瘦素可能参与了大绒鼠适应冷驯化及恢复过程中的能量平衡和体重的调节。