Types Of Heat Stress Research Articles

Impact of heat stress on the fitness outcomes of symbiotic infection in aphids: a meta-analysis.

Beneficial microorganisms shape the evolutionary trajectories of their hosts, facilitating or constraining the colonization of new ecological niches. One convincing example entails the responses of insect-microbe associations to rising temperatures. Indeed, insect resilience to stressful high temperatures depends on the genetic identity of the obligate symbiont and the presence of heat-protective facultative symbionts. As extensively studied organisms, aphids and their endosymbiotic bacteria represent valuable models to address eco-evolutionary questions about the thermal ecology of insect-microbe partnerships, with broad relevance to various biological systems and insect models. This meta-analysis aims to quantify the context-dependent impacts of symbionts on host phenotype in benign or stressful heat conditions, across fitness traits, types of heat stress and symbiont species. We found that warming lowered the benefits (resistance to parasitoids) and costs (development, fecundity) of infection by facultative symbionts, which was overall mostly beneficial to the hosts under short-term heat stress (heat shock) rather than extended warming. Heat-tolerant genotypes of the obligate symbiont Buchnera aphidicola and some facultative symbionts (Rickettsia sp., Serratia symbiotica) improved or maintained aphid fitness under heat stress. We discuss the implications of these findings for the general understanding of the cost-benefit balance of insect-microbe associations across multiple traits and their eco-evolutionary dynamics faced with climate change.

Comparing responses of dairy cows to short-term and long-term heat stress in climate-controlled chambers

Heat stress (HS) in dairy cows can be classified into short-term heat stress (STHS) and long-term heat stress (LTHS) according to the number of consecutive days in HS. The comparative study of these 2 types of HS is limited in terms of their effects on the production and energy metabolism of cows. In this study, 4 lactating Holstein cows (102.5 ± 12 days in milk, 605 ± 22 kg of body weight, second parity) fitted with rumen fistulae were randomly assigned to 1 of 2 groups in a 2 × 2 crossover design and allocated to 1 of 2 climate-controlled chambers. This study contained 2 periods, each with a control phase and a HS phase. There was a recovery phase between 2 periods. The HS phase comprised either STHS (3 d) or LTHS (7 d) treatments. Data collected from the 3 d of STHS and the last 3 d of LTHS were compared. The chambers were set at thermal neutral conditions (20°C, 50% humidity) during the control and recovery phases or cyclical HS conditions (26-38°C, 50% humidity) during the HS phase. Compared with STHS, LTHS decreased milk yield by 17.2% and dry matter intake by 12.6%, indicating that LTHS caused a more severe decline in milk production and feed intake. In addition, LTHS decreased milk protein concentration by 6.8% and milk protein yield by 22.4%. In comparison with STHS, LTHS decreased rumen liquor volatile fatty acid (29.7%), blood glucose (11.6%), and nonesterified fatty acid (13.6%) concentrations, but increased milk urea nitrogen by 15.1%, blood urea nitrogen by 8.6%, and creatine concentrations by 15.4%. Our results suggest that although reduced feed intake may be mainly responsible for reduced milk production during STHS, impaired rumen metabolism and suppressed mobilization of adipose tissue could be the main reasons for further reduction in milk yield during LTHS.

Quantitative Profiling of Arabidopsis Polar Glycerolipids under Two Types of Heat Stress.

At the cellular level, the remodelling of membrane lipids and production of heat shock proteins are the two main strategies whereby plants survive heat stress. Although many studies related to glycerolipids and HSPs under heat stress have been reported separately, detailed alterations of glycerolipids and the role of HSPs in the alterations of glycerolipids still need to be revealed. In this study, we profiled the glycerolipids of wild-type Arabidopsis and its HSP101-deficient mutant hot-1 under two types of heat stress. Our results demonstrated that the alterations of glycerolipids were very similar in wild-type Arabidopsis and hot-1 during heat stress. Although heat acclimation led to a slight decrease of glycerolipids, the decrease of glycerolipids in plants without heat acclimation is more severe under heat shock. The contents of 36:x monogalactosyl diacylglycerol (MGDG) were slightly increased, whereas that of 34:6 MGDG and 34:4 phosphatidylglycerol (PG) were severely decreased during moderate heat stress. Our findings suggested that heat acclimation could reduce the degradation of glycerolipids under heat shock. Synthesis of glycerolipids through the prokaryotic pathway was severely suppressed, whereas that through the eukaryotic pathway was slightly enhanced during moderate heat stress. In addition, HSP101 has a minor effect on the alterations of glycerolipids under heat stress.

Stimulation of ipt overexpression as a tool to elucidate the role of cytokinins in high temperature responses of Arabidopsis thaliana.

Cytokinins (CKs) are phytohormones regulating plant growth and development as well as response to the environment. In order to evaluate their function in heat stress (HS) responses, the effect of CK elevation was determined during three types of HS - targeted to shoots, targeted to roots and applied to the whole plant. The early (30min) and longer term (3h) responses were followed at the hormonal, transcriptomic and proteomic levels in Arabidopsis transformants with dexamethasone-inducible expression of the CK biosynthetic gene isopentenyltransferase (ipt) and the corresponding wild-type (Col-0). Combination of hormonal and phenotypic analyses showed transient up-regulation of the CK/abscisic acid ratio, which controls stomatal aperture, to be more pronounced in the transformant. HS responses of the root proteome and Rubisco-immunodepleted leaf proteome were followed using 2-D gel electrophoresis and MALDI-TOF/TOF. More than 100 HS-responsive proteins were detected, most of them being modulated by CK increase. Proteome and transcriptome analyses demonstrated that CKs have longer term positive effects on the stress-related proteins and transcripts, as well as on the photosynthesis-related ones. Transient accumulation of CKs and stimulation of their signal transduction in tissue(s) not exposed to HS indicate that they are involved in plant stress responses.

Recent Gene Duplication and Subfunctionalization Produced a Mitochondrial GrpE, the Nucleotide Exchange Factor of the Hsp70 Complex, Specialized in Thermotolerance to Chronic Heat Stress in Arabidopsis

The duplication and divergence of heat stress (HS) response genes might help plants adapt to varied HS conditions, but little is known on the topic. Here, we examined the evolution and function of Arabidopsis (Arabidopsis thaliana) mitochondrial GrpE (Mge) proteins. GrpE acts as a nucleotide-exchange factor in the Hsp70/DnaK chaperone machinery. Genomic data show that AtMge1 and AtMge2 arose from a recent whole-genome duplication event. Phylogenetic analysis indicated that duplication and preservation of Mges occurred independently in many plant species, which suggests a common tendency in the evolution of the genes. Intron retention contributed to the divergence of the protein structure of Mge paralogs in higher plants. In both Arabidopsis and tomato (Solanum lycopersicum), Mge1 is induced by ultraviolet B light and Mge2 is induced by heat, which suggests regulatory divergence of the genes. Consistently, AtMge2 but not AtMge1 is under the control of HsfA1, the master regulator of the HS response. Heterologous expression of AtMge2 but not AtMge1 in the temperature-sensitive Escherichia coli grpE mutant restored its growth at 43°C. Arabidopsis T-DNA knockout lines under different HS regimes revealed that Mge2 is specifically required for tolerating prolonged exposure to moderately high temperature, as compared with the need of the heat shock protein 101 and the HS-associated 32-kD protein for short-term extreme heat. Therefore, with duplication and subfunctionalization, one copy of the Arabidopsis Mge genes became specialized in a distinct type of HS. We provide direct evidence supporting the connection between gene duplication and adaptation to environmental stress.

Impact of two different types of heat stress on chloroplast movement and fluorescence signal of tobacco leaves

Although the chloroplast movement can be strongly affected by ambient temperature, the information about chloroplast movement especially related to high temperatures is scarce. For detailed investigation of the effects of heat stress (HS) on tobacco leaves (Nicotiana tabacum L. cv. Samsun), we used two different HS treatments in dark with wide range of elevated temperatures (25-45 degrees C). The leaf segments were either linearly heated in water bath at heating rate of 2 degrees C min(-1) from room temperature up to maximal temperature (T (m)) and then linearly cooled down to 25 degrees C or incubated for 5 min in water bath at the same T (m) followed by 5 min incubation at 25 degrees C (T-jump). The changes in light-induced chloroplast movement caused by the HS pretreatment were detected after the particular heating regime at 25 degrees C using a method of time-dependent collimated transmittance (CT) and compared with the chlorophyll O-J-I-P fluorescence rise (FLR) measurements. The inhibition of chloroplast movement started at about 40 degrees C while the fluorescence parameters responded generally at higher T (m). This difference in sensitivity of CT and FLR was higher for the T-jump than for the linear HS indicating importance of applied heating regime. A possible influence of chloroplast movement on the FLR measurement and a physiological role of the HS-impaired chloroplast movement are discussed.

Isolation and characterization of the Arabidopsis heat‐intolerant 2 (hit2) mutant reveal the essential role of the nuclear export receptor EXPORTIN1A (XPO1A) in plant heat tolerance

*The Arabidopsis heat-intolerant 2 (hit2) mutant was isolated on the basis of its impaired ability to withstand moderate heat stress (37 degrees C). Determination of the genetic mutation that underlies the hit2 thermosensitive phenotype allowed better understanding of the mechanisms by which plants cope with heat stress. *Genetic analysis revealed that hit2 is a single recessive mutation. Map-based cloning was used to identify the hit2 locus. The response of hit2 to other types of heat stress was also investigated to characterize the protective role of HIT2. *hit2 was defective in basal but not in acquired thermotolerance. hit2 was sensitive to methyl viologen-induced oxidative stress, and the survival of hit2 seedlings in response to heat stress was affected by light conditions. The mutated locus was located at the EXPORTIN1A (XPO1A) gene, which encodes a nuclear transport receptor. Two T-DNA insertion lines, xpo1a-1 and xpo1a-3, exhibited the same phenotypes as hit2. *The results provide evidence that Arabidopsis XPO1A is dispensable for normal plant growth and development but is essential for thermotolerance, in part by mediating the protection of plants against heat-induced oxidative stress.

Physiological and production responses when feeding Aspergillus oryzae to dairy cows during short-term, moderate heat stress

AbstractDairy operations located in many temperate climates experience a decline in milk production associated with short-term moderate heat stress during the summer months. The duration and intensity of this heat stress differs dramatically from the sustained, intense heat experienced in many tropical and subtropical countries where the vast majority of heat stress research has been conducted. As such, many of the strategies utilized to ameliorate production losses associated with sustained, intense heat may not be effective in temperate climates. The objective of this research was to characterize the production responses of lactating dairy cows during and after short-term, moderate heat exposure and, to determine if feeding a fungal culture, Aspergillus oryzae, during a 5-day heat stress period, could effectively alleviate the associated production losses. In a two-period, cross-over design, eight mature lactating cows were given a total mixed ration with or without Aspergillus oryzae. Each 15-day period consisted of a 5-day thermoneutral phase, a 5-day heat stress phase and a 5-day thermoneutral recovery phase. When exposed to moderate heat stress for a 5-day period, cows experienced a rise in vaginal temperature and a decline in dry-matter intake. Following the 5-day heat stress phase, milk yield declined by a factor of 0·09. Supplementation with Aspergillus oryzae had no effect on vaginal temperature, dry-matter intake, water intake, milk yield or milk components. These data indicate that short-term, moderate heat stress, which occurs during the spring and summer months in temperate climates, will significantly decrease production in the lactating cow. Addition of fungal cultures to the diet during the period of imposed heat did not ameliorate production losses associated with this type of heat stress.

Physiological and Production Responses to Feeding Schedule in Lactating Dairy Cows Exposed to Short-Term, Moderate Heat Stress

The objective of this research was to characterize the production responses of lactating dairy cows during and after short-term, moderate heat exposure, and to determine whether evening (p.m.) feeding would alleviate the associated production losses. In a two-period, crossover design, eight mature lactating cows were fed a total mixed ration at either 0830 or 2030h. Each 15-d period consisted of a 5-d thermoneutral phase, a 5-d heat stress phase and a 5-d thermoneutral recovery phase. Mean daily vaginal temperature and respiration rate increased by 0.6±0.04°C and 27±1.3 breaths/ min, respectively, during short-term heat exposure. Daily dry matter intake, milk yield and solids-not-fat were depressed by 1.4±0.13kg, 1.7±0.32kg and 0.07±0.023%, respectively, during heat exposure. During the recovery phase, dry matter intake remained depressed, milk protein declined by 0.05±0.020%, and daily milk yield exhibited a further decline of 1.2±0.32kg. Time of feeding had no effect on vaginal temperature, respiration rate, dry matter intake, water intake, milk yield, fat-corrected milk, protein percent, solids-non-fat percent or somatic cell count during heat exposure or during the recovery period that followed. Fat percent was, however, significantly lower in p.m.-fed animals. These data indicate that short-term, moderate heat stress, which occurs during the spring and summer months in Canada and the Northern United States, will significantly decrease production in the lactating cow. Shifting from morning to evening feeding did not alleviate production losses associated with this type of heat stress.