Detrimental Effects Of Heat Stress Research Articles

Comparative proteomics in tall fescue to reveal underlying mechanisms for improving Photosystem II thermotolerance during heat stress memory

BackgroundThe escalating impacts of global warming intensify the detrimental effects of heat stress on crop growth and yield. Among the earliest and most vulnerable sites of damage is Photosystem II (PSII). Plants exposed to recurring high temperatures develop heat stress memory, a phenomenon that enables them to retain information from previous stress events to better cope with subsequent one. Understanding the components and regulatory networks associated with heat stress memory is crucial for the development of heat-resistant crops.ResultsPhysiological assays revealed that heat priming (HP) enabled tall fescue to possess higher Photosystem II photochemical activity when subjected to trigger stress. To investigate the underlying mechanisms of heat stress memory, we performed comparative proteomic analyses on tall fescue leaves at S0 (control), R4 (primed), and S5 (triggering), using an integrated approach of Tandem Mass Tag (TMT) labeling and Liquid Chromatography-Mass Spectrometry. A total of 3,851 proteins were detected, with quantitative information available for 3,835 proteins. Among these, we identified 1,423 differentially abundant proteins (DAPs), including 526 proteins that were classified as Heat Stress Memory Proteins (HSMPs). GO and KEGG enrichment analyses revealed that the HSMPs were primarily associated with the “autophagy” in R4 and with “PSII repair”, “HSP binding”, and “peptidase activity” in S5. Notably, we identified 7 chloroplast-localized HSMPs (HSP21, DJC77, EGY3, LHCA4, LQY1, PSBR and DEGP8, R4/S0 > 1.2, S5/S0 > 1.2), which were considered to be effectors linked to PSII heat stress memory, predominantly in cluster 4. Protein-protein interaction (PPI) analysis indicated that the ubiquitin-proteasome system, with key nodes at UPL3, RAD23b, and UCH3, might play a role in the selective retention of memory effectors in the R4 stage. Furthermore, we conducted RT-qPCR validation on 12 genes, and the results showed that in comparison to the S5 stage, the R4 stage exhibited reduced consistency between transcript and protein levels, providing additional evidence for post-transcriptional regulation in R4.ConclusionsThese findings provide valuable insights into the establishment of heat stress memory under recurring high-temperature episodes and offer a conceptual framework for breeding thermotolerant crops with improved PSII functionality.

Heat‐stress‐induced fertility loss in summer maize (Zea mays L.): Quantitative analysis of contributions from developmental and physiological damage to pollen

AbstractIn recent years, the frequency and intensity of exposure to heat stress have increased gradually, seriously hampering the production of maize. This paper presents a study designed to analyze how the development, physiology and dispersal of pollen from the heat‐resistant maize variety Zhengdan958 and the heat‐sensitive maize variety Xianyu335 are affected by exposure to heat stress during the tasselling stage. Our results showed That exposure to heat stress significantly increased the antioxidant enzyme activity in pollen. Upon visual inspection of the pollen, we found that the lower water content had given rise to wrinkles in the pollen surface, sunken germination pores, and morphological deformations. In addition, the anther dehiscence process was hindered, resulting in a reduced amount of pollen being dispersed. We also found elevated levels of abscisic acid (ABA), jasmonic acid (JA) and its derivatives, indole acetic acid (IAA) and gibberellin‐3 (GA3) in heat‐pollens, as well as elevated ratios of IAA to ABA and ABA to GA3. Ultimately impaired pollen fertility. Summarizing, our experiment revealed that reduced pollen quantity and quality are significant contributors to fertility losses in summer maize exposed to heat stress at anthesis, and we hope that our analysis of the physiological mechanisms involved can contribute to the development of crop management measures aimed at countering the increasingly detrimental effects of heat stress on the production of summer maize.

Pre-hatch thermal manipulation of embryos and post-hatch baicalein supplementation mitigated heat stress in broiler chickens

BackgroundHigh environmental temperatures induce heat stress in broiler chickens, affecting their health and production performance. Several dietary, managerial, and genetics strategies have been tested with some success in mitigating heat stress (HS) in broilers. Developing novel HS mitigation strategies for sustaining broiler production is critically needed. This study investigated the effects of pre-hatch thermal manipulation (TM) and post-hatch baicalein supplementation on growth performance and health parameters in heat-stressed broilers.ResultsSix hundred fertile Cobb 500 eggs were incubated for 21 d. After candling on embryonic day (ED) 10, 238 eggs were thermally manipulated at 38.5 °C with 55% relative humidity (RH) from ED 12 to 18, then transferred to the hatcher (ED 19 to 21, standard temperature) and 236 eggs were incubated at a controlled temperature (37.5 °C) till hatch. After hatch, 180-day-old chicks from both groups were raised in 36 pens (n = 10 birds/pen, 6 replicates per treatment). The treatments were: 1) Control, 2) TM, 3) control heat stress (CHS), 4) thermal manipulation heat stress (TMHS), 5) control heat stress supplement (CHSS), and 6) thermal manipulation heat stress supplement (TMHSS). All birds were raised under the standard environment for 21 d, followed by chronic heat stress from d 22 to 35 (32–33 °C for 8 h) in the CHS, TMHS, CHSS, and TMHSS groups. A thermoneutral (22–24 °C) environment was maintained in the Control and TM groups. RH was constant (50% ± 5%) throughout the trial. All the data were analyzed using one-way ANOVA in R and GraphPad software at P < 0.05 and are presented as mean ± SEM. Heat stress significantly decreased (P < 0.05) the final body weight and ADG in CHS and TMHS groups compared to the other groups. Embryonic TM significantly increased (P < 0.05) the expression of heat shock protein-related genes (HSP70, HSP90, and HSPH1) and antioxidant-related genes (GPX1 and TXN). TMHS birds showed a significant increment (P < 0.05) in total cecal volatile fatty acid (VFA) concentration compared to the CHS birds. The cecal microbial analysis showed significant enrichment (P < 0.05) in alpha and beta diversity and Coprococcus in the TMHSS group.ConclusionsPre-hatch TM and post-hatch baicalein supplementation in heat-stressed birds mitigate the detrimental effects of heat stress on chickens' growth performance, upregulate favorable gene expression, increase VFA production, and promote gut health by increasing beneficial microbial communities.

Protective Effects of Niacin on Rumen Epithelial Cell Barrier Integrity in Heat-Stressed Beef Cattle.

The present study investigates the theoretical basis for maintaining normal physiological functions in heat-stressed beef cattle by exploring the effects of niacin supplementation on the permeability of the rumen epithelial cell barrier. Herein, 12 Jinjiang bulls with an average weight of approximately 400 ± 20.0 kg were randomly divided into three groups, thermoneutral (TN), heat-stressed (HS), and heat-stressed niacin-supplemented (HN) groups, with 4 bulls in each group. The experiment spanned 70 days, and the plasma concentrations of D-lactic acid, diamine oxidase (DAO), lipopolysaccharides (LPSs), and inflammatory cytokines were analyzed. Additionally, we assessed the gene expression of tight junction proteins to understand the effect of niacin supplementation on heat-stressed beef cattle. Our results revealed that heat stress significantly increased the D-lactic acid and LPS levels in beef cattle plasma on days 30 and 45 of the experiment (p < 0.05). Moreover, it led to a significant rise in DAO levels on day 30 (p < 0.05). Niacin supplementation significantly reduced the LPS levels on day 30 (p < 0.05). Heat stress significantly elevated the plasma concentrations of inflammatory cytokines interleukin-1β (IL-1β), IL-2, IL-6, and tumor necrosis factor-α (TNF-α) (p < 0.05), while reducing the IL-4 concentration (p < 0.05). However, niacin supplementation effectively mitigated the concentrations of these inflammatory factors by reducing IL-1β, IL-2, IL-6, and TNF-α concentrations and increasing IL-4 concentrations. The mRNA expressions of tight junction proteins zonula occluden-1 (ZO-1), claudin-1, claudin-4, and claudin-7 were significantly downregulated (p < 0.05) in the HS group compared to those in the TN group, and those of ZO-1 and occludin were significantly upregulated (p < 0.05) in the HN group compared to those in the HS group. Notably, no significant differences were observed in ruminal papillae length and width among the studied groups (p > 0.05). Our findings indicate that heat stress adversely impacted the tight junction structure of the rumen epithelium, leading to a significant reduction in the expression of tight junction protein mRNA. Consequently, heat stress impaired the rumen mucosal barrier function, resulting in increased intestinal permeability. The mechanism underlying this effect may be associated with the decreased expression of tight junction protein genes in the rumen epithelial cells. However, niacin supplementation mitigated the detrimental effects of heat stress on intestinal permeability in beef cattle and increased the expression of tight junction protein genes in the rumen epithelium, thereby effectively protecting the rumen barrier in heat-stressed beef cattle. These results highlight the potential of nicotinic acid as a protective agent against the negative impacts of heat stress on intestinal integrity in beef cattle.

PSVI-14 Mitigating the Negative Effects of Heat Stress in Grow-Finish Pigs Using Water Delivered Oregano Essential Oil

Abstract Grow-finish pigs (n = 192) were used in a 28-day experiment to determine if adding oregano essential oil to the water would mitigate the detrimental effects of heat stress. Pigs (initial BW = 51.9 kg) were blocked by sex and BW and randomly allotted to a 2x2 factorial arrangement of water treatment (oregano essential oil vs. control) and environment (heat stress vs. thermoneutral). There were 6 pigs/pen (4 barrows and 2 gilts/pen) and 8 pens/treatment. Pigs were given 15 d to acclimate to pens and water treatment under thermoneutral conditions (21.1℃). Following acclimation, one-half the pigs were subjected to a 3-day diurnal heat stress (12 h at 33.3℃ and 12 h at 26.7℃). On d 22 of the experiment (3 d post-heat stress), one barrow/pen was euthanized; jejunal mucosa scrapings were collected, flash frozen in liquid nitrogen, and stored at -80oC for subsequent RNA isolation and cDNA creation. Gene expression of CDKN1A, TP53, GPX1, SOD1, SLC2A2, SLC2A5, and MUC2 were determined by qPCR using SYBR green, normalized using housekeeper genes and expressed relative to the control treatment using the 2-ΔΔCT method. Data were analyzed as RCB using GLM procedure in SAS 9.4 with fixed effects of water treatment, environment, and the interaction. Heat-stressed pigs had reduced ADG (P &amp;lt; 0.003) and Gain:Feed (P &amp;lt; 0.008) during the 3d heat stress compared with pigs housed in thermoneutral conditions. Post-heat stress, ADG (P &amp;lt; 0.001) and Gain:Feed (P &amp;lt; 0.001) increased in previously heat-stressed pigs compared with thermoneutral pigs. There was no effect of oregano supplementation before or during heat stress. However, in the post-heat stress period, ADG was increased (P &amp;lt; 0.05) by oregano supplementation in the water for both heat stressed and non-heat stressed pigs. Oregano supplementation did not affect ADFI before heat stress. An interaction (P &amp;lt; 0.005) of heat stress and water treatment was observed for ADFI during heat stress and after heat stress. During heat stress, oregano supplementation resulted in reduced feed intake. Post-heat stress ADFI was lowest for non-heat stressed pigs with no oregano supplementation. Oregano essential oil increased water consumption before (P &amp;lt; 0.02), during (P &amp;lt; 0.03), and after heat stress (P &amp;lt; 0.02), with an overall increase in water consumption of 35% compared with control pigs (P &amp;lt; 0.04). No interactions of heat stress and oregano supplementation were observed for gene expression. SLC2A2 expression tended (P &amp;lt; 0.08) to be downregulated when oregano essential oils were added to the water and upregulated following an acute heat stress. SLC2A5 expression was increased in pigs given oregano compared with control pigs (P &amp;lt; 0.02), but was unaffected by heat stress. Water delivered oregano essential oil increased water intake and had a slight effect on intestinal gene expression but did not mitigate the effects of a short-term heat stress.

Effect of heat stress on seed protein quality in mungbean [Vigna radiata (L.) Wilczek

AbstractAbiotic and biotic stresses impair the productivity of agricultural crops. Among abiotic stresses, the higher temperature (i.e., heat stress) is unfavourable for plant growth and development. In recent years, the mungbean [Vigna radiata (L.) Wilczek] demand has been increasing, which can satisfy human protein requirements. However, its productivity and quality are negatively impacted by heat stress due to climate change. This requires a broadening scope of mungbean adaptation to warmer climates. Hence, the objective of this study was to assess the effects of heat stress on various mungbean genotypes for their seed protein characteristics (total seed protein content, proportion of four protein fractions, and electrophoretic patterns on SDS‐gels). The 13 mungbean genotypes were grown under normal and heat‐stressed conditions by sowing seeds at two different times, that is, the normal sowing time in the last week of March and late sowing in the last week of April in the experimental plots. In late‐sown plants, the total seed proteins decreased by 4.1% to 9.3%. In addition, the relative proportion of glutelins and prolamins increased significantly while globulins and albumins decreased at high temperatures. Moreover, the intensity of polypeptides decreased under high temperatures. In our studies, some polypeptides appeared, and others disappeared in late‐sown genotypes. The disappearance of bands reveals a higher rate of protein degradation than synthesis under heat stress. The detrimental effects of heat stress on seed protein characteristics studied were more prominent in MH 318, IPM 02‐3 and PM‐5 and less noticeable in MH 125, MH 421 and PDM 139 genotypes.

Evaluation of biochemical changes in wheat varieties as influenced by terminal heat stress under varying environments

Climate is considered as the major uncontrollable factor in crop production. Alternation in the climate worldwide is predicted to have critical impact on crop production. High temperature negatively affects growth process of wheat by upsetting various physiological and biochemical processes and thereby affecting the nutritional quality of the crop. Heat stress during reproductive growth stages of wheat is detrimental to chloroplast activity, reducing activity of source organs and thereby reducing its sink capacity. Reduction in starch content is the major reason leading to yield loss during heat stress and this is because of accumulation of starch is associated with activities of various enzymes like sucrose synthase, soluble starch synthase, etc which are highly heat labile. Metabolic pathways are most altered during heat stress followed by secondary metabolite biosynthesis pathways. A field experiment was conducted during the Rabi season of 2020-21 at Student’s Instructional Farm of Acharya Narendra Deva University of Agriculture and Technology, Kumarganj, Ayodhya, Uttar Pradesh to evaluate the biochemical changes in wheat varieties as influenced by terminal heat stress. The treatment for the experiment consisted of sowing on three different dates i.e. D1 (30th November), D2 (15th December), D3 (30th December). It was observed that delayed sowing decreased substantially total chlorophyll content, total soluble sugar content in leaves of V1 (PBW-343) and V2 (HD-2967). This reduction was caused due to onset of high temperature during reproductive stage of wheat crop. Variety V3 (Halna) reduced the detrimental effect of heat stress and thus showed greater total chlorophyll content, total soluble sugar content. Proline content in leaves increased with age of crop up to 75 DAS in all the sowing dates this varying dates of sowing because proline is thought to play an adaptive role in mediating osmotic adjustment and protecting sub cellular structure in stressed plants.

Live yeast supplementation altered the bacterial community's composition and function in rumen and hindgut and alleviated the detrimental effects of heat stress on dairy cows.

The objective of this study was to investigate the effects of live yeast (LY, Saccharomyces cerevisiae) on the lactation performance, bacterial community, and functions in the rumen and hindgut of dairy cows under heat stress. Thirty-three multiparous (parity 3.9 ± 0.8) Holstein dairy cows (189.1 ± 6.6 d in milk at the beginning of the experiment) were randomly assigned to three groups (11 cows per treatment). Cows in the three groups were fed a diet without yeast (CON), with 10 g yeast/d/head (LY-10), and with 20 g yeast/d/head (LY-20). The yeast product contained 2.0 × 1010 CFU/g. Supplementing LY decreased the rectal temperature and respiratory rate of cows, and increased dry matter intake, milk yield, milk fat yield, milk protein yield, and milk lactose yield (P < 0.001), yet decreased milk urea nitrogen concentration (P = 0.035). Interaction effects of treatment × week were observed for rectal temperature (P < 0.05), respiratory rate (P < 0.05), milk yield (P = 0.015), milk urea nitrogen (P = 0.001), milk protein yield (P = 0.008), and milk lactose yield (P = 0.030). In rumen, LY increased the concentrations of acetate, isobutyrate, isovaterate, valerate, total volatile fatty acids (VFAs), and NH3-N (P < 0.05). Miseq sequencing of the 16S rRNA genes showed that LY increased the relative abundance of Prevotella and Prevotellaceae UCG-003 at the genus level with a series of enriched pathways in the metabolism of carbohydrates and protein. In fecal samples, LY did not affect the profile of VFAs (P > 0.05). Clostridium sensu stricto 1 (P = 0.013) and Actinobacillus (P = 0.011) increased in the relative abundance by LY, whereas Bacteroides (P = 0.016) and Oscillospirales UCG-010 (P = 0.005) decreased with a series of enriched pathways in carbohydrate metabolism, secondary bile acid biosynthesis. In summary, LY supplementation altered the bacterial community's composition and function in rumen and hindgut, and simultaneously alleviated the detrimental effects of heat stress on dairy cows. These findings provide extended insight into the effects of LY in the rumen and hindgut of dairy cows exposed to heat stress.

Thermosensing in plants: Deciphering the mechanisms involved in heat sensing and their role in thermoresponse and thermotolerance

With a gradual increase in the ambient temperature plants need to perceive these changes accurately and adjust accordingly in order to adapt and survive. Heat stress affects various developmental stages of plants and adversely impacts yield. Therefore, approaches for developing crops with heat tolerance and high crop productivity have now become major agricultural goals. In the heat sensing process, high temperature causes several changes in various components of the cell, including changes in the membrane fluidity, calcium ions, cytoskeleton elements and protein unfolding. Although some information regarding the signaling mechanisms activated upon sensing of high temperature has been available, only recently new insights have been gained in the thermosensing mechanisms in plants. This review focuses on the various molecular changes that occur within a cell with the rise in temperature and how these are linked to thermomorphogenesis and thermotolerance. Moreover, in the light of upcoming research, the role of photoreceptors, phytohormones, DNA and RNA in heat perception has been given greater attention. • Detrimental effects of heat stress on plants. • Role of various cellular components i.e. cell membranes, proteins, cytoskeleton elements, DNA and RNA in heat perception. • Sensing of high ambient temperature leads to two different responses i.e. thermomorphogenesis and thermotolerance. • Photoreceptor function as thermosensor.

Sexual selection moderates heat stress response in males and females.

A widespread effect of climate change is the displacement of organisms from their thermal optima. The associated thermal stress imposed by climate change has been argued to have a particularly strong impact on male reproduction but evidence for this postulated sex-specific stress response is equivocal.One important factor that may explain intra- and interspecific variation in stress responses is sexual selection, which is predicted to magnify negative effects of stress. Nevertheless, empirical studies exploring the interplay of sexual selection and heat stress are still scarce.We tested experimentally for an interaction between sexual selection and thermal stress in the red flour beetle Tribolium castaneum by contrasting heat responses in male and female reproductive success between enforced monogamy and polygamy.We found that polygamy magnifies detrimental effects of heat stress in males but relaxes the observed negative effects in females. Our results suggest that sexual selection can reverse sex differences in thermal sensitivity, and may therefore alter sex-specific selection on alleles associated with heat tolerance.Assuming that sexual selection and natural selection are aligned to favour the same genetic variants under environmental stress, our findings support the idea that sexual selection on males may promote the adaptation to current global warming. Read the free Plain Language Summary for this article on the Journal blog.

Uso de biotecnologías reproductivas para mejorar la fertilidad de vacas lecheras repetidoras y con estrés por calor

Cows that do not become pregnant during early lactation after successive inseminations are usually classified as repeat-breeder cows. Furthermore, heat stress has a pronounced deleterious effect on fertility in dairy herds throughout the world, especially in hot and humid summer months in tropical and subtropical areas. Studies describes the detrimental effect of heat stress on reproduction, with emphasis on carry over effects of heat stress on oocyte quality, embryo development and P/AI. Additionally, lower fertilization rate is also an important characteristic associated with repeatbreeder cows. In repeat-breeder cows, decreased fertility has been related to a deleterious effect on oocyte quality. Thus, the fertility problems observed in repeat-breeder and heat stress cows may be related to poor oocyte quality associated with a metabolic status. Studies support thar embryo transfer can be a practical and effective solution to achieve pregnancy in repeat-breeder and heatstressed dairy cows (with reduced oocyte quality and fertility to insemination).

Deleterious Effects of Heat Stress on Poultry Production: Unveiling the Benefits of Betaine and Polyphenols

Managing and controlling environmental temperature conditions using practical strategies is crucial to avoid the negative impacts of high environmental temperature, improving poultry production and welfare. High environmental temperature is one of the significant factors challenging poultry production during hot seasons or in tropical areas causing heat stress (HS). The detrimental effects of HS on broilers range from reduced growth performance to impaired poultry meat quality. HS impairs physiological responses caused by alteration in blood parameters, which could lead to impaired product quality by reducing moisture content and altering the production of antioxidant enzymes resulting in increased oxidative stress. There has been a focus on the use of nutritional supplements as a cost effective HS amelioration strategy, such as betaine and polyphenols. Supplementing broiler chicken’s diets with polyphenols aims to enhance growth performance via reduced levels of oxidative stress in tissues under HS conditions. Furthermore, using betaine as an osmolyte aims to protect tissues during osmotic stress conditions. The current review reveals that betaine and polyphenols are essential under crucial conditions such as HS to protect tissues from oxidative damage.

Effects of Selenium-Methionine against Heat Stress in Ca2+-Cytosolic and Germination of Olive Pollen Performance

Climate change (CC), which causes temperatures to rise steadily, is causing global warming. Rising temperatures can reduce plant yield and affect pollen characteristics. In particular, heat stress strongly influences pollen viability for its sensitivity to this extreme environmental condition. This work evaluated the effect of heat stress on olive pollen after in vitro incubation at different temperatures (20, 30, and 40 °C). Furthermore, the potential of selenium-methionine (Se-met) in mitigating the detrimental effects of heat stress on olive pollen was investigated. In particular, how thermal stress can affect pollen was evaluated by testing the effect of temperature on pollen germinability and morphology and cytosolic Ca2+ content. The results suggest that the heat stress at 40 °C caused a marked reduction in the germination rate, changes in the morphology of the external pollen wall, and a decreased response to Ca2+-agonist agents. On the contrary, in vitro treatment of pollen with Se-met improved the germination rate and Ca2+-cytosolic homeostasis under heat stress conditions and confirmed the protective role of this compound in containing the hydrogen peroxide (H2O2) toxicity. Therefore, this study revealed that organic selenium could play a crucial role in promoting heat tolerance in olive tree pollen.

Impacts of Heat Stress on Rabbit Immune Function, Endocrine, Blood Biochemical Changes, Antioxidant Capacity and Production Performance, and the Potential Mitigation Strategies of Nutritional Intervention.

Heat stress has become a widespread concern in the world, which is one of the major environmental stressors and causes substantial economic loss in the rabbit industry. Heat stress leads to multiple damages to the health of rabbits, such as organ damage, oxidative stress, disordered endocrine regulation, suppressed immune function and reproductive disorders, ultimately, induces the decreased production performance and increased mortality. Nutritional approaches, including feeding strategies, adjusting feed formula, and supplementing vitamins, minerals, electrolytes, Chinese herbal medicines, and functional active substances to the feed, were reported to mitigate the detrimental effects of heat stress in rabbits. Therefore, elucidating the damage of heat stress to rabbits; proper management and nutritional approaches should be considered to solve the heat stress issue in rabbits. This review highlights the scientific evidence regarding the effects of heat stress on rabbit's immune function, endocrine, blood biochemical changes, antioxidant capacity and production performance, and the potential mitigation strategies of nutritional intervention to alleviate heat stress in rabbits; which could contribute to develop nutritional strategies in relieving heat stress of rabbits.

Heat Stress Affects Jejunal Immunity of Yellow-Feathered Broilers and Is Potentially Mediated by the Microbiome.

In the perspective of the global climate change leading to increasing temperature, heat stress (HS) has become a severe issue in broiler production, including the indigenous yellow-feathered broilers. The present study aimed to investigate the effects of HS on jejunal immune response, microbiota structure and their correlation in yellow-feathered broilers. A total of forty female broilers (56-days-old) were randomly and equally divided into normal treatment group (NT group, 21.3 ± 1.2°C, 24 h/day) and HS group (32.5 ± 1.4°C, 8 h/day) with five replicates of each for 4 weeks feeding trial. The results showed that HS exposure increased the contents of TNF-α, IL-1β, and IL-6 in jejunal mucosa (p < 0.05). The HS exposure up-regulated the relative fold changes of NF-κB, TNF-α, IL-1β, and IL-6 (p < 0.01) while down-regulated the relative fold change of IFN-γ in jejunal mucosa (p < 0.05). Meanwhile, HS had no significant impacts on alpha diversity of jejunal microbiota such as Simpson, Chao1 richness estimator (Chao 1), abundance-based coverage estimators (ACE), and Shannon index (p > 0.10). Broilers exposed to HS reduced the jejunal microbial species number at the class and order level (p < 0.05). Moreover, HS decreased the relative abundance of Ruminococcus, Bdellovibrio, and Serratia at the genus level in jejunum (p < 0.05). At the phylum level, four species of bacteria (Bacteroidetes, Cyanobacteria, Thermi, and TM7) were significantly associated with immune-related genes expression (p < 0.05). At the genus level, ten species of bacteria were significantly correlated with the expression of immune-related genes (p < 0.05), including Caulobacteraceae, Actinomyces, Ruminococcaceae, Thermus, Bdellovibrio, Clostridiales, Sediminibacterium, Bacteroides, Sphingomonadales and Ruminococcus. In particular, the microbial with significantly different abundances, Ruminococcus and Bdellovibrio, were negatively associated with pro-inflammatory cytokines expression (p < 0.05). These findings demonstrated that HS exposure promoted the production of pro-inflammatory cytokines in yellow-feathered broilers’ jejunum. The detrimental effects of HS on jejunal immune response might be related to dysbiosis, especially the reduced levels of Ruminococcus and Bdellovibrio.

Evaluation of Wheat Varieties for Terminal Heat Stress under Varying Environments

Climate change and global warming have increasingly become relevant factors in recent years in determining the success of wheat production under heat stress conditions. Throughout its growth period wheat crop requires varying degrees of temperature to achieve ideal growth. Any variation from optimal temperature adversely affects plant growth and development. Many places where wheat is grown have high temperatures at the time of grain filling which is a major constraint on yield potential. A field experiment was conducted during the Rabi season of 2020-21 at Student’s Instructional Farm of Acharya Narendra Deva University of Agriculture and Technology, Kumarganj, Ayodhya, Uttar Pradesh to evaluate the performance of wheat varieties under heat stress conditions. The treatment for the experiment consisted of sowing on three different dates i.e. D1 (30th November), D2 (15th December), D3 (30th December). It was observed that time of sowing decreased substantially almost all the yield components measured viz; number of ear bearing tillers per plant, number of grains per ear, ear length (cm), grain yield per plant (g), biological yield per plant (g), which caused severe reduction of yield in V1 (PBW-343) and V2 (HD-2967). This reduction was caused due to onset of high temperature during crop growth and particularly grain filling. Variety V3 (Halna) reduced the detrimental effect of heat stress by improving physiological traits which ultimately helped in obtaining higher yield.

Genetic Improvement of Heat Stress Tolerance in Cereal Crops

Crop heat stress is a threat to food supply, with heatwaves expected to increase in frequency and intensity globally. In addition to yield loss, heat stress dramatically reduces fertility and seed-setting rate, grain quality and weight, and seed germination and growth. Genetic variability for heat stress tolerance can be used in breeding programs to develop tolerant genotypes. The availability of genome assemblies with high-confidence sequences for many cereal crops, including rice, maize, wheat and barley, now allows the identification of heat stress tolerance-associated genes and gene networks. This review focuses on synthesizing current advances in understanding the detrimental effects of heat stress on cereal crop production at the physiological and genetic levels. It provides an account of available genomic resources, genetic variation, candidate genes, and molecular markers for heat stress tolerance. Lastly, this review offers insight into crop genetic improvement for heat stress tolerance, including germplasm screening in glasshouse and field trials, marker-assisted selection, mapping genomic loci and identification of candidate genes, and genomic-assisted breeding.

Constant and cyclic chronic heat stress models differentially influence growth performance, carcass traits and meat quality of broilers

This experiment compared the effects of 2 chronic heat stress (HS) models, constant (coHS), and cyclic (cyHS), on broiler performance, carcass characteristics, and meat quality. A total of 720 male chicks from a Cobb 500 line were placed in 12 environmentally controlled chambers divided into 2 pens of 30 birds. Before the experimental HS models were applied, chamber temperatures were gradually decreased from 32°C at placement to 24°C on d 20. From 20 to 41 d, 4 chambers were set to 35°C (coHS), and 4 chambers were set to 35°C for 12 h and 24°C for the next 12 h (cyHS). Four thermoneutral chambers were maintained at 24°C with half of the birds pair-fed to equalize feed intake (FI) with coHS birds (TN-coPF) and half fed ad-libitum (TN-al). From 20 to 41 d, FI and BW gain (BWG) of cyHS, coHS and TN-coPF birds were decreased (P < 0.001), whereas feed conversion ratio (FCR) was increased (P < 0.001) for coHS and TN-coPF birds compared with TN-al birds. The overall BWG and FCR of coHS birds were lower (P < 0.001) than TN-coPF birds. Both HS models reduced (P < 0.001) carcass weight, pectoralis major yield, total breast meat yield, and increased (P < 0.001) wing yield relative to TN-al birds, with each of these measurements more impacted by coHS than by cyHS. Pair-fed birds had lower (P < 0.001) fat pad and a higher total breast meat yield than coHS birds. They also had the lowest (P < 0.001) pectoralis major ultimate pH and yellowness, and these parameters were lower (P < 0.001) for coHS birds than for TN-al birds. Both HS models reduced (P < 0.001) the incidence of woody breast and white striping. Thus, these data indicate that the detrimental effects of HS cannot be entirely explained by reduced FI and that HS per se affects metabolic pathways associated with muscle and lipid accretion in broilers.

Glycine Betaine and β-Aminobutyric Acid Mitigate the Detrimental Effects of Heat Stress on Chinese Cabbage (Brassica rapa L. ssp. pekinensis) Seedlings with Improved Photosynthetic Performance and Antioxidant System.

Heat stress is one of the major abiotic factors that limit the growth, development, and productivity of plants. Both glycine betaine (GB) and β-aminobutyric acid (BABA) have received considerable attention due to their roles in stimulating tolerance to diverse abiotic stresses. In order to understand how GB and BABA biostimulants alleviate heat stress in a cool-weather Chinese cabbage (Brassica rapa L. ssp. pekinensis) plant, we investigated the GB- and BABA-primed heat-stressed plants in terms of their morpho-physiological and biochemical traits. Priming with GB (15 mM) and BABA (0.2 mM) was conducted at the third leaf stage by applying foliar sprays daily for 5 days before 5 days of heat stress (45 °C in 16 h light/35 °C in 8 h dark) on Chinese cabbage seedlings. The results indicate that GB and BABA significantly increased chlorophyll content, and the parameters of both gas exchange and chlorophyll fluorescence, of Chinese cabbage under heat stress. Compared with the unprimed heat-stressed control, the dry weights of GB- and BABA-primed plants were significantly increased by 36.36% and 45.45%, respectively. GB and BABA priming also greatly mitigated membrane damage, as indicated by the reduction in malondialdehyde (MDA) and electrolyte leakage through the elevation of proline content, and increased activity levels of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX). Taken together, GB and BABA have great potential to enhance the thermotolerance of Chinese cabbage through higher photosynthesis performance, osmoprotection, and antioxidant enzyme activity.

In ovo Feeding of L-Leucine Improves Antioxidative Capacity and Spleen Weight and Changes Amino Acid Concentrations in Broilers After Chronic Thermal Stress

L-Leucine (L-Leu) was demonstrated to confer thermotolerance by in ovo feeding in broiler chicks and chickens in our previous studies. However, the L-Leu-mediated roles in recovering from the detrimental effects of heat stress in broilers are still unknown. This study aimed to investigate the effects of L-Leu in ovo feeding on the growth performance, relative weight of organs, serum metabolites and antioxidant parameters, and gene expression profiles in broiler chickens after chronic heat stress. Fertilized broiler eggs (Ross 308) were subjected to in ovo feeding of sterile water (0.5 mL/egg) or L-Leu (69 μmol/0.5 mL/egg) on embryonic day 7. After hatching, the male chicks were separated and used for the current study. All chickens were subjected to thermal stress exposure from 21 to 39 days of age and 1 week of recovery from 40 to 46 days of age. The results showed that in ovo feeding of L-Leu did not affect the body weight gain or relative weight of organs under chronic heat stress; however, the serum glutathione peroxidase was significantly increased and serum malondialdehyde was significantly decreased by L-Leu at 39 days of age. After 1 week of recovery, in ovo feeding of L-Leu significantly improved the relative spleen weight at 46 days of age. Subsequent RNA-seq analysis in the spleen showed that a total of 77 significant differentially expressed genes (DEGs) were identified, including 62 upregulated DEGs and 15 downregulated DEGs. Aspartic-type endopeptidase and peptidase activities were upregulated after recovery in the L-Leu group. The expression of genes related to B cell homeostatic proliferation and vestibular receptor cell differentiation, morphogenesis and development was downregulated in the L-Leu group. Moreover, the concentrations of serum catalase, total antioxidative capacity, isoleucine and ammonia were significantly decreased by L-Leu in ovo feeding after recovery. These results suggested that L-Leu in ovo feeding promoted the recovery of antioxidative status after chronic heat stress in broiler chickens.