Severe Heat Stress Research Articles

Modelling THI effects on milk production and lactation curve parameters of Holstein dairy cows.

The main objective of this study was to determine the potential impact of heat stress (HS) on milk production and lactation curve parameters of Holstein dairy cows. Milk, fat, protein, and somatic cell count test-day records collected between 2013 and 2019 from 947 cows in 23 herds were combined with THI calculated from meteorological data recorded between 2013 and 2019. The temperature-humidity index (THI) was used to investigate the effect of heat stress. The severity of heat stress was measured using the temperature-humidity index (THI) and the impacts of different THIs-low (≤68), moderate (68-72), and high (≥72) on production performance and lactation curve parameters were measured. The nonlinear model of Wood was applied for modeling the lactation curve. Analysis of variance was applied to test the effects of three levels of THI on milk production, its composition, and lactation curve parameters. Results showed losses due to heat stress. A decrease in milk yield and fat and protein content was reported. Fat and protein contents tended to decrease steadily with increasing values of THI. Milk yield ranged from 17.882±0.064 (68<THI<72) to 16.503±0.035kg/j (THI>72), fat and protein contents ranged from 3.551±0.041 to 3.449±0.026 and from 3.246±0.031%, to 3.113 (0.029) for 68<THI<72 and THI>72, respectively. Somatic cell score was marked by an increase (from 4.143 to 4.358) at the highest ranges of THI>72 and decreased values (from 4.143 to 3.857) at the lowest ranges of THI. Heat stress showed a significant effect on the parameters of the lactation curve. The increased value of THI showed a significant effect on milk yield THI was in a significant negative correlation with the yield, and quality of milk. The effect of THI was highly significant (P<0.05) for all parameters of the lactation curve and milk yield. Cows exposed to THI between 68 and 72 achieved the highest peak milk yields and the highest total yield of 305 days of lactation (Y305).

Oxidative stress in response to heat stress in wild caught Namaqua rock mice, Micaelamys namaquensis.

Modelling of anthropogenic induced climate suggests more frequent and severe heatwaves in the future, which are likely to result in the mass die-off of several species of organisms. Oxidative stress induced by severe heat stress has previously been associated with a reduction in animal cognitive performance, depressed reproduction and lower life expectancy. Little is known about the non-lethal consequences of species should they survive extreme heat exposure. We investigated the oxidative stress experienced by the Namaqua rock mouse, a nocturnal rodent, using two experimental heat stress protocols, a 6 hour acute heat stress protocol without access to water and a 3-day heatwave simulation with ad libitum water. Oxidative stress was determined in the liver, kidney and brain using malondialdehyde (MDA) and protein carbonyl (PC) as markers of oxidative damage, and superoxide dismutase (SOD) and total antioxidant capacity (TAC) as markers of antioxidant defence. Incubator heat stress (heat and dehydration stress) was brought about by increasing the body temperatures of animals to 39-40.8°C for 6 hours. Following incubator heat stress, significantly higher levels of MDA were observed in the liver. Dehydration did not explain the variation in oxidative markers and is likely a combined effect of thermal and dehydration stress. Individual body mass was significantly negatively correlated to kidney SOD and lipid peroxidation. A heatwave was simulated using a temperature cycle that would naturally occur during a heatwave in the species' local habitat, with a maximal ambient temperature of 38°C. Following the simulated heatwave, SOD activity of the kidney demonstrated significantly lowered activity suggesting oxidative stress. Current heat waves in this species have the potential of causing oxidative stress. Heat and dehydration stress following exacerbated temperatures are likely to incur significant oxidative stress in multiple tissues demonstrating the importance of water availability to allow for rehydration to prevent oxidative stress.

Arbuscular Mycorrhizal Inoculation Enhances Endurance to Severe Heat Stress in Three Horticultural Crops

Global climate change is increasing temperatures worldwide, which greatly affects all biological relationships. Plant and soil ecosystems are also suffering in this new scenario, especially in semi-arid areas where water resources are limited. Regarding agricultural crops, temperatures that increase dramatically negatively affect fruit production and quality, making it mandatory to find sustainable practices to cope with these new situations. Symbiotic microorganisms in general and arbuscular mycorrhizal fungi in particular have been revealed as promising methods of alleviating stress that are respectful of the environment and soil equilibrium. In this work, we demonstrate the suitability of an ultra-pure, in vitro-issued arbuscular mycorrhizal inoculant for alleviating severe heat stress when applied to three important agricultural crops (tomato: Solanum lycopersicum L.; pepper: Capiscum annuum L.; cucumber: Cucumis sativus L.) under agronomic conditions. Inoculated plants had greatly improved endurance under heat stress because of increased vigor, productivity, and fruit quality. Considering the actual scenario of global climate change, our results shed a light of hope and indicate more sustainable cultivation practices adapted to global change.

Linking population size structure, heat stress and bleaching responses in a subtropical endemic coral

Anthropocene coral reefs are faced with increasingly severe marine heatwaves and mass coral bleaching mortality events. The ensuing demographic changes to coral assemblages can have long-term impacts on reef community organisation. Thus, understanding the dynamics of subtropical scleractinian coral populations is essential to predict their recovery or extinction post-disturbance. Here we present a 10-yr demographic assessment of a subtropical endemic coral, Pocillopora aliciae (Schmidt-Roach et al. in Zootaxa 3626:576–582, 2013) from the Solitary Islands Marine Park, eastern Australia, paired with long-term temperature records. These coral populations are regularly affected by storms, undergo seasonal thermal variability, and are increasingly impacted by severe marine heatwaves. We examined the demographic processes governing the persistence of these populations using inference from size-frequency distributions based on log-transformed planar area measurements of 7196 coral colonies. Specifically, the size-frequency distribution mean, coefficient of variation, skewness, kurtosis, and coral density were applied to describe population dynamics. Generalised Linear Mixed Effects Models were used to determine temporal trends and test demographic responses to heat stress. Temporal variation in size-frequency distributions revealed various population processes, from recruitment pulses and cohort growth, to bleaching impacts and temperature dependencies. Sporadic recruitment pulses likely support population persistence, illustrated in 2010 by strong positively skewed size-frequency distributions and the highest density of juvenile corals measured during the study. Increasing mean colony size over the following 6 yr indicates further cohort growth of these recruits. Severe heat stress in 2016 resulted in mass bleaching mortality and a 51% decline in coral density. Moderate heat stress in the following years was associated with suppressed P. aliciae recruitment and a lack of early recovery, marked by an exponential decrease of juvenile density (i.e. recruitment) with increasing heat stress. Here, population reliance on sporadic recruitment and susceptibility to heat stress underpin the vulnerability of subtropical coral assemblages to climate change.

Regulation of DNA (de)Methylation Positively Impacts Seed Germination during Seed Development under Heat Stress.

Seed development needs the coordination of multiple molecular mechanisms to promote correct tissue development, seed filling, and the acquisition of germination capacity, desiccation tolerance, longevity, and dormancy. Heat stress can negatively impact these processes and upon the increase of global mean temperatures, global food security is threatened. Here, we explored the impact of heat stress on seed physiology, morphology, gene expression, and methylation on three stages of seed development. Notably, Arabidopsis Col-0 plants under heat stress presented a decrease in germination capacity as well as a decrease in longevity. We observed that upon mild stress, gene expression and DNA methylation were moderately affected. Nevertheless, upon severe heat stress during seed development, gene expression was intensively modified, promoting heat stress response mechanisms including the activation of the ABA pathway. By analyzing candidate epigenetic markers using the mutants’ physiological assays, we observed that the lack of DNA demethylation by the ROS1 gene impaired seed germination by affecting germination-related gene expression. On the other hand, we also observed that upon severe stress, a large proportion of differentially methylated regions (DMRs) were located in the promoters and gene sequences of germination-related genes. To conclude, our results indicate that DNA (de)methylation could be a key regulatory process to ensure proper seed germination of seeds produced under heat stress.

Impacts on two dairy breeds of adding a third (night) cooling event under extreme ambient heat.

Impacts of an additional cooling event during the night on physiological and productive parameters of two breeds (B) of dairy cows under severe heat stress conditions were determined. Fifteen Holstein (H) and 15 Jersey x Holstein (JxH) cows were assigned to one of the two cooling strategies (CS), where the difference was an added 1 h cooling event during the night (i.e., 3X and 4X cooling events) with the 4X group having the added night cooling event. Maximum and minimum average temperature/humidity indices during the study were 86 and 77 units, respectively. There were no CS x B interactions for any response variable. Body condition score (BCS) was similar between CS, but H cows had higher (P<0.05) condition than JxH. There were no differences in rectal temperature due to CS or B. Respiration rate between breeds and cooling strategies were similar throughout the day. However body surface temperatures of head, thurl, right flank, and udder were higher (P<0.05) in 3X versus 4X cows, and H cows maintained a higher (P < 0.05) temperature in thurl and right flank than JxH during PM hours. Metabolites and hormone concentrations were not affected by CS, but H cows had lower (P < 0.05) triiodothyronine and higher (P < 0.05) thyroxine, than JxH. The 4X cows had higher (P<0.05) milk yield and milk energy output than 3X cows. While H cows produced more milk than JxH, the latter had higher (P < 0.05) milk component levels. In general, JxH cows were judged to have to demonstrate a more desirable physiological response and milk composition outcome than H cows. An additional night cooling event was judged to result in more desirable physiological and productive responses than in cows without this extra night cooling event under the extremely hot and dry environmental conditions during the study.

Severe Heat Stress Resulted in High Coral Mortality on Maldivian Reefs following the 2015–2016 El Niño Event

Coral cover worldwide has been declining due to heat stress caused by climate change. Here we report the impacts of the 2015–2016 El Niño mass coral bleaching event on the coral cover of reefs located on central and northern atolls of the Maldives. We surveyed six reef sites in the Alifu Alifu (Ari) and Baa (South Maalhosmadulu) Atolls using replicate 20 m benthic photo transects at two depths per reef site. Live and recently dead coral cover identified from images differed between reef sites and depth. Recently dead corals on average made up 33% of the coral assemblage at shallow sites and 24% at deep sites. This mortality was significantly lower in massive corals than in branching corals, reaching an average of only 6% compared to 41%, respectively. The best predictors of live coral cover were depth and morphology, with a greater percentage of live coral at deep sites and in massive corals. The same predictors best described the prevalence of recently dead coral, but showed inverse trends to live coral. However, there was high variability among reef sites, which could be attributed to additional local stressors. Coral bleaching and resulting coral mortalities, such as the ones reported here, are of particular concern for small island nations like the Maldives, which are reliant on coral reefs.

Characterization of Two Small Heat Shock Protein Genes (Hsp17.4 and Hs20.3) from Sitodiplosis mosellana, and Their Expression Regulation during Diapause.

Simple SummarySmall heat shock proteins (sHsps) play important roles in thermal adaptation of various organisms, and insect diapause. Sitodiplosis mosellana, a key pest of wheat worldwide, undergoes obligatory larval diapause in soil to survive adverse temperature extremes during hot summers and cold winters. The objectives of this study were to characterize two sHsp genes from S. mosellana (SmHsp17.4 and SmHsp20.3), and determine their expression in response to diapause, extreme high/low temperatures, or 20-hydroxyecdysone (20E) treatment. Expression of SmHsp17.4 was down-regulated upon entry into diapause, but up-regulated during the shift to post-diapause quiescence. In contrast, expression of SmHsp20.3 was not affected by entry into diapause, but was pronounced during summer and winter. Furthermore, transcripts of both SmHsps were highly responsive to heat (≥35 °C) and cold (≤−5 °C) during diapause, and topical application of 20E on diapausing larvae also induced SmHsp17.4 in a dose-dependent manner. Notably, the recombinant SmHsp17.4 and SmHsp20.3 exhibited significant molecular chaperone activity. In conclusion, SmHsp17.4 and SmHsp20.3 play essential roles in heat/cold adaptation, and 20E-mediated SmHsp17.4 was also likely involved in diapause termination. Results have improved our understanding of the molecular mechanism underlying diapause and related stress tolerance in S. mosellana.Sitodiplosis mosellana, a periodic but devastating wheat pest that escapes temperature extremes in summer and winter by undergoing obligatory diapause. To determine the roles of small heat shock proteins (sHsps) in diapause of S. mosellana, we characterized two sHsp genes, SmHsp17.4 and SmHsp20.3, from this species. Both SmHsps contained the conserved α-crystallin domain and the carboxy-terminal I/VXI/V motif of the sHsp family. SmHsp17.4 had one intron while SmHsp20.3 had none. Quantitative PCR revealed that SmHsp17.4 expression decreased after diapause initiation, but substantially increased during transition to post-diapause quiescence. In contrast, SmHsp20.3 expression was not affected by entry of diapause, but was clearly up-regulated during summer and winter. Short-term more severe heat-stress (≥35 °C) of over-summering larvae or cold-stress (≤−5 °C) of over-wintering larvae could stimulate higher expression of both genes, and SmHsp17.4 was more responsive to cold stress while SmHsp20.3 was more sensitive to heat stress. Notably, transcription of SmHsp17.4, but not SmHsp20.3, in diapausing larvae was inducible by 20-hydroxyecdysone (20E). Recombinant SmHsp17.4 and SmHsp20.3 proteins also displayed significant chaperone functionality. These findings suggest that both SmHsps play key roles in stress tolerance during diapause; and 20E-regulated SmHsp17.4 was also likely involved in diapause termination.

Heat precondition is a potential strategy to combat hepatic injury triggered by severe heat stress

AimEnvironmental heat stress alters physiological and biochemical functions which leads to multiorgan dysfunction including severe hepatic injury in animals. We hypothesize that heat preconditioning can be potential intervention in combating heat illnesses. Main methodsSprague Dawley rats were exposed to moderate heat stress, severe heat stress and heat preconditioning in heat simulation chamber. Mean arterial pressure, heart rate, skin and core temperature were monitored in pre and post heat exposed animals. After stress exposure, blood for hemodynamic and liver tissue for liver function tests, oxidative stress, inflammatory variables and structural studies were collected from rats. Hepatic mitochondria were isolated to study the key structural alterations and functional changes by transmission electron microscopy. Key findingsThe effect of heat precondition shows improvement in time to attain the core temperature, weight loss, blood pressure and heart rate in rats. Results exhibited decreased levels of liver function tests, elevated levels of free radicals and inflammatory cytokines in heat exposed liver as compared with heat preconditioned animals. Expression levels of mitochondrial heat shock protein 60, superoxide dismutase 1 and uncoupling protein 1 along with activity of electron transport chain complexes I-V were examined and found to be increased in heat preconditioned as compared to heat stressed animals. Morphological studies of liver parenchyma demonstrated reduction in structural deterioration of hepatic lobules and restoration of mitochondrial structural integrity in heat preconditioned rats. SignificancePresent study suggests that heat preconditioning intervention plays a crucial role in protection against heat induced hepatic injury in animals.

Kıl keçilerinde ısı stresinin toplam oksidan kapasitesine etkisi

Aim of this study was to investigate the effect of heat stress on total oxidant capacity (TOC) in hair goats grown at different altitudes in the same season. The study was carried out on 208 hair goats (25 male and 183 female) in 11 different districts of Adana province (Turkey) in the summer season. The districts were grouped as 0-99 m (Grop 1), 100-500 m (Group 2) and higher than 500 m (Group 3) according to altitude characteristics, and goats were classified into two groups as under 3 years and 4 years or older. Blood samples were collected, serums harvested and stored at -20°C until TOC analysis. Heat stress was determined according to temperature humidity index (THI). There were severe and moderate heat stress in groups 1 and 2, respectively (P&amp;lt;0.001). TOC was significantly lower in group 2 compared to the other groups (P&amp;lt;0.001). The highest TOC was measured in group 3 (P&amp;lt;0.001). And TOC was significantly higher in animals aged 4 and older compared to under 3 years of age (P&amp;lt;0.05). Although male goats were exposed to significantly higher THI than female goats (P&amp;lt;0.01), TOC levels were found similar in both groups (P&amp;gt;0.05). In conclusion, altitude, THI, age and gender had a complex effect on TOC.

Heat stress resistance drives coordination of emissions of suites of volatiles after severe heat stress and during recovery in five tropical crops

Severe heat stress leads to a major reduction in foliage photosynthetic characteristics and the initial reduction and degree of recovery depend on species heat resistance. However, how the emissions of biogenic volatile organic compounds (BVOC) from different biochemical pathways are coordinated with photosynthetic modifications from the initial stress response through recovery are poorly understood, and the data are especially limited for short-living tropical crop species. We exposed leaves of five tropical crop species (A. cruentus, A. hybridus, S. aethiopicum, T. occidentalis and V. unguiculata) to severe heat treatment of 49 °C and a control treatment of 25 °C for 5 min and studied the modifications in foliage photosynthetic characteristics and constitutive BVOC emissions and elicitation of stress-induced volatiles through a 48 h recovery period upon return to non-stressed conditions. Overall, heat shock application resulted in a major inhibition of net assimilation rate similarly in all species indicating cellular damage and photosynthetic decay. However, species strongly varied in photosynthetic recovery with A. hybridus recovering the most and S. aethiopicum the least. Heat shock stress led to enhancement of emissions characterizing increased leaf oxidative status, in particular to enhanced emissions of lipoxygenase pathway volatiles (LOX). Surprisingly, LOX emissions were not associated with species heat resistance, but were greater in physiologically more active species with greater photosynthetic capacity. Species with greater constitutive isoprenoid emission capacity were generally more heat resistant, but terpenoid emissions were induced to a greater degree in less heat resistant species that likely suffered the most from the applied level of stress. Heat stress affected different groups of terpenoids - isoprene, monoterpenes and sesquiterpenes - to a different degree in different species, resulting in unique species-specific emission blends at different times of recovery. Heat stress had relatively minor effects on benzenoid emissions with moderately enhanced emissions primarily in V. unguiculata that differed from the other species by lower constitutive terpenoid emissions correspondent to its relatively high heat resistance. The results collectively demonstrate that species heat resistance is associated with the quantitative and qualitative characteristics of heat stress-dependent volatile emissions in different tropical crop species. We argue that these species-specific patterns need consideration in simulating volatile emissions under heat stress.

Improving productivity of Australian wheat by adapting sowing date and genotype phenology to future climate

With global food demand predicted to grow by 50–80% by 2050, timely strategies are required to best adapt to the projected changes in agriculture. In this study, we illustrated how adaptation strategies not requiring additional inputs (sowing date and genotype choice) could be used to minimise the impact of projected stresses and raise wheat productivity in Australia. Yield and abiotic stresses impacting productivity of wheat crops were quantified in silico for the 1990s (1976–2005) and the 2050s (2036–2065) across the Australian wheatbelt using a modified version of the Agricultural Production Systems sIMulator (APSIM) and 33 Global Circulation Models (GCMs) under the Representative Concentration Pathways (RCP) 8.5. Two adaptation strategies were assessed: adaptation of sowing dates and/or adaptation of cultivars of contrasting phenology (i.e. fast-spring, mid-spring, slow-spring and fast-winter cultivars). For a given cultivar, optimum sowing windows associated with highest long-term yield were projected to shift to earlier dates by 2050 at most locations, with an average shift of 9.6 days for a mid-spring cultivar. Sowing early maturing cultivars enabled further increase in projected yield in major parts of the wheatbelt. In the tested conditions, sowing and cultivar adaptation allowed simulated crops to minimise the impact of abiotic stresses while limiting the shortening of the grain filling period due to global warming. Thanks to CO2 fertilisation and proper adaptation, the frequency of severe frost, heat and drought stress was reduced in all regions, except in the West where severe drought was projected to occur more frequently in the 2050s. This allowed a national yield increase of 4.6% with reduced risk of crop failure at most locations. While the study focused on stress avoidance through adaptations (sowing dates and choice of cultivar phenology), breeding for enhanced drought and heat tolerance appeared promising avenues to further improve wheat productivity.

Результати морфологічного дослідження крові корів за теплового стресу залежно від стадій температурно-вологісного індексу

The results of morphological studies of the blood of cows under heat stress indicate that the temperature - humidity index (THI) of animals in comfortable conditions (THI - 68-71) the number of erythrocytes is 5.78 ± 0.13 T / l, the hematocrit - 24.98 ± 1.02%, hemoglobin content - 89.96 ± 2.63 g / l, MCV - 39.76 ± 2.31 fl; MCH - 15.56 ± 1.32 pg; MCHC - 39.14 ± 1.95 g / dl. The total number of leukocytes in the blood of cows is 7.17 ± 0.54 G / l. The relative content (leukogram) and the absolute number of certain types of leukocytes in the blood of cows has no abnormalities. This suggests that the morphological parameters of the blood of cows in the comfortable conditions of THI meet the normative values for cattle and, in particular, Holstein breed. Under moderate heat stress (THI -72-78), in the blood of cows, along with a significant increase in respiratory rate and heart rate, there is a tendency to increase the number of erythrocytes to 5.82 ± 0.69 T / l, there is a significant increase in hematocrit and MCV by 20 and 47%, and a significant decrease in hemoglobin, MCH and MCHC - by 32, 35 and 55%, respectively, relative to control. However, in the blood of cows there is a tendency to decrease the number of leukocytes, with the simultaneous appearance of metamyelocytes, an increase in the number of eosinophils and rod neutrophils, and a significant decrease in the number of lymphocytes by 27% compared to control. Under severe heat stress (THI - 80-90), when the pulse in cows fluctuates between 88-140 beats per minute, and the respiratory rate is 82.0 ± 3.76 respiratory movements, the number of erythrocytes in the blood of cows tends to decrease and is 5.01 ± 0.91 T / l. The hematocrit value is 21% significantly (p≤0.05) less than in cows under moderate heat stress, and is almost the same as in cows under comfortable conditions. The content of hemoglobin in the blood of cows in this period is significantly lower by 28% (p≤0.05) compared to that in cows under comfortable conditions with a slight tendency to increase compared to this figure in cows under moderate heat stress. Color indices indicate that in the blood of cows under severe heat stress there is a large number of young erythrocytes-macrocytes (MCV - 53.69 ± 3.22 fl), which are poor in hemoglobin (MSN - 12.95 ± 3.48 pg) and impaired hemoglobin formation (MCHC - 24.11 ± 2.23 g / dl). The total number of leukocytes in the blood of cows under severe heat stress is 10.80 ± 1.55 G / l, which is 78% (P≤0.01) more than under moderate heat stress and increases due to the appearance of young and an increase of almost in twice rod-shaped and segment-nuclear neutrophils and eosinophils with a simultaneous decrease in the percentage of lymphocytes.

Photochemical responses of cucumber (Cucumis sativus L.) plants to heat stress

In this study, photochemical responses of cucumber (Cucumis sativus L.) cultivar, ‘Beith Alpha F1’, under moderate and severe heat stress (45 °C and 55 °C, 4 hours) was studied. Chlorophyll a fluorescence measurement and the results of the JIP test indicated that severe heat stress was more drastically affected the photosynthetic activity as compared to moderate heat stress in the cotyledons of cucumber plants. Severe heat stress, for example, led to the increased level of Fo and decreased level of Fm, Fv/Fo, and Fv/Fm, suggesting remarkable photoinhibition on electron transport reactions in cucumber plants. Also, severe heat stress caused the increased level of accumulation of inactive reaction centers, resulting in a decreased amount of trapped light energy and electron transport on PSII. The enhanced values of DIo/RC and fDo in the cotyledons of cucumber plants indicated that the trapped energy cannot be used for photochemical reactions and lost as heat. Consequently, the reduction of the plastoquinone pool was partly inhibited due to the decreased yield of photochemistry. As a result, it may be concluded that severe heat stress inhibited PSII activity in several points and decreased photosynthetic yield in the cotyledons of cucumber plants.

Investigation of a root zone heating system for greenhouse seedling and its effects on micro-environment

Under the extremely cold climatic condition, crops have to survive severe heat stress conditions, even if they are being kept in greenhouses. In the winter and spring of North China, the air and soil temperature is low inside the greenhouse, and when using a traditional heating system, the energy consumption is high. This paper reports on a study of different design solutions for a root zone heating system based on a kind of low temperature radiation material. Root zone heating systems offer increasing crop quality and productivity. A novel type of heat preservation and root zone heating system was applied in greenhouse seedling. And through multiple experiments, the effect of the root zone heating system on the ambient environment and seedbed surface was studied, and the heat preservation effect and heating uniformity were discussed. Results show that single-layer film covering on the root zone heating system can make the average temperature at night increase 1°C. And the average seedbed surface and substrate temperature can increase 11.3°C and 5.2°C, respectively. In conclusion, the root zone heating system can effectively improve the environmental temperature of seedling and the uniformity of heating is high, which provides a strong guarantee for high-quality seedling cultivation. Keywords: greenhouse, root zone heating system, micro-environment, seedling, substrate temperature, air temperature DOI: 10.25165/j.ijabe.20201306.5905 Citation: He F, Hou Y, Li K, Wei X M, Liu Y Q. Investigation of a root zone heating system for greenhouse seedling and its effects on the micro-environment. Int J Agric & Biol Eng, 2020; 13(6): 47–52.

Novel approaches to mitigate heat stress impacts on crop growth and development

Heat stress is a major constraint to crop production and food security. The incidence of heat stress in crops has increased due to rapid changes in the global climate. Heat stress has a tremendous impact on crop growth and productivity due to its direct and indirect effects on water. Therefore, it is important to understand the morphological, physiological, biochemical, molecular, and ecological basis of heat stress in crop plants to minimize its impact on food production. Several genes alter their expression, proteins, and transcription factors to cope with heat stress. Adverse effects on macromolecules and genes change the signaling pathways for heat stress resistance. In the early phase of heat stress, plants regulate their immunity and plant nutrition management to alleviate the heat stress. All the self management of plants gets fail in severe heat stress situation to overcome from heat stress condition a judicious combination of conventional breeding and new technologies will help plants to cope efficiently with heat stress, including maintaining/enhancing yield to contribute to the nutritional requirements of the growing population. A better understanding of plant responses to heat stress has practical implications for remedies and management.

Deterioration effects of heat stress on farm animals performance in tropical and subtropical regions

The thermal comfort region for greatest animals is between 4 °C and 25 °C and when environmental temperature surpasses 25°C, animals suffer from heat stress conditions. Over 50% of the cattle population is located in the tropics and it has been appraised that heat causes severe economic loss in approximately 60% of the dairy farms around the world. In tropical and subtropical countries, the climatic characteristic is the major constraint on animal productivity. In severe heat stress, growth, milk yield, milk composition and reproductive traits are reduced as a result of the extreme changes in biological functions affected by heat stress. Heat stress disturbs the steady-state concentrations of free radicals, resulting in both cellular and mitochondrial oxidative damage. Although heat stress causes a decline in dry matter intake, the cow's energy and protein requirements in hot environments increase. This review provides an overview of the impact of heat stress on farm animals.

Impaired autophagy following ex vivo heating at physiologically relevant temperatures in peripheral blood mononuclear cells from elderly adults.

With the increasing threat of climate change and the accompanying rise in the frequency and severity of extreme heat events, there are growing health concerns for heat-vulnerable elderly adults. Elderly adults are at increased risk of developing heat-related injuries, in part due to age-related declines in thermoregulatory and cellular function. Regarding the latter, the process of autophagy is activated as a cellular protective mechanism to counter heat-induced stress, but the extent that heat stress activates autophagy in elderly adults is not known. Further, the interplay between autophagy, the heat shock response (HSR), the acute inflammatory response, and apoptosis remains poorly understood in elderly adults. Therefore, the purpose of this study was to examine changes in autophagy, the HSR, inflammation, and apoptosis following increasing levels of ex vivo heat stress representative of physiologically relevant increases in body core temperatures (37-41°C). Whole blood from 20 elderly adults (72±4 years; 14 men, 6 women) was heated (via water immersion) to temperatures representative of normal resting conditions (normothermia; 37°C), in addition to moderate and severe heat stress conditions (39, and 41°C, respectively) for 90 min. Peripheral blood mononuclear cells (PBMC) were isolated and protein markers of autophagy, the HSR, acute inflammation, and apoptosis were examined. No significant increases in markers of autophagy or the HSR were observed following any temperature condition. However, an increase in acute inflammation was observed above baseline following moderate heat stress (39°C), with further increases in inflammation and apoptosis observed during severe heat stress (41°C). Our findings indicate that PBMCs from elderly adults do not exhibit increases in autophagy or the HSR following severe heat stress, potentially contributing to the elevated risk of cellular dysfunction seen in elderly adults during heat stress.

Heat and dehydration induced oxidative damage and antioxidant defenses following incubator heat stress and a simulated heat wave in wild caught four-striped field mice Rhabdomys dilectus.

Heat waves are known for their disastrous mass die-off effects due to dehydration and cell damage, but little is known about the non-lethal consequences of surviving severe heat exposure. Severe heat exposure can cause oxidative stress which can have negative consequences on animal cognition, reproduction and life expectancy. We investigated the current oxidative stress experienced by a mesic mouse species, the four striped field mouse, Rhabdomys dilectus through a heat wave simulation with ad lib water and a more severe temperature exposure with minimal water. Wild four striped field mice were caught between 2017 and 2019. We predicted that wild four striped field mice in the heat wave simulation would show less susceptibility to oxidative stress as compared to a more severe heat stress which is likely to occur in the future. Oxidative stress was determined in the liver, kidney and brain using malondialdehyde (MDA) and protein carbonyl (PC) as markers for oxidative damage, and superoxide dismutase (SOD) and total antioxidant capacity (TAC) as markers of antioxidant defense. Incubator heat stress was brought about by increasing the body temperatures of animals to 39-40.8°C for 6 hours. A heat wave (one hot day, followed by a 3-day heatwave) was simulated by using temperature cycle that wild four striped field mice would experience in their local habitat (determined through weather station data using temperature and humidity), with maximal ambient temperature of 39°C. The liver and kidney demonstrated no changes in the simulated heat wave, but the liver had significantly higher SOD activity and the kidney had significantly higher lipid peroxidation in the incubator experiment. Dehydration significantly contributed to the increase of these markers, as is evident from the decrease in body mass after the experiment. The brain only showed significantly higher lipid peroxidation following the simulated heat wave with no significant changes following the incubator experiment. The significant increase in lipid peroxidation was not correlated to body mass after the experiment. The magnitude and duration of heat stress, in conjunction with dehydration, played a critical role in the oxidative stress experienced by each tissue, with the results demonstrating the importance of measuring multiple tissues to determine the physiological state of an animal. Current heat waves in this species have the potential of causing oxidative stress in the brain with future heat waves to possibly stress the kidney and liver depending on the hydration state of animals.

A study on stress response and fertility parameters in phenotypically thermotolerant and thermosensitive dairy cows during summer heat stress.

It is well documented that heat stress (HS) causes subfertility in dairy cows. However, during the last ten years we have been observing that, under high temperature-humidity index (THI≥75), despite the overall reduced fertility, some cows conceive at the first artificial insemination (AI). Here, we examined distinctive features of cows with conserved fertility under severe HS. From the databases of three herds, 167 lactating Holstein cows were selected; group TT cows (n=57) conceived in the previous summer (THI≥75) at the 1st AI, and group TS (n=110) failed to conceive at the same period after at least 2 consecutive AIs. The animals calved in spring, and in August, blood samples were collected during a hot day (THI≥81) for the determination of cortisol and HSP70 concentrations. In one farm, the validity of fertility data of the previous year was re-examined. In 28 cows from group TT and in 39 cows from group TS, the conception rate was examined during July and August. In 6 cows from each group (TT and TS) the oestrous cycles were synchronized, ovulation was induced with GnRH (THI=80), and the concentration of the pre-ovulatory LH surge was determined in 9 blood samples. The progesterone concentration in the ensuing cycle was determined in blood samples collected every other day. Overall, cortisol and HSP70 were significantly lower in TT group compared to TS. More (p<.05) animals from group TT conceived at the first AI compared with those from group TS. The induced pre-ovulatory LH surge peaked at higher level (p<.002) in group TT than in group TS, while no difference was recorded among groups either in mean progesterone concentrations or in the duration of the ensuing oestrous cycle. These results are highly suggestive that thermotolerance in some dairy cows is an inherent characteristic, warranting further genetic investigation.