Effect of Rht alleles on the tolerance of wheat grain set to high temperature and drought stress during booting and anthesis

Factorial pot experiments were conducted to compare the responses of GA-sensitive and GA-insensitive reduced height (Rht) alleles in wheat for susceptibility to heat and drought stress during booting and anthesis. Grain set (grains/spikelet) of near isogenic lines (NILs) was assessed following three day transfers to controlled environments imposing day temperatures (t) from 20 to 40°C. Transfers were during booting and/or anthesis and pots maintained at field capacity (FC) or had water withheld. Logistic responses (y = c/1+e-b(t -m)) described declining grain set with increasing t, and t5 was that fitted to give a 5% reduction in grain set. Averaged over NIL, t5 for anthesis at FC was 31.7±0.47°C (S.E.M, 26 d.f.). Drought at anthesis reduced t5 by <2°C. Maintaining FC at booting conferred considerable resistance to high temperatures (t5=33.9°C) but booting was particularly heat susceptible without water (t5 =26.5°C). In one background (cv. Mercia), for NILs varying at the Rht-D1 locus, there was progressive reduction in t5 with dwarfing and reduced gibberellic acid (GA) sensitivity (Rht-D1a, tall, 32.7±0.72; Rht-D1b, semi-dwarf, 29.5±0.85; Rht-D1c, severe dwarf, 24.2±0.72). This trend was not evident for the Rht-B1 locus, or for Rht-D1b in an alternative background (Maris Widgeon). The GA-sensitive severe dwarf Rht12 was more heat tolerant (t5=29.4±0.72) than the similarly statured GA-insensitive Rht-D1c. The GA-sensitive, semi-dwarfing Rht8 conferred greater drought tolerance in one experiment. Despite the effects of Rht-D1 alleles in Mercia on stress tolerance, the inconsistency of the effects over background and locus led to the conclusion that semi-dwarfing with GA-insensitivity did not necessarily increase sensitivity to stress at booting and flowering. In comparison to effects of semi-dwarfing alleles, responses to heat stress are much more dramatically affected by water availability and the precise growth stage at which the stress is experienced by the plants.

Identification of expressed HSP`s in blacklip abalone (Haliotis rubra Leach) during heat and salinity stresses

Both prokaryotes and eukaryotes express a set of highly conserved proteins in response to external and internal stress. The stressors include tissue trauma,anoxia, heavy metal toxicity, infection, changed salinity, and the mmost characterized, heat shock. The result is an expression of stress proteins or heat shock proteins (HSP's) which lead to protection of protein integrity, and also to tolerance under continued heat stress conditions. The Australian backflip abalone (Haliotis rubra) is found principally in southern coastal water and also in estuarine/bay environments. Esturaine/bay environments have greater fluctuations in environmental conditions, especially those of salinity and water temperature, than they are found along oceanic coasts. Abalone from esturaine/bay and oceanic coastal environments were subjected to either increased temperature (2° C/day for a total of 10°C) or hyposalinity (80% seawater). Esturaine/bay abolone were less affectes than the oceanic animals by temperature increase and also demonstrated the ability to volume regualte 3 h after the initial salinity shock. SDS-PAGE and Western blotting techniques, together with dot blots of total protein, using HSP70 specific antibodies, were used to detect HSP70s in the foot muscle of the animals and indicated an expression of HSP70 in response to heat shock in abalone, but not following hyposalinity shock. RT-PCR yeilded a partial cDNA clone of HSP70 from the foot muscle.

Effect of carbohydrate ingestion on glucose kinetics during exercise in the heat

Six endurance-trained men [peak oxygen uptake (VO₂) = 4.58 ± 0.50 (SE) l/min] completed 60 min of exercise at a workload requiring 68 ± 2% peak VO₂ in an environmental chamber maintained at 35°C (<50% relative humidity) on two occasions, separated by at least 1 wk. Subjects ingested either a 6% glucose solution containing 1 µCi [3-³H]glucose/g glucose (CHO trial) or a sweet placebo (Con trial) during the trials. Rates of hepatic glucose production [HGP = glucose rate of appearance (R_a) in Con trial] and glucose disappearance (R_d), were measured using a primed, continuous infusion of [6,6-^₂H]glucose, corrected for gut-derived glucose (gut R_a) in the CHO trial. No differences in heart rate, VO₂, respiratory exchange ratio, or rectal temperature were observed between trials. Plasma glucose concentrations were similar at rest but increased (P < 0.05) to a greater extent in the CHO trial compared with the Con trial. This was due to the absorption of ingested glucose in the CHO trial, because gut R_a after 30 and 50 min (16 ± 5 µmol · kg^-1 · min^-1) was higher (P < 0.05) compared with rest, whereas HGP during exercise was not different between trials. Glucose R_d was higher (P < 0.05) in the CHO trial after 30 and 50 min (48.0 ± 6.3 vs 34.6 ± 3.8 µmol · kg^-1 · min^-1, CHO vs. Con, respectively). These results indicate that ingestion of carbohydrate, at a rate of ~1.0 g/min, increases glucose Rd but does not blunt the rise in HGP during exercise in the heat.

Characterization of heat waves affecting mortality rates of broilers between 29 days and market age

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Hepatic concentration of heat shock protein 70 kD (Hsp70) in broilers subjected to different thermal treatments

1. The relationship between repeated thermal treatments and hepatic synthesis of Hsp 70 was studied in broiler chickens.2. Sixty broilers were submitted to 5 different treatments (12 birds each) from day 1 to day 42. Four groups were kept in a thermoneutral environment and subjected to 0, 1, 2 and 3 heat stress episodes at 35 degrees C for 4 h per week (TN-0, TN-1, TN-2 and TN-3, respectively). The last group (HT-35) was reared at a room temperature of 35 degrees C.3. From 39 to 42 old, the birds experienced acute heat stress at 41 degrees C. Resistance to heat stress was evaluated by the time taken for rectal temperature to increase by 3 degrees C above the pre-treatment value. Livers were collected (before and after heat stress) and Hsp70 was determined using Western Blot analysis with monoclonal anti-Hsp70 antibody.4. Resistance to heat stress and concentration of Hsp70 were higher in those birds subjected to more heat stress episodes during the experimental period (TN-3) and HT-35. A positive correlation was observed between Hsp70 concentration and the time taken for a 3 degrees C increase in rectal temperature (r=0.42; P<0.01).5. Exposing birds to episodes of heat stress (35 degrees C) during rearing may improve their resistance to acute heat stress, but the previous thermal history did not seem to influence the hepatocyte Hsp70 content after exposure to more severe heat stress (41 degrees C).

Effect of heat exposure on the thermoregulatory responses of selected naked neck chickens

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

SIRT1 Deacetylase Activity and the Maintenance of Protein Homeostasis in Response to Stress: An Overview

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effect of thermal stress on physiological parameters, feed intake and plasma thyroid hormones concentration in Alentejana, Mertolenga, Frisian and Limousine cattle breeds

The aim of the present study was to assess the heat tolerance of animals of two Portuguese (Alentejana and Mertolenga) and two exotic (Frisian and Limousine) cattle breeds, through the monitoring of physiological acclimatization reactions in different thermal situations characterized by alternate periods of thermoneutrality and heat stress simulated in climatic chambers. In the experiment, six heifers of the Alentejana, Frisian and Mertolenga breeds and four heifers of the Limousine breed were used. The increase in chamber temperatures had different consequences on the animals of each breed. When submitted to heat stress, the Frisian animals developed high thermal polypnea (more than 105 breath movements per minute), which did not prevent an increase in the rectal temperature (from 38.7 degrees C to 40.0 degrees C). However, only a slight depression in food intake and in blood thyroid hormone concentrations was observed under thermal stressful conditions. Under the thermal stressful conditions, Limousine animals decreased food intake by 11.4% and blood triiodothyronine (T3) hormone concentration decreased to 76% of the level observed in thermoneutral conditions. Alentejana animals had similar reactions. The Mertolenga cattle exhibited the highest capacity for maintaining homeothermy: under heat stressful conditions, the mean thermal polypnea increased twofold, but mean rectal temperature did not increase. Mean food intake decreased by only 2% and mean T3 blood concentration was lowered to 85,6% of the concentration observed under thermoneutral conditions. These results lead to the conclusion that the Frisian animals had more difficulty in tolerating high temperatures, the Limousine and Alentejana ones had an intermediate difficulty, and the Mertolenga animals were by far the most heat tolerant.

Protein levels for heat-exposed broilers: Performance, nutrients digestibility, and energy and protein metabolism

Heat stress causes significant economic losses on broilers production due to poorer performance and carcass quality. Considering that protein has the highest heat increment among nutrients, it has been suggested that protein levels should be reduced in diets for heat-exposed broilers. Nevertheless, there are no conclusive results on the benefits of such practice, and further studies should be performed to elucidate some reported discrepancies. Thus, a trial was carried out to evaluate the effects of dietary protein levels (17, 20 and 23%) and environmental temperature (22 and 32°C) on the performance, nutrients digestibility, and energy and protein metabolism of broiler chickens from 21 to 42 days of age. Nutrients digestibility was determined by total excreta collection, and energy and protein metabolism was evaluated by comparative slaughter method. It was concluded that (1) heat exposure impairs broilers performance and increases nitrogen excretion, but do not change nutrients digestibility; (2) high-protein diets are technically feasible and promotes lower heat production for broilers reared under thermoneutral or hot environments, however, high-protein diets increases nitrogen excretion. © Asian Network for Scientific Information, 2007.

Blood parameters of chicks from eggs injected with ascorbic acid and subjected to thermal stress

This study was aimed to verify if chicks from eggs injected with ascorbic acid and subjected to thermal stress would have higher immunity than chicks from incubation at thermoneutrality without injection of ascorbic acid. The parameters evaluated were temperature on oxygen saturation in hemoglobin, glucose, number of erythrocytes, hematocrit rate and number of hemoglobins of newly hatched male chicks, hatched from eggs injected with ascorbic acid (AA) and subjected to thermal stress during incubation. The experimental design was completely randomized in factorial scheme 5 (application levels of ascorbic acid) x 2 (incubation temperatures). The data were subjected to analysis of variance using the General Linear Model procedure (GLM) of SAS ®. For the parameters (number of erythrocytes, rate of hematrocit and values of hemoglobin), there was significant interaction (p <0.05) between treatments in egg and incubation temperatures. Analyzing the interactions for these parameters, it was observed that the application of 0% ascorbic acid in egg minimized the effect of heat stress when compared with treatment without injection. The application of ascorbic acid levels in eggs incubated under heat stress failed to maximize the immunity of newly hatched chicks. It is assumed that the increased liquid in the amniotic fluid, in those embryos injected with water, favored the lower heat conductance for these embryos, thus helping in their development in relation to immunity. Considering that hemoglobin is related to the transport of gases, these data suggest that increasing the concentration of AA solution inoculated may influence the respiratory rates of eggs.

Balance of pH of chicks from eggs injected with ascorbic acid and subjected to thermal stress

This study aimed to verify that chicks from eggs injected with ascorbic acid and subjected to heat stress would have changes in acid-base balance, compared to chicks incubated at thermoneutral without injection of ascorbic acid. The parameters evaluated were blood pressure of carbon dioxide and oxygen, base excess, total carbon dioxide, concentration of sodium, potassium, ionized calcium, bicarbonate and pH of newly hatched male chicks, hatched from eggs injected with acid ascorbic acid (AA) and subjected to heat stress during incubation. The experimental design was completely randomized in factorial scheme 5 (application levels of ascorbic acid) x 2 (incubation temperatures). The data were subjected to analysis of variance using the General Linear Model procedure (GLM) of SAS ®. For the blood pH was observed significant interaction (p <0.05) between treatments with application in eggs and incubation temperatures. For the other parameters were not significant effects (p< 0.05) of AA level and neither temperature of incubation. Analyzing the unfolding of the interaction to pH was observed that chicks from eggs injected with 6% ascorbic acid and subjected to heat stress during incubation had a higher pH value compared with the thermoneutral temperature incubated (p <0.05). Therefore, it is suggested that the incubation of eggs in high temperature (39°C) can alter the metabolic rate of these embryos.

Differential Expression of IGF Family Members in Heat-Stressed Embryos Produced In Vitro from OPU-Derived Oocytes of Nelore (Bos indicus) and Holstein (Bos taurus) Cows

Contents The IGF system is related to embryo quality. We aim to determine the effect of the heat stress on the mRNA expression of IGF1 and IGF2, IGFR1 and IGFR2, IGFBP2 and IGFBP4, and PAPPA in in vitro production (IVP) blastocysts from Nelore and Holstein after ovum pick up (OPU) to better understand the differences between these breeds.Oocytes from four Nelore and seven Holstein were collected in six OPU sessions. Following in vitro maturation and fertilization using six Nelore or Holstein sires, embryos were divided into control (cultured at 39 degrees C) and heat stress (HS; exposed to 41 degrees C for 9h). Blastocysts were submitted to RNA extraction. The IGF1 expression was higher in blastocysts under HS in both breeds, and the expression of IGFBP2 and IGFBP4 was higher in Holstein blastocysts under HS. The high PAPPA expression and the low expression of IGFBP2 and IGFBP4 are associated with a more efficient degradation of IGFBPs, which results in greater IGF bioavailability in Nelore blastocysts and may contribute to the superior HS tolerance in Nelore, when compared to Holstein.

Comparative study of resistance to heat in two species of leaf-cutting ants

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Inhibition of photosynthesis by high temperature in oak (Quercus pubescens L.) leaves grown under natural conditions closely correlates with a reversible heat-dependent reduction of the activation state of ribulose-1,5-bisphosphate carboxylase/oxygenase

Inhibition of the net photosynthetic CO2 assimilation rate (Pn) by high temperature was examined in oak (Quercus pubescens L.) leaves grown under natural conditions. Combined measurements of gas exchange and chlorophyll (Chl) a fluorescence were employed to differentiate between inhibition originating from heat effects on components of the thylakoid membranes and that resulting from effects on photosynthetic carbon metabolism. Regardless of whether temperature was increased rapidly or gradually, Pn decreased with increasing leaf temperature and was more than 90% reduced at 45 °C as compared to 25 °C. Inhibition of Pn by heat stress did not result from reduced stomatal conductance (gs), as heat-induced reduction of gs was accompanied by an increase of the intercellular CO2 concentration (Ci). Chl a fluorescence measurements revealed that between 25 and 45 °C heat-dependent alterations of thylakoid-associated processes contributed only marginally, if at all, to the inhibition of Pn by heat stress, with photosystem II being remarkably well protected against thermal inactivation. The activation state of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) decreased from about 90% at 25 °C to less than 30% at 45 °C. Heat stress did not affect Rubisco per se, since full activity could be restored by incubation with CO2 and Mg2+. Western-blot analysis of leaf extracts disclosed the presence of two Rubisco activase polypeptides, but heat stress did not alter the profile of the activase bands. Inhibition of Pn at high leaf temperature could be markedly reduced by artificially increasing Ci. A high Ci also stimulated photosynthetic electron transport and resulted in reduced non-photochemical fluorescence quenching. Recovery experiments showed that heat-dependent inhibition of Pn was largely, if not fully, reversible. The present results demonstrate that in Q. pubescens leaves the thylakoid membranes in general and photosynthetic electron transport in particular were well protected against heat-induced perturbations and that inhibition of Pn by high temperature closely correlated with a reversible heat-dependent reduction of the Rubisco activation state.