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The heat shock response is a highly conserved genetic mechanism which is induced by a wide range of environmental stimuli. Although intensively studied in both prokaryotes and eukaryotes, no regulatory mechanism has been identified by which the environmental stimuli affect expression of the heat shock genes. In addition, although many inducers of the heat shock response are known to cause DNA damage, the role of heat shock in repair of DNA damage remains unclear. Mutants of Escherichia coli defective in the recA, uvrA, and xthA genes are more sensitive to heat than wild type. However, these mutants are able to develop thermotolerance, suggesting that thermotolerance is an inducible response capable of repairing heat-induced DNA damage independent of recA, uvrA, and xthA. Thermotolerance itself is shown to depend on the dnaK gene, directly linking the E. coli heat shock response to thermotolerance. In addition, the dnaK mutant is sensitive to heat and H₂O₂, but not to UV suggesting that the DnaK protein may function to protect cells from the specific DNA damage caused by heat and H₂O₂. An E. coli grpE mutant was found to be substantially more resistant to 50°C heat treatment than wild type. However, grpE⁻ cells have the same H₂O₂ and UV sensitivity as wild type. This implies that the conditions, for which a grpE mutation is beneficial, are unique to heat exposure and are not caused by H₂O₂ or UV exposure. Furthermore, heat shock protein synthesis occurs sooner in the grpE mutant than in wild type, indicating that the grpE gene product of E. coli may act as a negative regulator of the heat shock response. An adenyl cyclase deletion mutant of E. coli (cya) failed to exhibit a heat shock response even after 30 min. at 42°C. Furthermore, a presumptive cyclic AMP receptor protein (CRP) binding site exists within the promoter region of the E. coli htpR gene. Together, these results suggest that the cya gene may regulate the heat shock response, through cyclic AMP, by directly affecting the level of expression of the heat shock sigma factor.

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Call number: LD2668 .T4 1986 T42 / Master of Science / Horticulture, Forestry, and Recreation Resources

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Passive and active heat loading causes cardiovascular strain, which can have diverse and substantial effects. Thus, cardiovascular function is integral to work and heat stress tolerance, but recent hyperthermia and exercise literature has not emphasised this relationship, instead focusing on the roles of upper �critical� core temperature or rate of heat storage as primary mechanisms of fatigue. Therefore, the aim of this thesis was to examine some potential causes and effects of cardiovascular strain under heat stress, including potential strategies for attenuating that strain. Body precooling before exercise increases heat storage capacity; the primary mechanism by which attenuations in thermal and cardiovascular strain, and improved work capacity is thought to occur. However, no precooling study has utilised realistic airflow in the laboratory, possibly inflating its purported benefits. Therefore, Study One examined the cardiovascular, thermal, psychophysical and ergogenic effects of precooling with and without airflow in the heat (30�C, 50% rh). Ten males completed four trials in balanced order, comprising 60- min immersion in thermoneutral (35�C) or cool (24�C) water before cycling at 95% ventilatory threshold with airflow (~4.8 m�s⁻�) or no airflow, until exhaustion. Heart rate and mean core, body, and skin temperatures were attenuated for 15 min into cycling after precooling. Endurance time was extended by 30 � 23 min with airflow, and 16 � 15 min with precooling relative to control (28 � 12 min) but not further extended with strategies combined (29 � 21 min). Precooling removed 784 � 223 kJ�m⁻� (calorimetrically); less than the effect of airflow alone (1323 � 1128 kJ�m⁻�). Competition for blood between tissues is pronounced during exercise in the heat: skin and gut have marked increases and decreases, respectively. Gut ischemia affects epithelial tight junction integrity, allowing lippopolysaccharide ingress and immune responses. Bovine colostrum may attenuate gut permeability. Study Two (double-blind, placebo controlled) investigated the effects of aerobic fitness (7 highly fit, 8 moderately fit) and bovine colostrum on physiological and perceived strain, and performance during mixed-mode exercise; cycle 15 min at 50% maximal heart rate range (HRR), run 30 min at 80% HRR then 30 min self-selected paced before another 15 min cycle at the same work-rate. Airflow was graded to running speed. During the last cycle, blood pressure, stroke volume and total peripheral resistance were lower, heart rate and skin blood flow increased, and skin temperature was unchanged compared to the first cycle. Indices of fever response (IL-1β, TNF-α) were not evident during exercise, nor were those of blood-brain barrier permeability (S100β) or cognitive impairment (Stroop test). Neither bovine colostrum, nor higher fitness modified these measures. Moving to upright posture is orthostatically stressful and can initially decrease cerebral perfusion. Compression garments are used to assist venous return; while their effectiveness is unknown, they could reduce heat or orthostatic-induced hypoperfusion. Study Three investigated the cardiovascular and cerebrovascular responses to orthostatic stress with and without passive heating (+0.5�C). Fifteen participants completed two trials (compression v placebo garments) in balanced order. Cerebral autoregulation was assessed via 3-min stand, and via thigh cuff inflation. All participants experienced initial orthostatic hypotension upon standing in one or more trials, with 4/15 individuals experiencing presyncopal symptoms, aborting the standing protocol. In those who "fainted", reductions in blood pressure and partial pressure of end-tidal CO₂ reduced middle cerebral artery velocity. Neither training status nor compression trousers modified the responses. Collectively, cardiovascular strain to heat stress is attenuated when realistic airflow is provided. Increased cardiovascular strain does not inevitably result in clinical outcomes to heat stress. Higher fitness does not necessarily attenuate cardiovascular responses or higher tolerance to heat stress.

Pepper plants (Capsicum annuum L.) were grown in field and a greenhouse in Arizona to determine the effects of water stress, root temperature, and exogenously applied growth regulators on cytokinin production and the resulting growth. Research showed that vegetative plants were significantly higher in cytokinin activity and growth parameters than fruiting plants. Also, in root-pruned fruiting plants, cytokinin activity was less than that of intact fruiting plants. In vegetative plants, the competition between removed sinks and the rest of the shoot was reduced and, hence, more cytokinin came from the roots to the shoots. Besides, additional carbohydrates were available and recycled to the roots. In respect to temperature effect, elevating temperature from 15 to 30°C had a pronounced effect of increasing the growth rate and cytokinin activity. The measured parameters declined when temperature exceeded 30°C. Temperatures between 25 and 30°C were found to be optimum. Under experimental conditions, growth regulators (Cytex® and Burst®) applied to the soil or foliage had no significant effect on growth rates or cytokinin activity in roots. Also, applying Burst® or kinetin to the nutrient medium had inconsistent and statistically nonsignificant effects on photosynthesis and transpiration.

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The technical feasibility of ohmic heating was evaluated for viscous liquids in static ohmic heating cells in three stages. First, electrical conductivities and time/temperature profiles were measured and compared for selected hydrocolloids (carrageenan, gelatin, pectin, starch and xanthan) in water at various concentrations (1--6%). Of the thickening agents examined, carrageenan gave the highest value for electrical conductivity and the shortest time to raise the temperature from 20 to 100°C. It was followed by xanthan. Pectin and gelatin samples were found to exhibit lower, but similar electrical conductivities and heating profiles. Starch samples had the lowest electrical conductivity and the temperature of starch solutions never exceeded 62°C within the specified time limit of 10000 s. / In the second stage, the effect of salt and acid concentration was evaluated on electrical conductivities and time/temperature profiles of the above selected hydrocolloids in water solutions at a concentration necessary to achieve a similar apparent viscosity of 0.2 Pa.s at 300 s-1 and 20°C (carrageenan 1.7%, pectin 2.5%, starch 4.3% and xanthan 2%). / In the third stage, measurements of electrical conductivities, time/temperature and heating rate profiles were performed applying six voltage gradients (5.26, 7.14, 13.16, 17.86, 21.05 and 25 V/cm), with two electrode cross-sectional surface areas (19.84 and 37.95 cm2) and the electrodes separated at three specific distances (10.05, 14.33 and 20.01 cm) at 150 V. Applied voltage gradients had a major effect on temperature and heating rate profiles but no effect on electrical conductivities. / Rheological properties of carrageenan, pectin, starch and xanthan solutions were investigated at various temperatures (20--80°C) and concentrations (carrageenan 1.5, 1.7 and 1.9%; pectin 2.3, 2.5 and 2.7%; starch 3.8, 4 and 4.2%; xanthan 1.6, 1.8 and 2%) in the presence of 1% salt. Both temperature and concentration influenced the rheological properties of solutions. / Finally, electrical conductivity measurements and rheological properties of starch at 4% and 1% salt were used as input to evaluate a theoretical model for the electrical, thermal and flow behaviour in a continuous ohmic heating unit. (Abstract shortened by UMI.)