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At least 145 records · Page 8Linked to original sources
PubMed1995

Perspectives of plant cold tolerance: physiology and molecular responses.

An enormous range in sensitivity to low temperature exists in the plant kingdom from those that show injury beginning at 15 degrees C to those able to withstand freezing to the lowest temperatures attainable in nature. Plants capable of surviving exposure to temperatures below 0 degrees C must be able to endure extreme stresses and strains as liquid water in their tissues undergo the transition to ice. The mechanisms which allow hardy plants to survive freezing, although complex, are becoming better understood. This article briefly describes some of the physiological and molecular aspects associated with plant tolerance to low-temperature stress.

Acclimatization↗
PubMed1985

Physiology of cold tolerance in insects.

From the available experimental data a relatively clear picture can be established with regard to the physiological importance of some of the mechanisms involved in insect cold hardening. In freeze-avoiding insects, all potent ice-nucleating agents are removed or inactivated, leading to a depression of the supercooling points to about 20 degrees C. Accumulation of polyols causes a further depression with a magnitude of about twice the corresponding melting-point depression. Production of thermal hysteresis factors causes a stabilization of the supercooled state. In freeze-tolerant insects, potent ice-nucleating agents are produced in the extracellular body fluid, ensuring a protective extracellular freezing at a few degrees below zero. Accumulation of polyols causes a steep drop in the lethal temperature, due to a reduction of the amount of ice by a colligative mechanism. However, there is still much to be learned about the mechanisms by which ice-nucleating agents, polyols, and thermal hysteresis agents are acting. Furthermore, the regulatory mechanisms involved in the production and elimination of these components from the body fluid of the insects are not understood. Also, when it comes to the influence of environmental factors, like photoperiod and temperature, there is much to be learned. In addition to giving attention to these topics, future research should be focused on the possible role of other factors in cold hardening such as bound water, dehydration, low-molecular-weight solutes other than polyols, and the biochemical mechanisms forming the basis of the seasonal changes in the cold hardiness of insects.

Adaptation, Physiological↗
PubMed2003

A novel cold-tolerant Clostridium strain PXYL1 isolated from a psychrophilic cattle manure digester that secretes thermolabile xylanase and cellulase.

A Clostridium strain PXYL1 was isolated from a cold-adapted cattle manure biogas digester at 15 degrees C. It could grow at temperatures as low as 5 degrees C up to 50 degrees C with highest specific growth rate at 20 degrees C and is a psychrotroph. It produced extracellular hydrolytic enzymes namely xylanase, endoglucanase, beta-xylosidase, beta-glucosidase and filter paper cellulase, all of which had maximal activity at 20 degrees C. The induction of xylanase was highest on birch wood xylan (37 IU(mg protein)(-1)) compared with xylose (1.11 IU(mg protein)(-1)), cellobiose (1.43 IU(mg protein)(-1)) and glucose (no activity). The xylanase was thermolabile with a half-life of 30 min at 40 degrees C and 8 min at 50 degrees C but stable for over 2 h at 20 degrees C. The crude enzyme released reducing sugars (1.25 g l(-1)) from finger millet flour at 20 degrees C, while commercial food-grade xylanases showed no hydrolysis at this temperature. This is the first report of a Clostridium strain growing at 20 degrees C and producing an array of xylanolytic and cellulolytic enzymes, possessing low temperature optima of 20 degrees C, which may facilitate degradation of plant fibre under low-temperature conditions.

Animals↗
PubMed1991

Effects of aging on human cold tolerance.

The risk of hypothermia is widely considered to be greater for older than younger persons due to a reduced ability to maintain body temperature during cold exposure. Epidemiological surveys of body temperature normally maintained by older persons while in their own homes do not indicate a large incidence of hypothermia. Uncontrolled ambient conditions during body temperature measurements may have influenced those observations. Comparisons of the thermoregulatory responses to cold stress in younger and older subjects have been performed under controlled conditions in laboratory experiments. Results of these laboratory studies indicate that older men appear less able than younger men to defend their core temperature during experimental cold exposures. Cold exposure may elicit a slightly smaller rise in metabolic heat production, and the cutaneous vasoconstrictor response to cold may be slower in older than younger men. These aging effects may be limited, however, to men. In a recent study, older women appeared to defend core temperature during cold exposure as well as, or better than younger women. The possibility that preventable changes in body composition and physical fitness, rather than aging per-se, may account for impaired thermoregulatory responses to cold has not been adequately studied.

Acclimatization↗
PubMedDate not supplied

Aging and human cold tolerance.

Hypothermia is widely considered to be a more serious threat for older than for younger persons because of older person's impaired ability to defend body temperature during cold exposure. Some epidemiological studies indicate that the incidence of death from hypothermia increases with age, but surveys of body temperature normally maintained by older persons while in their own homes do not indicate a large incidence of hypothermia. More reliable comparisons of thermoregulatory responses to cold stress in younger and older subjects have been performed under controlled conditions in laboratory experiments. Generally, older men appear less able than younger men to defend their core temperature during experimental cold exposures. Cold exposure may elicit a slightly smaller rise in metabolic heat production, and the cutaneous vasoconstrictor response to cold may be less responsive in old than in young men. These aging effects may, however, be limited to men. In a recent study, older women appeared to defend core temperature during cold exposure as well as, or better than, younger women. Preventable changes in body composition and physical fitness rather than aging per se may contribute to impaired thermoregulatory responses to cold observed in older workers.

Aging↗
PubMed1995

Enhancing tolerance to cold exposure--how successful have we been?

The risk of accidental hypothermia is always present in persons living at high latitudes, with cold water immersion representing the most extreme challenge. While most of the effort concerned with protection against cold exposure has involved finding ways of decreasing heat loss by improving insulation some attempts have been made in finding ways of improving cold tolerance by modifying the thermoregulatory response to cold. The main strategies that have been used are: - thermal acclimation, physical exercise, dietary enhancement of thermogenesis, pharmacological enhancement of thermogenesis and manipulation of thermoregulatory set-point. This paper briefly reviews the success of these strategies. While none of the strategies examined have resulted in concrete methods which are routinely used to improve cold tolerance, it is concluded that the pharmacological enhancement of cold thermogenesis using ephedrine in combination with methylxanthine represents the most promising method for delaying the onset of hypothermia in humans.

Adaptation, Physiological↗
PubMed1975

[Sensitivity to noradrenaline and cold tolerance of rats treated chronically with ACTH and adrenocortical hormone (author's transl)].

Rats treated with ACTH and hydrocortisone for 4 weeks were infused i.v. with noradrenaline or exposed to cold at -15 degrees C for 2 hours, and changes in the rectal temperature and plasma concentrations of NEFA, sugar, and lactate were observed. Rats received single injection of ACTH and hydrocortisone, warm- and cold-acclimated rats were used as controls. In ACTH- and hydrocortisone-treated rats, the noradrenaline infusion caused a significant elevation of the rectal temperature, but lowering of the rectal temperature induced by the acute cold exposure in these treated rats did not differ from the changes in control groups. Moreover, considerable differences were found between these treated rats and cold-acclimated ones in plasma concentrations of NEFA, sugar and lactate after noradrenaline infusion and acute cold exposure. From the results it was inferred that chronic treatment with ACTH and hydrocortisone did not produce similar adaptive metabolic alterations to those found in the course of cold acclimation.

Acclimatization↗