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4 Thermotolerance, Thermoresistance, and Thermosensitization

George M. Hahn, Gloria C. Li


When organisms or cells in culture are exposed to temperatures that are outside their normal growth range, the response to that change is modulated by many environmental factors. These include parameters such as availability of nutrients, including glucose and oxygen, and the pH of the old and the new milieu, to name two of the more important ones. Our concern in this chapter is, however, with an intrinsic determinant that also influences responses to temperature changes, namely, the thermal history of the organism. The importance of thermal history has been known for a considerable time, particularly to plant pathologists (Alexandrov 1977) and, for that matter, to farmers and gardeners. These know from experience that if a plant is to be moved from a cold to a warm environment, the probability of its survival is vastly enhanced if the move is not made in one step, but gradually. In other words, if the plant is given a chance to adapt to small changes in temperature, it acquires additional thermal resistance. This acquired characteristic increases the temperature range of survival. In the last few years, it has been shown that the same considerations apply not only to plants, but also to bacteria, mammalian cells, and even complex organisms such as rodents. Humans survive fevers; these reach temperatures that kill un-adapted cells in vitro. Human cells in vivo must, therefore, also develop temporary heat resistance. The molecular basis of this adaptive process has, until recently, been totally unknown. We now have...

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