Heat shock and the heat shock proteins.

As all biologists appreciate, there is constant interaction between life and the environment, and temperature plays a critical role. It establishes distribution limits, it affects rates of function as well as the survival of organisms. Notoriously sensitive to temperature is plant growth. Critical steps in plant life such as germination, flowering and breaking of dormancy can be manipulated by the application of certain temperature treatments. Animal life is mainly limited to a narrow range of temperatures, from a few degrees below the freezing point of water to approximately 50 'C. Animals nevertheless differ in the range of temperatures that they can tolerate. Temperature tolerance may however change with time and a certain degree of adaptation is possible. The limits of temperature tolerance for a given animal are not fixed. Indeed, it has been known for some time that exposure to a near lethal temperature often leads to a degree of adaptation so that a previously lethal temperature is tolerated. This particular response to heat shock has attracted considerable attention from molecular biologists over the last decade, which has resulted in a rapid accumulation of data providing considerable insights, not only into the molecular basis of acquired thermotolerance, but into stress physiology in general. The heat shock response is now known to occur in bacteria and in plants as well as in animals, and is a rapid but transient reprogramming of cellular activities to ensure survival during the stress period, to protect essential cell components against heat damage and to permit a rapid resumption of normal cellular activities during the recovery period.