Heat Shock Proteins in Tobacco Cell Suspension during Growth Cycle

Tobacco (Nicotiana tabacum L. cv Wisconsin 38) cells grown in suspension culture at 26 degrees C produce heat shock proteins (HSPs) when exposed to elevated temperature of 34 to 42 degrees C. At 34 and 38 degrees C, synthesis of normal proteins is maintained while HSPs are expressed within 30 minutes after initiation of the shock. At 42 degrees C, HSPs are still expressed but normal proteins are made at a reduced rate or not at all. Exposure of cells to 38 degrees C allows for a full expression of HSPs without inhibition of the synthesis of normal proteins. Induced synthesis of HSPs at 38 degrees C is maximal 1 to 2 hours after elevation of temperature and diminishes thereafter through at least 6 hours. Cells growing asynchronously in the logarithmic phase of growth produce HSPs at a much higher rate than those in the stationary phase. The ability to synthesize HSPs disappears about one generation time before the cells reach a growth plateau.