Characterization of the heat shock response in cultured sugarcane cells : I. Physiology of the heat shock response and heat shock protein synthesis.

Effect of heat shock on the growth of cultured sugarcane cells (Saccharum officinarum L.) was measured. Heat shock (HS) treatment at 36 to 38 degrees C (2 hours) induced the development of maximum thermotolerance to otherwise nonpermissive heat stress at 54 degrees C (7 minutes). Optimum thermotolerance was observed 8 hours after heat shock. Development of thermotolerance was initiated by treatments as short as 30 minutes at 36 degrees C. Temperatures below 36 degrees C or above 40 degrees C failed to induce maximum thermotolerance. In vivo labeling revealed that HS at 32 to 34 degrees C induced several high molecular mass heat shock proteins (HSPs). A complex of 18 kilodalton HSPs required at least 36 degrees C treatment for induction. The majority of the HSPs began to accumulate within 10 minutes, whereas the synthesis of low molecular mass peptides in the 18 kilodalton range became evident 30 minutes after initiation of HS. HS above 38 degrees C resulted in progressively decreased HSP synthesis with inhibition first observed for HSPs larger than 50 kilodaltons. Analysis of two-dimensional gels revealed a complex pattern of label incorporation including the synthesis of four major HSPs in the 18 kilodalton range and continued synthesis of constitutive proteins during HS.