Long-lived and short-lived heat-shock proteins in tobacco mesophyll protoplasts.

We have studied modifications in the pattern of proteins synthesized by tobacco (Nicotiana tabacum var Maryland) mesophyll protoplasts when they are transferred from 25 degrees C to 40 degrees C. The synthesis of one group of proteins is practically unaffected by the heat shock. On the other hand, the synthesis of most other 25 degrees C proteins is greatly reduced, while specific heat-shock proteins appear: 17 stable, neutral, major proteins, which are synthesized throughout the culture period at the higher temperature and which correspond to those observed in other organisms, and two basic proteins with a short lifetime and which are synthesized only during the first 2 hours of heat shock. We suggest that these latter proteins are regulatory peptides which intervene in the inhibition of 25 degrees C syntheses.