Interaction of Heat and Salt Shock in Cultured Tobacco Cells

Cultured tobacco cells (Nicotiana tabacum L. var Wisconsin-38) developed tolerance to otherwise nonpermissive 54 degrees C treatment when heat-shocked at 38 degrees C (2 h) but not at 42 degrees C. Heat-shocked cells (38 degrees C) exhibited little normal growth when the 54 degrees C stress came immediately after heat shock and normal growth when 54 degrees C stress was administered 8 hours after heat shock. Heat shock extended the length of time that the cells tolerated 54 degrees C. Tobacco cells developed tolerance to otherwise lethal 2% NaCl treatment when salt-shocked (1.2% NaCl for 3 hours). The time course for salt tolerance development was similar to that of thermotolerance. Heat-shocked cells (38 degrees C) developed tolerance of nonpermissive salt stress 8 hours after heat shock. Alternatively, cells heat-shocked at 42 degrees C exhibited immediate tolerance to lethal salt stress followed by a decline over 8 hours. Radioactive methionine incorporation studies demonstrated synthesis of heat shock proteins at 38 degrees C. The apparent molecular weights range from 15 to 115 kilodaltons with a protein complex in the 15 to 20 kilodalton range. Synthesis of heat shock proteins appeared to persist at 42 degrees C but with large decreases in incorporation into selected heat shock protein. During salt shock, the synthesis of normal control proteins was reduced and a group of salt shock proteins appeared 3 to 6 h after shock. Similarities between the physiology and salt shock proteins/heat shock proteins suggest that both forms of stress may share common elements.