HEAT-SHOCK-PROTEIN EXPRESSION IN LEAVES OF CABERNET-SAUVIGNON

Cabernet Sauvignon plants grown at 25 degrees C were heat shocked at 3 5 degrees C, 40 degrees C, 45 degrees C, or 50 degrees C for four hour s, followed by a four-hour incubation at 25 degrees C. A group of non- heat shocked plants was held continuously at 25 degrees C. Proteins fr om the first fully expanded leaf on the main shoot of each plant were extracted and separated by two-dimensional electrophoresis. The protei ns were visualized by silver-staining, or by western immunoblotting wi th a monoclonal antibody raised against mung bean HSP70. Twelve protei ns accumulated following heat shock at 35 degrees C, 41 accumulated fo llowing heat shock at 40 degrees C, and 17 accumulated following heat shock at 45 degrees C, Heat shock at 50 degrees C was a lethal treatme nt and lead to the breakdown of most leaf proteins. Over half of the p roteins synthesized following heat shock at 35 degrees C, 40 degrees C , and 45 degrees C were 15-30 kD in size, suggesting that they may be members of the low molecular weight heat shock protein family. Western immunoblots revealed that the antisera recognized two HSP70 isoforms in the control leaves with molecular weights of approximately 70 kD an d pIs of 5.86 and 5.90. Neither isoform increased following heat shock at 35 degrees C, but both increased slightly following heat shock at 40 degrees C. A small amount of a third isoform (pI 5.93) was also pre sent following heat shock at 40 degrees C, When the heat shock tempera ture was 45 degrees C, one HSP70 isoform (pI 5.86) increased dramatica lly, another (pI 5.90) increased slightly, and the third isoform that was present at 40 degrees C (pI 5.93) was not visible. Expression of H SP70 was largely inhibited when the heat shock temperature was 50 degr ees C. Because HSP70 is thought to be induced by the presence of denat ured proteins, this suggests that a large number of heat-denatured pro teins may accumulate in the cells at 45 degrees C. Heat shock protein synthesis may be related to the increased thermotolerance that has pre viously been observed following heat shock of Cabernet Sauvignon plant s at 40 degrees C for four hours.