Changes in the level of chloroplast transcripts in pumpkin cotyledons during heat shock.

The levels of plastid gene transcripts are shown to be controlled by temperature in isolated pumpkin cotyledons. The temperature at which maximum transcript accumulation occurs varies between 38 and 42 degrees C for the genes studied (rbcL, psaA, psbA, psbB, psbC, psbD, psbE, atpA). Heat shock-induced transcript accumulation is transitory with a maximum after an approximately 3 h exposure at high temperatures. On the other hand, the accumulation of rbcL transcript was only moderately thermosensitive. A temperature increase to 46-48 degrees C induces a sharp decrease of transcript levels which correlates with damage to the plant. Relatively little correlation has been noted between RNA and protein patterns. However, there is a remarkable coincidence between temperature dependence of the accumulation of transcripts and the temperature dependence (28-46 degrees C) of the synthesis of chloroplast-located heat shock proteins indicating that both processes may be related.