The heat shock phenomenon described in a variety of animal and plant systems, including corn (see Can. J. Biochem. 60:569-579, 1982), has generally involved rapid shifting of the tissue from the "normal" growing temperature to an elevated incubation temperature for brief periods of time. Seedlings of Oh43 were grown at several temperatures ranging from 27 to 37 C and were subjected to a series of shift regimes: (1) to ascertain the influence of pre-shift temperature (including some temperatures at which the heat shock response is observed, e.g. 37 C) on the types of polypeptides synthesized, and (b) to estimate the minimum temperature shift increments required to elicit new and/or enhanced synthesis of the heat shock peptides (HSPs). The following observations have emerged: (1) Seedlings grown at different temperatures exhibit very similar polypeptide patterns but also reveal some temperature-specific differences. (2) The HSPs are not produced as a result of exceeding a critical absolute temperature. While seedlings grown at 27 C first exhibit enhanced synthesis of the HSPs at 35 C, seedlings grown at 32 C and shifted to 35 C, or those grown directly at 35 C, do not synthesize these HSPs. (3) Rapid, upward temperature shifts from any of the growing temperatures result in new and/or enhanced synthesis of the HSPs described previously. The intensity of the response is dependent on the temperature range over which the seedlings are shifted, as well as the actual number of degrees. For example, a 6 C shift from 35 to 41 C yields a response similar to a 10 C shift from 27 to 37 C, and a 9 C shift from 35 to 44 C elicits the same response as a 15 C shift from 27 to 42 C. In all cases, enhanced synthesis of the same six Mr classes of polypeptides is observed.
These results suggest that the change in polypeptide synthetic patterns is qualitatively similar in response to a variety of temperature shifts, but that the intensity of the response is dependent on the actual temperature range and increment over which the seedlings are shifted.
C. L. Baszczynski
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