We reported in last year's Newsletter (Baszczynski et al., MNL 57:161-162, 1983) that upward and downward temperature shifts over a number of temperature ranges and increments can lead to alterations in polypeptide synthetic patterns. We have extended these studies to examine the impact of normal growing temperatures on the polypeptide synthetic patterns prior to and following 'heat shock' and other temperature shifts. Seedlings of Oh43 were grown at 15, 20, 25, 30 or 35 C. Since temperature influences rate of growth, seedlings used in experiments were always selected at a similar developmental stage (plumules 1-2 cm). The results from 1-D and 2-D gel separations of polypeptides obtained from seedlings grown at the different temperatures indicate that while many similarities exist in the polypeptide synthetic patterns, each growing temperature yields a unique spectrum of newly synthesized products. From plumules grown at 15, 20, 25, 30 or 35 C, subjected to upward temperature shifts, we note that: (a) there is a change in the types of polypeptides synthesized, and (b) the initial growing (pre-shift) temperature influences the polypeptide synthetic patterns obtained following the upward temperature shifts. Most striking is the response to a one-hour 'heat shock' at 42 C. While the same six molecular weight classes of HSPs (Baszczynski et al., 1982, 1983) are observed following a shift to 42 C from each of the growing temperatures, some additional polypeptides, dependent on the initial growing temperature, also exhibit enhanced synthesis following the heat shock. For example, a 31 kD polypeptide is strongly enhanced following a temperature shift from 20 C to 42 C, is less enhanced following a shift from 25 C to 42 C or from 30 C to 42 C, and is not present following a shift from 15 C to 42 C. Similarly, a 23 kD polypeptide intensifies dramatically following a shift from 30 C to 42 C, but shows much less enhancement following a shift to 42 C from 15, 20 or 25 C.

Another observation is that a 10 C upward temperature shift from 15, 20 or 25 C leads to the enhanced synthesis of some of the high molecular weight HSP classes. This strongly suggests that the production of these polypeptides may reflect a change in response to temperature shifts in general. The low molecular weight, 18 kD HSP class, on the other hand, does not exhibit enhanced synthesis following these upward temperature shifts, suggesting that it may represent a 'heat-shock'specific' class of polypeptides. However, when mRNA is isolated from plumules shifted from 15 C to 25 C or from 20 C to 30 C and translated in vitro, all classes of HSPs (including the 18 kD class) are detected. The synthesis of these, relative to the other polypeptides, is comparable to that observed following heatshock in vivo. This finding indicates that mRNAs for the HSPs are present following these lower temperature shifts, but that the translation of these mRNAs in vivo is under some form of temperature-dependent regulation. Further characterization of the temperature shift response in maize is in progress.

Chris L. Baszczynski, D. B. Walden and B. G. Atkinson
 
 

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