To further investigate the role and/or response of mitochondria to heat shock, we have looked at the effect of various chemicals on both corn seedling in vivo and isolated mitochondrial in organello protein synthesis. We recently reported that Oh43 seedling (4-5 d etiolated) mitochondria respond to a 10 C, 30 min temperature shift by a slight but significant increase in 35S-methionine incorporation in part manifested in the large enhancement of a 52 kD protein we have termed a mitochondrial HSP (heat shock protein) (Nebiolo and White, Plant Phys., in press). Dinitrophenol (DNP), KCN/oligomycin and arsenite induce the heat shock response in Drosophila and various other animal systems (Ashburner, Cell 17:241, 1979) but of these only arsenite has been shown to significantly induce mRNAs for the HSPs in a plant system, specifically soybean (Czarnecka, PMB 3:45, 1983). In our study, 700 uM DNP significantly reduced 35S-methionine incorporation in purified mitochondria, while 100 uM, 70 uM and 10 uM had no effect. Protein profiles generated by SDS/PAGE/fluorography showed no evidence of the 52 kD HSP KCN/oligomycin effectively abolished 35S-methionine incorporation at the concentrations used in our study (Czarnecka, ibid.). Arsenite induced both nuclear-encoded HSPs in seedlings and the 52 kD mitochondrial HSP in purified mitochondria at all concentrations monitored (100 uM - 10 uM), optimally at 50 uM arsenite. This finding strengthens the hypothesis that the mitochondrial 52 kD HSP is a "stress" rather than a "heat shock" protein as well as ruling out preferential enhanced synthesis due to slight increase in temperature. We are continuing our investigation by treating mitochondria with various heavy metals, specifically cadmium, which has been shown to induce HSP mRNA in soybean tissue, and various agrichemicals hypothesized to induce a "stress" response.
Christine M. Nebiolo, D. B. Walden and Richard Rockar
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