Mitochondria isolated from 2-day-old etiolated soybean (Glycine max) seedlings which had been subjected to various heat shock treatments, i.e. (A) 280C (2 h), (B) 380C (2 h), (C) 380C (2 h)-42.50C (0.5 h), and (D) 38°C (2 h)-42.50C (0.5 h)-280C (4 h), were monitored for 02 uptake using an oxygen electrode. Mitochondria isolated after all four heat shock treatments were active in 02 consumption at 280C in response to succinate and ADP (derived P/O ratios were 1.6, 1.7, 1.3, and 1.3, respectively.) The mitochondria from all four treatments were also active in 02 uptake at 42.50C. However, only mitochondria isolated after treatment (C) were tightly coupling at 42.50C (derived ADP/O ratio was about 1.4). Combined with our earlier findings on the subcellular localization of heat shock proteins, our present data demonstrate that association of heat shock proteins with mitochondria by treatment (C) enables them to phosphorylate at 42.50C (i.e. they become thermotolerant). Isolated mitochondria from treatment (C) and treatment (A) were compared by electron microscopy. They appeared to be very similar and no significant ultrastructural differences were noted.When soybean seedlings are shifted from a normal growth temperature of 28°C to 40°C HS,3 there is a dramatic change in protein synthesis and a new set of proteins known as HSPs are produced (1, 6, 7).There is a strong positive correlation between the accumulation of HSPs and the acquisition of thermotolerance (9-12, 14, 15, 19). The acquisition of thermotolerance appears to depend not only upon the synthesis of HSPs but also on their cellular localization (10, 24). In soybean seedlings, several HSPs become selectively localized in or associated with nuclei, mitochondria, ribosomes, and plasma membranes, as demonstrated by sucrose gradient centrifugation (10, 1 1). Specifically, the complex group of 15 to 18 kD HSPs was localized in these fractions during HS of soybean seedlings. The 70 kD HSP also exhibited similar localization, although to a lesser extent. In addition, some 22 and 24 kD HSPs were selectively localized in the mitochondrial fraction (10). This selective localization of HSPs was shown to be temperature dependent (10).The nature ofthe association ofthe HSPs with the organelle fraction of soybean is not known. We have tested whether the 'Supported by National Science Council of ROC under grant NSC76-0201-B002-1 1 to C. Y. Lin.
Soybean seedlings (Glycine max) were incubated in narrow temperature regimes to study the effects of heat shock on cell structures. The incubation temperatures used were as follows: 1.28 ~ (2 h); 2. 40~ (2h); 3. 45~ (2h); 4. 40~ (2h)-,45~ (2h); 5. 47.5~ (10 min); 6.40 ~ (2h) ~ 47.5 ~ (10 min). Both optical and electron micrographs were taken of the different tissues of root meristems as they responded to heat shock. Cells of roots heated to 45 ~ (2h) or 47.5 ~ (10 min) with lethal treatment showed drastic heat injuries: e.g., membrane damage, coagulated plasmolysis, protoplasmic contraction, and leakage of cell content. Nucleolar segregation occurred in cells treated at both lethal and supraoptimal temperatures. Seedlings preincubated at 40 ~ (2 h) became thermo-tolerant to lethal temperature treatment of 45 ~ (2 h) or 47.5 ~ (10 min), by protecting the plasmalemma, mitochondria, plastids and nuclei from heat damage. Without preincubation, however, these structures were destroyed.
A low-molecular-weight protein, isolated from bovine brain, inhibits the actin-stimulated Mg-ATPase activity of myosin from striated muscle. This inhibition is probably related to its ability to cause actin to revert from its polymerized to its depolymerized state and to prevent the polymerization of actin. Its effect on the polymeric state of the actin has been demonstrated by viscosity studies. DNase inhibition assay, and electron microscopy. Heavy meromyosin can overcome the effect of the brain protein and stimulate the polymerization of actin. The inhibition of ATPase activity is in part dependent upon the relative amounts of brain protein, actin, and myosin. The apparent molecular weight of the brain protein is approximately 20,000 daltons. It appears to be a heat-labile glycoprotein containing 5-6% carbohydrate.
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