The present work was aimed at the investigation of DNA synthesis in the system in organello in mitochondria of maize and Elymus sibiricus under various temperature conditions. The mitochondria were prepared from 3-day-old etiolated seedlings of maize (Zea mays L. hybrid VIR 42 MV) and 9-day-old etiolated seedlings of Elymus sibiricus by a standard method of differential centrifugation. DNA synthesis was measured in mitochondria according to the method of Schegget and Borst (Biochim. Biophys. Acta 95:235-248, 1971) with the use of 32P-dATP (specific radioactivity was 148 PBq mol-1). All kinetic data were obtained from at least 3 independent experiments. Statistical analysis was performed using Students paired t-test.
The crucial peculiarity of DNA-synthesizing system of mitochondria of Elymus sibiricus (Fig. 1) is a high level of mtDNA synthesis with a low temperature (+5 C). With the optimal temperature (+30 C) the activity of mtDNA synthesis of Z.mays and E.sibiricus showed practically no difference. The increase of incubation temperature up to +40 C demonstrated significant growth of mtDNA synthesizing activity of Z. mays and a considerable repression of this process in mitochondria of E. sibiricus. With the objective to clarify peculiarities of structural and functional organization of E. sibiricus, mitochondrial genome cloning of mtDNA sequences of this crop was conducted in bacterial plasmid vectors.
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