Irkutsk, USSR

Siberian Inst. Plant Physiol. Biochem.

Krasnodar, USSR

Krasnodar Research Institute of Agriculture

The low level of RNA synthesis in mitochondria of heterotic hybrids --Yuri Konstantinov, A. S. Mashnenkov, Galina Lutsenko and Vladimir Podsosonny According to our hypothesis that the level of organism adaptation is negatively associated with the level of mtDNA transcription (MNL 61:61, 1987), a low rate of mtRNA synthesis was expected in hybrid mitochondria. The assumption was strongly confirmed by the rate of mtRNA synthesis determined in 10 inbred lines and 17 hybrids. The conditions for the reaction of RNA synthesis to occur in intact mitochondria were essentially similar to those described elsewhere (J. Carlson et al., Curr. Genetics 11:151, 1986). The kinetics of mtRNA synthesis in organello was registered by 3H-UTP (370 TBq.mol-1). The kinetic data on transcription activity of mtDNA in each line and hybrid were obtained from 6-8 (3-4 independent) experiments. The data were analysed by conventional statistic methods and are given in the table.
Source of mitochondria Incorporation of 3H-UTP into acid insoluble mitochondrial fraction, counts/min mg protein
  5 min 10 min 15 min 20 min
Lines (10) 6909±1436 11701±1170 23774±4829 38823±11092
Hybrids (17) 6958±897 9764±879 12330±1148 18211±1674

By the 5th min, the average rate of mtRNA synthesis was similar in mitochondria of the lines and hybrids. However the rate further increased with different acceleration. By the 20th min, the rate showed 5.6-fold increase in the mitochondria of the lines and only 2.5-fold increase in hybrid mitochondria. The high rate of mtDNA transcription in inbred lines may be partially accounted for by stimulating effect of recessive alleles of the nucleus (MNL 62:67, 1988).

As a whole, the data reported here and elsewhere (MNL 61:61, 1987) could also indicate the existence of negative nuclear control of transcriptive activity of maize mitochondrial DNA.

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