NUCLEAR GENES CONTROL CHANGES IN THE ORGANIZATION OF THE MITOCHONDRIAL GENOME IN TISSUE-CULTURES DERIVED FROM IMMATURE EMBRYOS OF WHEAT

Although the mitochondrial genomes of the Chinese Spring and Aquila varieties of wheat are normally similar in organization, this is not so in tissue cultures initiated from their immature embryos where the mitochondrial genomes of both are rearranged and in different, characteristic, ways. However, the mitochondrial genomes of tissue cultures of reciprocal F1 crosses between these varieties were almost identical to one another, showing that nuclear genes control the rearrangement processes. These rearrangements are either due to the appearance of new structures or else result from changes in the relative amounts of subgenomic components. The severe reduction in the amount of certain molecular configurations in tissue cultures from reciprocal crosses is probably due to the presence of dominant information in the Aquila nuclear genome. Data obtained from tissue cultures initiated from F2 embryos of the cross Aquila x Chinese Spring suggest that at least two complementary genes are involved in this control. In contrast, the presence of new molecular arrangements appears to be under the control of a dominant allelic form of a Chinese Spring gene or genes. Thus, this study demonstrates that at least two sets of nuclear genes control the reorganization of the mitochondrial genome which occurs when tissue cultures are initiated from the immature embryos of wheat.