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The inheritance of mitochondrial (mt) DNA was studied in two parents and 32 F1 progeny from an inter-specific cross between Pinus nigra (Arnold) and Pinus sylvestris (L.). To provide new genetic information about elimination of the alternative cytoplasmic genomes, we have tested whether mt- and chloroplast (cp) DNA are present in pollen and megagametophytes of these two species. The occurrence of cp- and mtDNA was assessed by PCR amplification of the chloroplast trnT-trnF region and three intra-genic segments of the mitochondrial genes: coxI, coxIII and orf25. MtDNA polymorphisms distinguishing the two pines were detected with several restriction enzymes on the amplified coxI fragment. On the other hand, restriction fragment patterns for coxIII and orf25 were identical in all samples analysed. The detected coxI RFLPs were used to analyse the mtDNA transmission in the F1 progeny. All the F1 individuals tested had the coxI restriction fragment patterns specific for the maternal parent P. nigra (Fig. 1 ) which provides further genetic evidence for the maternal inheritance of mtDNA in the genus Pinus. The biparental mtDNA inheritance suggested by cytological studies was not observed. Both cp- and mtDNA were present in haploid megagametophytes and pollen. These results suggest that the elimination of alternative mt- and cpDNA in Pinus occurs through different mechanisms. Moreover, our results suggest that more than one copy of the coxI gene is present on the mitochondrial genome of the two pines studied.
by Alfred E. Szmidt