Natural history of the narrow endemics Ipomoea cavalcantei and I. marabaensis from Amazon Canga savannahs.

Amazon comprises a vast variety of ecosystems, including savannah-like Canga barrens that evolved on iron-lateritic rock plateaus of the Carajás Mountain range. Individual Cangas are enclosed by the rain forest, indicating insular isolation that enables speciation and plant community differentiation. To establish a framework for the research on natural history and conservation management of endemic Canga species, seven chloroplast DNA loci and an ITS2 nuclear DNA locus were used to study natural molecular variation of the red flowered Ipomoea cavalcantei and the lilac flowered I. marabaensis. Partitioning of the nuclear and chloroplast gene alleles strongly suggested that the species share the most recent common ancestor, pointing a new independent event of the red flower origin in the genus. Chloroplast gene allele analysis showed strong genetic differentiation between Canga populations, implying a limited role of seed dispersal in exchange of individuals between Cangas. Closed haplotype network topology indicated a requirement for the paternal inheritance in generation of cytoplasmic genetic variation. Tenfold higher nucleotide diversity in the nuclear ITS2 sequences distinguished I. cavalcantei from I. marabaensis, implying a different pace of evolutionary changes. Thus, Canga ecosystems offer powerful venues for the study of speciation, multitrait adaptation and the origins of genetic variation.

Electron microscopic investigation of mitochondrial DNA from Chenopodium album (L.).

DNA molecules from mitochondria of whole plants and a suspension culture of Chenopodium album were prepared, by a gentle method, for analysis by electron microscopy. Mitochondrial (mt) DNA preparations from both sources contained mostly linear molecules of variable sizes (with the majority of molecules ranging from 40 to 160 kb). Open circular molecules with contour lengths corresponding to 0. 3-183 kb represented 23-26% of all mtDNA molecules in the preparations from the suspension culture and 13-15% in the preparations from whole plants. More than 90% of the circular DNA was smaller than 30 kb. Virtually no size classes of the mtDNA molecules could be identified, and circular or linear molecules of the genome size (about 270 kb) were not observed. In contrast, plastid (pt) DNA preparations from the suspension culture contained linear and circular molecules falling into size classes corresponding to monomers, dimers and trimers of the chromosome. About 23% of the ptDNA molecules were circular. DNA preparations from mitochondria contained a higher percentage of more complex molecules (rosette-like structures, catenate-like molecules) than preparations of ptDNA. Sigma-like molecules (putative intermediates of rolling-circle replication) were observed in mtDNA preparations from the suspension culture (18% of the circles), and in much lower amount (1%) in preparations from whole plants. The results are compared with data obtained previously by pulsed-field gel electrophoresis and discussed in relation to the structural organization and replication of the mt genome of higher plants.