Mosaicism in Old Trees and Its Patterns

Mosaicism has been confirmed in several studied old trees from both gymnosperms and angiosperms, in a pattern not always following the actual branching of the tree. Eight individuals from two gymnosperm and three angiosperm species of trees were studied for age-related mosaicism. We compare the level of intra-organismal genetic variability found within an individual old and an individual young tree of the same species to prove its relation to age. In five cases, we found statistically significant differences in intra-organismal genetic variability between young and old trees. In three cases of mosaicism, the constructed dendrogram corresponded with the actual branching of the tree, but it differed in the remaining two. We offer an explanation of the cases when the dendrogram does not correspond with the branching structure of the tree through the patterns of sectorial and mericlinal chimerism. In the studied gymnosperms, we found that the growth rate possibly influenced the level of intra-organismal variability, while in angiosperms the dependence was rather on age. The differences between angiosperm and gymnosperm molecular evolution and meristem stratification may play a role in this, but further research is needed in this area.