CYTOLOGICAL AND MOLECULAR RELATIONSHIPS BETWEEN LARIX-DECIDUA, L-LEPTOLEPSIS AND LARIX X EUROLEPIS - IDENTIFICATION OF SPECIES-SPECIFIC CHROMOSOMES AND SYNCHRONIZATION OF MITOTIC CELLS

The effects of different concentrations of hydroxyurea (HU) and aphidi colin (APH) on the mitotic index (MI) were compared in cells of embryo genic cultures of Larix decidua, L. leptolepis, and L. decidua x L. le ptolepis(Larix x eurolepis). The highest enhancement of the MI was obt ained with HU at 1.25 mM and 0.6% colchicine. In general the MI decrea sed with an increase of HU or APH concentration (over 1.25 mM for HU a nd 5 mu M for APH). Detailed karyotype analyses were made on the somat ic complement of L. decidua, L. leptolepis, and their hybrid. These ka ryotypes were asymmetrical and advanced, with the smaller chromosomes being more submedian than the larger ones. The topography of chromosom e 7 of L. decidua and chromosome 9 of L. leptolepis was found to be th e most significant cytotaxonomic characteristic in differentiating the se two species. Cytological data indicate that Japanese larch (L. lept olepis) is phylogenetically closer to European larch (L. decidua) than the Siberian larch group (L. sibirica and L. sukaczewii). Chromosomes with unusually long kinetochores were found in both species and the h ybrid. Hyperploid cells (2n = 25) were observed in the hybrid (Larix x eurolepis) material analyzed. A genomic L. decidua probe hybridized s trongly to dots of DNA from L. leptolepis indicating that there is hig h sequence homology between these two species.