Silver birch telomeres shorten in tissue culture

Abstract

Shortening of telomeres has been connected with ageing and loss of cell replication or regeneration capacity. The aim of the present study was to examine potential variation in the length of telomeric repeats in silver birch (Betula pendula Roth) using clonal materials consisting of different-aged outdoor trees and tissue cultures of seven genotypes. The overall average length of telomeres was 13.6 kb (±0.3), the minimum length of repeats in the different genotypes varied from 5.9 kb (±0.5) to 9.6 kb (±0.6), and the maximum length varied from 15.3 kb (±1.1) to 22.8 kb (±0.4). When germinated seeds and leaf and cambium samples from 15- and 80-year-old trees were compared, no correlation of ageing and the length of telomeric repeats was found. Positional variation in the telomere length was, however, observed in the cambium of mature trees, the stem base having longer repeats than the upper parts of the tree. Tissue cultures were found to have shorter telomeres than outdoor trees: prolonged culture, callus culture and stressful conditions were all observed to shorten telomeric repeats and should thus be avoided in birch micropropagation. There were significant differences among the studied silver birch genotypes in their telomere length, and these differences were consistent over the sample types. This is the first report on variation of telomeric repeats in a long-living organism studied with clonal materials.