DEVELOPMENTAL CONTROL OF TELOMERE LENGTHS AND TELOMERASE ACTIVITY IN PLANTS

Telomere lengths and telomerase activity were studied during the devel opment of a model dioecious plant, Melandrium album (syn Silene latifo lia). Telomeric DNA consisted of Arabidopsis-type TTTAGGG tandem repea ts. The terminal positions of these repeats were confirmed by both Bal 31 exonuclease degradation and in situ hybridization. Analysis of term inal restriction fragments in different tissues and ontogenetic stages showed that telomere lengths are stabilized precisely and do not chan ge during plant growth and development. Telomerase activity tested by using a semiquantitative telomerase repeat amplification protocol corr elated with cell proliferation in the tissues analyzed. Highest activi ty was found in germinating seedlings and root tips, whereas we observ ed a 100-fold decrease in telomerase activity in leaves and no activit y in quiescent seeds. Telomerase also was found in mature pollen grain s. Telomerase activity in tissues containing dividing cells and telome re length stability during development suggest their precise control d uring plant ontogenesis; however, the telomere length regulation mecha nism could be unbalanced during in vitro dedifferentiation.