PHYSIOLOGICAL-ASPECTS OF GENOME VARIABILITY IN TISSUE-CULTURE .1. GROWTH PHASE-DEPENDENT DIFFERENTIAL DNA METHYLATION OF THE CARROT GENOME (DAUCUS-CAROTA L) DURING PRIMARY CULTURE

Investigations were performed on growth phase-dependent EcoRII site-sp ecific DNA methylation of the carrot genome during primary culture to elucidate physiological aspects of genome DNA variability in tissue cu lture. While DNA methylation of the root cambium and the secondary phl oem and petioles of carrot leaves were strikingly different, the methy lation level of the secondary phloem seemed to be independent of culti var origin, the age of the plants and the extent of secondary root gro wth. As was shown earlier a change in the differentiated state of the secondary phloem by tissue culture leads to changes in genome modifica tion. Whereas de novo methylation was observed during the first 2 week s of growth initiation, the results presented demonstrate genome de-me thylation during the transition to stationary growth indicating differ ential genome methylation during different phases of culture. The pres ence of kinetin in the nutrient medium of the primary culture was foun d to be antagonistic to changes in genome modification in general. De novo methylation and subsequent de-methylation of the carrot genome ar e discussed as gross changes obviously essential to molecular genome d ifferentiation during tissue culture.