Epigenetic aspects of somaclonal variation in plants

Somaclonal variation is manifested as cytological abnormalities, frequent q ualitative and quantitative phenotypic mutation, sequence change, and gene activation and silencing. Activation of quiescent transposable elements and retrotransposons indicate that epigenetic changes occur through the cultur e process. Epigenetic activation of DNA elements further suggests that epig enetic changes may also be involved in cytogenetic instability through modi fication of heterochromatin, and as a basis of phenotypic variation through the modulation of gene function. The observation that DNA methylation patt erns are highly variable among regenerated plants and their progeny provide s evidence that DNA modifications are less stable in culture than in seed-g rown plants. Future research will determine the relative importance of epig enetic versus sequence or chromosome variation in conditioning somaclonal v ariation in plants.