ABSTRACT
This chapter shows some examples of experimental data have been cited showing that frequently the repetitive fraction of the plant genome may be correlated with environmental factors. In particular have seen how such factors may be able to cause qualitative and quantitative variations of repetitive DNA sequences within the genome. In fact, research of shown that environmental factors, although they do not usually have a direct effect on the "coding" part of the genome, nevertheless, can cause quantitative modifications on a particular type of DNA, the repetitive noncoding DNA. Research has provided evidence that the repetitive fraction of the genome may be susceptible to the action of stress from the environment. The repetitive DNA variations caused by environmental stimuli are generally temporary, linked to the time course of the stress itself. In fact, the sequences of repetitive DNA that are amplified following the external stimulus usually remain extrachromosomal and, hence, are eventually eliminated from the cell.
