Abstract
Transposable elements (TE) are natural constituents of plant genomes. However, their presence only becomes apparent if they become dislodged from their resident positions in the genome and transpose into another gene, thereby inducing a mutation. Such TE-induced mutations are somatically unstable because they revert to wild type and hence reconstitute the expression of the mutated gene. The frequent somatic excision of the TE results in a variegated phenotype. Since this instability is inherited in a Mendelian manner the variegated phenotype is nuclear determined. By this criterion TE have been shown to occur in more than 30 species belonging to different families and genera. Many questions arise when dealing with TE: their structure and functions, and the biological significance of the activity of elements in the differentiation of a normal plant or in the evolution of plant genes.
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