A most interesting observation is that
the stripes almost disappear in the 6th or 7th leaf in almost every mutant
that manages to grow up to mature plants in the greenhouse. Taking into
account the fact that the embryo of mature seeds already contains 5-6 leaf
primordia, if, indeed, gradual loss of the phenotypic expression of the
mutant were due to the epigenetic switch of the resident element, the epigenetic
modification might be subject to the developmental processes of the plant.
A relationship between developmental processes and such reversible genetic
change in transposable elements already has been implied in the early work
of McClintock on Spm elements and recently has been characterized
at the molecular level (for review see Fedoroff et al., BioEssays 10:139-144).
Further characterization on the ij-Mu*1 mutant should be followed
up to verify the hypothesis.
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