Can epigenetic control explain pronounced within-plant heterogeneity of meiosis in a translocation trisome ofSecaleL.?

Abstract

Meiotic metaphase I configuration frequencies were determined in different tillers of genetically related plants of rye ( Secale cereale L.) heterozygous for reciprocal translocation T248W (between chromosome arms 1RS and 6RS) and with an additional (telocentric) arm 1RS. Seventeen different configurations could be recognized, grouped into three categories. Very different configuration frequencies were found not only between sister plants from the same parents but also between tillers of the same plant grown under identical conditions (climate chambers at 15°C and 20°C). The heterogeneity reflects variation in chromosome pairing and crossing over, and is variable and unpredictable. Anthers within florets were homogeneous. Between tiller heterogeneity is insufficient to explain differences between sister plants. It is ascribed to random somatic variation in the conditions of the chromatin which, at meiosis, govern chromosome pairing. During sexual differentiation, these conditions are fixed and subsequent cell lineages have the same pairing and crossing over characteristics. As homology search is an activity of DNA, this control of pairing and crossing over, consistent over long cell lineages, may be considered to be epigenetic even when no realistic suggestions concerning its character can be given.