One dose of P carried on the displaced duplication (Dp 10-1) conditions a significantly lower pigment content in sporophytic tissues than a P gene component in its normal position. It has been suggested that position effect phenomena might account for this difference. The difference, however, is highly reduced or completely suppressed if the seedlings are grown on a medium supplemented with BA, as shown in Table 1. Seedlings were grown on a 2.5% sucrose solution solidified with 9% agar under continuous light and 21 C ± 2. BA concentration is 1x10-6 M. Pigment extraction in roots (75 mm sections) and first internodes (20 mm sections) was done on 11 and 15 day old seedlings respectively.
Even though BA enhances the pigment content in the plant tissues of both genotypes, the response of P Dp is more pronounced and, at least in the internode, it leads to the same amount of pigment conditioned by P.
These results indicate that a displaced P is capable, under the proper conditions, of reaching the same level of gene expression conditioned by a normal P gene component. This observation attaches more credit to the view that position effect phenomena account for the low pigment level conditioned by P Dp.
G. Gavazzi and M. Sandri
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