Previously (MNL 70:42, 1996) we reported that two A188 isoperoxidases: Px9, which is predominantly expressed in roots, and the root-specific Px12, were manifest in the leaves of several A188 somaclones. The disrupted tissue-specific expression was inherited; however, (A188 x somaclone R27) F2 plants did not segregate for the newly established staining pattern. We presumed that somaclonal variation affects trans-control of peroxidase expression rather than the coding sequences of px9 and px12.

Teichmann et al. (Eur. J. Biochem. 247:826-832, 1997) cloned ZmAP1 coding for an anionic peroxidase, which was active predominantly in roots, the mesocotyl, and the coleoptile, whereas no ZmAP1 expression was found in the primary leaf of maize seedlings. By its expression pattern, ZmAP1 resembles px9 and/or px12.

We compared the amplification products of ZmAP1 cDNA and genomic DNA isolated from the leaves of A188 inbred and its two somaclones, R27 (4th seed generation) and R105 (2nd seed generation). Dr. T. Teichmann (Max-Delbrück-Laboratorium, Köln, FRG) kindly provided the ZmAP1 clone (Genbank accession Y13905). Two pairs of primers were constructed to flank two functionally important regions corresponding to 165-316 and 843-1043 nucleotides of ZmAP1 cDNA sequence.

When genomic DNAs from three genotypes were amplified with these primer pairs, the lengths of DNA fragments were similar to those produced by cDNA amplification. It follows that somaclonal variation produced no sizable inserts into two regions of ZmAP1.
 

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