Genetics of the peroxidase isoenzymes in Petunia : Part 5. Differential temporal expression of prxA alleles.

In P. hybrida and the putative progenitor species P. axillaris s. l. and P. integrifolia s. l. five mobility alleles of the structural gene prxA were found. The five alleles show differential expression during development of tissue and plant, caused by internal site mutations. Analysis of young but not yet flowering plants heterozygous for prxA showed that the allele prxA3 is expressed first, followed by the alleles prxA2, prxA5, prxA4 and prxA1, in that order. In mature leaves of young flowering plants the prxA2 allele has the highest expression level, followed by the alleles prxA3, prxA5, prxA4 and prxA1. In mature and old leaves of old plants the expression level of the alleles prxA2, prxA3, prxA4 and prxA5 is about equal, whereas that of the prxA1 allele is about twice as high. Crossing experiments suggested that between the plants used no external site differences exist that cause clearly detectable changes in developmental allozyme balance. Fast moving anodic peroxidases were detected that have a variable mobility over a considerable distance. The probability that these enzymes are precursors of the PRXa enzymes is discussed.