Isozyme relative mobility (Rm) changes related to leaf position; apparently smooth Rm trends and some implications

Relative mobilities (Rm's) of peroxidase and acid phosphatase isozymes were examined in leaves of flax (Linum usitatissimum L.). The leaves were sampled from four equidistantly spaced positions from main stem base to apex in various genotypes. Rm's for the two slowest-migrating isozymes of each enzyme system changed in a simple, coherent fashion in leaves from stem bases toward apices. The Rm trends up the stem seen in two highly branched flax types were somewhat different from those in two sparsely branched types. The coherent Rm trends in the four types, suggesting a smooth continuum and a potentially large number of slightly different forms of these isozymes, are discussed in relation to other data for such Rm trends. In the study reported here, both enzyme systems behaved similarly. This fact and the simple Mendelian genetical system with no codominance controlling Rm's in flax peroxidases and acid phosphatases suggest posttranscriptional or posttranslational modifications as plausible mechanisms underlying the numerous, presumably small molecular changes generating the small, consistent changes in Rm's.