Relative mobility and activity of leaf malate dehydrogenase in flax (Linum usitatissimum) genotrophs and genotypes

Malate dehydrogenase (MDH) band relative mobility (Rm) and activity were examined in leaf extracts of Durrant's flax genotrophs, L and S, and flax genotypes, R and M. MDH activity in leaves from just below the inflorescence was higher in the two smaller, sparsely branched plant types, S and M, than in the larger, more branched plant types, L and R. The MDH electrophoretic banding pattern in flax leaf extracts consisted of three major anionic bands, MDH-1, MDH-2, and MDH-3. No Rm differences were detected between corresponding isozymes of genotypes R and M. For the genotrophs, however, all three bands of S migrated faster than the corresponding bands of L. Codominance was absent in F1 hybrids; S Rm was dominant for MDH-2 and MDH-3 and L Rm was dominant for MDH-1. The observations suggest that MDH Rm in L and S may be controlled by a modifier locus (or loci). Previous studies indicate that a modifier locus may also control heritable genotrophic differences in peroxidase (PER) and acid phosphates (AP) Rm. The three enzyme systems are compared.