A reciprocal relationship between the genetic diversity at two metabolically-linked isozyme loci in several conifer species

In the context of a general survey on genetic variation of isozyme-gene systems which function in the carbohydrate degradation and conversion, we detected a reciprocal relationship between genetic diversity at the hexokinase (HEK-A) and phosphoglucose isomerase (PGI-B) loci in Scots pine populations. Further studies on Norway spruce, Douglas-fir and Siberian stone pine revealed that this relationship appears to be a more general phenomenon in conifers such that increasing diversity at one locus is correlated with a decrease in diversity at the other locus. Since the two gene loci are not structurally linked but are encoding enzymes of two sucessive metabolic steps in the glucose conversion towards glycolysis, it is assumed that some sort of selection, especially during germination and early embryo development, may be the causal explanation. A metabolically-based model incorporating selective advantage and disadvantage of alternate two-locus genotypes at HEK-A/PGI-B was presented in order to elucidate the possible adaptive nature of this reciprocal relationship.