Adaptive significance of ADH activity variants in Trifolium repens L.
To understand the relevance of enzyme variants in adaptive evolution, we need to know the physiological role that the enzyme performs, the in vivo consequences of the variants, and the relevance of the resulting physiological phenotypes to the organism's ecology. In our study, we chose the metabolic response to anaerobic stress in higher plants as a system for analyzing how differences at the molecular level might contribute to differences at the organism level. White clover (Trifolium repens L.) collected from natural sites that differ in their history of flooding, exhibit within and between site variation in the level of alcohol dehydrogenase (ADH) activity induced by anaerobic stress. These variants were found to be repeatable among clones and to have a heritable basis. Though the electrophoretic pattern of ADH is also polymorphic among the individuals collected, ADH activity is not correlated to zymograms. ELISA study indicated that the level of ADH activity corresponds to the amount of ADH protein present in the tissue, suggesting that individual differences in activity is due to differences in the regulation of the enzyme. On the physiological level, the amount of ethanol produced by roots under anaerobic stress significantly correlates with the amount of ADH activity measured in vitro, suggesting that the differences measured at the molecular level has physiological relevance. This correlates well with our result measured at the organism level; we found that the level of ADH activity expressed by an individual during flooding is a strong predictor of the ability of that individual to tolerate flooding as measured by relative growth rate. Since white clover is a long-lived clonal perennial, growth is a major factor in competition for site dominance. On the population level, random samples from a site prone to flooding has a significantly higher mean value of induced ADH activity than samples from sites not susceptible to flooding. Our finding of a striking association between the regulation of a biochemical response to a specific stress and the physiological performances of the organism under the same stress is one of a very few examples found in the literature.
Chan, Wing Yui, "Adaptive significance of ADH activity variants in Trifolium repens L." (1990). Dissertations available from ProQuest. AAI9026532.