Correlating molecular markers with physiological expression in Hordeum, a developing approach using stable isotopes

This paper describes a developing approach for correlating molecular markers with phenotypic expression in barley, and research examples are given. This approach is intended to elucidate the connection between defined parts of the barley genome and their physiological expressions. To illustrate our approach (up to the point of marker correlation), the materials, methods and results of an experiment are presented. Briefly, the natural abundance levels of carbon and nitrogen isotopes (δ¹³C and δ¹⁵N) serve as the primary screening tools for assessing barley genotypes for their responses to imposed abiotic stresses. The isotopic responses are then correlated with molecular markers as the first step in identifying the mechanisms relating genetic variation with phenotypic expression. A well-described mechanistic model exists for interpreting plant δ¹⁸C, and this enables partitioning of the physiological processes contributing to the whole plant δ¹³C. Although plant δ¹⁵N appears to be equally well correlated with genotype and environment, there is no mechanistic model explaining this isotopic signature. Hence, δ¹⁵N is used empirically and in parallel with attempts to understand its underlying mechanism(s).