Knowledge discovery, especially in the field of literature mining, is often involved in searching for interconnecting concepts between two different literature domains, which might bring new understanding of the two domains. This paper presents a new approach to discovering dependencies between different biological domains based on copula analysis of literature mining results. In the use case of the domains of plant defence response and redox potential literatures we have first performed relation extraction with Bio3graph, which is a rule-based natural language processing tool for extracting relations in the form (subject, predicate, object) triplets. The results of triplets extraction were analysed by using copula-based approach, which showed that dependencies exist between the two domains indicating a potential for cross-domain literature exploration. Both Bio3graph and software for Clayton and Frank fully nested copulas, which were used in this work, are publicly available.