The significance of mutants in phytochrome research.

Genotypes (often as induced mutants) in which certain parts of the photomorphogenetic pathway(s) are eliminated, will exhibit a different and often simpler photomorphogenesis than their wild type. The relevance of the deleted part in the mutant is directly indicated by its difference in response compared to its isogenic wild type. Mutations may not only lead to the absence of a particular photoreceptor or response, but may result in an amplified response. Such high-response mutants would facilitate the study of a photoresponse. Phytochrome (P) mutants can be divided simplistically into three groups.