Phenotypic characterization of a photomorphogenic mutant

Summary Light is arguably the most important abiotic factor controlling plant growth and development throughout their life cycle. Plants have evolved sophisticated light‐sensing mechanisms to monitor fluctuations in light quality, intensity, direction and periodicity (day length). In Arabidopsis , three families of photoreceptors have been identified by molecular genetic studies. The UV‐A/blue light receptors cryptochromes and the red/far‐red receptors phytochromes control an overlapping set of responses including photoperiodic flowering induction and de‐etiolation. Phototropins are the primary photoreceptors for a set of specific responses to UV‐A/blue light such as phototropism, chloroplast movement and stomatal opening. Mutants affecting a photoreceptor have a characteristic phenotype. It is therefore possible to determine the specific developmental responses and the photoreceptor pathway(s) affected in a mutant by performing an appropriate set of photobiological and genetic experiments. In this paper, we outline the principal and easiest experiments that can be performed to obtain a first indication about the nature of the photobiological defect in a given mutant.