Determination of photoperiodic flowering time control in Arabidopsis and barley.

The circadian clock serves to prepare plants for predictable changes in the environment both on a daily and a seasonal basis. Floral transition in most plants is dependent on day length and, thus, on the season. Sensing day length allows plants to synchronize their reproduction with favorable outside conditions. This process is known as the photoperiodic pathway of flowering time control, and it is tightly linked with the circadian clock of the plant. Thus, mutants with defects in the circadian system can also be impaired in photoperiodic flower induction. This chapter provides a detailed description of the methods used to determine flowering time in the model species Arabidopsis thaliana and Hordeum vulgare and to assign a mutant or a transgenic plant to the photoperiodic pathway of flowering.