How plants identify the season by using a circadian clock

Abstract

Daylength as a function of the time of year (long days in the summer, short days in the fall, winter and spring) allows plants and other organisms to react photoperiodically in developmental steps and morphological features such as cyst formation in certain algae, succulence of stems and leaves, and the formation of storage organs and flowers. Bnning proposed in 1936 that the circadian clock of plants, with its 24-h cycling, is used in these photoperiodic reactions to measure daylength. Critical tests have corroborated this hypothesis. The functioning and molecular basis of the circadian clock of plants especially of Arabidopsis is presented and it is shown how this clock is entrained to the day. The photoperiodic timing of flower induction is more closely described.