Petals of Cut Rose Flower Show Diurnal Rhythmic Growth

Some flowers including rose open in a rhythmic fashion during specific times of the day. We used time-lapse cinematography to understand the mechanism of rhythmic opening and perception of light in cut rose flowers. Cut rose flowers exposed to a 12 h light/12 h dark photoperiod started opening shortly before the light period had begun and stopped during the light period even when their leaves were removed, indicating that petals and/ or sepals perceive light and synchronize flower opening to photoperiods. This rhythmic opening could be seen in constant darkness even though the time of flower opening shifted to an earlier point in constant darkness compared with the 12 h photoperiod, but it was not observed in constant light. We also evaluated the effect of exposing cut flowers first to a 12 h photoperiod and then shifting them to an 18 h photoperiod. During the 12 h photoperiod, flower opening started shortly before the light period had begun and stopped during the light period, while in the 18 h photoperiod, it proceeded in the middle of the dark period. These results suggested that changes of light to darkness or vice versa were important signals for the start and maintenance of rhythmic flower opening. In addition, we found that even a petal removed from a rose flower showed rhythmic growth when exposed to a 12 h light/12 h dark photoperiod, showing that petals could perceive light and synchronize their growth to the photoperiod.