Diurnal Rhythm of Petal Growth in Cut Rose Flowers

Many flowers including rose flowers open in a rhythmic fashion during specific times of the day. To clarify the relationship between the diurnal rhythm of cut flower opening and perception of light, effects of red and blue light on rhythmic opening of cut rose flowers was studied using time-lapse cinematography. Cut rose flowers exposed to a 12-h light/12-h darkness photoperiod by white light (fluorescent light) showed rhythmic opening, starting shortly before the light period had begun and lasting a few hours, even when their leaves were removed. The petals and/or sepals seem to be the sites of photoperception. Rhythmic opening was also observed when cut flowers were exposed to red and blue light. These results suggest that cut rose flowers without leaves can perceive red and blue light, and synchronize its opening to a photoperiod. Furthermore, effects of light exposure on flower opening differed among treatments with white, red and blue light. When cut flowers were held in constant darkness, they opened little although they showed rhythmic opening. The speed of flower opening was delayed in cut flowers exposed to red and blue light compared with those exposed to white light. In conclusion, we presume that exposing cut flowers to specific wavelengths of light might be useful for controlling flower opening.