TWO DISTINCT PHYTOCHROME-MEDIATED REGULATION SYSTEMS CONTRIBUTE TO NIGHT-BREAK RESPONSE IN FLOWERING OF THE SHORT-DAY PLANT CHRYSANTHEMUM
Chrysanthemum (Chrysanthemum morifolium Ramat.) is a short-day plant that initiates flowering when nights are longer than critical night length, and flowering is inhibited by an illumination at the middle of the long night (night break; NB). NB with red light effectively inhibits flowering, which is repromoted by subsequent exposure to far-red (FR) light (Cathey and Borthwick, 1957). This suggests the involvement of phyB-type receptors. To elucidate the role of light signalling on photoperiodic flowering in chrysanthemum, flowering response under various photoperiodic treatments was tested using different light qualities. When white light was used during the main photoperiod, NB with red light had the strongest effect on inhibition of flowering, whereas NB with blue (NB-B) or far-red (NB-FR) light had little inhibitory effect. However, with a main photoperiod of blue light (B_NB), NB-B and NB-FR strongly suppressed flowering, which suggests the involvement of a blue/FR light-absorbing photoreceptor such as phyA. Moreover, the inhibitory effect of NB-B was partially reversed by subsequent exposure to a FR light pulse. The inhibitory effects of NB-B and NB-FR were cancelled when red light supplemented blue light during the main photoperiod (BR_NB). Although B_NB and BR_NB similarly affected the expression of circadian clock-related genes, only B_NB suppressed expression of the chrysanthemum orthologue of FLOWERING LOCUS T (CmFTL3). Therefore, at least two distinct phytochromes may be involved in NB-induced inhibition of flowering, and light quality during the main photoperiod affects sensitivity to light irradiation at the middle of the flower-inductive dark period.
Higuchi, Y., Sumitomo, K., Oda , A. and Hisamatsu, T. 2012. TWO DISTINCT PHYTOCHROME-MEDIATED REGULATION SYSTEMS CONTRIBUTE TO NIGHT-BREAK RESPONSE IN FLOWERING OF THE SHORT-DAY PLANT CHRYSANTHEMUM. Acta Hort. (ISHS) 956:201-206
chrysanthemum, flowering, light quality, night break, phytochrome