Night interruption light quality changes morphogenesis, flowering, and gene expression in Dendranthema grandiflorum

We investigated the effects of the quality of light used for interrupting the night period, termed the night interruption light (NIL), on morphogenesis, flowering, and the expression of photoperiodic genes in chrysanthemum (Dendranthema grandiflorum) cultivar Gaya Yellow', a qualitative short-day (SD) plant. Plants were raised in a closed-type plant factory under white (W) light-emitting diodes (LEDs) providing a light intensity of 180molm(-2)s(-1) photosynthetic photon flux density, under a condition of long-day (LD, 16h light/8h dark), short-day (SD, 10h light/14h dark), or SD with a 4-h night interruption (NI) provided by 10molm(-2)s(-1) PPF green (NI-G), blue (NI-B), red (NI-R), far-red (NI-Fr), or W (NI-W) LEDs. Plants grown in the LD condition were the tallest. The SD, NI-B, and NI-Fr conditions induced flowering. Phytochrome A (phyA) and cryptochrome 1 (cry1) were expressed at high levels in plants in NI-B, NI-Fr, and SD conditions. These results suggest that the NIL quality has significant implications on morphogenesis, flowering, and the expression of photoperiodic genes. Flowering was positively affected by the expression of phyA, cry1, and FLOWERING LOCUS T (FT), whereas it was negatively affected by the expression of phyB and anti-florigenic FT/TFL1 (AFT).