The effects of light quality on flowering time were investigated in Gypsophila paniculata, which is a long-day cut flower, and with Arabidopsis under long-day conditions with light-emitting diodes (LEDs). Gypsophila paniculata plants were grown under natural daylight and flowering was controlled by long-day treatment with a weak LED light of a single color in the night. Flowering was promoted not by blue light, but by far-red light in G. paniculata, while flowering was promoted by both light colors in Arabidopsis. FT homologs of G. paniculata GpFT1 and GpFT2 were differentially expressed under long-day conditions with white light, suggesting that they play roles in flowering at different stages of reproductive development. GpFTs and FT gene expression was not induced by far-red light in G. paniculata or Arabidopsis. Instead, the expression of the SOC1 homolog of G. paniculata GpSOC1 and SOC1 was induced by far-red light in G. paniculata and Arabidopsis. Flowering was promoted by induction of FT and SOC1 expression with blue light in Arabidopsis, whereas GpFTs and GpSOC1 expression was low with blue light induction in G. paniculata. The relationship between flowering and the expression of FT and SOC1 in Arabidopsis was confirmed with ft and soc1 mutants. These results suggest that long-day conditions with far-red light promote flowering through SOC1 and its homologs, while the conditions with blue light do not promote flowering in G. paniculata, because of low expression of GpFTs and GpSOC1 in contrast to that in Arabidopsis.

A low red (R): far-red (FR) ratio is known to promote flowering of Arabidopsis and several long-day cut flowers, whereas not much information is available on the effects of single light qualities and their combinations on flowering. Therefore, the effects of light quality on the flowering of Gypsophila paniculata were investigated using light-emitting diodes (LEDs) emitting the following lights: FR, R, and blue (B). Flowering and flower budding were observed under long-day conditions with FR, while no flowering was observed under short-day conditions. Promotion of flowering and flower budding was increased under FR supplemented with R compared to FR alone. Although generally R inhibits flowering in long-day plants, a certain intensity of R, for example, the R:FR ratio between 0.23 and 0.71, may be necessary for effective promotion of flowering. In contrast, B supplementation of FR was not effective at the ratio in this study in inducing flowering and flower budding. The quality of cut flowers produced under long-day conditions with LEDs that promoted flowering was not lower than that under incandescent lamps. These results will provide basic knowledge for the development of LED bulbs as a replacement for incandescent bulbs.

The flowering response to monochromatic light and flowering-related genes underlying this response need to be characterized to efficiently use light-emitting diodes for lighting culture. The flowering response to far-red light has been well studied in long-day cut flowers, but there have been few studies investigating the response to blue light. Flowering and the expression of the G. paniculata homologs of the FLOWERING LOCUS T and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 genes (GpFT, GpSOC1) were not previously promoted in Gypsophila paniculata, an important long-day cut flower, 'Bristol Fairy' under long-day conditions with blue light. In the present study, we found that flowering was promoted in another G. paniculata 'Million Star', under long-day conditions with blue light, suggesting that there is variation in G. paniculata's flowering response to blue light. Therefore, we analyzed the expression of GpFT and GpSOC1 in the 'Million Star'. The expression of GpFT and GpSOC1 was promoted with flowering in 'Million Star' under long-day conditions with blue light in contrast to 'Bristol Fairy'. We next analyzed the G. paniculata homologs (GpFKF1, GpGI) of FLAVIN-BINDING KELCH REPEAT F-BOX 1 and GIGANTEA genes, which participate in the flowering response to blue light. GpFKF1 and GpGI amino acid sequences were well conserved; gene expression showed a diurnal rhythm with different peaks under short-day and long-day conditions, as previously observed in Arabidopsis thaliana. GpFKF1 interacted with GpGI. There were no important differences in GpFKF1 or GpGI amino acid sequences between the two cultivars. Our results suggest that variation in the flowering response to blue light is associated with GpFT and GpSOC1, rather than GpFKF1 and GpGI.