Specific functions of red, far red, and blue light in flowering and stem extension of long-day plants

For many long-day plants (LDP), adding far red light (FR, 700 to 800 nm) to red light (R, 600 to 700 nm) to extend the day or interrupt the night prom otes extension growth and flowering. Blue light OB, 400 to 500 nm) independ ently inhibits extension growth, but its effect on flowering is not well de scribed. Here, we determined how R-, FR-, or B-deficient (R-d, FRd, or B-d, respectively) photoperiods influenced stem extension and flowering in five LDP species: Campanula carpatica Jacq., Coreopsis xgrandiflora Hogg ex Swe et, Lobelia xspeciosa Sweet, Pisum sativum L., and Viola xwittrockiana Gams . Plants were exposed to R-d, FRd, B-d, or normal (control) 16-hour photope riods, each of which had a similar photosynthetic (400 to 700 nm) photon fl ux. Compared with that of the control, the R, environment promoted extensio n growth in C. carpatica (by 65%), C. xgrandiflora (by 26%), P. sativum (by 23%), and V. xwittrockiana (by 31%). The FRd environment suppressed extens ion growth in C. xgrandiflora (by 21%), P. sativum (by 17%), and V xwittroc kiana (by 14%). Independent of the R : FR ratio, the B, environment promote d stem extension (by 10 % to 100 %) in all species, but there was little or no effect on flowering percentage and time to flower. Extension growth was generally linearly related to the incident wide band (100 nm) R : FR ratio or estimated phytochrome photoequilibrium except when B light was specific ally reduced. A high R : FR ratio (i.e., under the FR, filter) delayed newe r initiation (but not development) in C. carpatica and C. xgrandiflora and inhibited flower development (but not initiation) in V.xwittrockiana. There fore, B light and the R : FR ratio independently regulate extension growth by varying magnitudes in LDP, and in some species, an FRd environment can s uppress flower initiation or development.