Analysis of Arabidopsis Light-sensitive Mutants Grown under Different Ratios of LED and Compared to Florescent Lighting

Energy efficiency and increased light spectrum control have begun to drive many plant growth facilities to switch from fluorescent light bulbs to light-emitting diodes (LEDs).  We were interested to learn whether seemingly equivalent conditions between fluorescent lights and LEDs were functionally equivalent for plant growth.  To test this, we fitted half of a walk-in chamber with LumiGrow Lumibar LED lamps (red, blue, and white lights) and maintained the other half of the chamber with the traditional fluorescent lighting (cool white bulbs).  Using Arabidopsis as a model system we measured plant growth traits in six genotypes selected for their light-sensitive phenotypes: the wild-type Columbia-0, and two natural accessions, Kondara and Knox18, with extreme and mild shade response phenotypes, respectively. Additionally, the light signaling mutants phyB, cry1/2, and hy5 were selected for their sensitivity to varying light conditions.  Plants were grown under four different light conditions at a PAR of approximately 150 micromoles/m2/sec where the light conditions were adjusted for different light ratios:  Red (R) 143 red, 0 blue, 7 white; High Blue (HB) 73 red, 80 blue, 7 white, Mid Red Blue (MRB) 113 red, 30 blue, 7 white, and fluorescent light (F).  In addition, plants were grown with the Maximum PAR (MP) output for the LED light, approximately 350 micromoles/m2/sec PAR where the light ratio was 75% red: 20 %blue: 5%white.  Our analysis of leaf size, shape, and number, as well as days to flowering, indicated differences in growth patterns between light conditions.  PAR-matched and maximum PAR LEDs also showed some phenotypic growth differences compared to fluorescent lighting.  However, the LED lighting did not cause the same temperature increase as fluorescent lights (~5 degrees Celsius cooler); many of the major growth differences might therefore be due to differences in temperature, rather than light.  Overall, our findings suggest no reason to delay a transition to LEDs, even for studies involving light signaling.