Intermittent Supplemental Irradiation With Blue Light Promotes Leafy Heads in Lettuce

Abstract

Red and blue lights are the most effective spectral components absorbed by plants and are typically applied in a constant spectrum in plant factory agricultural practices. Research and application of non-constant light modes are relatively rare. In this study, we examined the impacts of varying blue light photon intensity and durations at 5-, 15-, 30-, and 45-min intervals of intermittent exposure on the growth and development of lettuce (Lactuca sativa) in plant factories while maintaining a constant red light photon flux and daily light integral (DLI). Compared to the constant light condition, intermittent blue light irradiation treatments accelerated the emergence of the leafy head trait in lettuce without compromising photosynthetic capacity and biomass. Specifically, intermittent blue light treatment with 15-min intervals led to a reduction of 8 days in the time needed for half of the lettuce plants to reach the heading stage. Furthermore, the petiole bending angle in treated lettuce was just 70.2% of that observed under constant light conditions, with strong correlations between multiple hormone levels and bending angle in petioles. Transcriptome sequencing analyses revealed significant differential expression of signaling-related genes between constant and intermittent blue light treatments. The transient and dynamic expression of light-responsive and hormone metabolism-related genes indicated that 15-min intermittent blue light exposure better maintained the rhythmic differential expression of response genes, leading to different hormone accumulations and consequently accelerating the development of leafy heads.