The regulation of photosynthesis and growth of rapeseed seedling by the interaction of red and yellow lights with blue light

The interactive regulation among different lights on plant life-activities has not yet been fully understood. In the study, we investigated the interaction of red light (R) and yellow light (Y) with blue light (B) on growth and photosynthesis of rapeseed seedlings. The results showed Y and R as well as their combination of RY were not beneficial for plant photosynthesis and growth, but a quarter addition of B (RB, YB and RBY) obviously reversed these negative effects, improving stomatal behavior, leaf and root developments, photosynthetic traits, as well as synthesis and transport of photosynthetic products. Available light energy and B intervention together decreased the ratio of chlorophyll b (Chl b) to carotenoid (Car), while the opposite effect was observed in the absence of B treatments. Among the various lights, RY and Y significantly upregulated the majority of genes associated with chlorophyll metabolism, while RB predominantly upregulated genes related to the two photosystems (PS). Conversely, B and YB treatments generally suppressed the expression of these genes. Despite these differences in gene expression, the ratios of PSI/PSII to Chl b/Car were consistently maintained around 0.56 in the RB, YB, and RBY treatments. In contrast, this ratio was higher at 0.64 in the B treatment and lower, at less than 0.44, in the R, Y, and RY treatments. These ratios reflect the balance between light supply and utilization in plants under different lights, where plants under RB, YB, and RBY might achieve optimal light environments, while plants under B and under R, Y, and RY experienced high and low light stress, respectively. In conclusion, all combinations of B with R, Y or RY can be used for rapeseed cultivation, and the ratio of Chl b/Car to PSI/PSII might be an important reference index to select optimal light combinations for crop production.