LAUSR

Abstract The light frequency of red (R) and blue (B) plays a crucial role within plant growth cycle. Whereas, the relationship between the metabolic pathways involved in photosynthesis and carbohydrate accumulation in tomato seedling and hormone regulation still needs further investigation. This research comprehensively analyzed changes in leaf anatomy, stomatal traits, pigment content, gas exchange parameters, chlorophyll fluorescence, Rubisco and Calvin cycle-related enzyme expression and activities, as well as endogenous hormones biosynthesis in tomato (Solanum lycopersicum L.) seedlings, which radiated by four light qualities, including monochromatic white light (W), B, R and mixed light of R and B (RB). The findings showed the biomass accumulation as well as CO2 assimilation were greatly increased in seedlings under B and especially under RB light. Their leaves were also thicker, and stomatal conductance, levels of pigment, photosynthetic electron transport capacity, and the photosynthetic rate were enhanced. In addition, enzyme expression level and activity related to the Calvin cycle were up-regulated. Moreover, RB-induced growth was accompanied by a significant inhibition in gibberellin (GA) concentration as well as an increment in auxin (indole-3-acetic acid (IAA)) in stem and root. Overall, photosynthesis of RB-treated seedlings was positively regulated by leaf anatomy and photosynthetic electron transportation as well as maintaining the activation states of the Calvin cycle, and then inducing changes in carbohydrate accumulation. In addition, both GA and IAA were found to be involved causally in the increased shoot and root biomass of tomato seedlings under RB treatment.