Mixed red and blue light promotes tomato seedlings growth by influencing leaf anatomy, photosynthesis, CO2 assimilation and endogenous hormones

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.

Automated summary

The research found that biomass accumulation and CO2 assimilation were significantly increased in tomato seedlings under blue light and especially under mixed red and blue light. Additionally, leaf thickness, stomatal conductance, pigment levels, photosynthetic electron transport capacity, and photosynthetic rate were all enhanced under these light conditions. The up-regulation of enzyme expression and activity related to the Calvin cycle was observed, along with changes in gibberellin concentration and auxin levels in stem and root tissues.