The role of monochromatic red and blue light in tomato early photomorphogenesis and photosynthetic traits

Plant development and physiology are strongly influenced by the environmental light spectrum that triggers and controls several functional and structural response in plants. However, few studies investigated the effect of monochromatic light during plant photomorphogenesis from seed imbibition up to seedling development. The present research aimed to assess the mechanisms engaged by plants to optimize light harvesting and utilization of different wavelengths during the early photomorphogenesis in tomato, a high-value crop cultivated worldwide. Seeds were germinated in a growth chamber under four light treatments (100 % red light, R; 100 % blue light, B; 60 % red 40 % blue light, RB; white light, W) and seedlings were grown up to sixteen days. Hypocotyl and cotyledon development were measured during the early stages of growth. Chlorophyll fluorescence measurements, D1 and Rubisco protein expression, as well as chlorophyll and carotenoids content, were determined on the first true leaves to assess in the early growth stage the efficiency of photosynthetic apparatus. Tomato early photomorphogenesis was strongly influenced by light quality. The seedling growth under red-blue and white light determined comparable responses, enhancing both photosynthesis and biomass production compared to monochromatic treatments. The pure R light stimulated hypocotyl elongation, cotyledon expansion, plant height, and leaf area, but produced seedlings with reduced photosynthetic capacity as indicated by the lowest Rubisco content and photochemical efficiency, and the highest thermal dissipation. Monochromatic blue light induced in seedlings the highest Rubisco amount, more compact size and reduced biomass, but similar level of pigments and photochemical efficiency compared to other light treatments. Our data indicate that the lack of blue or red light negatively affects early tomato development, in term of morphology and physiology. However, blue wavelengths resulted more critical than red ones for the functionality of the photosynthetic apparatus.