Effects of light quality on growth, photosynthetic characteristics, and endogenous hormones in in vitro-cultured Lilium plantlets

Red (R, 640 nm) and blue (B, 464 nm) light are the most important regions in the spectrum absorbed by plants. Lilium plantlets cultured in vitro were exposed to 40 +/- 2 mu mol m(-1) s(-1) irradiance (spectral range: 400-800 nm) supplied by plant-growth fluorescent lamps (PGFL) under a 12-h light/12-dark photoperiod and cultured for 50 days under six light quality treatments: control (PGFL only); R (100% R); R:B = 8:2; R:B = 7:3; R:B = 5:5; B (100% B). Plant height and leaf number increased with increasing R light, and increasing B light inhibited fresh weight accumulation. The R:B = 7:3 treatment resulted in the highest pigment contents (chlorophyll b, carotenoids, total chlorophyll), photosynthetic indicator values (net photosynthetic rate, stomatal conductance, and intercellular CO2 concentration), and chlorophyll fluorescence parameters (maximal efficiency of photosystem II, relative quantum efficiency of photosystem II photochemistry, and photochemical quenching). The highest contents of total sugars, fructose, sucrose, and soluble protein in leaves were in the B-only treatment. At day 50, the trans-zeatin content was higher in the B-only treatment than in the R-only treatment, while the cis-zeatin content showed the opposite trend. The highest levels of indole acetic acid and gibberellin were in the R-only treatment, and the highest abscisic acid content was in the B-only treatment on day 50. We conclude that R light promoted stem elongation and leaf number, and B light increased the sugars and soluble protein contents in Lilium cultured in vitro. The R:B = 7:3 treatment was optimal for photosynthesis. These results will be useful for producing high-quality Lilium plants in vitro.