Effects of green light supplementation to a mixture of red and blue light on chlorophyll and ribulose-1,5-bisphosphate carboxylase/oxegenase contents and growth in leaf lettuce

To evaluate the usefulness of green light in artificial lighting cultivation, the effects of green light supplementation to a mixture of blue and red light on growth and photosynthesis in leaf lettuce (Lactuca sativa L. 'Green-wave') grown at three different planting densities (33, 44 and 55 plants m(-2)) were investigated. Plants were grown under a mixture of red, green and blue light (RGB; red/green/blue light intensity ratio of 2/1/1) or a mixture of red and blue light (RB; red/ blue light intensity ratio of 3/1), at 200 mu mol m(-2) s(-1) for two weeks. At 44 plants m(-2), the shoot fresh weight under ROB was significantly lower than that under RB, which was due to the decrease in the leaf number. There was no difference in the shoot fresh weight between the light treatments at 33 and 55 plants m(-2). Chlorophyll and ribulose-1,5-bisphosphate carboxylase/oxygenase contents in the lower leaves were significantly higher under RGB than under RB conditions. These data indicated that increases in these components did not lead to improving of the growth under the RGB condition compared with the RB condition, while green light irradiation could be valuable in suppressing leaf senescence of the lower leaves of Green-wave. We evaluated green light as useful because it reduces the waste of leaf blades in the pre-shipment trimming process.