Light quality during early seedling development influences the morphology and bitter taste intensity of mature lettuce (Lactuca sativa) leaves

The genetic constitution of a vegetable crop species such as lettuce (Lactuca sativa) is an important determinant of characteristics such as leaf size, shape, texture, color, and taste. Whereas introduction of improved traits by breeding or genetic engineering is possible, an alternative approach involves modification of the mature phenotype by manipulation of the early growth environment. To explore this phenomenon, lettuce was grown under specific light quality treatments (red, red + far-red, blue, and white light), both continuously and with color switching at various intervals. Leaves grown in continuous light quality showed characteristic differences in leaf area, shape, dry weight, and bitter taste intensity as determined by an analytical sensory panel. However, red light supplied for the first 7 d of growth conditioned weak bitterness intensity whether or not plants were switched to white light for 18 or 26 d. Leaf area and dry weight were determined by the first 7 d in red or blue light whether or not plants were switched to the opposite color light for 9 or 35 d. These observations demonstrate that persistent photomorphogenic switching of leaf development can take place before leaf emergence, and that light quality signals received in the early growth environment can have a latent effect on subsequent plant development.