Abstract:

The seedlings of lettuce（Lactuca sativa L.）were illuminated with blue light（442 ± 9）nm and（457 ± 7），red light（627 ± 7）nm and（655 ± 11）nm and green light（521 ± 14）nm LEDs（300 µmol · m^-2 · s^-1，12 h photoperiod）respectively，based on the difference of absorption spectrum of chlorophyll in cells of higher plants. Natural light in greenhouse was applied as a control treatment（CK）. After three weeks of illumination，the nutritive accumulation，distribution and growth characteristic in the different parts of lettuce were measured to investigate the regulation effect of LEDs spectrum. The most remarkable increase（57.89%–85.04%）in leaf area，fresh weight and dry weight were detected in the red light₆₅₅ treatment compared with the CK. Treated with short wavelength of LEDs spectrums，blue light enhanced allocation of soluble proteins in leaf，root and whole-plant，and more soluble proteins were found to centralize in the leaf of lettuce when the wavelength got further shortened（e.g. blue light₄₄₂）. Meanwhile，the contents of soluble sugar in leaf，stem and whole-plant increased by 97.26%–357.54% under the red and blue irradiation. With the increase of wavelength of LEDs spectrums，more soluble sugar was also recorded in the leaf of lettuce after the illumination of red light ₆₅₅ treatment. However，the red light reduced the free amino acid content（52.79%–59.01%）and inhibited the GOT activity in leaf of lettuce，which could transfer more free amino acid into stem and then into root. This seems to indicate that red light Abstract. favored the growth of lunar organs or parts of lettuce by transporting and distributing more amino acids.