Abstract
The present study evaluated the growth response and sugar accumulation of lettuce exposed to different lighting modes of red and blue LED light based on the same daily light integral (7.49 μmol·m−2). Six lighting treatments were performed, that were monochromatic red light (R), monochromatic blue light (B), simultaneous red and blue light as the control (RB, R:B = 1:1), mixed modes of R, B and RB (R/RB/B, 4 h R to 4 h RB and then 4 h B), and alternating red and blue light with alternating intervals of 4 h and 1 h respectively recorded as R/B(4 h) and R/B(1 h). The Results showed that different irradiation modes led to obvious morphological changes in lettuce. Among all the treatments, the highest fresh and dry weight of lettuce shoot were both detected with R/B(1 h), significantly higher than the other treatments. Compared with plants treated with RB, the contents of fructose, glucose, crude fiber as well as the total sweetness index (TSI) of lettuce were significantly enhanced by R treatment; meanwhile, monochromatic R significantly promoted the activities of sucrose degrading enzymes such as acid invertase (AI) and neutral invertase (NI), while obviously reduced the activity of sucrose synthesizing enzyme (SPS). Additionally. The highest contents of sucrose and starch accompanied with the strongest activity of SPS were detected in plants treated with R/B(1 h). The alternating treatments R/B(4 h) and R/B(1 h) inhibited the activity of SS, while enhanced that of SPS compared with the other treatments, indicating that different light environment might influence sugar compositions via regulating the activities of sucrose metabolism enzymes. On the whole, R/B(1 h) was the optimal lighting strategy in terms of lettuce yield, taste and energy use efficiency in the present study.
Highlights
Soluble sugar and crude fiber are carbohydrates affecting the sweetness and crispness of lettuce[8,9,10]
Li16 studied the effects of light quality on the activities of the above mentioned enzymes in tomato seedling leaves, and found that RB promoted SS activity compared with monochromatic R, B or W; monochromatic R significantly increased the activities of acid invertase (AI) and neutral invertase (NI) while reduced that of sucrose phosphate synthase (SPS) in comparison with RB or W
After 14 days, seedlings were transplanted into hydroponic boxes under different light environments The environmental conditions in the plant factory were 23 ± 2 °C, 600 μmol·mol−1 CO2 level and 65% relative humidity (RH). 15 plants spaced 20 cm apart were planted in each hydroponic box (100 × 60 × 10 cm)
Summary
Soluble sugar and crude fiber are carbohydrates affecting the sweetness and crispness of lettuce[8,9,10]. Www.nature.com/scientificreports monochromatic R significantly increased the contents of fructose and glucose in tomato seedling leaves compared with W (white LED light), B or RB. Li16 studied the effects of light quality on the activities of the above mentioned enzymes in tomato seedling leaves, and found that RB (especially 3R1B) promoted SS activity compared with monochromatic R, B or W; monochromatic R significantly increased the activities of AI and NI while reduced that of SPS in comparison with RB or W. The purpose of the study was to compare the effects of consistent RB light environment and dynamic RB light environment on sugar accumulation and growth of lettuce based on the same light quantum. Lettuce biomass, morphology, the amounts of sucrose, fructose, glucose, starch, crude fiber and the enzyme activities related to sucrose metabolism were studied to determine the functions of different light environment. The study will help for a deeper understanding of the relationship between red and blue light when acting on plants; the results are expected to optimize the application modes and lighting strategies of red and blue light in a horticultural production system
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