To study the effects of light quality of continuous light before harvest on the growth and ascorbic acid (AsA) metabolism of lettuce (Lactuca sativa L.) grown under relative high nitrogen level, lettuce plants grown under different nitrogen levels (8, 10 and 12 mmol·L⁻¹) were subjected to continuous light with different red: blue light ratios (2R:1B and 4R:1B) before harvest. The results showed that the shoot fresh weight of lettuce under 12 mmol·L⁻¹ nitrogen level was significantly higher than that under other treatments. There were no significant differences in shoot dry weight, root fresh weight, root dry weight, soluble sugar content, nitrate content and AsA content in leaves among the treatments at different nitrogen levels. The content of AsA in leaves was significantly higher than that in petioles before and after continuous light. Under the same nitrogen level, the fresh weight of lettuce under continuous light quality 4R:1B was significantly higher than that under other treatments. The content of AsA in lettuce leaves increased in different degrees after continuous light before harvest. High yield and AsA content could be obtained by 72 h continuous light with red and blue light 4R:1B at 12 mmol·L⁻¹ nitrogen level. After continuous light, the content of AsA increased significantly due to the increase of the ratio of red light and nitrogen level, which increased the activities of L-galactono-1,4-lactone dehydrogenase (GalLDH) and dehydroascorbic acid reductase (DHAR) involved in AsA synthesis and in the recycling of DHAR to AsA respectively.

中文翻译：

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氮增加剂量下连续采光前LED的光质量影响水培生菜的生长和AsA代谢。

为了研究收获前连续光的光质量对在相对高氮水平下生长的生菜（Lactuca sativa L.）的生长和抗坏血酸（AsA）代谢的影响，在不同氮水平下（8、10和12）在收获前，对mmol·L ^-1）进行连续的不同红，蓝比率（2R：1B和4R：1B）的光照。结果表明：12mmol·L ^-1以下的生菜芽鲜重氮水平明显高于其他处理。在不同氮水平下，各处理的枝干重，根鲜重，根干重，可溶性糖含量，硝酸盐含量和AsA含量均无显着差异。连续光照前后叶片中的AsA含量明显高于叶柄中。在相同氮含量下，连续光照质量4R：1B下的生菜鲜重显着高于其他处理。收获前连续光照后，莴苣叶片中的AsA含量有不同程度的增加。在12mmol·L ^-1下，以红色和蓝色4R：1B连续发光72 h，可获得高收率和AsA含量氮水平。连续光照后，由于红光和氮含量的比率增加，AsA含量显着增加，从而增加了所涉及的L-半乳糖-1,4-内酯脱氢酶（GalLDH）和脱氢抗坏血酸还原酶（DHAR）的活性。在AsA合成中以及将DHAR回收到AsA中。