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Exogenous Application of Amino Acids Improves the Growth and Yield of Lettuce by Enhancing Photosynthetic Assimilation and Nutrient Availability

Institute of Vegetables and Flowers, Chinese Academy of Agricultural Sciences (CAAS), No.12 Zhongguancun South Street, Haidian District, Beijing 100081, China
College of Horticulture and Landscape, Tianjin Agricultural University, Tianjin 300000, China
Author to whom correspondence should be addressed.
The authors equally contributed to this work.
Agronomy 2019, 9(5), 266;
Received: 19 April 2019 / Revised: 14 May 2019 / Accepted: 16 May 2019 / Published: 26 May 2019
PDF [1822 KB, uploaded 26 May 2019]


As natural plant growth stimulators, amino acids are widely used to improve the yield and quality of crops. Several studies have illustrated the effects of different amino acids on lettuce plant parts. However, the effects of applying single amino acids on root growth remain elusive. The objective of this study was to evaluate the effect of root application of L-methionine on the growth of lettuce. In this study, two successive experiments on butterhead lettuce were conducted under hydroponic conditions. Three amino acids, L-methionine (20 mg/L), L-glycine (210 mg/L), and L-tryptophan (220 mg/L), were applied separately. L-methionine significantly increased the growth performance by 23.60%, whereas growth using L-tryptophan and L-glycine decreased by 98.78% and 27.45%, respectively. Considering the results of the first experiment, a second experiment was established with different concentrations of L-methionine (2200 mg/L, 220 mg/L, 22 mg/L, 2.2 mg/L, 0.2 mg/L, and 0.02 mg/L). The plants were allowed to grow for four weeks. Leaf width, plant area, leaf area, chlorophyll contents, etc., were evaluated. The results show that plant growth significantly improved by applying L-methionine at the lowest concentrations of 0.2 mg/L and 0.02 mg/L, which can, therefore, improve hydroponic production of lettuce and, accordingly, human nutrition. View Full-Text
Keywords: L-methionine; L-tryptophan; L-glycine; lettuce; nitrogen L-methionine; L-tryptophan; L-glycine; lettuce; nitrogen

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Khan, S.; Yu, H.; Li, Q.; Gao, Y.; Sallam, B.N.; Wang, H.; Liu, P.; Jiang, W. Exogenous Application of Amino Acids Improves the Growth and Yield of Lettuce by Enhancing Photosynthetic Assimilation and Nutrient Availability. Agronomy 2019, 9, 266.

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