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

Abstract

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.

Glycine mitigates fertilizer requirements of agricultural crops: case study with cucumber as a high fertilizer demanding crop

“…Similarly, exogenous application of glycine at 0, 5, 10 and 20 mM in Chorispora bungeana showed that 10 mM was best to improve plant growth trait of leaf biochemical reactions, while application of 20 mM glycine showed an opposite effect [40]. Lettuce growth was also improved by applying l-methionine at the lowest concentrations of 0.2 mg/L rather than higher concentrations [14]. The ANOVA for number of fruits and total yield in plant was significant at P = 0.01 (Table 4).…”

“…In the present study, all mineral nutrients were influenced by glycine, particularly in soil application. The enhancement in leaf mineral nutrients due to application of glycine [20,21,41] or even other amino acids [3,9,14,17] has been reported. In a study with lettuce plants only leaf Zn, but not other minerals, was increased by foliar application of 500 ppm glycine [2].…”

“…In coriander (Coriandrum sativum) application of glycine at 300 and 600 mg/kg soil reduced the number of flowered plants and resulted in longer growth period and higher yield and biomass production [20]. Glycine with different mechanisms may increase cucumber economic life including, optimization of plant growth, nutrient uptake and photosynthetic activity that are associated with biostimulation, signaling and protective effects of glycine on plants [14,30]. Glycine also has semi-hormonal effects on plant growth [34] and sometimes is regarded as a plant growth regulator [16].…”

“…It is often used for production of a wide range of aminochelate fertilizers (amino acid-chelated nutrients). Exogenous application of amino acids can increase nitrogen status and concentration of mineral elements in plant tissues [14]. However, many factors govern the effectiveness of the applied amino acid (glycine), including plant species, growth stage, climatic conditions, number of foliar or soil applications and particularly the applied concentration [9,32].…”

Toward a Sustainable Agriculture Through Plant Biostimulants: From Experimental Data to Practical Applications

“…Different amino acids (L-methionine, L-glycine and L-tryptophan at 20, 210 and 220 mg/L, respectively) were applied separately on hydroponically grown butterhead lettuce to assess their stimulators role [29]. In their study, L-methionine boosted lettuce growth parameters, whereas a negative effect was observed when L-glycine and L-tryptophan were applied.…”