Stimulation Effects of Foliar Applied Glycine and Glutamine Amino Acids on Lettuce Growth

Amino acids have various roles in plant metabolism, and exogenous application of amino acids may have benefits and stimulation effects on plant growth and quality. In this study, the growth and nutrient uptake of Romain lettuce (Lactuca sativa subvar Sahara) were evaluated under spray of glycine or glutamine at different concentrations of 0 (as control), 250, 500 and 1000 mg.L-1, as well as a treatment of 250 mg.L-1 glycine+250 mg.L-1 glutamine. The results showed that there was significant increase in leaf total chlorophyll content under Gly250+Glu250, Gly250 and Glu1000 mg.L(-1 )treatments, and in leaf carotenoids content under 250 mg.L-1 glutamine spray compared with the control plants. Shoot fresh and dry weights were highest under 500 mg.L-1 glycine, whereas root fresh weight was highest under 250 mg.L-1 glycine spray. Foliar application of glycine and glutamine had no significant increase in leaf mineral concentrations except for iron, in which 1000 mg.L-1 Gly spray resulted in significantly higher leaf Fe concentration compared with the control plants. Leaf vitamin C was increased at 250 and particularly 500 mg.L-1 spray of glycine and glutamine compared with the control. Nevertheless, different amino acid treatments had no significant effect on plant height, leaf SPAD value, root dry weight, and leaf concentrations of N, K, Ca, Mg and Zn. The results indicate that foliar application of glycine and glutamine amino acids can have beneficial effects on lettuce growth, as higher fresh yield, leaf chlorophyll content and vitamin C were obtained by low to moderate concentrations of glycine and/or glutamine amino acids.