Effect Of Exogenous L-methionine On Growth,physiology,and Antioxidants System Of Lettuce In Hydroponics

Amino acids are well-known bio-stimulants which have positive effects on pl ant growth,yield and significantly mitigate the injuries caused by abiotic stresses.Lettuce is one of the most important salad vegetables,is considered to be a sensitive or a relatively salt-sensitive vegetable crop.The deleterious effects of salt stress in lettuce have been recorded on biomass production,due to ionic imbalance,toxic and osmotic effects and an increase in antioxidants.This study was carried out to obtain optimum amino acid type,suitable concentration in nutrient solution to study the influence of amino acid on phy siological,biochemical parameters,vegetative growth,leaf parameters,yield,content of vitamin C,antioxidants and to reduce destructive effects of lettuce plants under salinity.The experiment was divided into three parts;firstly,three different amino acids L-Glycine,LTryptophan and L-Methionine were applied to select the appropriate amino acid for lettuce plants.Secondly,the chosen one amino acid(L-Methionine)gave six different concentration levels to check the appropriate level for growth characteristics of lettuce plants.Thirdly,by using two different salt levels(40 mM/L NaCl and 80 mM/L NaCl)evaluate the effect of L-Methionine in lessening the deleterious effect of saline water and antioxidant activity of lettuce plants.The main results summarized as follows:1-The effect of individually treated three amino acids was studied for lettuce plants grown in the nutrient solution.Leaf width increased significantly by 17.46 % with L-Methionine application but decreased when treated with L-Glycine and L-Tryptophan by 18.25 % and 63.49 % respectively.Furthermore,leaf length in plants treated with L-Tryptophan decreased the by 61.92 % as compared to control plants.Similarly,leaf area increased significantly by L-Methionine by 31.41 %.L-Tryptophan inhibited plant height by 82.91 % and the leaf number by 50.36 % as compared to control plants.L-Methionine increased plant fresh weight by 20.88% and dry weight by 15.71%.Thus,this amino acid(L-Methionine)is a good candidate for the hydroponic culture of lettuce plants.2-Addition of different levels of L-Methionine in the hydroponic nutrient solution to improve the yield and growth characteristics as well as nutrient availability and nutrient uptake in lettuce plants was studied.The results showed that plant growth was significantly improved by L-Methionine application at lower concentration of 0.2 mg/L.The lower applied concentration of L-Methionine increased overall performance of plant vegetative growth as compared to control treated plants.Not only vegetative growth characters like leaf width,plant area,leaf area,chlorophyll contents improved by smaller quantity of L-Methionine but also an increase the N,P,K and S contents of lettuce leaves and roots was observed.Photosynthetic activity was also found greater at this level of concentration applied to plants hence increased plant biomass and quality.Whereas,the plant growth parameters(leaf length,width,plant height,total number of leaves per plant,leaf area,plant area,fresh and dry weight of roots and leaves,root length,total chlorophyll contents and relative water contents)were decreased at high levels of concentration especially 2200 mg/L and 220 mg/L decreased significantly plant growth as compared to control plants.Thus,it is recommended to use lower level of exogenously applied L-Methionine to lettuce plants when grow in the hydroponic nutrient solution.3-Soil salinity is common abiotic stress for plants that is having an increasing impact on international food production.Plants treated with L-Methionine showed better growth performance than the plants without L-Methionine subjected to salinity stress.Briefly,the application of L-Methionine with(moderate salt level)40 mM/L NaCl significantly enhanced growth parameters,i.e.plant height;root length;number of leaves per plant;plant fresh and dry weight;leaf relative water content(LRWC);membrane permeability(MP);total chlorophyll content in leaf when compared to both plants with stress but without amino acid and the control plants.Thus L-Methionine can reduce the plant stress by increasing plant growth and antioxidant activity hence make the plant tolerant towards different salinity levels.Finally,we concluded that Lettuce is sensitive to salinity plant.Supplying with exogenous L-Methionine in hydroponic solutions can increase its yield,quality,0.2 mg/L was observed feasible dose to make plant tolerant,increase quality of lettuce as well as increase in total fresh and dry mass of plants.