Effect of foliar application of amino acids on the salinity tolerance of tomato plants cultivated under hydroponic system

Salinity is one of the most critical problems faced by agriculture in all the arid and semi-arid climates in the world. Many biostimulant-producing companies utilize different raw materials to palliate the negative effects of salinity on crops. Some of these active materials are amino acids (AAs). In this study, the effect of the foliar application of free amino acids or as a mixture of them was studied in tomato plants cv Optima, grown in a controlled environment growth chamber in a hydroponic system with Hoagland's solution with added 50 mM NaCl. The following treatments were applied: i) Control (-salt), ii) salt (+ salt), and the salt treatments with amino acids (AAs + salt): iv) L-Arg, v) L-Pro, vi) Glu, vii) L-Trp, viii) L-met + L-Arg, ix) L-met + L-Trp, x) Glu + L-Pro. At the end of the assay, vegetative growth parameters, relative water content, mineral nutrient content, carbohydrates and organic solutes and chlorophylls were measured. The results showed that salinity decreased the growth of the plants, but those treated with the L-Met, Pro + Glu and Met + Trp reversed the negative effect of salinity. Also, this result was not due to differences in the concentration of Cl- or Na+ in the leaves, or to changes in the water status of the plants, but to a greater accumulation of total soluble sugars induced by the application of AAs, which could have de-activated the reactive oxygen species created by the toxicity of these ions. The results of this experiment also highlight the antagonistic or synergistic effects between the AAs, which should be taken into account by fertilizer producers.