Maria M. Akishina

Currently, the physiological and biochemical role of certain groups of phenols that have high biological activity remains poorly understood. Thus, the functions of hydroxycinnamic acids, related to phenylpropanoids, and, in particular, caffeic acid (CA), remain unclear.

The purpose of this work was to study the effect of different concentrations of caffeic acid on barley productivity, both under normal plant development conditions and in the presence of salt stress.

In a series of laboratory experiments using different test cultures and in a growing season on spring barley plants Hordeum vulgare L., the effect of CA was studied. The activity of different concentrations of caffeic acid was determined using several methodological approaches to phytotesting: the express method in Petri dishes; in plastic flat tablets using the applicate method; in conditions of growing plants in aqueous solutions. The vegetation experiment was carried out on gray forest medium-loamy soil with an organic matter content of 3.8%, a slightly acidic reaction of the soil solution (pH_KCl 5.9). NaCl solution (7.5 g×l^–1) was added to the 2–3 leaf phase. Plants were treated with CA foliarly once during the tillering phase. Three concentrations of CA were used in the experiment, based on the results of preliminary laboratory experiments: 100 µM, 50 µM, 10 µM. At the beginning of booting, the barley plants were harvested and soil samples were taken. Potassium, sodium and total nitrogen content were determined in dry plant mass. The flag leaf of plants was used to determine the content of chlorophyll and carotenoids.

According to the results of phytotesting, it was established that for monocotyledonous and dicotyledonous crops the greatest activity is manifested in variants with the lowest concentrations of CA (10 and 25 μM), while higher concentrations of CA (50 and 100 μM) significantly reduce all test indicators. Based on the results of the growing season, it was established that CA does not have a reliable stimulating effect. Under conditions of sodium chloride salinity with the use of a high concentration of CA (100 μM), a slight increase in the potassium content in the soil occurs. The sodium content in the soil decreased with the use of CA. The total plant weight per vessel decreased significantly from 1.25g/vessel to 0.25g/vessel. Without the use of NaCl, CA treatment was not accompanied by significant changes in barley weight. The content of chlorophyll (a and b) in the control variant (1.83 mg×g^–1) was significantly lower compared to their content in the leaves of plants that were treated with CA (4.03 mg×g^–1 — 10 µM and 3.14 mg×g^–1 — 100 µM). Against the background of NaCl, the content of total chlorophyll decreased to 0.24 mg/g, and when plants were treated with CA it increased from 1.26 mg×g^–1 at low concentration (10 µM) and to 2.14 mg×g^–1 at high concentration (100 µM). The use of CA at a concentration of 100 µM was accompanied by an increase in carotenoid content from 0.22 mg×g^–1 to 0.61 and, against the background of salinity, from 0.16 to 0.38 mg×g^–1. Thus, the use of CA for treating plants during the growing season under salinity conditions affects changes in physiological processes, which contributes to their adaptation.

The article considers the possibility of foliar application of amino acids (proline, methionine and lysine) for the regulation of metabolism and the formation of stress resistance in plants contaminated with heavy metals (cadmium). In the green pot experiment, stress was created due to the introduction of Cd(NO3)2 into the soil at a dose of 10 mg·kg–1, which corresponds to 5 permissible concentration (SanPiN 1.2.3685-21). In an experiment with «Nur» barley, the effect of these amino acids on biomass, the content of total and protein nitrogen in leaves, the content of pigments and their ratios (Cl a, Cl b, carotenoids, Cl a / Cl b) were studied. Foliar treatment of plants with amino acids in the absence of stressful conditions was accompanied by a significant increase in aboveground biomass. The use of proline, methionine and lysine in conditions of high Cd concentrations in the soil had a positive effect on barley biomass and ear formation. All plants treated with proline and lysine showed an increase in the content of all pigments (Cl a, Cl b, carotenoids) compared with the control. Methionine had a positive effect on the chlorophyll content precisely under stress, whereas in the absence of stress, the pigment content in the plant decreased. In the Cd-contaminated variants, there was a decrease in the content of both total and protein nitrogen in barley, which indicated a violation of metabolic processes in the plant under stress. Foliar treatment with amino acids during the tillering phase is accompanied by an increase in nitrogen content both under stress and without it.