Diagnostic significance of the synthesis of phenolic compounds and proline in the leaves of Schisandra chinensis and Actinidia arguta for the indication of the stress levels of plants under conditions of mixed plantings

The peculiarities of the accumulation of polyphenolic compounds and free proline were investigated in the leaves of Actinidia arguta and Shisandra chinensis during their cultivation in vegetation containers with different ratios of the number of plants, namely 1 : 1, 2 : 1, 1 : 2. Monocultural (single-species) planting was used as a control. The content of free proline in plant leaves was carried out according to the method, which is based on the interaction of proline with a ninhydrin reagent, forming a pink-red color. The amount of polyphenolic compounds was determined by the Folin-Ciocalteu method. It was found that the ratio of plants grown together significantly affects the accumulation of primary and secondary metabolites in their leaves. Under conditions of mixed planting, more proline and phenolic substances are accumulated in plant leaves compared to monoculture. The maximum proline content, 19.44 ± 0.91 mg/g of dry weight (DW), was observed in the leaves of A. arguta in the experiment combination with a prevailing number of schisandra plants at a ratio of S. chinensis and A. arguta plants of 2:1. In the same combination, the leaves of actinidia contained the highest amount of phenolic compounds (36.87 ± 2.22 mg/g DW). The studied root exudates of the experimental plants had an allelopathic inhibitory effect on the test culture. The exudates caused 12.0 % average decrease in root growth of A. arguta test objects, and 30.0 % average decrease in root growth of S. chinensis test objects compared with the control. This allows us to conclude about the high activity of schisandra’s allelochemicals, which negatively affect the development of actinidia plants. The optimal ratio of plants A. arguta and S. chinensis when grown together is 2 : 1, since a higher concentration of schisandra plants in a container more stress in actinidia plants, expressed as an increased accumulation of phenols and prolines in its leaves. The result of a comparative analysis of the amount of proline and phenolic compounds can be used to assess the mutual influence of plants in mixed plantings to optimize their growing conditions, which confirms the diagnostic significance of these metabolites for indicating the stress state of the studied plants.