Analysis of Phenolic Compounds of Reynoutria sachalinensis and Reynoutria japonica Growing in the Russian Far East

The Russian Far East is a region of unique biodiversity, with numerous plant species, including <i>Reynoutria japonica</i> and <i>Reynoutria sachalinensis</i>. These plants are considered a serious threat to biodiversity and are classified as threatened species. However, <i>Reynoutria</i> plants synthesize and accumulate a variety of metabolites that are valued for their positive effects on human health. The main objective of this study is to quantitatively and qualitatively evaluate the content of secondary metabolites in different parts of <i>R. japonica</i> and <i>R. sachalinensis</i> plants. In this study, the results of phylogenetic analysis of the <i>ITS2</i>, <i>matK</i>, and <i>rps16</i> genes showed that samples collected in the Sakhalin region were closest to <i>R. sachalinensis</i>, while samples collected in Primorsky krai were closer to <i>R. japonica</i>. The high-performance chromatography and mass spectrometry (HPLC-MS/MS) method was used to identify the compounds. As a result of the identification of metabolites in the leaves, stem, and roots of <i>R. japonica</i> and <i>R. sachalinensis</i>, we showed the presence of a total of 31 compounds, including stilbenes, phenolic acids, flavan-3-ols, flavones and flavonols, naphthalene derivatives, anthraquinones and derivatives, and phenylpropanoid disaccharide esters. The root of <i>R. japonica</i> was shown to be a rich source of stilbenes (up to 229.17 mg/g DW), which was 8.5 times higher than that of <i>R. sachalinensis</i> root (up to 27.04 mg/g DW). The root also contained high amounts of emodin derivatives and vanicoside B. Quercetin and its derivatives were the major metabolites in the leaves and stems of both <i>Reynoutria</i> species. In <i>R. japonica</i> leaves, quercetin-3-<i>O</i>-pentoside was the major compound, reaching a total of 7 mg/g DW, accounting for 34% of all compounds analyzed. In contrast, in <i>R. sachalinensis</i> leaves, quercitrin was the major compound (up to 13.96 mg/g DW), accounting for 62% of all compounds and 12.7 times higher than in <i>R. japonica</i> leaves. In turn, <i>R. japonica</i> leaves also contained high amounts of phenolic acids (up to 10 mg/g DW). Thus, the obtained results showed significant differences in the qualitative and quantitative composition of metabolites between <i>R. japonica</i> and <i>R. sachalinensis</i> plants. Additionally, in this work, a cell culture of <i>R. japonica</i> was obtained and tested for its ability to synthesize and accumulate stilbenes.