Interspecific differences of antioxidant ability of introduced Chaenomeles species with respect to adaptation to the steppe zone conditions

Plants of the genus Chaenomeles are traditionally used in the countries of South-East Asia, due to their high nutritional and health-promoting properties. However, the successful introduction of species promising for gardening from geographically remote areas requires the study of plant ontogeny under the conditions of new habitat. This is a very substantial problem for the steppe zone, where the continental climate has features of aridity and complicates the process of increasing the diversity of fruit crops by introducing the desired species. The present study aims to assess the effectiveness of the protective enzymatic system of different Chaenomeles genotypes subject to a steppe climate as well as the accumulation of the biologically active compounds with high antioxidant capacity. The study was performed on the basis of the introduced horticultural plants collection in the Botanical Garden of the DNU, and the Chaenomeles fruits, leaves, and the seeds were examined. The highest activity of catalase, benzidine-peroxidase and guaiacol-peroxidase, and the greatest enzymes activation during vegetation were found in leaves of Ch. cathayensis and Ch. speciosa, while the lowest activity was in leaves of both Japanese species. The biggest total phenolic content in the isopropanolic plant extracts, determined by Folin–Ciocalteau assay, was found in leaves of Ch. × superba, Ch. × californica and Ch. cathayensis (44.8, 52.8, and 43.6 mg GAE/g WW); a less high level was found in leaves of Ch. japonica and Ch. japonica var. maulei (43.1 and 40.2 mg GAE/g), while the lowest was in leaves of Ch. speciosa (29.3 mg GAE/g). The total flavonoids content determined using the aluminum chloride method, did not differ by variety or species in the plant leaves, being in the range of 2.6–2.9 mg of RE per g WW (accordingly, in leaves of Ch. japonica var. maulei and Ch. × californica). The high total reducing power determined by potassium ferricyanide assay was found in leaves of both hybridogenic species and Ch. cathayensis (respectively, 11.6, 14.1, and 11.4 AAE/g WW); leaves of both Japanese species had slightly lower values and the lowest was in leaves of Ch. speciosa (7.7 AAE/g). In the Chaenomeles fruits, the total phenolic content was the lowest in Ch. speciosa (17.8 mg GAE/g), average in both Japanese species (28.7 and 27.8 mg GAE/g), and the highest (33.3 mg GAE/g) was in Ch. cathayensis. The flavonoid accumulation was highest in the fruits of Ch. cathayensis and Ch. ja