Melatonin and Selenium Regulate Growth and Oxidative Status of Saussurea orgaadayi In Vitro Cell Cultures Derived from Different Explants

Abstract

Effects of 0.1 pM melatonin, 1.0 nM sodium selenite ( $${\text{SeO}}_{3}^{{2 - }}$$ ), and the combined application of these agents on morphogenesis and metabolism of two callus cell lines of Saussurea orgaadayi (Khanm.) Krasnob. were examined. Phenotypic distinctions were revealed for cell cultures obtained from different explants, namely, hypocotyls and cotyledons. The number and dimensions of large-sized cells were higher in the hypocotyl-derived cell culture (HCC) than in the cotyledonary cell culture (CCC). The relation between the growth of two callus cultures and specific traits of their metabolism was noted. The actively growing HCC differed from CCC by a higher content of proline (2.5-fold increase) and ecdysterone-like compound (2.3-fold rise), an increased rate of lipid peroxidation (twofold), and by a lower content of flavonoids. Accordingly, the CCC line exhibited a threefold higher level of flavonoids compared to HCC and a lower content of other compounds. In both cell lines treated with exogenous melatonin, the growth index calculated on a fresh weight basis was increased throughout 20 days after subculture, whereas the presence of $${\text{SeO}}_{3}^{{2 - }}$$ elevated the growth index on the 20th–25th days in the CCC line and did not affect the growth index in the HCC line. The combined treatment with melatonin and $${\text{SeO}}_{3}^{{2 - }}$$ raised the growth index starting from the 15th day; the stimulatory influence was larger in the HCC than in the CCC line. Melatonin and $${\text{SeO}}_{3}^{{2 - }}$$ had a regulatory action on the cellular antioxidant system. Melatonin retarded lipid peroxidation and elevated proline content in both lines. The influence of $${\text{SeO}}_{3}^{{2 - }}$$ was less effective than that of melatonin. Under combined action of both factors, changes in lipid peroxidation in CCC were smaller than under the action of melatonin alone, whereas changes in the proline content were enhanced. The effect of the combined treatment on lipid peroxidation and proline content in HCC did not differ from the effects exerted by melatonin alone. Melatonin and $${\text{SeO}}_{3}^{{2 - }}$$ were hypothesized to differentially affect the cell culture respiration as a source of reactive oxygen species.