The Impact of Drought Stress on Antioxidant Responses and Accumulation of Flavonolignans in Milk Thistle (Silybum marianum (L.) Gaertn)

Abstract

Biosynthesis and accumulation of flavonolignans in plants are influenced by different environmental conditions. Biosynthesis and accumulation of silymarin in milk thistle (Silybum marianum L.) were studied under drought stress with respect to the antioxidant defense system at the physiological and gene expression level. The results revealed a reduction in leaf chlorophyll, ascorbic acid, and glutathione contents. In contrast, H2O2, proline, and antioxidative enzyme activities, such as superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), and glutathione reductase (GR), were increased. These results confirmed that milk thistle undergoes oxidative stress under drought stress. Furthermore, transcription levels of APX, SOD, CAT, 1-Cys-Prx, and PrxQ were significantly increased in milk thistle under drought stress. Overall this suggests that protection against reactive oxygen species and peroxidation reactions in milk thistle are provided by enzymatic and non-enzymatic antioxidants. Flavonolignans from milk thistle seeds after different drought treatments were quantified by high-performance liquid chromatography (HPLC) and showed that severe drought stress enhanced the accumulation of silymarin and its components compared with seeds from the control (100% water capacity). Silybin is the major silymarin component and the most bioactive ingredient of the milk thistle extract. Silybin accumulation was the highest among all silymarin components in seeds obtained from drought-stressed plants. The expression of the chalcone synthase (CHS) genes (CHS1, CHS2, and CHS3), which are associated with the silybin biosynthetic pathway, was also increased during drought stress. These results indicated that milk thistle exhibits tolerance to drought stress and that seed derived from severe drought-stressed plants had higher levels of silymarin.

Optimal Duration of Drought Stress Near Harvest for Promoting Bioactive Compounds and Antioxidant Capacity in Kale with or without UV-B Radiation in Plant Factories

“…The results were in agreement with a previous report by Oh et al, which showed that the drought stress induced by withholding water for 4 days improved the TPC and TAC in lettuce [15]. Furthermore, numerous studies have shown that drought stress enhances one or both enzymatic and nonenzymatic antioxidants in a wide range of plants [31][32][33][34][35]. Moderate drought stress can improve plant drought tolerance, and enhance the antioxidant system [30,36].…”

Flavonoids improve drought tolerance of maize seedlings by regulating the homeostasis of reactive oxygen species

“…Plants alleviate stress-induced oxidative damage by changing antioxidant enzymes activity and accumulation of non-enzyme antioxidants, such as ascorbic acid, flavonoids, etc. (Wang et al 2018;ElSayed et al 2019). In milk thistle (Silybum marianum [L.] Gaertn), the activities of antioxidative enzymes, such as catalase (CAT), superoxide dismutase (SOD), ascorbate peroxidase (APX), and peroxidase (POD), increased under drought stress, and the biosynthesis and accumulation of flavonolignans (non-enzyme antioxidants) also increased during drought stress (ElSayed et al 2019).…”

“…(Wang et al 2018;ElSayed et al 2019). In milk thistle (Silybum marianum [L.] Gaertn), the activities of antioxidative enzymes, such as catalase (CAT), superoxide dismutase (SOD), ascorbate peroxidase (APX), and peroxidase (POD), increased under drought stress, and the biosynthesis and accumulation of flavonolignans (non-enzyme antioxidants) also increased during drought stress (ElSayed et al 2019). Flavonoids are secondary metabolites in the phenylpropane pathway and reportedly, they play important roles in plant responses to biological and non-biological stresses (Liu et al 2011a;Akram et al 2018;Brunetti et al 2018).…”

Antifungal Activity against Botryosphaeriaceae Fungi of the Hydro-Methanolic Extract of Silybum marianum Capitula Conjugated with Stevioside

“…The standardized extract obtained from the dried fruits of S. marianum contains 70–80% of silymarin and 20–30% of polymeric and oxidized polyphenolic compounds [ 3 ]. Silymarin is a flavonolignan complex of polyphenolic molecules, which includes diasterereoisomers silybin A and silybin B (whose mixture in a 1:1 ratio is named silibinin), silydianin, silychristin, isosilychristin, isosilybin A and isosilybin B, and the taxifolin flavanonol [ 4 ]. Biosynthesis of silybins from taxifolin and coniferyl alcohol is schematized in Figure S1 [ 5 ].…”