Biochemical responses of Silybum marianum seedlings to independent and combined salt and SiO2 treatments

In recent years, silicon dioxide (SiO2) particles have drawn increasing attention due to their potential to enhance plant tolerance to various stresses by modulating physiological and biochemical processes. Salinity is an important abiotic stress with a harmful impact on crop growth and productivity. In this context, the aim of this study was to investigate the influence of silicon dioxide (SiO2) addition on milk thistle (Silybum marianum (L.) Gaertn.) under salinity stress. Thus, individual and combined effects of the application of sodium chloride (NaCl, 50 and 100 mM) and SiO2 particles (0.1 mM) on some physiological and oxidative stress parameters, such as growth variables, photosynthetic pigments and soluble protein contents, the levels of an oxidative stress biomarker (malondialdehyde), and the specific activity of several antioxidant enzymes (superoxide dismutase, catalase and peroxidase) were evaluated. The results revealed that salt stress (100 mM) inhibited plant growth and decreased chlorophyll and carotenoid levels, whereas the added SiO2 partially mitigated these negative effects. In addition, the 100 mM NaCl treatment significantly increased peroxidise (POD) activity and decreased soluble protein content after 22 days, while no significant differences were found for group subjected to salt stress in the presence of SiO2. Results suggest that application of SiO2 on salt-stressed milk thistle may modify the seedling metabolism and increase the plant salt tolerance capacity.