The Effect of Silicon on Growth, Physiological, and Phytochemical Attributes of Calendula Seedlings Under Lead Stress

Today, soil contamination with heavy metals has become one of the main problems for food safety and sustainable agriculture. Here, in order to investigate the interaction between silicon (Si) and lead (Pb), hydroponic research was conducted to study the effects of Si (0.5 and 1 mM) on calendula (Calendula officinalis L.) under the toxicity of Pb (150 and 300 µM). The results demonstrated that Pb toxicity diminished the leaf accumulation of mineral nutrients and photosynthetic pigment content, which was associated with reduced plant growth and biomass. Pb stress also raised the leaf accumulation of hydrogen peroxide, anion superoxide, and methylglyoxal and rendered oxidative stress in calendula seedlings, which enhanced malondialdehyde levels and damaged membrane lipids. According to the obtained results, the greatest effects of Pb toxicity were created at a concentration of 300 μM Pb. The addition of Si lessened the accumulation of Pb, improved the contents of chlorophyll a, b, and carotenoids, and enhanced the function of photosynthetic apparatuses in calendula seedlings under Pb stress, thereby improving plant growth and biomass. The application of Si ameliorated the oxidative stress induced by Pb toxicity by upregulating the activity of enzymes involved in the antioxidant defense system and glyoxalase systems and modulating the ascorbate–glutathione redox state. Therefore, the results verified that the external application of Si reduced Pb toxicity by reducing Pb absorption, strengthening the antioxidant defense system, and maintaining ion homeostasis and the ascorbate–glutathione redox state, which can be considered as a potential chemical strategy to improve the adaptation of Pb-stressed plants. However, in order to better understand the interactions between Pb and Si, deeper studies at the genetic and molecular levels are needed.