Heavy metal-induced oxidative stress on seed germination and seedling development: a critical review

Abstract

Heavy metal contamination in soils can influence plants and animals, often leading to toxicosis. Heavy metals can impact various biochemical processes in plants, including enzyme and antioxidant production, protein mobilization and photosynthesis. Hydrolyzing enzymes play a major role in seed germination. Enzymes such as acid phosphatases, proteases and α-amylases are known to facilitate both seed germination and seedling growth via mobilizing nutrients in the endosperm. In the presence of heavy metals, starch is immobilized and nutrient sources become limited. Moreover, a reduction in proteolytic enzyme activity and an increase in protein and amino acid content can be observed under heavy metal stress. Proline, is an amino acid which is essential for cellular metabolism. Numerous studies have shown an increase in proline content under oxidative stress in higher plants. Furthermore, heat shock protein production has also been observed under heavy metal stress. The chloroplast small heat shock proteins (Hsp) reduce photosynthesis damage, rather than repair or help to recover from heavy metal-induced damage. Heavy metals are destructive substances for photosynthesis. They are involved in destabilizing enzymes, oxidizing photosystem II (PS II) and disrupting the electron transport chain and mineral metabolism. Although the physiological effects of Cd have been investigated thoroughly, other metals such as As, Cr, Hg, Cu and Pb have received relatively little attention. Among agricultural plants, rice has been studied extensively; additional studies are needed to characterize toxicities of different heavy metals on other crops. This review summarizes the current state of our understanding of the effects of heavy metal stress on seed germination and seedling development and highlights informational gaps and areas for future research.

Assessment of phytotoxicity of leachates from landfilled waste and dust from foundry

“…The toxicity of arsenic is closely dependant on its chemical form. As has a negative impact on the root and shoot length of plants (Seneviratne et al 2019). In contrast, selenium is a microelement which stimulates germination and plant development (Barrientos et al 2012;Praveen et al 2017).…”

“…The roots are responsible for the absorption of water, nutrients and contaminants, which affects the development of the plant. However, most of the nutrients are taken by the germ from the seeds, so the impact of contaminants on plant development in the first stage of growth may not be apparent (Khan et al 2018;Seneviratne et al 2019). During the germination test, different leachate effects were observed on Lepidium sativum seeds.…”

“…Among them, are biomarkers sensitive to heavy metals which have an impact on various biochemical processes in plants, e.g. enzyme and antioxidant production, oxidative stress protein mobilization and photosynthesis (Liu et al 2009;Wang et al 2010;Gupta et al 2013;Alonso-Blázquez et al 2015;Hu et al 2015;Oztetik 2015;Rout et al 2015;Seneviratne et al 2019). In the phytotoxicity assessment of waste, leachate is usually tested, because nutrients and pollutants may be uptaken by the plants directly from aqueous solutions, in dissolved form.…”

“…It is considered that seed germination bioassay could be less sensitive to toxic substances than root growth tests (Fuentes et al 2004). Some authors suggest that toxic substances may not be absorbed by seeds, because the embryon (germ) of seeds is effectively isolated from the environment and draws nutrients (carbohydrates, macro-and microelements) from the seed (Mitelut and Popa 2011;Seneviratne et al 2019). The roots are responsible for the absorption of water and nutrients, for this reason root lengths are affected by the concentration of the contaminants present in the water solution.…”

“…The advantage of this species is the availability of seeds, rapid growth, sensitivity to environmental factors, including heavy metals, and low humidity requirements. Lepidium sativum is a recommended plant in many standards for biotoxicity test (Baumgarten and Spiegel 2004) and is used by many authors (Hoekstra et al 2002;Fuentes et al 2004, Barrientos et al 2012Baran et al 2014;Visioli et al 2014; Baran and Tarnawski 2015;Wierzbicka et al 2015;Praveen et al 2017;Khan et al 2018;Mañas and De las Heras 2018;Seneviratne et al 2019).…”