Combined Citric Acid and Glutathione Augments Lead (Pb) Stress Tolerance and Phytoremediation of Castorbean through Antioxidant Machinery and Pb Uptake

Abstract

Lead (Pb) is one of the most toxic elements on earth. The main origins of Pb pollution are automobiles, paint and electroplating industries. Pb-induced stress has very toxic effects on plant growth and biomass. The concentration of reactive oxygen species (ROS) in plant cells significantly increases under Pb stress, which interrupts the biochemical cycles in cells and leads to cell death. Therefore, it is essential to clean up the Pb-polluted soils. Among all techniques that are used to clean soil that is metal-contaminated, the best technique is phytoremediation. The present study intends to determine the role of citric acid (CA) and glutathione (GSH) in the phytoremediation of Pb by using castor bean plants. Plant biomass was significantly reduced due to Pb stress. Lead toxicity was also harmful to the photosynthetic pigments and antioxidant enzymes activities. In reverse, the content of malondialdehyde (MDA), H2O2 concentration and electrolyte leakage (EL) were increased under Pb stress. The combined application of GSH and CA enhanced photosynthetic pigments, antioxidant enzyme activities and plant biomass and minimized MDA, H2O2 and EL under Pb stress. The amount of Pb in roots and leaves remarkably increased by the joint application of CA and GSH. The combined application of CA and GSH (5 mM + 25 mM, respectively) was proven to be beneficial compared to the control. From the present results, we can conclude that the combined application of CA and GSH promoted the phytoremediation of Pb and helped the host plant to combat Pb toxicity.

Attenuating Effect of an Extract of Cd-Hyperaccumulator Solanum nigrum on the Growth and Physio-chemical Changes of Datura innoxia Under Cd Stress

“…Stimulating impacts of SNE were noticeable owing to the existence of citric acid (CA), ascorbic acid (AsA) and proline (as antioxidants) and some micro and macronutrients (Fe, iron; Zn, zinc; Mg, magnesium) in the plant extract (Table 1). Study of Zeng et al (2021) on castor bean proved that foliar sprayed citric acid alleviated lead (Pb) stress via improving growth, as well as fresh and dry biomass. Also, a study of Zhang et al (2019) on Cd-stressed maize plants revealed that AsA application induced growth improvement via stimulation in photosynthetic pigments, amino acids, and protein, which might have enhanced cell enlargement and growth of plant (Aziz et al 2018).…”

Mitigation of Environmental Stress-Impacts in Plants: Role of Sole and Combinatory Exogenous Application of Glutathione

“…CA is the initial intermediate of the TCA cycle. It plays a vital role as a mild antioxidant and metal chelation agent that interacts effectively with HMs to facilitate their immobilization, which alleviates the HM-induced stress on plants ( Godoy et al, 2021 ; Zeng et al, 2021 ). Recently, Zeng et al (2021) investigated the effects of combined application of GSH and CA on castor bean ( Ricinus communis L.) plants and demonstrated successful results in alleviating Pb-induced stress.…”

“…It plays a vital role as a mild antioxidant and metal chelation agent that interacts effectively with HMs to facilitate their immobilization, which alleviates the HM-induced stress on plants ( Godoy et al, 2021 ; Zeng et al, 2021 ). Recently, Zeng et al (2021) investigated the effects of combined application of GSH and CA on castor bean ( Ricinus communis L.) plants and demonstrated successful results in alleviating Pb-induced stress. The synergistic effects of GSH and CA are shown through the improved growth parameters such as length, dry weight of shoots and roots, number of leaves per plant and leaf area in Pb-stressed plants.…”

“…The enhanced biomass and growth traits are correlated to the increase in water use efficiency (WUE), stomatal conductance, transpiration rate and photosynthetic performance. The amelioration of Pb-induced stress was also evident as enzymatic activities such as SOD, POD, CAT, APX were significantly increased, which led to the significant decrease in the overproduced H 2 O 2 , MDA and electron leakage (EL) in the roots and leaves ( Zeng et al, 2021 ).…”

“…For example, among concentrations (5 mM, 10 mM, 15 mM and 20 mM), 10 mM of GSH resulted in the best growth parameters for rice species MR 253, while 20 mM of GSH resulted in the best growth parameters for rice species MR220 ( Teh et al, 2015 ). Hence, in recent years, researchers have started to investigate the sequenced or combined application of GSH together with different bioactive compounds, categorized as plant metabolites such as proline, citric acid, ascorbic acid, melatonin; biostimulants such as putrescine, Moringa leaf extract, selenium and humic acid; and microorganism like cyanobacteria, in attempt to improve the stress tolerance further and overcome the limitations of possessed by GSH in conferring growth and yield of plants ( Semida et al, 2018 ; Zaki et al, 2019 ; Goodarzi et al, 2020 ; Rehman et al, 2021 ; Zeng et al, 2021 ). Therefore, this review discusses the recent progress (2017–2021) in the individual and combined application of GSH with other bioactive compounds while reinforcing our understanding of the biosynthesis, metabolism, and roles of GSH when mitigating abiotic and biotic stresses.…”