Adaptations to oxidative stress in Zea mays roots under short-term Pb2+ exposure

Abstract

Lead (Pb), a widespread contaminant in terrestrial landscape, is highly detrimental to plant and animal life. Specifically, Pb-contaminated soils cause a sharp decrease in crop productivity, thereby posing a serious risk to agriculture. A study was planned to investigate the toxic effect of Pb 2+ (0, 16, 40 and 80 mg L −1 ) in the seedlings of maize (Zea mays), in terms of induced physiological and biochemical changes at initial hours of treatment (0-8 h). Increased accumulation of malondialdehyde (MDA) served as an indicator of cellular peroxidation. At 80 mg L −1 Pb 2+ , MDA content enhanced over the control by 175% after 2 h of exposure and increased further to 461% greater over the control after 8 h of exposure. Elevated superoxide ion (O −.2 ) and H2O2 contents suggested oxidative damage to the plants. The level of H2O2 increased over control by 70%, 80%, 135% and 182% at 2, 4, 6, and 8 h after exposure to 16 mg L −1 Pb 2+ , respectively. In situ histochemical localization confirmed the level of lipid peroxides, increased accumulation of O −. 2 and loss of membrane integrity upon Pb 2+ treatment. Pb 2+ -induced oxidative stress triggered significant changes in the activities of antioxidant enzymes. A concentration-dependent increase was observed in the activities of the superoxide dismutase (SOD), ascorbate peroxidase (APX), guaiacol peroxidase (GPX) and glutathione reductase (GR) in response to Pb 2+ , whereas catalases (CAT) was not able to provide protection against oxidative stress. These observations imply that Pb 2+ -induced oxidative stress during initial period (0-8 h) of exposure involved ROS accumulation and upregulation of scavenging enzymes except CAT as a defense against Pb 2+ -toxicity.

Exogenous Nitric Oxide (NO) Interferes with Lead (Pb)-Induced Toxicity by Detoxifying Reactive Oxygen Species in Hydroponically Grown Wheat (Triticum aestivum) Roots

“…CAT activity was determined by monitoring the disappearance of H 2 O 2 at 240 nm and calculated using ε = 39.4 mM −1 cm −1 [ 22 ]. APX activity was determined as the oxidation of ascorbic acid at 290 nm and calculated using ε = 2.8 mM −1 cm −1 [ 3 ]. GPX activity was determined at 470 nm in terms of guaiacol oxidized and calculated using ε = 26.6 mM −1 cm −1 [ 22 ].…”

“…The phytotoxic effects of heavy metals have been attributed to pro-oxidative effects of metal ions, that disrupt various physiological and biochemical processes [ 2 ]. Lead (Pb) has been reported to induce reactive oxygen species (ROS) generation and alter enzymatic machinery in lupin roots, pea root cells, rice plants, maize roots, and aquatic plants such as Wolffia arrhiza and Elodea canadensis [ 3 ].…”

Lead Toxicity: Health Hazards, Influence on Food Chain, and Sustainable Remediation Approaches

“…Lead induced oxidative stress is reported to produce reactive oxygen species (ROS) in plants [146,147]. These ROS synthesized as a result of oxidative stress in plants can cause deleterious effects such as lipid peroxidation, disrupted cell membrane, DNA and protein damage, inhibition of photosynthesis, and inhibition of ATP production [148].…”

Lead Toxicity in Cereals: Mechanistic Insight Into Toxicity, Mode of Action, and Management

“…Researchers observed that NO significantly reduced the negative impact of Pb toxicity in the form of oxidative stress induced by ROS (malondialdehyde, conjugated dienes, hydroxyl ions and superoxide anion). Furthermore, exogenous NO interferes ROS detoxification mechanism and enhances the antioxidant enzyme activity in wheat roots ( Kaur et al, 2015a ). Based on the above results, eco-remediation technologies are therefore primarily applicable in the field of wet land agriculture.…”