Adaptations to oxidative stress in Zea mays roots under short-term Pb2+ exposure
Tóm tắt
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 Pb2+ (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 Pb2+, 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 Pb2+, respectively. In situ histochemical localization confirmed the level of lipid peroxides, increased accumulation of OO
2
−.
and loss of membrane integrity upon Pb2+ treatment. Pb2+-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 Pb2+, whereas catalases (CAT) was not able to provide protection against oxidative stress. These observations imply that Pb2+ -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 Pb2+-toxicity.
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