الفهرس 
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Abstract
Cadmium (Cd), a readily absorbed and translocated toxic heavy metal, inhibits plant growth, interrupts metabolic homeostasis and induces oxidative damage. Responses towards Cd-stress differ among plant cultivars, and the complex integrated relationships between Cd accumulation, detoxification mechanisms and antioxidant defenses still need to be unraveled. To this end, twelve Egyptian maize cultivars were grown under Cd-stress to test their Cd-stress tolerance. Out of these cultivars, tolerant (TWC360 and TWC321), moderately sensitive (TWC324) and sensitive (SC128) cultivars were selected, and their response to Cd in terms of biomass, Cd accumulation and antioxidant defense system were determined. The reduction in biomass was highly obvious in sensitive cultivars, while TWC360 and TWC321 showed high Cd tolerance. The cultivar TWC321 showed lower Cd uptake concurrently with an enhanced antioxidant defense system. Interestingly, TWC360 accumulated more Cd in the shoot, accompanied with increased Cd detoxification and sequestration. Principal component analysis revealed a clear separation between the sensitive and tolerant cultivars with significance of the antioxidant defenses, including superoxide dismutase (SOD). To confirm the involvement of SOD in Cd tolerance, the effect of Cd-stress on a transgenic maize line (TG) constitutively overexpressing AtFeSOD gene in comparison to its wild type (WT) were investigated. Compared to their WT, the TG plants showed less Cd accumulation and improved growth, physiology and antioxidant and detoxification systems. These results demonstrate the role of SOD in determining Cd tolerance.
Keywords: Cd; maize; detoxification; oxidative stress; superoxide dismutase; Cd-tolerance mechanisms.