The photochemical and antioxidant defense strategies of two maize genotypes exposed to zinc toxicity at the seedling stage

Abstract

The main objective of the current study was to elucidate photochemical and antioxidant strategies in two maize genotypes, namely DK626 and 3223, exposed to increased zinc (Zn2+) toxicity at the early seedling stage. Both maize genotypes accumulated similar levels of Zn in leaves, however, shoot and root lengths, and biomass further decreased in DK626 than 3223. The malondialdehyde content in the leaves of genotypes increased gradually depending on the Zn concentrations, and the deterioration of membrane structure was greater in DK626 compared to 3223. Reduction in photochemical activity (FV/FM, F′V/F′M, ETR and ΦPSII) was accompanied by non-photochemical quenching (NPQ) and excess energy was removed from the reaction centers by fluorescence and non-radiative inactivation (ΦC) in genotypes under Zn toxicity. The increase in the Zn concentration of the leaves significantly decreased the amounts of chlorophyll and carotenoid while increased the anthocyanin accumulation in maize, especially in DK626. Also, the activities of antioxidant enzymes and isoenzymes were induced at different levels in genotypes depending on the Zn toxicity level. SOD and POD in DK626 under low Zn toxicity, and SOD and ascorbate-glutathione pathway enzymes (APX and GR) in 3223 under high Zn concentrations participated in antioxidant defense. Although the accumulation of great amounts of zinc, the happening of membrane damages, and a decrease in photosynthetic pigment contents in both maize genotypes, the seedlings under zinc stress have achieved to sustain their growth by regulating their photosynthetic efficiency and their antioxidant defence system. Considering growth, chlorophyll fluorescence parameters and antioxidant defence system, these maize genotypes can be proposed cultivated in Zn-contaminated areas, and also used in the biofortification of plant.