Zinc-cadmium interactions instigated antagonistic alterations in lipid peroxidation, ascorbate peroxidase activity and chlorophyll synthesis in Phaseolus vulgaris leaves

Understanding the functional role of zinc interaction during cadmium-induced oxidative changes and photosynthetic response in the leaves of Phaseolus vulgaris plant was central in this study, as driven by Box-Behnken Design (BBD), a typified Response Surface Methodology (RSM). The design considered 0–50 mg each of CdCl2 and ZnCl2 per kilogram of soil contaminated daily in a time-dependent process, and for the post-germination of P. vulgaris seeds, malondialdehyde (MDA) level, ascorbate peroxidase (APX) activity and total chlorophyll content (TCC) were evaluated in seventeen “experimental runs” for nine weeks of study. The findings from the RSM-BBD study indicated significant generation (p<0.05) of response surface models with 87.08, 97.78 and 98.10 % r-squared values for MDA level, APX activity and TCC respectively, and these were validated in the laboratory through numerical optimization approach (NOA). The study also revealed that increasing dose of Cd significantly inhibited (p<0.05) the synthesis of TCC in plant leaves, which was significantly relieved (p<0.05) by increasing dose of Zn compound. The significant increase (p<0.05) in MDA levels, as a biomarker of Cd-induced oxidative stress, was ameliorated by marked increase in Zn concentration at p<0.05. The interaction also showed that the Cd-instigated inhibition of APX activity was significantly improved by increasing levels of Zn compound. Therefore, the present study resolved the controversies associated with previous conventional studies by establishing antagonistic effects from Zn-Cd interaction for the assessed responses in the leaves of P. vulgaris by RSM-BBD at defined optimal conditions.