Abstract
Lead (Pb) is toxic to plants. In this study, the differential tolerance to Pb in contrasting wheat (Triticum aestivum) genotype was studied cultivated under control and Pb-toxic (300 mu M Pb) hydroponic conditions. Pb-toxicity caused retardation in morphological characteristics, membrane stability, cell viability and redox state in Bari Gom-26 (Pb-sensitive), but not in Akbar (Pb-tolerant), indicating that Akbar can combat Pb toxicity. Pb accumulation in root and shoot of was 5-fold lower in Akbar than that of Bari Gom-26, implying that restricting Pb uptake in roots may be linked to Pb tolerance. Also, we observed a significant increase of Fe in Bari Gom-26 accompanied by upregulation of TaNAAT1 (nicotianamine aminotransferase) and TaDMAS1 (deoxymugineic acid synthase), whereas Akbar showed steady Fe status and downregulation of TaNAAT1 in roots of genome A. This is correlated with the steady chlorophyll score and Fv/Fm (maximum quantum yield of PSII) in leaves of Akbar while these were severed affected in Bari Gom-26 that may be linked to Pb-induced oxidative damage. In interactome analysis, YS1 gene network (Fe-PS transporter) was found to interact with TaDMAS1. Genome A and B of TaNAAT1 were located in chloroplast while D was in mitochondria; however, A, B and D of TaDMAS1 were localized in the cytoplasm. Additionally, we observed no changes in citrate and malate in the roots of Akbar, implying the ability of this genotype to regulate Fe-chelation under Pb stress. These suggest that genetic variation in Pb-toxicity tolerance in wheat is primarily root-based and that the Pb limitation is primarily driven by strictly limiting Fe-uptake and chelation in roots. These findings may encourage breeding or transgenic strategies to develop Pb-tolerant wheat.