Biomarker changes and oxidative damage in living plant cells as new biomonitoring indicators for combined heavy metal stress assessment

The damage that combined heavy metals cause to plants is a global environmental problem, and it is also harder to detect compared with that from solitary heavy metal. One mechanism, heavy metal-induced cellular oxidative damage, occurs during the early stage of stress. For early monitoring of plant damage from combined heavy metals, in-situ detection of oxidative damage in soybean leaf cells was performed under the combined lanthanum (La, an emerging heavy metal pollutant) and lead (Pb, a conventional heavy metal pollutant) stress, using vitronectin-like protein (VN, a Lewis base that binds heavy metal ions) as a biomarker. A living cell electrochemical biosensor was used to detect the VN content in leaf cells by measuring the electrochemical output signal (electron-transfer resistance, Ret) coupled with oxidative damage indices, including reactive oxygen species (ROS), peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT), malondialdehyde (MDA), and the fresh weight and area of leaves, to comprehensively assess oxidative damage in living cells. The linear relationship between Ret (3884.85-6072.00 Ohm) and oxidative damage indices (145.01%-1196.02% and 135.53%- 252.91% of the control group in ROS and MDA) was established under the combined La (10-80 & mu;M) and Pb (5 & mu;M) stress providing an early warning interval (127.38%-160.15% of the control group in Ret) for the occurrence of oxidative damage in living cells. This electrochemical biosensor was successfully used to detect changes in VN content and oxidative damage in leaves exposed to the combined La and Pb found in the rainfall of China, Africa, and Turkey. Real-time in-situ detection of biomarker changes and oxidative damage in plant cells caused by combined heavy metals provided a basis to monitor the degree of damage and obtain an early warning of heavy metal stress.