Integration of metal chemical forms and subcellular partitioning to understand metal toxicity in two lettuce (Lactuca sativa L.) cultivars

Metal chemical forms and subcellular partitioning model (SPM) in organisms can provide valuable insights into metal toxicity. Two cultivars of lettuce (Lactuca sativa L.) were grown in Cd and Cu contaminated soils and chemical forms and subcellular distribution of Cd and Cu within the lettuce shoots were determined. Examination of the inhibition of superoxide dismutase (SOD) and catalase (CAT) activities, as well as the production of H2O2 showed that Lactuca sativa L. var. longifolia is more sensitive to metal-stress than is Lactuca sativa L. var. crispa. In L. crispa, the majority of accumulated Cd was in the pectate- and protein-integrated forms (53.7-62.9 %), while in L. longifolia, a higher proportion of the Cd was in the water soluble forms (33.0-39.2 %) and in the organelles fraction - these forms being potentially associated with toxicity. The chemically-based chemical form approach agreed closely with independent biologically-based SPM, as demonstrated by their significant linear relationships. This study provides a first step towards the integration of chemical form approach and SPM into a common mechanistic framework, which is important for predicting the likelihood of toxic effects of metals in the environment of interest.