Heavy metal stress induces adaptative responses in the liverwort Conocephalum conicum L. (Dum.): An integrated biologic and metabolomic study

Abstract

Bioaccumulation, ultrastructural and DNA damage, oxidative stress, and metabolomic analyses were carried out in vitro on the liverwort Conocephalum conicum L. in response to the heavy metal concentrations measured in two sites along the Sarno river (C1 and C2) representative of two different environmental conditions. Bioaccumulation and bioconcentration data confirm C. conicum is a good bioindicator. Our TEM observations showed typically preserved ultrastructure of the chloroplasts in C1 samples, nearly identical to the chloroplasts of the control sample (CTRL; freshly collected and not exposed), whereas in C2 samples they appeared misshaped, swollen and with poorly developed thylakoids in a rather clear stroma. DNA damage, antioxidant enzymatic activity, ROS production and localization showed no difference between CTRL and C1 samples, instead significant differences between C1 and C2 samples. In addition, in this study, we used for the first time the untargeted MS-based molecular networking to examine the role of heavy metal stress in the differential production of the secondary metabolites (SM) in C. conicum. Metabolome analysis evidenced no changes between CTRL and C1 samples, instead a dramatic change in SM production under metal stress conditions, in particular a remodeling of the lipid metabolism through the production of members of betaine and oxidated lipid classes, as well as production of flavonoids was observed. All the occurred variations respond consistently with the heavy metal concentration trend so we can propose them as pollution biomarkers.