Upregulation of Antioxidant Enzymes Contribute to the Elevated Tolerance of Juncus Acutus Offspring from Metal Contaminated Environments.

Long-term environmental exposure to metals e.g. zinc (Zn), may allow saltmarsh halophytes to develop metal tolerance to improve the chance of survival of their progeny in future metal-contaminated scenarios. Juncus acutus seeds were collected from mature parents (F0) inhabiting a legacy Zn-contaminated location (Cockle Creek) and an uncontaminated reference location (Swansea) of Lake Macquarie, NSW, Australia. Seeds (J. acutus) were exposed to Zn (0.00 mM (control), 0.01 mM (effective concentration, EC10) and 0.74 mM (EC50)) and resultant germinants (F1) were allowed to grow until 15 days. Seedling growth parameters i.e. biomass, root length and 1st leaf length, and seedling biochemical responses i.e. superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) antioxidant enzyme activity and lipid peroxidation products, malondialdehyde (MDA), were examined in order to assess if enzymes may be implicated in conferring tolerance to the offspring of metal-exposed parents. Control locations exhibited significantly greater declines in biomass and root length with Zn dose compared to seed from contaminated locations, suggesting F1 offspring from contaminated parents were conferred tolerance to Zn. Furthermore, significant upregulation of CAT and GPx enzymes were evident in the seedlings derived from parents of contaminated locations. These are the antioxidative enzymes responsible for minimizing metal-induced oxidative stress, and may, in part, be responsible for increasing seedling fitness and observed tolerance.