# Redox Homeostasis Disclosed in the Saltmarsh Plant Halimione portulacoides upon Short Waterborne Exposure to Inorganic Mercury

## TL;DR

This study explores how a saltmarsh plant responds to mercury exposure, showing early biochemical defenses before significant mercury accumulation.

## Contribution

The study reveals early antioxidant responses in a saltmarsh plant under short-term mercury exposure, indicating adaptive mechanisms.

## Key findings

- Plants from contaminated sites showed higher antioxidant thresholds and lower lipid peroxidation after mercury exposure.
- Exposure to mercury did not impair photosynthetic activity in the saltmarsh plant.
- Biochemical changes occurred before noticeable mercury accumulation, signaling early toxicity responses.

## Abstract

The saltmarsh plant Halimione portulacoides was shortly exposed to realistic levels of inorganic mercury (iHg) with the aim of investigating the adaptative processes of the roots and leaves regarding redox homeostasis, physiology, and Hg accumulation. Plants were collected at a contaminated (CONT) and a reference (REF) site to address the interference of contamination backgrounds. The influence of major abiotic variables (i.e., temperature and light) was also examined. Total Hg levels, antioxidant enzymes, lipid peroxidation (LPO), and photosynthetic activity were analyzed after 2 and 4 h of exposure. A poor accumulation of Hg in the roots was noticed, and no translocation to the stems and leaves was found, but plants from the CONT site seemed more prone to iHg uptake (in winter). Despite this, antioxidant modulation in the roots and leaves was found, disclosing, in winter, higher thresholds for the induction of enzymatic antioxidants in CONT leaves compared to REF plants, denoting that the former are better prepared to cope with iHg redox pressure. Consistently, CONT leaves exposed to iHg had remarkably lower LPO levels. Exposure did not impair photosynthetic activity, pinpointing H. portulacoides’ ability to cope with iHg toxicity under very-short-term exposure. Biochemical changes were noticed before enhancements in accumulation, reinforcing the relevance of these responses in precociously signaling iHg toxicity.