The saltmarsh plant Halimione portulacoides was shortly exposed to realistic levels of inorganic mercury (iHg), aiming to investigate adaptative processes of the roots and leaves regarding re-dox homeostasis, physiology, and Hg accumulation. Plants were collected at a contaminated (CONT) and a reference (REF) site, addressing the interference of contamination background. The influence of major abiotic variables (i.e., temperature and light) was also examined. Total Hg lev-els, antioxidant enzymes, lipid peroxidation (LPO), and photosynthetic activity were analyzed after 2 and 4 hours of exposure. Accumulation of iHg in the roots was noticed poorly, and no translocation to stems and leaves was found, but plants from CONT seemed more prone to iHg uptake (in winter). Despite that, antioxidant modulation in roots and leaves was found, disclos-ing, in winter, higher thresholds for the induction of enzymatic antioxidants in CONT leaves compared to REF, 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 the photosynthetic activity, pinpointing H. portulacoides ability to cope with iHg toxicity under a very short-term exposure. Biochemical changes were noticed before enhancements in ac-cumulation, reinforcing the relevance of these responses in precociously signaling iHg toxicity.