Exploring Cd tolerance and detoxification strategies of <i>Arabidopsis halleri</i> ssp. <i>gemmifera</i> under high cadmium exposure

<i>Arabidopsis halleri</i> ssp. <i>gemmifera</i> is well known as a Cd hyperaccumulator. Yet, understanding how this plant survives in a high Cd environment without appearing toxicity signs is far from complete. Therefore, this study emphasized on high level of Cd to be applied to evaluate Cd detoxification and tolerance strategies in the hyperaccumulator <i>A. halleri</i> ssp. <i>gemmifera.</i> The results showed that under 300 µM of Cd exposure in a hydroponic system for 56 days, Cd tends to be transported to the stem and leaves. The availability of more than 60% of Cd mobile fractions supported Cd translocation to leaves. EPMA at the cellular level identified Cd localization at the rim of leaf cells that might be associated with the Cd-cell wall form. The Cd soluble fraction in the leaves was found as Cd-free ion and Cd-complexed compound. Interestingly, this plant can still grow despite some inhibition, such as significantly decreasing total chlorophyll and anthocyanins content in the leaves. It was predicted that Cd-free ions were sequestered into the vacuole of leaves cells, by complexing it into organic acid compounds. Therefore, tolerance strategies in <i>A. halleri</i> ssp. <i>gemmifera</i> at high Cd is proved to be associated to compartmentalization and complexation strategies. The study examined how <i>Arabidopsis halleri</i> ssp. <i>gemmifera</i>, a Cd hyperaccumulator, responds to high levels of Cd exposure both at the organ and subcellular level. Our analysis revealed that Cd was primarily stored in leaves in the leaf rim, as confirmed by spatial imaging EPMA analysis. Furthermore, we found that Cd existed in the soluble fraction equally in two forms: as a Cd-free ion and as a Cd complexed with organic compounds. The study has successfully proved that compartmentalization and complexation are pivotal in the tolerance mechanisms of the hyperaccumulator <i>Arabidopsis halleri</i> ssp. <i>gemmifera</i>.