Influence of Cd exposure on H+ and Cd2+ fluxes in the leaf, stem and root of a novel aquatic hyperaccumulator - Microsorum pteropus

Abstract

Microsorum pteropus has been proven to be a potential novel aquatic Cd hyperaccumulator. In this study, Non-invasive Micro-test Technology (NMT) was used to observe the ion fluxes of different M. pteropus tissues under Cd exposure. M. pteropus can hyperaccumulate more than 1000 mg/kg Cd in roots and leaves and approximately 600 mg/kg Cd in stems after seven days of exposure to 500 μM Cd, showing that this plant have a great capacity for Cd enrichment and resistance. The NMT test found H⁺ fluxes increased in all tissues after Cd exposure, with the largest increases being observed in stems, followed by the leaves and roots. Cd²⁺ fluxes showed different accumulation levels in different tissues, with low-level Cd exposure leading to influxes into roots and leaves, and high-level Cd exposure resulting in effluxes from roots. No significant influxes or effluxes were observed in leaves under high-level Cd exposure, or in stems under low- and high-levels of Cd exposure. However, transient high-level Cd exposure showed long-term Cd²⁺ influxes into roots and short-term Cd²⁺ effluxes out of stems and leaves. The roots of M. pteropus had greater regulation mechanisms for Cd enrichment and resistance, with influxes occurring following low-level exposure and effluxes occurring from high-level exposure. When exposed to Cd, M. pteropus stems showed less transportation and absorption. Low-level Cd exposure resulted in individual leaves directly absorbing Cd from hydroponic solutions. Different Cd enrichment and resistance mechanisms were exhibited by different M. pteropus tissues.

Keywords: Cadmium hyperaccumulator; Cd(2+); H(+); Ion fluxes; Microsorum pteropus; NMT.