Disarrangement of actin filaments and Ca2+ gradient by CdCl2 alters cell wall construction in Arabidopsis thaliana root hairs by inhibiting vesicular trafficking

Cadmium (Cd), one of the most toxic heavy metals, inhibits many cellular and physiological processes in plants. Here, the involvement of cytoplasmic Ca2+ gradient and actin filaments (AFs) in vesicular trafficking, cell wall deposition and tip growth was investigated during root (hair) development of Arabidopsis thaliana in response to CdCl2 treatment. Seed germination and root elongation were prevented in a dose- and time-dependent manner by CdCl2 treatment. Fluorescence labelling and non-invasive detection showed that CdCl2 inhibited extracellular Ca2+ influx, promoted intracellular Ca2+ efflux, and disturbed the cytoplasmic tip-focused Ca2+ gradient. In vivo labelling revealed that CdCl2 modified actin organization, which subsequently contributed to vesicle trafficking. Transmission electron microscopy revealed that CdCl2 induced cytoplasmic vacuolization and was detrimental to organelles such as mitochondria and endoplasmic reticulum (ER). Finally, immunofluorescent labelling and Fourier transform infrared (FTIR) analysis indicated that configuration/distribution of cell wall components such as pectins and cellulose was significantly altered in response to CdCl2. Our results indicate that CdCl2 induces disruption of Ca2+ gradient and AFs affects the distribution of cell wall components in root hairs by disturbing vesicular trafficking in A. thaliana.