Cadmium and arsenic affect quiescent centre formation and maintenance in Arabidopsis thaliana post-embryonic roots disrupting auxin biosynthesis and transport

The research was focussed on the effects of cadmium (Cd) and arsenic (As), alone or combined, on Arabidopsis post-embryonic roots, with attention to quiescent centre formation and development in relation to auxin homeostasis. To the aim, morphological and histochemical analyses were carried out on seedlings, exposed or not to Cd and/or As, of wild type, and transgenic lines useful for monitoring quiescent centre identity, auxin localization and cellular influx and efflux. Moreover, auxin levels and expression of the YUC6 auxin biosynthetic gene were monitored in Cd and/or As exposed wild type seedlings. Results showed that Cd and Cd plus As increased the lateral and adventitious root density, whereas As alone reduced it. In the lateral and adventitious root apices Cd and/or As negatively affected quiescent centre identity and auxin localization, changed auxin levels, expression of YUC6, and of PIN1 and LAX3, auxin efflux and influx carriers, respectively. The alteration in auxin homeostasis was different for the two pollutants, explaining their contrasting response on the post-embryonic roots.