Roles of root cell wall components and root plaques in regulating elemental uptake in rice subjected to selenite and different speciation of antimony

Abstract

Root plaques and cell wall components play important roles in regulating the uptake of heavy metals in rice plants. Proper doses of selenium (Se) can reduce heavy metal uptake in plants. Whether Se can influence both the formation of root plaques and the contents of root cell wall components to affect heavy metal uptake in plants is unknown. A hydroponic culture system was set up using rice plants (Yangdao No.6) to mainly investigate the roles of root plaques and cell wall components in regulating the uptake of antimony (Sb) and Se in rice plants subjected to Se and different speciation of antimony [antimonite (Sb(III)) and antimonate (Sb(V))]. Se alone or plus different speciation of Sb showed a negative effect on plant growth. Addition of Se did not counteract the toxic effect of inhibiting rice plant growth exerted by Sb, despite the addition of Se to the solution containing 20 mg L−1 Sb(III) or Sb(V) significantly reduced Sb concentration in the roots. Addition of Se stimulated the formation of Mn plaque and addition of 5 mg L−1 Sb(III) or Sb(V) increased the formation of Fe plaque. When compared to the 20 mg L−1 Sb(III) treatment, the addition of 0.8 mg L−1 Se significantly increased the Fe plaque, but did not result in more accumulation of Sb on the root plaques. Other levels of Se did not show positive effects on the formation of Fe plaque on the roots of this rice plant when exposed to Sb(III) or Sb(V). In many cases, the single addition of Se, Sb(III) or Sb(V), especially for Se, can significantly increase the production of pectin, hemicelluloses and lignin. Additional Se helped rice plants exposed to Sb(III) or Sb(V) generate more pectin, hemicelluloses and lignin, especially when exposed to Sb(V). In summary, we speculate that Se inhibits, in most cases, the uptake of Sb in rice plants by affecting the root cell components rather than the formation of root plaques.