Protective role of mucilage against Al toxicity to root apex of pea (Pisum sativum)

Mucilage can strongly bind Al in the rhizosphere. Although there are still debates about the role of mucilage in protection of the root apex from Al toxicity, we considered that it might be associated with the characteristics of Al adsorption in mucilage. When the mucilage was kept intact, the accumulation of Al and induction of callose in root tips of pea (Pisum sativum) remained lower; thus root elongation was less inhibited than when mucilage was removed under Al exposure in mist culture. Size exclusion chromatography showed both a high and a low molecular weight polysaccharide fraction from root mucilage. Aluminum was predominately detected in high molecular weight polysaccharides, which strongly bound cations. The results indicate that the persistence of mucilage does protect the root apex from Al toxicity by immobilizing Al in high molecular weight polysaccharides.