Cell wall adaptations to multiple environmental stresses in maize roots.

A municipal solid-waste bottom slag was used to grow maize plants under various abiotic stresses (high pH, high salt and high heavy metal content) and to analyse the structural and chemical adaptations of the cell walls of various root tissues. When compared with roots of control plants, more intensive wall thickenings were detected in the inner tangential wall of the endodermis. In addition, phi thickenings in the rhizodermis in the oldest part of the seminal root were induced when plants were grown in the slag. The role of the phi thickenings may not be a barrier for solutes as an apoplastic dye could freely diffuse through them. The chemical composition of cell walls from endodermis and hypodermis was analysed. Slag-grown plants had higher amounts of lignin in endodermal cell walls when compared to control plants and a higher proportion of H-type lignin in the cell walls of the hypodermis. Finally, the amount of aliphatic suberin in both endo- and hypodermal cell walls was not affected by growing the plants on slag. The role of these changes in relation to the increase in mechanical strengthening of the root is discussed.