Cell wall modifications in roots of in vitro grown Douglas-fir plantlets exposed to aluminum

Aluminum (Al) is a trace element that may hamper plant growth and development. Tolerance mechanisms could imply the cell wall as it is the first barrier before entry into the plant cell. Douglas-fir plantlets were grown in vitro on media supplemented with different aluminum chloride (AlCl₃) concentrations up to 1 mM. The characterization of the cell wall revealed quantitative and qualitative modifications in the polysaccharidic composition of the wall, in particular in roots whose pectins showed a higher galacturonic acid content with less ramification and a lower degree of methylesterification (DME) explained by a higher pectin methylesterase activity; these Al-induced changes suggest an Al-trapping process in cell wall structures. In stems and needles, the observed increase in DME rather suggests an exclusion of Al from the cell wall.