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Novel type II cell wall architecture in dichlobenil-habituated maize calluses

Mélida, Hugo, García-Angulo, Penélope, Alonso-Simón, Ana, Encina, Antonio, Álvarez, Jesús, Acebes, José Luis
Planta 2009 v.229 no.3 pp. 617-631
Zea mays, arabinoxylan, callus, callus culture, carbohydrate content, cell wall components, cell walls, cellulose, corn, culture media, dichlobenil, enzymes, ferulic acid, mannans, molecular weight, pectins, polymers, proteins, xyloglucans
Growth of maize (Zea mays L.) callus-culture cells was inhibited using dichlobenil (2,6 dichlorobenzonitrile, DCB) concentrations >=1 μM; I ₅₀ value for the effect on inhibited fresh weight gain was 1.5 μM. By increasing the DCB concentration in the culture medium, DCB-habituated cells became 13 times more tolerant of the inhibitor (I ₅₀: 20 μM). In comparison with non-habituated calluses, DCB-habituated calluses grew slower, were less friable and were formed by irregularly shaped cells surrounded by a thicker cell wall. By using an extensive array of techniques, changes in type II cell wall composition and structure associated with DCB habituation were studied. Walls from DCB-habituated cells showed a reduction of up to 75% in cellulose content, which was compensated for by a net increase in arabinoxylan content. Arabinoxylans also showed a reduction in their extractability and a marked increase in their relative molecular mass. DCB habituation also involved a shift from ferulate to coumarate-rich cells walls, and enrichment in cell wall esterified hydroxycinnamates and dehydroferulates. The content of polymers such as mixed-glucan, xyloglucan, mannans, pectins or proteins did not vary or was reduced. These results prove that the architecture of type II cell walls is able to compensate for deficiencies in cellulose content with a more extensive and phenolic cross-linked network of arabinoxylans, without necessitating β-glucan or other polymer enhancement. As a consequence of this modified architecture, walls from DCB-habituated cells showed a reduction in their swelling capacity and an increase both in pore size and in resistance to polysaccharide hydrolytic enzymes.