Aerenchyma formation in roots of maize (Zea mays L.) involves programmed death of cortical cells that is promoted by exogenous ethylene (1 muL L-1) or by endogenous ethylene produced in response to external oxygen shortage (3%, v/v). In this study, evidence that degeneration of the cell wall accompanies apoptotic-like changes previously observed in the cytoplasm and nucleus (Gunawardena et al. Planta 212, 205-214, 2001), has been sought by examining de-esterified pectins (revealed by monoclonal antibody JIM 5), and esterified pectins (revealed toy monoclonal antibody JIM 7). In controls, de-esterified wall pectins were found at the vertices of triangular junctions between cortical cells (untreated roots). Esterified pectins in control roots were present in the three walls bounding triangular cell-to-cell junctions. After treatment with 3% oxygen or 1 muL L-1 ethylene, this pattern was lost, but walls surrounding aerenchyma gas spaces became strongly stained. The results showed that cell wall changes commenced within 0.5 d and evidently were initiated by ethylene in parallel with cytoplasmic and nucleoplasmic events associated with classic intracellular processes of programmed cell death.
