Rapid changes in cell wall pectic polysaccharides are closely associated with early stages of aerenchyma formation, a spatially localized form of programmed cell death in roots of maize (Zea mays L.) promoted by ethylene

Aerenchyma formation in roots of maize (Zea mays L.) involves programmed death of cortical cells that is promoted by exogenous ethylene (1 µL 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 by 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 µL 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.