XVI International Botanical Congess

Soil flooding and associated partial oxygen shortage promotes the lytic collapse of target cells in the cortex. The effect is mediated by ethylene and creates gas-filled passages (aerenchyma) that help aerate the root. We studied the extent to which the creation of aerenchyma resembles programmed cell death (apoptosis) in animal cells and also looked for cell wall changes that would be unique to plants. Nuclear DNA fragmentation is a characteristic of apoptosis in animal cells and detected with the TUNEL reagent that links chemically to breaks in DNA. Using fluorescence microscopy we detected many TUNEL positive nuclei in cortical cells of roots grown in 3% oxygen, which promotes aerenchyma. This suggests a close affinity with apoptosis in animals. However, hypoxic cortical cells also showed altered cell walls that stain with a monoclonal antibody (JIM 5) which binds to methylated pectin fragments. Thus, programmed cell death in maize roots appears also to involve mechanisms unrelated to animal apoptosis.