TRANSDUCTION OF AN ETHYLENE SIGNAL IS REQUIRED FOR CELL-DEATH AND LYSIS IN THE ROOT CORTEX OF MAIZE DURING AERENCHYMA FORMATION INDUCED BY HYPOXIA

Ethylene has been implicated in signaling cell death in the lysigenous formation of gas spaces (aerenchyma) in the cortex of adventitious ro ots of maize (Zea mays) subjected to hypoxia. Various antagonists that are known to modify particular steps in signal transduction in other plant systems were applied at low concentrations to normoxic and hypox ic roots of maize, and the effect on cell death (aerenchyma formation) and the increase in cellulase activity that precedes the appearance o f cell degeneration were measured. Both cellulase activity and cell de ath were inhibited in hypoxic roots in the presence of antagonists of inositol phospholipids, Ca2+-calmodulin, and protein kinases. By contr ast, there was a parallel promotion of cellulase activity and cell dea th in hypoxic and normoxic roots by contact with reagents that activat e C-proteins, increase cytosolic Ca2+, or inhibit protein phosphatases . Most of these reagents had no effect on ethylene biosynthesis and di d not arrest root extension. These results indicate that the transduct ion of an ethylene signal leading to an increase in intracellular Ca2 is necessary for cell death and the resulting aerenchyma development in roots of maize subjected to hypoxia.