Figure 1.

Schematic representation of Pgb-regulation of avoidance (aerenchyma formation) and acclimation (maintenance of a functional root meristem) responses in hypoxic maize roots. The gradient of Pgb along the root profile determines the type of response. High levels of Pgbs at the root tip lower the hypoxia-induced accumulation of ethylene by scavenging NO, and attenuate ethylene responses possibly through regulation of MYC2. These effects reduce ROS-induced PCD and auxin over-production in the meristematic cells that remain functional. In mature tissue, characterized by low expression of Pgb, the accumulation of ethylene triggers PCD contributing to the formation of aerenchyma (*). In this response NO production is also induced by ethylene. Repressed responses are faded. ACS, 1-aminocyclopropane-1-carboxylic acid synthase; ACO, 1-aminocyclopropane-1-carboxylic acid oxidase; ERFs, ethylene response factors; RBHOs, respiratory burst oxidase homologs.