Ethylene-Mediated Acclimations to Flooding Stress

Abstract

Flooding is detrimental for plants, primarily because of restricted gas exchange underwater, which leads to an energy and carbohydrate deficit. Impeded gas exchange also causes rapid accumulation of the volatile ethylene in all flooded plant cells. Although several internal changes in the plant can signal the flooded status, it is the pervasive and rapid accumulation of ethylene that makes it an early and reliable flooding signal. Not surprisingly, it is a major regulator of several flood-adaptive plant traits. Here, we discuss these major ethylene-mediated traits, their functional relevance, and the recent progress in identifying the molecular and signaling events underlying these traits downstream of ethylene. We also speculate on the role of ethylene in postsubmergence recovery and identify several questions for future investigations.

Figure 1.

Oxygen dynamics during flooding. The root and shoot of a flooded plant have very different oxygen dynamics. Depicted are the general trends in endogenous oxygen levels in the shoot and root of plants when submerged in the light or in darkness. Also shown are typical oxygen concentrations in the surrounding floodwater and soil. Generalized trend lines shown are based on measurements on submerged Arabidopsis plants over a 24-h period (Vashisht et al., 2011).

Figure 2.

Ethylene-mediated flood-adaptive traits. An overview of the ethylene signaling networks regulating flooding-induced shoot elongation (A), hyponasty (B), aerenchyma (C), and AR growth (D). Depicted are generalized schemes based on studies in one or more species. Interactions and hierarchy of signaling components can vary depending on species. Images shown are R. palustris (A), Arabidopsis (B), barley (Hordeum vulgare) root cross sections (C), and rice stem nodes (D). Photographs courtesy of Shiono Katsuhiro (B) and Bianka Steffens (D). COP1, CONSTITUTIVE PHOTOMORPHOGENIC1; MT2B, METALLOTHIONEIN 2B; PIF, PHYTOCHROME INTERACTING FACTOR; RBOH, RESPIRATORY BURST OXIDASE HOMOLOG; SLR1, SLENDER RICE1; SLRL1, SLENDER RICE-LIKE1; XTH, XYLOGLUCAN ENDOTRANSGLUCOSYLASE/HYDROLASE.