NADPH Oxidase RbohD and Ethylene Signaling are Involved in Modulating Seedling Growth and Survival Under Submergence Stress.

In higher plants under low oxygen or hypoxic conditions, the phytohormone ethylene and hydrogen peroxide (HO) are involved in complex regulatory mechanisms in hypoxia signaling pathways. The respiratory burst oxidase homolog D (RbohD), an NADPH oxidase, is involved in the primary stages of hypoxia signaling, modulating the expression of downstream hypoxia-inducible genes under hypoxic stress. In this study, our data revealed that under normoxic conditions, seed germination was delayed in the / double mutant, whereas postgermination stage root growth was promoted. Under submergence, the double mutant line had an inhibited root growth phenotype. Furthermore, chlorophyll content and leaf survival were reduced in the double mutant compared with wild-type plants under submerged conditions. In quantitative RT-PCR analysis, the induction of / () and () transcripts was lower in the double mutant during hypoxic stress than in wild-type plants and in and mutant lines. Taken together, our results indicate that an interplay of ethylene and RbohD is involved in regulating seed germination and post-germination stages under normoxic conditions. Moreover, ethylene and RbohD are involved in modulating seedling root growth, leaf chlorophyll content, and hypoxia-inducible gene expression under hypoxic conditions.