The etr1‐2 mutation in Arabidopsis thaliana affects the abscisic acid, auxin, cytokinin and gibberellin metabolic pathways during maintenance of seed dormancy, moist‐chilling and germination

Abstract

Summary: In Arabidopsis thaliana, the etr1‐2 mutation confers dominant ethylene insensitivity and results in a greater proportion of mature seeds that exhibit dormancy compared with mature seeds of the wild‐type. We investigated the impact of the etr1‐2 mutation on other plant hormones by analyzing the profiles of four classes of plant hormones and their metabolites by HPLC‐ESI/MS/MS in mature seeds of wild‐type and etr1‐2 plants. Hormone metabolites were analyzed in seeds imbibed immediately under germination conditions, in seeds subjected to a 7‐day moist‐chilling (stratification) period, and during germination/early post‐germinative growth. Higher than wild‐type levels of abscisic acid (ABA) appeared to contribute, at least in part, to the greater incidence of dormancy in mature seeds of etr1‐2. The lower levels of abscisic acid glucose ester (ABA‐GE) in etr1‐2 seeds compared with wild‐type seeds under germination conditions (with and without moist‐chilling treatments) suggest that reduced metabolism of ABA to ABA‐GE likely contributed to the accumulation of ABA during germination in the mutant. The mutant seeds exhibited generally higher auxin levels and a large build‐up of indole‐3‐aspartate when placed in germination conditions following moist‐chilling. The mutant manifested increased levels of cytokinin glucosides through zeatin‐O‐glucosylation (Z‐O‐Glu). The resulting increase in Z‐O‐Glu was the largest and most consistent change associated with the ETR1 gene mutation. There were more gibberellins (GA) and at higher concentrations in the mutant than in wild‐type. Our results suggest that ethylene signaling modulates the metabolism of all the other plant hormone pathways in seeds. Additionally, the hormone profiles of etr1‐2 seed during germination suggest a requirement for higher than wild‐type levels of GA to promote germination in the absence of a functional ethylene signaling pathway.