Internodal elongation under submergence in the Amazonian wild rice species Oryza glumaepatula: the growth response is induced by hypoxia but not by ethylene

Whole plants of Oryza glumaepatula (accession W1246) displayed rapid internodal elongation under partial submergence, comparable with those of deepwater or floating Oryza sativa cultivars. In excised stem segments of O. glumaepatula, submergence and hypoxia equally induced internodal elongation, whereas ethylene, which plays an important role in the rapid internodal elongation of deepwater rice, induced internodal elongation of only one-third relative to submergence or hypoxia. Pretreatments of stem segments with 1-methylcyclopropene (an ethylene action inhibitor) almost completely blocked ethylene-induced internodal elongation but had limited effects on submergence-induced internodal elongation. These results indicate that hypoxia, but not ethylene, triggers rapid internodal elongation during submergence in O. glumaepatula. O. glumaepatula W1246 possessed a homologue of SNORKEL1 (SK1) and two homologues of SNORKEL2 (SK2). SK1 and SK2 encode ethylene response factors and evoke rapid internodal elongation in response to ethylene in O. sativa. However, none of these homologues showed an increased expression level in internodes of stem segments treated with hypoxia.