title: Induction of secondary dormancy by hypoxia in barley grains and its hormonal regulation.
abstract: In barley, primary dormant grains did not germinate at 30 °C in air and at 15 °C in an atmosphere containing less than 10% O2, while they germinated easily at 15 °C in air. O2 tension in embryos measured with microsensors was 15.8% at 15 °C but only 0.3% at 30 °C. Incubation of grains at 30 °C is known to induce secondary dormancy in barley, and it was shown here that secondary dormancy was also induced by a 3 d treatment in O2 tensions lower than 10% at 15 °C. After such treatments, the grains lost their ability to germinate subsequently at 15 °C in air. During seed treatment in 5% O2, embryo abscisic acid (ABA) content decreased more slowly than in air and was not altered after transfer into air. Hypoxia did not alter the expression of ABA metabolism genes after 1 d, and induction of HvNCED2 occurred only after 3 d in hypoxia. Embryo sensitivity to ABA was similar in both primary and hypoxia-induced secondary dormant grains. Gibberellic acid (GA) metabolism genes were highly regulated and regulated earlier by the hypoxia treatment, with major changes in HvGA2ox3, HvGA3ox2 and HvGA20ox1 expression after 1 d, resulting in reduced GA signalling. Although a high temperature has an indirect effect on O2 availability, the data showed that it did not affect expression of prolyl-4-hydroxylases and that induction of secondary dormancy by hypoxia at 15 °C or by high temperature in air involved separate signalling pathways. Induction by hypoxia at 15 °C appears to be more regulated by GA and less by ABA than the induction by high temperature.
authors.affiliation: UPMC Univ Paris 06, UR5-EAC 7180 CNRS, PCMP, Boîte courrier 156, Bat C, 4 place Jussieu, F-75005 Paris, France.
authors.forename: Hai Ha
authors.initials: HH
authors.lastname: Hoang
authors.forename: Christophe
authors.initials: C
authors.lastname: Bailly
authors.forename: Françoise
authors.initials: F
authors.lastname: Corbineau
authors.forename: Juliette
authors.initials: J
authors.lastname: Leymarie
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology; D015687:Cell Hypoxia / Q000187:drug effects / Q000502:physiology; D018525:Germination / Q000187:drug effects / Q000235:genetics; D005875:Gibberellins / Q000494:pharmacology; D001467:Hordeum / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D012639:Seeds / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects; D013696:Temperature
chemical_list: D005875:Gibberellins; D010940:Plant Proteins; D000040:Abscisic Acid