title: In vivo cell wall loosening by hydroxyl radicals during cress seed germination and elongation growth.
abstract: Loosening of cell walls is an important developmental process in key stages of the plant life cycle, including seed germination, elongation growth, and fruit ripening. Here, we report direct in vivo evidence for hydroxyl radical ((*)OH)-mediated cell wall loosening during plant seed germination and seedling growth. We used electron paramagnetic resonance spectroscopy to show that (*)OH is generated in the cell wall during radicle elongation and weakening of the endosperm of cress (Lepidium sativum; Brassicaceae) seeds. Endosperm weakening precedes radicle emergence, as demonstrated by direct biomechanical measurements. By (3)H fingerprinting, we showed that wall polysaccharides are oxidized in vivo by the developmentally regulated action of apoplastic (*)OH in radicles and endosperm caps: the production and action of (*)OH increased during endosperm weakening and radicle elongation and were inhibited by the germination-inhibiting hormone abscisic acid. Both effects were reversed by gibberellin. Distinct and tissue-specific target sites of (*)OH attack on polysaccharides were evident. In vivo (*)OH attack on cell wall polysaccharides were evident not only in germinating seeds but also in elongating maize (Zea mays; Poaceae) seedling coleoptiles. We conclude that plant cell wall loosening by (*)OH is a controlled action of this type of reactive oxygen species.
authors.affiliation: University of Freiburg, Faculty of Biology, Institute for Biology II, Botany/Plant Physiology, D-79104 Freiburg, Germany.
authors.forename: Kerstin
authors.initials: K
authors.lastname: Müller
authors.forename: Ada
authors.initials: A
authors.lastname: Linkies
authors.forename: Robert A M
authors.initials: RA
authors.lastname: Vreeburg
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Fry
authors.forename: Anja
authors.initials: A
authors.lastname: Krieger-Liszkay
authors.forename: Gerhard
authors.initials: G
authors.lastname: Leubner-Metzger
mesh_terms: D019607:Brassicaceae / Q000187:drug effects / Q000254:growth & development*; D002473:Cell Wall / Q000187:drug effects / Q000378:metabolism*; D018525:Germination / Q000187:drug effects; D006861:Hydrogen Peroxide / Q000378:metabolism; D017665:Hydroxyl Radical / Q000378:metabolism*; D009928:Organ Specificity / Q000187:drug effects; D010937:Plant Growth Regulators / Q000494:pharmacology; D011134:Polysaccharides / Q000378:metabolism; D036226:Seedlings / Q000187:drug effects / Q000378:metabolism; D012639:Seeds / Q000187:drug effects / Q000254:growth & development*; D013481:Superoxides / Q000378:metabolism; D003313:Zea mays / Q000187:drug effects / Q000378:metabolism
chemical_list: D010937:Plant Growth Regulators; D011134:Polysaccharides; D013481:Superoxides; D017665:Hydroxyl Radical; D006861:Hydrogen Peroxide