In Vivo Cell Wall Loosening by Hydroxyl Radicals during Cress Seed Germination and Elongation Growth

• Published in: Plant physiology (Bethesda) Vol. 150; no. 4; pp. 1855 - 1865
• Main Authors: Müller, Kerstin, Linkies, Ada, Vreeburg, Robert A.M, Fry, Stephen C, Krieger-Liszkay, Anja, Leubner-Metzger, Gerhard
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Biologists 01.08.2009
• Subjects: abscisic-acid; arabidopsis; Biochemical Processes and Macromolecular Structures; Biological and medical sciences; Brassicaceae - drug effects; Brassicaceae - growth & development; Cell Wall - drug effects; Cell Wall - metabolism; Cell walls; Coleoptiles; dormancy alleviation; endo-beta-mannanase; Endosperm; endosperm cap; Fundamental and applied biological sciences. Psychology; Germination; Germination - drug effects; Hydrogen Peroxide - metabolism; hydrogen-peroxide; Hydroxyl Radical - metabolism; mechanisms; nadph oxidase; Organ Specificity - drug effects; Plant cells; Plant Growth Regulators - pharmacology; Plant physiology and development; Plants; pollen-tube growth; Polysaccharides; Polysaccharides - metabolism; Seed germination; Seedlings; Seedlings - drug effects; Seedlings - metabolism; Seeds; Seeds - drug effects; Seeds - growth & development; Superoxides - metabolism; vitro; Zea mays - drug effects; Zea mays - metabolism; In vivo; Seeds; Plant physiology; Growth; Germination; Elongation; Hydroxyl; Cell wall
• ISSN: 0032-0889; 1532-2548; 1532-2548
• DOI: 10.1104/pp.109.139204

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 ³H 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.