Plant Physiology 150: 1855-1865 (2009)

In vivo cell wall loosening by hydroxyl radicals during cress (Lepidium sativum L.) seed germination and elongation growth  [W][OA]

Kerstin Müller, Ada Linkies, Robert A.M. Vreeburg, Stephen C. Fry, Anja Krieger-Liszkay, Gerhard Leubner-Metzger

University of Freiburg, Faculty of Biology, Institute for Biology II, Botany / Plant Physiology, Schänzlestr. 1, D-79104 Freiburg, Germany, Web: 'The Seed Biology Place' (K.M., A.L., G.L.-M.)
The Edingburgh Cell Wall Group, Institute of Molecular Plant Sciences, The University of Edinburgh, The King's Buildings, Mayfield Road, Edinburgh EH9 3JH, United Kingdom (R.A.M.V., S.C.F.)
Commissariat à l'Energie Atomique (CEA), iBiTecS, CNRS URA 2096, Service de Bioénergétique, Biologie Structurale et Mécanisme, 91191 Gif-sur-Yvette Cedex, France (A.K.-L.)

Received April 9, 2009; accepted May 29, 2009; published June 3, 2009

Abstract. Loosening of cell walls is an important developmental process in key stages of plant life cycles, 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 (EPR)-spectroscopy to show that OH is generated in the cell wall during radicle elongation and weakening of the endosperm of cress (Lepidium sativum L., Brassicaceae) seeds. Endosperm weakening precedes for radicle emergence, as demonstrated by direct biomechanical measurements. By 3H-fingerprinting we showed that wall polysaccharides are oxidised 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 not only evident in germinating seeds, but also in elongating maize (Zea mays L., Poaceae) seedling coleoptiles. We conclude that plant cell wall loosening by OH is a controlled action of this type of reactive oxygen species (ROS).

Key words: abscisic acid, cell wall losening, elongation growth, endosperm rupture, endosperm weakening, hydroxyl radicals (OH), hydrogen peroxide (H2O2), polysaccharide attack, reactive oxygen species (ROS), seed germination, seedling growth, superoxide (O2-)

Financial support: This work was supported by grants from the Deutsche Forschungsgemeinschaft (grant no. DFG LE720/6) and the Deutscher Akademischer Austauschdienst (DAAD grant nos. D/0628197 and D/07/09926) to G.L.-M., and the UK Biotechnology and Biological Sciences Research Council to S.C.F.
Article in PDF format (1.7 MB)
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Figure 6         Suppl. Figures S1&S2          Suppl. Table S1
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