University of Freiburg, Faculty of Biology, Institute for Biology II, Botany / Plant Physiology, Schänzlestr. 1, D-79104 Freiburg, German (AV, KG, KO, DJ, GLM)
School of Biological Sciences, Plant Molecular Science, Royal Holloway, University of London, Egham, Surrey TW20 0EX, Uk (AV, KG, GLM);
Web: 'The Seed Biology Place' - www.seedbiology.eu
Department of Plant Physiology, Warsaw University of Life Sciences-SGGW, 15 Nowoursynowska 159, 02-776, Warsaw, Poland (KO)
Laboratory of Growth Regulators, Faculty of Science, Palacky University and Institute of Experimental Botany AS CR, v.v.i., Šlechtitelu 11, CZ-783 71, Olomouc, Czech Republic (DT, VT, TU, MS)
Centre of the Region Haná for Biotechnological and Agricultural Research, Faculty of Science, Palacky University, Šlechtitelu 11, CZ-783 71, Olomouc, Czech Republic (MS)
Received March 10 2012; Revised June 11 2012; Accepted June 15 2012
Advance Acess publication July 21 2012
Myrigalone A (MyA) is a rare flavonoid in fruit leachates of Myrica gale, a deciduous shrub adapted to flood-prone habitats. As a putative allelochemical it inhibits seed germination and seedling growth. Using Lepidium sativum as a model target species, we investigated how environmental cues modulate the MyA interference with key processes of seed germination. Time course analyses of L. sativum testa and endosperm rupture at different light conditions and water potentials were combined with quantifying testa permeability, endosperm weakening, tissue-specific gibberellin (GA) and abscisic acid (ABA) contents, as well as embryo growth and apoplastic superoxide production important for cell expansion growth. Lepidium sativum testa permeability and early water uptake by imbibition is enhanced by MyA. During late germination, MyA inhibits endosperm weakening and embryo growth, both processes are required for endosperm rupture. Inhibition of embryo cell expansion by MyA depends on environmental cues, which is evident from the light-modulated severity of the MyA-mediated inhibition of apoplastic superoxide accumulation. Several important key weakening and growth processes during early and late germination are targets for MyA. These effects are modulated by light conditions and ambient water potential. We speculate that MyA is a soil seed bank destroying allelochemical that secures the persistence of M. gale in its flood-prone environment.
Key words: allelochemical, apoplastic superoxide, embryo growth, endosperm cap weakening, gibberellins (GA), imbibition, Lepidium sativum, myrigalone A (MyA), seed germination, testa permeability.
Financial support: Our work was funded by grants from the Deutsche Forschungsgemeinschaft (Grants DFG LE720/6 and LE720/7) to G.L.-M., the Alexander von Humboldt Foundation (AvH Research Fellowship 06/2009) to K.O., and the Czech Science Foundation (GD522/08/H003), the Grant Agency of the Academy of Sciences CR (KAN200380801) and EU funding Operational Program Research and Development for Innovations (ED0007/01/01) to M.S.