Centre for Plant Sciences, Faculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, UK (KL, PK)
Wageningen Seed Lab, Laboratory of Plant Physiology, Wageningen University, Droevendaalsesteeg 1, 6708 PB, Wageningen, The Netherlands (BD, LB)
Department of Molecular Plant Physiology, Utrecht University, 3584 CH Utrecht, The Netherlands (BD, LB)
University of Freiburg, Faculty of Biology, Institute for Biology II, Botany/Plant Physiology, D-79104 Freiburg, Germany (TS*, GLM*)
ARC Centre of Excellence in Plant Cell Walls, School of Botany, University of Melbourne, Parkville, Victoria 3010, Australia (BD, LB)
* Current Address: School of Biological Sciences, Royal Holloway, University of London, Bourne Building 3-30, Egham, Surrey, TW20 0EX, UK
Received July 13, 2012; Accepted September 4, 2012; Published September 6, 2012.
In some species, a crucial role has been demonstrated for the seed endosperm during germination. The endosperm has been shown to integrate environmental cues with hormonal networks that underpin dormancy and seed germination – a process that involves the action of cell wall remodelling enzymes (CWREs). Here we examine the cell wall architectures of the endosperms of two related Brassicaceae, Arabidopsis thaliana and the close relative Lepidium sativum, and that of the Solanaceous species, tobacco (Nicotiana tabacum). The Brassicaceae species have a similar cell wall architecture that is rich in pectic homogalacturonan, arabinan and xyloglucan. Distinctive features of the tobacco endosperm, that are absent in the Brassicaceae representatives, are major tissue asymmetries in cell wall structural components that reflect the future site of radicle emergence and abundant heteromannan. Cell wall architecture of the micropylar endosperm of tobacco seeds has structural components similar to those seen in Arabidopsis and Lepidium endosperms. In situ and biomechanical analyses were used to study changes in endosperms during seed germination and suggest a role for mannan degradation in tobacco. In the case of the Brassicaceae representatives, the structurally homogeneous cell walls of the endosperm can be acted on by spatially regulated CWRE expression. Genetic manipulations of cell wall components present in the Arabidopsis seed endosperm demonstrate the impact of cell wall architectural changes on germination kinetics.
Key words: cell-wall polysaccharides, endosperm, embryo, seed germination.
Financial support: We acknowledge funding from the UK Biotechnology and Biosciences Research Council to JPK (BB/G024898/1), the Netherlands Organisation for Scientific Research to LB and the German Research Foundation to GL-M (DFG Le720/8-1) through the ERA-NET support of the vSeed programme. LB is also funded by the Dutch Technology Foundation (STW), which is the applied science division of the Netherlands Organization for Scientific Research and the Technology Program of the Ministry of Economic Affairs. CTW and AB acknowledge the support of the ARC Centre of Excellence in Plant Cell Walls.