1. Plant Cell Biology, Institute of Botany, University of Bonn, Kirschallee 1, D–53115 Bonn, Germany (F.B., A.H., D.M., D.V.);
2. Institute of Plant Genetics and Biotechnology, Slovak Academy of Sciences, Akademická 2, SK–95007 Nitra, Slovakia (J.Š.);
3. Max-Delbrück-Laboratorium in der Max-Planck-Gesellschaft, D–50829 Köln, Germany (K.P.);
4. HIP Zellbiologie, University of Heidelberg, Im Neuenheimer Feld 230, D–69120 Heidelberg, Germany (D.G.R.);
5. Laboratory of Plant Nutrition, Kyoto University, Kyoto 606–01, Japan (T.M.); and
6. School of Environmental and Life Sciences, The University of Newcastle, Newcastle, New South Wales 2308, Australia (D.W.M.)