1. Department of Biochemistry, Arrhenius Laboratories for Natural Sciences, Stockholm University, S–106 91 Stockholm, Sweden (A.R., B.A., A.V.V);
2. Department of Biology, University of Turku, FIN–20014, Turku, Finland (A.R., E-M.A);
3. Botanisches Institut der Ludwig-Maximilians-Universität, Menzinger Strasse 67, D–80638 München, Germany (R.G.H.); and
4. Division of Cell Biology, Linköping University, S–581 85 Linköping, Sweden (B.A.)