1. Department of Chemistry, P.O. Box 35, FIN-40014 University of Jyväskylä, Finland, Institute of Physics, University of Tartu, Riia 142, 51014 Tartu, Estonia, Plant Biochemistry Laboratory, Department of Plant Biology, The Royal Veterinary and Agricultural University, 40 Thorvaldensvej, DK-1871 Fredriksberg C, Copenhagen, Denmark, and Facolta di Scienze MM.FF.NN., Università di Verona, Strada Le Grazie-Cà Vignal, 37134 Verona, Italy