1. Department of Biochemistry and Pharmacy, Åbo Akademi University, BioCity, P.O. Box 66, FIN-20521 Turku, Finland.
2. Corresponding author: Fax: +358-2-2154745. E-mail: eric.bertoft@abo.fi
3. Oregon State University, Department of Horticulture, Agriculture and Life Science 4017, Corvallis, OR 97331-7304.