1. Umeå Plant Science Center, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, SE-901 83, Umeå, Sweden
2. Center for Molecular Biotechnology, Fraunhofer USA, Newark, Delaware 19711
3. Department of Biology, Boston University, Boston, Massachusetts 02215
4. Department of Biology, Indiana University, Bloomington, Indiana 47405
5. Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, Massachusetts 01003