1. Department of Biochemistry, University of Birmingham, Birmingham B15 2TT, U.K.
2. Istituto di Chimica Biologica, Padova 35100, Italy
3. Department of Botany and Microbiology, University College, Aberystwyth SY23 3DA, Wales, U.K.
4. Department of Agricultural Botany, University of Reading, Reading RG6 2AS, U.K.