1. a The University of Birmingham, School of Geography and Environmental Sciences, Edgbaston, Birmingham, B15 2TT. Tel: +44 121 414 5557, Fax: +44 121 414 5528;
2. b CINVESTAV-IPN, Dept. de Biotecnología y Bioingenierìa, Av. Instituto Politécnico Nacional 2508, San Pedro Zacatenco, 07360, México, D.F. Tel. :+(525) 747-7000 ext. 4351. Fax: +(525) 747-7000 ext. 4305.