Plant Science Letters, 5 (1975) 293--304 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands ARABIDOPSIS THALIANA AS A MODEL SYSTEM IN SOMATIC CELL GENETICS I° CELL/~ ND TISSUE CULTURE I. NEGRUTIU, F. BEEFTINK and M. JACOBS Laboratorium poor Plantengenetica, Free University of Brussels, Paardenstraat 65, B-1640 8int-Genesius-Rode (Belgium) (Received May 20th, 1975) (Revision received and accepted September 1st, 1975) SUMMARY Induction and growth of callus from seeds, stems and pieces of leaf of Arabidopsis thaliana were successful on a Gamborg Bs medium and on a modified ~5 medium (PG2). Actively growing calluses have been obtained on agar and in liquid cultures. Cell suspensiori cultures were established on the same culture media, with cell densities up to 1.6-10 6 cells/ml. A culture system is described which enables us to use large cell aggregates as a contin- uous source of single cells and small cell aggregates (containing up to 10 cells} for mutagenesis, plating and protoplast production. Arabidopsis plants were regenerated from young calluses grown in solid or liquid cultures, by a sequential transfer from a medium (PG3), where shoot initiation takes place, to a PG4 medium which induces root formation. The morphogenetic potential appeared to depend on the age of the callus in culture. A wide range of heteroploidy has been observed in tissue cultures. The influence of factors such as the age of the callus, the type of organ used to induce calluses, the hormone ratio and the composition of the medium was determined. A procedure for the isolation of protoplasts from leaves and. cell cultures is described. INTRODUCTION The application of microbial-like techniques to plant cells has recently led to the development of somatic cell genetics in higher plants [2]. One of the most significant advances in this field consists in the isolation of defined bio- chemical mutants [ 3]. However, the species used in this type of experiments Abbreviations: 2,4-D, 2,4-dichlorophenoxyacetic acid; IAA, indoleacetic acid; NAA, naphthaleneacetic acid; PCV, packed cell volume.