Single androgenetic structures of maize (Zea mays L.) for the initiation of homogeneous cell suspension and protoplast cultures.

Induction of androgenesis in maize leads to heterogeneous callus types in terms of chromosome number and regeneration ability. In order to obtain homogeneous cell suspensions from androgenetic material we initiated maize cultures from single microspore-derived structures. Cultures were established either by transfer of previously selected type-II callus or by transfer of single aggregates directly into suspension medium. During establishment no selection was performed. Independent suspension lines were analysed with respect to their chromosome number, their embryogenic capacity, and their regeneration ability. Cytological analysis revealed that most of the cultures tested showed a constant chromosome number over a period of 18 months, indicating a homogeneous constitution. Within regenerable lines no difference in embryogenic capacity could be observed when smaller (1mm) and larger (4mm) aggregates were compared. Furthermore, their homogeneous character was confirmed by the regeneration of only green or albino plants from the individual lines. Chromosome analysis of regenerants by root tip cytology showed that their numbers corresponded to that of the suspension they were regenerated from. Similar results showing the homogeneous nature of the lines were obtained in protoplast culture and regeneration experiments.