Morphohistological study of the different constituents of a banana (Musa AAA, cv. Grande naine) embryogenic cell suspension

Five types of cellular aggregates have been characterised in embryogenic ce ll suspensions of banana (Musa AAA Grande naine cv.), Type I corresponded t o isolated cells or to small cell aggregates. Type II were composed of embr yogenic cells. Type III can be distinguished from type II due to the presen ce of peripheral proliferation zones with embryonic cells. Type IV were com posed of protodermic masses histologically comparable to proembryos. Type V were nodules composed of a central zone of meristematic cells and of an ex ternal zone of starchy cells. Each culture flask of a cell line contained a majority of one of the above-mentioned aggregate types. Histological studi es of somatic embryo developement on semi-solid regeneration medium showed that there were close similarities between the initial steps of ontogenesis of the embryos and the different cell aggregates in liquid multiplication medium. It appeared that aggregates II-IV of the suspension belong to the s ame development continuum which reproduces the initial phases of somatic em bryo ontogenesis on semi-solid medium. Type V resulted from the development of type IV, for which ontogenesis is hindered by direct contact with 2,4-d ichlorophenoxyacetic acid and the shaken liquid multiplication medium. Type I aggregates probably do not belong to the development continuum but rathe r correspond to the degeneration of the other types of aggregates in the su spension. The presence of intermediate types in the liquid medium reinforce s the hypothesis of a relationship between the aggregates. The aggregates t ended to develop through time from a majority of type II or III at the begi nning of their culture to types IV-V for older suspensions.