THE INFLUENCE OF SUCROSE, MANNITOL, L-PROLINE, ABSCISIC-ACID AND GIBBERELLIC-ACID ON THE MATURATION OF SOMATIC EMBRYOS OF ZEA-MAYS L FROM SUSPENSION-CULTURES

The effects of the application of exogenous factors, such as osmotic c ondition and phytohormones, on the maturation of somatic embryos obtai ned from suspension cultures of maize were investigated. Mannitol in t he proliferation medium was needed to keep the callus embryogenic rath er than rhizogenic. In liquid culture a pre-maturation step with ABA a dded to the 2,4-D containing proliferation medium was beneficial. Both conditions promoted the formation of a meristematic layer at the outs ide of the callus. During the embryo maturation phase, which was done on solid media, and can be characterized by the formation of meristems and a starchy scutellum and by the suppression of precocious germinat ion, the percentage of calli showing embryo maturation, the number of developing embryos per callus, the suppression of root development and of root growth was influenced by the combinations of sucrose, mannito l, L-proline, ABA and GA. The effect of mannitol differed from that of sucrose; both promoted embryogenesis, but sucrose in addition effecte d starch accumulation. L-proline counteracted mannitol, and stimulated embryo maturation in the presence of GA. The effect of ABA resembled that of sucrose, and GA counteracted ABA. The reported effects of thes e substances on in vitro behaviour will be of value in improving the f requency and uniformity of somatic embryo maturation, and therefore re generation, in maize.