MORPHOLOGICAL AND PHYSIOLOGICAL-CHANGES DURING THIDIAZURON-INDUCED SOMATIC EMBRYOGENESIS IN GERANIUM (PELARGONIUM X HORTORUM BAILEY) HYPOCOTYL CULTURES

Somatic embryogenesis in geranium (Pelargonium xhortorum Bailey cv. Sc arlet Orbit Improved) was achieved by culturing hypocotyl explants on media supplemented with either thidiazuron (TDZ) or indol-3-yl-acetic acid (IAA) and 6-benzylaminopurine (BAP). The physiological relationsh ips between the morphological changes that lead to complete developmen t of somatic embryos and the endogenous levels of plant growth regulat ors were studied. TDZ induced similar but more pronounced and earlier morphological changes in cultured tissues than did IAA and BAP, but af ter 21 d in culture, both treatments promoted the formation of somatic embryos of different developmental stages that were similar to zygoti c embryos. TDZ induced a higher number of somatic embryos, with simila r but greater increases in the endogenous levels of auxins and cytokin ins, than did IAA and BAP. This may indicate that TDZ may be a more po tent plant growth regulator in inducing physiological and morphologica l changes than combined auxin and cytokinin, during the process of som atic embryogenesis in geranium.