HORMONES AND EARLY IN VITRO DEVELOPMENT OF EPIPHYLLOUS PROPAGULES ON BRYOPHYLLUM CALYCINUM

Uniform leaf discs of Bryophyllum calycinum, each containing a single marginal notch, were explanted onto sterile media. These media contained the minerals and vitamins of Murashige and Skoog, 2% sucrose, and 1% agar. Hormones used included indoleacetic acid (IAA), gibberellic acid (GA), 2,4-dichlorophenoxyacetic acid (2,4-D), and benzylaminopurine (BAP). Explants were grown for 1 wk at which time the length of the longest leaf was measured. These observations represent the most rapid in vitro development of these isolated structures yet reported in the literature. The number of roots was also recorded and the average length of the two longest roots was calculated. BAP at concentrations of 10^-6 to 10^-8 m provided the only growth stimulation of the propagules observed, while 10^-4 m completely inhibits roots and reduces leaf development by 60% and 10^-5 m significantly decreases number and length of roots. Except at 10^-3 m, which was inhibitory, IAA had no effect on propagule leaf development. Concentrations of 10^-3 m 2,4-D induced callus and no roots, 10^-4 m induced both callus, leaves, and roots, and multiple root primordia at the notch in explants grown for 2 wk at 10^-4 m. When callus formed it never arose at a cut surface, but broke through the epidermis only at the notch of the leaf. Gibberellic acid and 2,4-D were generally inhibitory to leaf development but 10^-5 m GA significantly enhanced root length. With the exception of 10^-5 m GA, both 2,4-D and GA generally inhibit both average length of longest two roots and average number of roots. Concentrations of BAP of 10^-7 m and 10^-8 m stimulated root production as did 10^-7 m IAA and 10^-7 m 2,4-D while other concentrations of hormones used were either without effect or were inhibitory. Gibberellic acid at 10^-4 m produced leaves without any of the notches typical of this species. As the concentration of the hormone was reduced to 10^-5 m notches began to be formed and by 10^-6 and 10^-7 m normal notching was restored.