Cytokinins and in vitro development of Phaseolus coccineus embryos

Phaseolus coccineus embryos at the heartshaped and the middle cotyledonary stages were cultured in vitro on media added with different concentrations of zeatin (Z) or zeatin riboside (Zr). Growth of early embryos was clearly favored by concentrations of Z from 10-8 M to 10-5 M, lower concentrations having no effect. Zr also promoted in vitro growth of early embryos, but in concentrations from 10-12 M to 10-10 M, higher concentrations being inhibitory. More developed embryos were scarcely sensitive to the presence in the culture medium of either Z or Zr at any concentration.