ORGANOGENESIS IN CALLUS-TISSUE OF MEDICAGO-SATIVA - TEMPORAL SEPARATION OF INDUCTION PROCESSES FROM DIFFERENTIATION PROCESSES

A callus culture system of alfalfa has been developed which demonstrates the quantitative control of root and shoot organogenesis by growth regulators of the auxin and cytokinin type. Unlike many conventional systems in which organogenesis has been studied, callus from alfalfa produces roots after induction by a 4 day exposure to relatively high kinetin and relatively low 2,4-dichlorophenoxyacetic acid (2,4-D). Shoots are produced after a 4 day induction period in relatively high 2,4-D concentrations and low kinetin concentrations. Differentiation does not occur on induction medium, but only upon transfer of tissue to growth regulator free regeneration medium. This system enables the temporal separation of organogenetic induction from subsequent differentiation. In addition, a diameter of 105 μm represents the lower limit for callus cellular aggregates that are morphogenetically competent. Single cells and small cellular aggregates are not competent, but become so upon subsequent growth. © 1979.