Investigating the Skoog-Miller Model for Organogenesis Using Sweet Potato Root Explants

Abstract

Regeneration of tobacco (Skoog & Miller 1957) from explants or calluses is the classical example used to demonstrate organogenesis. It is a good choice since effects of auxins and cytokinins on tobacco are specific and reproducible (Flick et al. 1983). High auxin and low cytokinin concentrations promote callus formation. Shoot formation occurs with low auxin and high cytokinin concentrations. Roots form with high auxin and very low cytokinin concentrations, or with auxin alone. Also, tobacco callus may be obtained easily from any of several biological supply houses and subcultured to produce the quantity needed. This Skoog-Miller model for tobacco callus holds for many species (Hussey 1986). There are exceptions though, and these exceptions allow an opportunity to bring experimentation and problem solving into the classroom. Problem probing is a powerful vehicle for teaching the content of the domain along with its working procedures, according to Peterson & Jungck (1988) and Flannery (1991). With this in mind, students in a plant tissue culture course were asked to test application of the Skoog-Miller model to sweet potato root explants. A two-way factorial experimental design, similar to that used by Skoog and Miller (1957), was selected for this purpose. This approach allows determination of the effects of indole-3-acetic acid (IAA, an auxin) and kinetin (a cytokinin), alone and in combination, on organogenesis. As a control, tobacco callus was also tested. Students worked in pairs to make manipulations easier and to increase interaction during analysis and writing.