Only a few plants are suitable for reliably demonstrating rapid direct and indirect shoot organogenesis in vitro. A laboratory exercise has been developed using internodes of Myriophyllum aquaticum, an amphibious water garden plant. Stock shoot cultures are established and maintained in vitro from nodal explants cultured on agar-solidified medium consisting of half-strength Murashige & Skoog salts (MS) and 30 g·liter-1 sucrose. Students use these cultures as the source of internode explants. Explants are cultured on agar-solidified full-strength MS with 30 g·liter-1 sucrose, 100 mg·liter-1myo-inositol, and 0.4 mg·liter-1 thiamine·HCL and factorial combinations of 0 to 10 μM 2iP and 0 to 1.0 μM NAA. Adventitious shoot development occurs directly from the explant epidermis within 4 days and is promoted in media supplemented with 2iP alone. Cytokinin-supplemented media amended with NAA induce organogenetic callus formation, but reduce 2iP promotion of direct shoot organogenesis. After 4 weeks, shoot organogenesis on the various media is quantified and can be analyzed statistically. Chemical names used: N-(3-methyl-2-butenyl)-1H-purin-6-amine (2iP); α-naphthaleneacetic acid (NAA).
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