Effects of the steroidal alkaloid tomatine in auxin bioassays and its interaction with indole-3-acetic acid.

The steroidal alkaloid tomatine did not enhance elongation of oat coleoptile and first internode sections, or of wheat coleoptile sections. Higher concentrations of the alkaloid inhibited elongation and interacted antagonistically with IAA. Although 10(-4) M tomatine alone did not influence elongation of oat coleoptile sections, it did reduce growth response to exogenous IAA. Tomatine concentrations less than 10(-4) M did not influence response to IAA. The auxin activity of tomatine, reported by Vendrig, was therefore not confirmed.