Time-courses of Growth Inhibition and Recovery for Narcotic Chemicals and 2,6-Dinitrophenol in Pollen Suspensions of Nicotiana sylvestris.

In a previous structure-activity analysis of chlorophenol and nitrophenol toxicity, the pollen tube growth test was shown to discriminate between oxidative uncoupling and narcotic mechanisms of action. To examine the suitability of the use of pollen tubes in screening for narcotic chemicals, we used tobacco pollen suspensions and performed time-course experiments on pollen tube growth inhibition and recovery after exposure to 1-butanol, 2-chloroaniline, 2,4-dichlorophenol and 2,6-dinitrophenol, during pollen culture for 22 hours. After exposure to the chemicals for 2 hours, pollen tubes exposed to 1-butanol and 2,6-dinitrophenol were able to recover, whereas recovery was poor after exposure to 2-chloroaniline and 2,4-dichlorophenol. Dilution experiments to remove the narcotics from the pollen suspension indicated that 2-chloroaniline and 2,4-dichlorophenol accumulated in the pollen grain wall, presumably due to their high octanol/water partition coefficients. Therefore, we suggest that the pollen tube growth test is not suitable for correctly predicting the narcotic potencies of highly lipophilic compounds. In the presence of 1-butanol, pollen grains did not germinate, but became characteristically enlarged. This observation suggests that 1-butanol inhibits the establishment of the cell polarity necessary for initiating pollen tube outgrowth.