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 t oxicity, the pollen tube growth test was shown to discriminate between oxid ative uncoupling and narcotic mechanisms of action. To examine the suitabil ity 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-chloroa niline, 2,4-dichlorophenol and 2,6-dinitrophenol, during pollen culture for 22 hours. After exposure to the chemicals for 2 hours, pollen tubes expose d to 1-butanol and a,6-dinitrophenol were able to recover, whereas recovery was poor after exposure to 1-chloroaniline and 2,4-dichlorophenol. Dilutio n 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. T herefore, we suggest that the pollen tube growth test is not suitable for c orrectly predicting the narcotic potencies of highly lipophilic compounds. In the presence of 1-butanol, pollen grains did not germinate, but became c haracteristically enlarged. This observation suggests that 1-butanol inhibi ts the establishment of the cell polarity necessary for initiating pollen t ube outgrowth.