pollen tube growth

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

Stefan Sichtling, Hartmut Quader and Udo Kristen

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.
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In Vitro Pollen Tube Growth Reveals the Cytotoxic Potential of the Flavonols, Quercetin and Rutin

Fabiana Antognoni, Elisa Ovidi, Anna Rita Taddei, Gabriella Gambellini and Anna Speranza

Flavonols are phytochemicals widely found in commonly consumed foods. In spite of their beneficial effects on human health, however, cytotoxicity and even suspected genotoxicity have also been reported for the flavonol, quercetin. This points to the need for preventive studies to identify any cytotoxic effects associated with pure flavonol intake. This work was performed with the aim of verifying whether a plant-based in vitro system, the pollen tube, could be used to evaluate the cytotoxic potential of exogenous flavonols. Increasing concentrations of the aglycone, quercetin, and its glycoside, rutin, were assayed with regard to tube growth of kiwifruit pollen, determined by applying the pollen tube growth test protocol. This test, based on the photometric quantification of pollen tube mass production in suspension cultures, has already been applied in the sensitive and reliable toxicological evaluation of a wide range of chemicals. Whereas 60–800μM rutin promoted kiwifruit pollen tube elongation, 10–50μM quercetin strongly inhibited growth, and also produced irreversible malformations, such as screw-like tube growth, abnormal vacuolation, alteration of organelle streaming, and nuclear positioning. Thus, the cytotoxic potentials of the two flavonols have been confirmed to differ. Pollen tubes seem to afford a promising test system for a preventive, rapid in vitro biosafety assessment of antioxidant nutritional supplements, without using laboratory animals.
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