Inhibition of intracellular pectin transport in pollen tubes by monensin, brefeldin A and cytochalasin D

Specific inhibitors of the secretory pathway represent important tools for investigation of cell wall synthesis and tip growth in pollen tubes. Brefeldin A completely inhibits germination of Nicotiana tobacum pollen tubes at 2.2 mu M. Ultrastructural investigation of pollen tube cytoplasm showed that brefeldin A caused the appearance of reticular structures and ''brefeldin A compartments'' containing unesterified pectins. Monensin caused inhibition of pollen tube germination at 80 nM. The drug induced swelling of the Golgi cisternae, many of which contained methyl-esterified pectins. Cytochalasin D was effective at 1 mu g/ml, the inhibition of germination being fully reversible. Application of the drug caused accumulation of secretory vesicles containing methyl-esterified pectin around the dictyosomes. In contrast to brefeldin A and monensin, cytochalasin D caused a slowdown of cytoplasmic streaming. Monensin, but not the other drugs, caused a considerable decrease in pollen tube diameter. The characterization and quantification of the effects of the drugs on pollen tubes represents a necessary prerequisite for their application in physiological studies.