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 tub es. Brefeldin A completely inhibits germination of Nicotiana tobacum p ollen tubes at 2.2 mu M. Ultrastructural investigation of pollen tube cytoplasm showed that brefeldin A caused the appearance of reticular s tructures and ''brefeldin A compartments'' containing unesterified pec tins. Monensin caused inhibition of pollen tube germination at 80 nM. The drug induced swelling of the Golgi cisternae, many of which contai ned 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 methy l-esterified pectin around the dictyosomes. In contrast to brefeldin A and monensin, cytochalasin D caused a slowdown of cytoplasmic streami ng. Monensin, but not the other drugs, caused a considerable decrease in pollen tube diameter. The characterization and quantification of th e effects of the drugs on pollen tubes represents a necessary prerequi site for their application in physiological studies.