Meetings of the Royal Botanical Society of The Netherlands

Pollen of Nicotiana tabacum L, were germinated in vitro. The distribution of various organelles was studied in serial sections of cryo-fixed, freezesubstituted pollen tubes and in living pollen tubes using video microscopy. The organelles show a typical zonal distribution. In the tip, Golgi vesicles accumulate. At various distances behind the tip the different organelles accumulate: mitochondria at 5-15 pm, rough endoplasmic reticulum at 15-25 pm and Golgi bodies at 25-30 pm, from the tip. Video microscopy shows that mitochondria generally follow the pattern of plasma streaming in these tubes, though they sometimes even occur in the extreme tip. The Golgi bodies that accumulate in the tip remain there for long periods, up to 20 minutes, while other Golgi bodies follow the pattern of plasma streaming. At the plasma membrane, 15-25 pm behind the tip, coated pits accumulate. They are probably involved in retrieval of excess membrane, which results from wall secretion at the tip. The distribution of the coated pits is related to that of the microtubules. Often coated pits are connected with the microtubules, either directly by short bridges or via putative actin filaments. It is suggested that coated vesicle transport may depend on microtubule based motor proteins.