EFFECTS OF HEAVY-METALS ON POLLEN-TUBE GROWTH AND ULTRASTRUCTURE

The influence of different concentrations of the heavy metals cadmium (Cd2+), cobalt (Co2+), copper (Cu2+, iron (Fe2+ and Fe3+), mercury (Hg 2+), manganese (Mn2+), and zinc (Zn2+), plus aluminium (Al3+) (a toxic metal in polluted areas), on pollen germination and tube growth of Li lium longiflorum was investigated using light microscopy. Effects coul d be observed with 3 mu M and 100 mu M of heavy metal, added as chlori de salts to the medium. Cd2+, Cu2+, and Hg2+, showed the greatest toxi city, whereas germination and growth rate was less affected by Mn2+. A ffected tubes showed swelling of the tip region. Tubes treated with Cd 2+, Co2+, Fe2+ Fe3+, Hg2+, and Mn2+ were also prepared for ultrastruct ural studies. In all cases, the main effect was abnormal cell wall org anization, mostly at the lip, where round, fibrillar aggregates, the s hape and size of secretory Golgi Vesicles were formed. They built up a loose network which could be up to 10 mu m thick compared to untreate d tubes where the cell wall was composed of thin layers of long fibril s and about 100 nm thick. Cd2+ was the only metal which produced effec ts at the intracellular level: organelle distribution within the tip r egion appeared disorganized. A general mechanism of heavy metal action on pollen tube growth is discussed.