THE ANTI-MICROTUBULE DRUG CARBETAMIDE STOPS NICOTIANA-SYLVESTRIS POLLEN-TUBE GROWTH IN THE STYLE

Recently, we found that the anti-microtubule drugs colchicine and propham caused the absence of microtubules and thus loss of cytoplasmic zonation in in vitro growing pollen tubes of Nicotiana sylvestris, but did not seriously affect growth. in the present study we used the herbicide carbetamide as an anti-microtubule drug. It had the same effect as colchicine and propham: the cytoplasm, including the generative cell, was no longer concentrated in the tip but was distributed randomly. In addition, ultrastructural investigations have shown that even the vesicle zone, usually found at the very tip of pollen tubes, had disappeared in some tubes. Nonetheless, in vitro growth was not inhibited by more than 20% over a period of 22 h. In contrast, tube growth in plants ceased 1 cm down in the style when carbetamide was applied to the stigma before pollination. At the lowest concentration causing this effect, microtubules of the vegetative cell had disappeared and the cytoplasm was distributed randomly, as it was for in vitro grown tubes. It can be concluded that microtubules of the vegetative cell are essential for pollen tube growth in the style.