RESUMPTION OF MITOTIC-ACTIVITY IN ALLIUM-CEPA L ROOT-TIPS DURING TREATMENT WITH LEAD SALTS

Allium cepa L. root meristem cells were observed for 30 hr during treatment with 2.5 mug ml-1 Pb2+ from PbCl2. Root growth and mitotic activity were gradually inhibited during the initial hours of incubation and were accompanied by a rise in the incidence of abnormal mitoses (c-mitoses) to about 40%. The most pronounced effects of lead were found between 7.5 and 12 hr of incubation. Metabolic activity resumed in the roots from 13.5 to 30 hr, as manifested by intensification of root growth, mitotic activity comparable to control levels and a normal course of cell division. The toxicity of lead to meristematic cells decreased as incubation progressed. This result correlates well with the observed lack of symptoms of lead poisoning in plants growing under natural conditions.