Effect Of ZnO Nanoparticles On The Mitosis Of Garlic Root Tip Cells

Zinc oxide (ZnO) is a wide gap II-VI semiconductor, which has hexagonal wurtzite structure. Because of its semiconducting, optical, piezoelectric, and ultraviolet (UV)-shielding properties, ZnO NPs have been used in a large variety of commercial products. For example, electronics devices, transparent UV-protection films, chemical sensors, UV-filters in sunscreens, as well as textiles. However, with the increased presence of ZnO NPs in the commercial products, a growing public debate is emerging on toxicological and environmental effects of ZnO NPs. Unfortunately, toxicological studies carried out in the last 10 years have shown that ZnO NPs had potential health and environmental risks. It poses serious toxicity to bacteria, Daphnia magna, freshwater micro alga, mice, and even to human cells. To date, although investigations about the toxicological effects of ZnO NPs continue to increase with time, few studies have been conducted to assess the effects of ZnO NPs on plants. Therefore, in order to increase our understanding about the effects of NPs on plants, we investigated the ZnO NPs phytotoxic effects on root growth and genotoxic effects on mitotic index and mitotic divisions in garlic root tip cells during mitosis.ZnO NPs caused a reduction of root length, with an almost complete block of growth in garlic treated with 50ml/L, for 24h of treatment. The fifty percent inhibitory concentration (IC50) was estimated to be near 15mg/L. The mitosis index values were also decreased by ZnO NPs in concentration- and time-dependent manners. This is statistically significant at P<0.05,P<0.01 and P<0.001 levels. In addition, ZnO NPs induced a number of mitotic abnormal cells, mainly consisting of chromosome stickiness, chromosome bridges ,chromosome breakages and chromosome laggings. And the total percentage of abnormal cells increased with an increase of the ZnO concentration and the prolongation of the treatment time. This is statistically significant at P<0.05, P<0.01 and P<0.001 levels. The present investigation provides new information about the phytotoxic and genotoxic effects of ZnO NPs on plants.