The effects of different concentrations of Zn on growth of an aquatic macrophyte, Ipomoea aquatica Forsk. were studied. Fresh weight, dry weight, shoot length, root length, number of nodes, development of leaves, and chlorophyll and carotene contents were the different growth parameters considered. Toxicity symptoms like browning and decaying of roots could be observed in plants treated at 22.7 mg L-1 Zn as early as 3rd day of experiment while yellowing of older leaves appeared during the later period of exposure. High concentration of Zn (12.71 – 22.7 mg L-1) significantly inhibited the growth of plant while lower Zn concentrations up to 4.09 mg L-1 enhanced its growth. However, at 7.26 mg L-1 Zn the chlorophyll as well as total carotene content in leaf of I. aquatica were significantly reduced from that in control on 5th day of exposure and subsequently the reduction was observed in lower concentrations. Thus, I. aquatica can be employed in biomonitoring of Zn polluted aquatic ecosystems using root browning, root and shoot growth inhibition, and chlorophyll and total carotene contents as sensitive biomarkers.
