MECHANISM OF CHEMICAL ROOT PRUNING IN KANGAROO PAW (ANIGOZANTHOS-FLAVIDUS) BY SELECTED HEAVY-METAL CARBONATES

Heavy metal carbonates/hydroxides of copper (Cu), cobalt (Co) and zinc (Zn) were tested for their ability to induce root pruning in containe r-grown Anigozanthos flavidus (kangaroo paw). Co (1 and 2 mol eq l(-1) ) and Cu (2 and 5 mol eq l(-1)) were the best heavy metals for root pr uning, while Zn was only effective at 5 mol ecl l(-1). Successful root pruning was accompanied by 80% of root tips at or near the container wall being morphologically dead, whilst within the media a maximum of 25% of roots were dead. Increase in shoot/root ratios and a decrease i n the root branching coefficient were strongly correlated with root pr uning ability. The mitotic index was significantly lower in heavy meta l pruned root lips, and this was accompanied by an uptake of the respe ctive heavy metal. Heavy metals also significantly reduced the amounts of potassium present in root tips at or near the container wall, demo nstrating some nutritional imbalances, and that potassium levels may b e a sensitive indicator of heavy metal toxicity. During the eight-week experimental period, heavy metals were slowly released into the media water, the amounts were low and below water quality guidelines. The m oderate effects of Co in affecting mitosis and potassium nutrition dur ing root pruning, and its general lower toxicity in the environment su ggest that Co may be utilized as a suitable and effective chemical roo t pruning agent.