Hyperaccumulation of inorganic contaminants
Bacteria containing ACC deaminase activity modulate stress-induced accelerated production of ethylene in plants, and might cause an enhanced uptake of inorganic contaminants through modification of root architecture and of the root uptake system of the plant. Burd et al. [14] reported the greater potential of the ACC deaminase bacterium, Kluyvera ascorbata SUD165 (which is resistant to the toxic effects of nickel, lead, zinc and chromate ions), to protect canola (Brassica napus) and tomato (Lycopersicon esculentum) seeds from the toxicity of high concentrations of nickel chloride (NiCl2) grown under gnotobiotic conditions. They attributed this effect to the ability of the bacterium to lower the level of stress ethylene induced by the nickel. In another study, Burd and co-workers [26] recorded similar observations in the case of tomato (L. esculentum), canola (B. napus) and Indian mustard (B. napus) seeds, which were grown in soil for 25–42 days in the presence of nickel, lead or zinc. Similarly, Belimov et al. [27] reported the potential of ACC deaminase bacteria to promote root and shoot growth of the seedlings of Indian mustard and rape (B. napus) grown in the presence of 300 μM cadmium chloride (CdCl2) in the nutrient solution. Primarily in these studies, the use of ACC deaminase bacteria exhibiting resistance to heavy metals was to test their potential to facilitate plant growth under stress conditions created by heavy metals. They concluded that ACC deaminase bacteria offer a great potential to be used for development of bacterial inocula for improvement of plant growth under unfavorable environmental conditions, particularly for hyperaccumulators.