The plant growth promotion observed in response to inoculation with bacteria containing ACC-deaminase has prompted scientists to develop transgenic plants that express ACC deaminase genes [36]. To date, many plant species have been genetically engineered with ACC deaminase expression to protect the plant against multiple biotic and abiotic stresses 37, 38, 39 and 40. Grichko et al. [41] expressed bacterial ACC deaminase in tomato (Lycopersicum esculentum) cv. Heinz 902 under the transcriptional control of either two tandem 35S cauliflower mosaic virus promoters (constitutive expression), the rolD promoter from Agrobacterium rhizogenes (root-specific expression) or the pathogenesis-related prb-1b promoter from tobacco. The growth of transgenic tomato plants in the presence of cadmium, copper, cobalt, magnesium, nickel, lead or zinc was monitored. Parameters tested were metal accumulation and ACC deaminase activity in both plant shoots and roots, root and shoot development, and leaf chlorophyll content. Transgenic tomato plants expressing ACC deaminase particularly controlled by the prb-1b promoter accumulated larger amounts of metals within the plant tissues. However, because the tomato (L. esculentum) plants are unlikely to be used in the phytoremediation of contaminated sites, Nie et al. [42] expressed ACC deaminase genes in canola (B. napus) plants and tested their potential to grow in the presence of high levels of arsenate in the soil for metal accumulation in plant tissues. They also tested the ability of the plant growth-promoting bacterium E. cloacae CAL2 to facilitate the growth of both non-transformed and ACC deaminase-expressing canola (B. napus) plants for developing a successful phytoremediation strategy. In all cases, transgenic canola (B. napus) expressing ACC deaminase genes accumulated larger amounts of arsenate from the contaminated soil than non-transformed canola plants. Recently, Stearns et al. [9] reported similar results in the case of phytoremediation of a nickel-contaminated soil environment. They observed that the growth of transgenic plants constructed through rolD promoters demonstrated more growth under high nickel concentration compared with control (non-transgenic) and other transgenic plants constructed through (CaMV) 35 S and prb-1b promoters expressing ACC deaminase genes ( Figure 3).
The plant growth promotion observed in response to inoculation with bacteria containing ACC-deaminase has prompted scientists to develop transgenic plants that express ACC deaminase genes [36]. To date, many plant species have been genetically engineered with ACC deaminase expression to protect the plant against multiple biotic and abiotic stresses 37, 38, 39 and 40. Grichko et al. [41] expressed bacterial ACC deaminase in tomato (Lycopersicum esculentum) cv. Heinz 902 under the transcriptional control of either two tandem 35S cauliflower mosaic virus promoters (constitutive expression), the rolD promoter from Agrobacterium rhizogenes (root-specific expression) or the pathogenesis-related prb-1b promoter from tobacco. The growth of transgenic tomato plants in the presence of cadmium, copper, cobalt, magnesium, nickel, lead or zinc was monitored. Parameters tested were metal accumulation and ACC deaminase activity in both plant shoots and roots, root and shoot development, and leaf chlorophyll content. Transgenic tomato plants expressing ACC deaminase particularly controlled by the prb-1b promoter accumulated larger amounts of metals within the plant tissues. However, because the tomato (L. esculentum) plants are unlikely to be used in the phytoremediation of contaminated sites, Nie et al. [42] expressed ACC deaminase genes in canola (B. napus) plants and tested their potential to grow in the presence of high levels of arsenate in the soil for metal accumulation in plant tissues. They also tested the ability of the plant growth-promoting bacterium E. cloacae CAL2 to facilitate the growth of both non-transformed and ACC deaminase-expressing canola (B. napus) plants for developing a successful phytoremediation strategy. In all cases, transgenic canola (B. napus) expressing ACC deaminase genes accumulated larger amounts of arsenate from the contaminated soil than non-transformed canola plants. Recently, Stearns et al. [9] reported similar results in the case of phytoremediation of a nickel-contaminated soil environment. They observed that the growth of transgenic plants constructed through rolD promoters demonstrated more growth under high nickel concentration compared with control (non-transgenic) and other transgenic plants constructed through (CaMV) 35 S and prb-1b promoters expressing ACC deaminase genes ( Figure 3).
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