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Abstract
1-Aminocyclopropane deaminase (ACC) and tryptophan monooxygenase are two enzymes involved
in plant senescence-inhibiting and growth-promoting regulation, respectively. In this
study, two binary vectors were constructed in which the Agrobacterium iaaM gene was
under the transcriptional control of a xylem-specific glycine-rich protein promoter
alone, or co-expressed with the bacterial ACC deaminase gene, which was driven by
the constitutive CaMV 35S promoter. Transgenic petunia shoots co-expressing both genes
were able to root on medium supplemented with 7.5 mg l(-1) CoCl2. When T1 transgenic
tobacco plants were grown in sand supplemented with Cu2+ and Co2+, tissue specific
co-expression of both iaaM and ACC deaminase genes showed faster growth with larger
biomass with a more extensive root system, and accumulated a greater amount of heavy
metals than the empty vector control plants. When T1 transgenic tobacco plants were
grown in soil watered with different concentrations of CuSO4, xylem specific expression
of the iaaM gene caused the accumulation of more Cu2+ than the empty vector control
at lower CuSO4 concentrations, but showed severe toxic symptoms at concentration of
100 mg l(-1) CuSO4. T1 transgenic plants co-expressing both genes accumulated more
heavy metals into the plant shoots and can tolerate CuSO4 at 150 mg l(-1). In addition,
plants co-expressing these two genes can grow well in a complex contaminated soil
containing both inorganic and organic pollutants, while the growth of the control
plants was greatly inhibited.