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ECOLOGICAL RISK ASSESSMENT OF ALFALFA (MEDICAGO VARIA L.) GENETICLALY ENGINEERED TO EXPRESS A HUMAN METALLOTHIONEIN (HMT) GENE
Citation:
Watrud, L S., S. Misra, L. Gedamu, T Shiroyama, S. Maggard, AND G. D. Di Giovanni. ECOLOGICAL RISK ASSESSMENT OF ALFALFA (MEDICAGO VARIA L.) GENETICLALY ENGINEERED TO EXPRESS A HUMAN METALLOTHIONEIN (HMT) GENE. WATER, AIR, AND SOIL POLLUTION. Springer, New York, NY, 176:329-349, (2006).
Impact/Purpose:
The objectives of these studies were two-fold: (1) to determine efficacy of low and high expression hMT gene constructs by assessing accumulation of Cu in shoots of parental and transgenic plants of alfalfa (Medicago varia L.) exposed to different concentrations of CuSO4 by addition of CuSO4 solutions to soil and (2) to identify potential unintended effects of the genetic engineering on root and shoot biomass, shoot nutrient content, arbuscular mycorrhizal infection and on the metabolic functions of microbial communities in the rhizosphere.
Description:
The objectives of these studies were two-fold: (1) to determine efficacy of low and high expression hMT gene constructs by assessing accumulation of Cu in shoots of parental and transgenic plants of alfalfa (Medicago varia L.) exposed to different concentrations of CuSO4 by addition of CuSO4 solutions to soil and (2) to identify potential unintended effects of the genetic engineering on root and shoot biomass, shoot nutrient content, arbuscular mycorrhizal infection and on the metabolic functions of microbial communities in the rhizosphere. In the absence of exogenous CuSO4 additions to soil shoot biomass and the macronutrient (C, P, K, Ca, Mg and N) content of plants expressing hMT were not significantly different from the parental control. In the 0.5 mM and 1.0 mM CuSO4 treatments transgenic plants expressing the commonly used transgenic ß-glucuronidase (GUS) marker had significantly higher Fe content than the parental genotype. Significant differences were observed in the carbon substrate utilization patterns of rhizosphere microbial communities among the transgenic plants; no significant differences were observed in the percent mycorrhizal infection of parental and transgenic plants. Shoot biomass increased significantly in all genotypes treated with 0.5 mM CuSO4 and decreased in all genotypes at CuSO4 concentrations of 1.5 mM and 2.0 mM. Root dry weights decreased significantly in all genotypes at concentrations of 1.0 mM, 1.5 mM and 2.0 mM CuSO4. The largest decreases in root dry weight were observed in hMT genotypes grown in soil treated with 1.5 and 2.0 mM CuSO4. In plants treated with 1.5 mM CuSO4, shoots of transgenic plants expressing the hMT gene accumulated nominally, but not statistically significantly higher levels of Cu in shoot tissue. Our results were surprising with regard to lack of sufficient efficacy of the current hMT constructs for significant accumulation of Cu from soil treated with CuSO4. However, our results suggest the utility of applying adverse levels of CuSO4 or other environmental stressors to identify potential unintended effects of genetic engineering that may not be apparent under typically more optimal plant growth test conditions.