Identification of six differentially expressed genes in response to copper exposure in the aquatic plant Lemna gibba (Duckweed).

Aquatic plants are susceptible to metal pollution and provide an entry point for metals, such as copper, into the aquatic biosphere. Exposure of the aquatic plant Lemna gibba to copper has been associated with the production of reactive oxygen species (ROS) and oxidative damage, caused in large part by the ability of this metal to redox cycle. In particular, copper-mediated production of ROS, a known group of signaling molecules, triggers numerous defense responses in L. gibba. Therefore, the objective of the present study was to examine to what extent acute copper exposure alters gene expression. First, the kinetics of copper uptake was assessed to determine if assimilation occurred within the short exposures needed to induce gene expression. Subsequently, using differential display polymerase chain reaction, we identified six genes with expressions that were putatively altered in response to copper. Differential expression was confirmed by northern hybridization analysis and showed that copper causes an accumulation of transcripts that encode for callose synthase, heat shock protein 90, serine decarboxylase, and the biotin carboxylase subunit of acetyl-coenzyme A carboxylase. Conversely, copper caused a decline in transcript levels for genes encoding the HAP5 subunit of the heme-activated protein (HAP) transcription factor in addition to the chloroplast nucleoid DNA-binding protein CND41. Interestingly, the expressions of these genes are sensitive to cellular ROS levels. We believe that these gene products provide valuable information regarding the molecular mechanisms of copper toxicity.