Cadmium stress induces production of thiol compounds and transcripts for enzymes involved in sulfur assimilation pathways in Arabidopsis

One of the defense systems against toxic heavy metals in plants is to employ cysteine-rich chelating compounds, phytochelatins, which are polymeric forms of glutathione. In the present study cadmium stressed Arabidopsis was employed in order to investigate the response of genes involved in glutathione biosynthesis via cysteine and production of thiol compounds. The results showed a 13-fold increase in transcripts for ATP sulfurylase, 6 to 10-fold for APS reductase and 2-fold for sulfite reductase, all of which are involved in cysteine synthesis. In addition, a 3-fold increase in total thiols was noted, mainly of glutathione, phytochelatins and cysteine. It is suggested that, to cope with toxic heavy metals, plants activate the sulfur assimilation pathway by increasing transcription of related genes to provide an enhanced supply of glutathione for phytochelatin biosynthesis.