Sulphate assimilation under Cd2+ stress in Physcomitrella patens--combined transcript, enzyme and metabolite profiling.

Cd(2+) causes disturbance of metabolic pathways through severe damage on several levels. Here we present a comprehensive study of Cd(2+)-mediated effects on transcript, enzyme and metabolite levels in a plant without phytochelatin (PC). The moss Physcomitrella patens (Hedw.) B.S.G. was stressed with up to 10 microm Cd(2+) to investigate the regulation of gene transcription and activities of enzymes involved in the assimilatory sulphate reduction pathway and in glutathione biosynthesis. Real-time PCR, specific enzyme assays as well as thiol peptide profiling techniques were applied. Upon supplementation of 10 microm Cd(2+), the moss showed a more than fourfold increase in expression of genes encoding ATP sulphurylase (ATPS), adenosylphosphosulphate reductase, phosphoradenosylphosphorsulphate reductase, sulphite reductase (SiR) and gamma-glutamyl cysteine synthetase (gamma-ECS). Likewise, elevated enzyme activities of gamma-ECS and glutathione synthetase were observed. Contrarily, activity of O-acetylserine (thiol) lyase (OAS-TL), responsible for biosynthesis of cysteine, was diminished. At the metabolite level, nearly doubling of intracellular cysteine and glutathione content was noted, while the moss did not produce any detectable amounts of PCs. These results suggest a Cd(2+)-induced activation of the assimilatory sulphate reduction pathway as well as of glutathione biosynthesis on different levels of regulation.