Plant thioredoxin systems revisited

Thioredoxins, the ubiquitous small proteins with a redox active disulfide b ridge, are important regulatory elements in plant metabolism. Initially rec ognized as regulatory proteins in the reversible light activation of key ph otosynthetic enzymes, they have subsequently been found in the cytoplasm an d in mitochondria. The various plant thioredoxins are different in structur e and function. Depending on their intracellular location they are reduced enzymatically by an NADP-dependent or by a ferredoxin (light)-dependent red uctase and transmit the regulatory signal to selected target enzymes throug h disulfide/dithiol interchange reactions. In this review we summarize rece nt developments that have provided new insights into the structures of seve ral components and into the mechanism of action of the thioredoxin systems in plants.