Analysis of the roles of the Arabidopsis peroxisomal isocitrate dehydrogenase in leaf metabolism and oxidative stress

• A T-DNA mutant for peroxisomal isocitrate dehydrogenase (pxICDH) was studied.
• pxICDH transcripts were undetectable, but total leaf activity was similar to wild-type.
• Specific metabolites were increased in the mutant, notably lysine and pipecolic acid.
• The mutant did not show altered responses to oxidative stress.
• The mutant showed increased resistance to bacteria.

Peroxisomes are important organelles in cell signalling, notably because of their highly active reactive oxygen species metabolism, while NADP-dependent isocitrate dehydrogenases may play several roles in plant metabolism, including contributing to redox homeostasis. In this work, the role of the peroxisomal enzyme (pxICDH) was analysed by studying an Arabidopsis T-DNA mutant. Although pxICDH transcripts were undetectable in the mutant, no decrease in extractable ICDH activity or marked effect on rosette phenotype or redox state was apparent. Profiling of more than 80 compounds by gas chromatography–mass spectrometry revealed little impact of the mutation on leaf metabolism, apart from increases in a small number of compounds such as ribose, lysine and pipecolic acid. To examine whether the enzyme is important in oxidative stress conditions, pxicdh was crossed with a catalase-deficient mutant compromised in peroxisomal H2O2 metabolism. The pxicdh mutation did not markedly affect either the cat2 phenotype or cat2-triggered redox profiles. A slight increase in bacterial resistance was observed in pxicdh. We conclude that the peroxisomal enzyme makes a very minor contribution to overall leaf ICDH capacity and is dispensable for plant growth and redox homeostasis, but that it could play subtle roles in responses to environmental challenges such as biotic stress.