Arginase activity in Arabidopsis thaliana infected with Heterodera schachtii

The activity of arginase (ARGAH), which results in ornithine and urea production, is important for nitrogen metabolism in all organisms as well as for defence responses. The second-stage juveniles of the cyst-forming nematode Heterodera schachtii penetrate roots and induce the formation of a permanent feeding site. To determine whether infection with H.schachtii causes the induction of arginase, the expression was studied in Arabidopsis roots and shoots at the day of inoculation and at 3, 7 and 15days post-inoculation (dpi). Parasite infection caused a strong decrease of root arginase activity and ARGAH1 gene expression, which persisted over the entire examination period. In shoots, the mRNA expression of ARGAH2 increased at 3 and 7dpi, but the enzymatic activity was significantly enhanced only at 3dpi. Thus, while arginase down-regulation occurs in roots, which is apparently due to the presence of nematode effectors, in shoots the activity is only transiently up-regulated despite persistently high gene expression. As oxidative stress is possible during nematode infection, the activity and gene expression of glutathione reductase, a marker of the redox equilibrium, were estimated and found to be significantly enhanced at 7dpi in shoots of infected plants. The level of proline, an amino acid known for its ability to scavenge free radicals, was increased 60-fold. The results suggest that the disruption of redox homeostasis, as reflected by increased proline level and glutathione reductase expression and activity, accompanies changes in arginine metabolism in the shoots, indicating systemic changes induced by nematode infection.