Enzymatic activity and arginase gene expression in Arabidopsis plants infected with a cyst-forming nematode

The nematode Heterodera schachtii is a sedentary endoparasite of sugar beet and many Brassicaceous plants. Its second-stage juveniles penetrate host roots and induce permanent feeding site (a syncytium) being the sole source of nutrients for the developing nematode. Increased contents of many amino acids (including proline) in syncytia induced in Arabidopsis thaliana roots were found. Proline and polyamines are important for cell protection and repair processes. They are synthesized from ornithine, the product of arginase-catalyzed reaction. Arginase (EC is an important enzyme for nitrogen metabolism as it produces urea aside from ornithine. Recently, the role of arginase in plant defense has attracted attention, as the arginase gene expression is induced as a result of viral or microorganism infections, as well as after wounding. Because our experiments have shown an elevated activity of arginase in shoots of A. thaliana infected with H. schachtii , we studied arginase gene expression in syncytia, roots and shoots of the nematode-infected plants. Using semi-quantitative RT-PCR we showed the presence of arginase1 and arginase2 RNAs in shoots of A. thaliana, whereas only arginase 1 was expressed in roots. In plants collected on the third and seventh day after infection, expression of arginase1 both in roots and shoots was lower than in uninfected plants. Similarly, the arginase2 expression was strongly inhibited in shoots on the seventh day after nematode infection. However, fifteen days after infection, a higher expression of arginase1 was found in infected plants than in appropriate control shoots. Thus, we infer that cell wall damage and/or metabolic changes caused by invading nematodes influence the profile of arginase expression in H. schachtii -infected Arabidopsis plants.