Antioxidant enzymes in plant-nematode interaction.

Activities of antioxidant enzymes, such as catalase (CAT), ascorbate peroxidase (APX), and superoxide dismutase (SOD), were assayed in roots and leaves of Mi-1-bearing tomato, resistant to root-knot nematodes. The tests were carried out as soon as 24 h after a heavy inoculation of very young seedlings with Meloidogyne incognita active juveniles. CAT and SOD, but not APX, were markedly inhibited in roots by nematode infestation; CAT and APX, but not SOD, were inhibited in leaves of inoculated seedlings. It is suggested that an early specific CAT inhibition may contribute to raise H2O2 level in cells undergoing HR and, in turn, induce further inhibition of the whole antioxidant enzyme detoxification system, which may lead to cell death and lesion formation at the site of nematode infection.