Relationship Between Ascorbic Acid and Resistance in Tomato Plants toMeloidogyne incognita

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Abstract
The role of ascorbic acid in the defense mechanism of tomato (Lycopersicon esculentum) plants against attack by the root-knot nematode, M. incognita, was studied under controlled conditions. The ascorbic acid concentration in roots of either nematode-resistant or -susceptible plants was varied experimentally and the reaction of these plants to attacks by the nematode was tested. A decrease in ascorbic acid, obtained by application of lycorine (an inhibitor of ascorbic acid synthesis), induces a reduction of plant resistance to the nematode, but an artificial increase in ascorbic acid concentration transforms susceptible plants into resistant ones. The amount of ascorbic acid in susceptible plants was unaltered by nematode attacks but in resistant plants ascorbic acid synthesis always was stimulated. Ascorbic acid is probably utilized for the synthesis of mitochondrial hydroxyproline proteins which control the development of cyanide-resistant respiration.