Salicylic acid (SA) applied as 10 mM foliar spray to okra (Abelmoschus esculentus) cv. Purbani Kranti and cowpea (Vigna unguiculata) cv. Pusa Ruby plants 24 h before inoculation of roots with Meloidogyne incognita juveniles, reduced infestation. Salicylic acid had no direct influence on plant growth and did not kill nematodes in an in vitro test. It induced increased accumulation of a 14 kDa pathogenesis-related protein (PR-1) in roots of both non-inoculated and inoculated salicylic acid-sprayed okra but not in the treated leaves. Salicylic acid sprays enhanced phenylalanine ammonia lyase (PAL) activity in roots of both non-inoculated and inoculated cowpea, estimated at 15 days after inoculation. Infected roots had higher PAL activity than roots of the corresponding non-inoculated treatments. Both PAL activity and SA-induced resistance gradually declined with plant age after treatment.

Acaciaside A and B, two acylated triterpenoid bisglycoside saponins originally isolated from the funicles of Acacia auriculiformis, are known to have antihelmintic activity. In our previous investigation it was suggested that the conjugated unsaturated system of the saponins is involved in producing the damaging effect of saponins, probably by resulting free radicals that induce membrane damage through peroxidation. Here the interaction of saponins and the microsomal membrane was investigated in the presence and absence of superoxide dismutase, catalase and thiourea. Our results showed that superoxide dismutase significantly blocked the effect of saponins-induced membrane damage. Catalase had only a minor effect on saponins-induced membrane damage and thiourea had no effect. The results suggest that in our model, saponins can generate superoxide anions and initiate lipid peroxidation.

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