Effect of Paraquat on Tomato Roots Cultured in Vitro Susceptible and Resistant to Nematodes

Roots from two tomato cultivars, one resistant (Rossol) andthe other susceptible (Roma VF) to root-knot nematodes, werecultured in vitro and tested for their response to paraquat,an herbicide which generates superoxide in cells. The effectof paraquat on the permeability of root membranes was testedby the safranine method. Membranes from resistant roots wereinjured more markedly than susceptible ones. A statistical analysisof the variations on a series of enzyme activities from rootsincubated for 2 days with paraquat was carried out. Superoxidedismutase was repressed in treated resistant roots togetherwith ascorbate and glutathione peroxidases. In susceptible rootsthese enzymes were not significantly affected by paraquat treatmentexcept for ascorbate peroxidase which increased slightly. Syringaldazineand polyphenol oxidases, two enzymes active in the hypersensitiveresponse to nematodes, increased in resistant but not in thesusceptible cultivar. p-Phenilendiamine-pyrocathecol oxidasewas not affected while catalase increased markedly by paraquattreatment in both cultivars. (Received January 21, 1991; Accepted August 6, 1991)