Effect of paraquat on tomato roots cultured in vitro susceptible and resistant to nematodes

Roots from two tomato cultivars, one resistant (Rossol) and the other susceptible (Roma VF) to root-knot nematodes, were cultured in vitro and tested for their response to paraquat, an herbicide which generates superoxide in cells. The effect of paraquat on the permeability of root membranes was tested by the safranine method. Membranes from resistant roots were injured more markedly than susceptible ones. A statistical analysis of the variations on a series of enzyme activities from roots incubated for 2 days with paraquat was carried out. Superoxide dismutase was repressed in treated resistant roots together with ascorbate and glutathione peroxidases. In susceptible roots these enzymes were not significantly affected by paraquat treatment except for ascorbate peroxidase which increased slightly. Syringaldazine and polyphenol oxidases, two enzymes active in the hypersensitive response to nematodes, increased in resistant but not in the susceptible cultivar. p-Phenilendiamine-pyrocathecol oxidase was not affected while catalase increased markedly by paraquat treatment in both cultivars. © 1991 The Japanese Society of Plant Physiologists (JSPP).