Fumigation of plants of five species with NO2in darkness caused visible injuries to leaves, with the most severe injuries in kidney bean plants and the least severe in spinach plants. Fumigation of these plants in the light caused virtually no visible injuries. NO2-fumigated leaves accumulated nitrite in the darkness but not in the light. The level of accumulated NO2−was decreased by light much more rapidly in spinach leaves than in those of kidney bean, with much less injury to spinach leaves than to those of kidney bean. A larger amount of NO2−accumulated in the trifoliate leaves of kidney bean plants cultivated with NO3−as a main source of nitrogen than in those of plants cultivated with NH4+, and the former plants were more susceptible to injury from NO2than the latter. Administration of NO2−to leaves of spinach and kidney bean plants induced the destruction of Chi in the light. The extent of the destruction of Chi was smaller in spinach than in kidney bean, consistent with their respective responses to NO2. The NO2−-induced destruction of Chi was inhibited to some extent by scavengers of free radicals. Activities of superoxide dismutase (SOD) were higher in leaves of spinach than in those of kidney bean. These results indicate that NO2−is the toxic species generated by fumigation with NO2and that spinach has a greater tolerance for NO2than kidney bean, probably as a result both of a higher capacity for reduction of NO2−and a higher level of ac
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