The pre-treatment of rice seeds with sodium nitroprusside (SNP) was used to investigate the effect of exogenous nitric oxide on the pigment content and the activity of antioxidant enzymes during the inhibition of the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway by the herbicide clomazone. The seeds were soaked in SNP solution (200 mM) for one and 10 hours and sprayed with clomazone, at postseeding and at the needle-point, with 612 (experiment 1) and 1,224 g a.i. ha -1 (experiment 2). The control of both factors received distilled water. Carotenoids, chlorophylls a, b and total, superoxide dismutase (SOD), guaiacol peroxidase (POD) and the correlation between the variables were evaluated in the shoot of the plants. When compared to the control (no SNP), the imbibition for one hour increased carotenoid and total chlorophyll content by 24 and 54%, respectively, in experiment 1, where clomazone was applied in post-seeding. In the absence of the herbicide, the values were 37 and 59% higher. The SOD and POD activity, respectively, was increased by 48 and 51%, when the seeds were soaked for 10 hours and exposed to 612 g a.i. ha -1 of clomazone in post-seeding application. In a similar condition, in experiment 2, there were no changes in enzyme activity. Seed pretreatment with SNP increases the carotenoid and chlorophyll contents in rice plants, even with the inhibition of the MEP pathway by clomazone. The behavior of the SOD and POD activity indicates that other mechanisms besides the increase in the photosynthetic pigment contents are involved in the detoxification of the reactive oxygen species induced by the mode of action of clomazone. Keywords: chlorophyll, carotenoids, Oryza sativa, superoxide dismutase, guaiacol peroxidase. RESUMO -O pré-tratamento das sementes de arroz com nitroprussiato de sódio (SNP) foi usado para investigar o efeito do óxido nítrico exógeno sobre o conteúdo de pigmentos e a atividade de enzimas antioxidantes durante a inibição da rota 2-C-metil-D-eritritol 4-fosfato (MEP), pelo herbicida clomazone. As sementes foram embebidas em solução de SNP (200 mM) por uma e 10 horas e pulverizadas com clomazone, em pós-semeadura e no ponto de agulha, com 612 (experimento 1) e 1.224 g i.a. ha -1 (experimento 2). As testemunhas de ambos os fatores receberam água destilada. Carotenoides, clorofilas a, b e total, superóxido dismutase (SOD), guaiacol peroxidase (POD) e a correlação entre as variáveis foram avaliados na parte aérea das plantas. Quando comparados à testemunha (sem SNP), a embebição por uma hora aumentou o conteúdo de carotenoides e clorofila total em 24 e 54%, respectivamente, no experimento 1, onde clomazone foi aplicado em pós-semeadura. Na ausência do herbicida, os valores foram 37 e 59% superiores. A atividade da Planta Daninha 2019; v37:e019185130 SILVA, K.S. et al. Contents of pigments and activity of antioxidant enzymes in rice plants pre-treated with sodium ... 2 SOD e POD foi aumentada em 48 e 51%, respectivamente, quando as sementes foram embebidas por 10 horas e expostas a 612 ...