In rice (Oryza sativa var. Jackson) at least three copies of hemoglobin (hb) gene exist. Rice hb1 and hb2 genes are differentially expressed in roots and leaves from mature plants. We used polyclonal antibodies raised to recombinant rice Hb1 and Western blotting to analyze the synthesis of Hbs in rice plants growing under normal or stress conditions. Results showed that rice Hbs are synthesized in coleoptiles, seminal roots and embryos from seeds germinated for 6 days, and also in leaves and roots from plants 2-14 weeks after germination. Analysis of Hb synthesis in stressed rice showed that: (i) level of Hbs was higher in etiolated than control plants, (ii) level of Hbs increased in roots from flooded rice, and (iii) level of Hbs did not change under oxidative (H(2)O(2)), nitrosative (SNP) and hormonal (2,4-D) stresses. These results suggest that the effect of light withdrawal in etiolated leaves and O(2)-limiting conditions in flooded roots, but not oxidative, nitrosative and hormonal stresses, modulate the synthesis of rice Hbs.