Induction of class-1 non-symbiotic hemoglobin genes by nitrate, nitrite and nitric oxide in cultured rice [Oryza sativa] cells
2005
Ohwaki, Y.(National Agricultural Research Center, Tsukuba, Ibaraki (Japan)) | Kawagishi Kobayashi, M. | Wakasa, K. | Fujihara, S. | Yoneyama, T.
Non-symbiotic hemoglobins (ns-Hbs) are found in all plants, although their physiological function remains to be determined. The present study was undertaken to explore the mode of induction of ns-Hb genes by metabolites of nitrate assimilation using cultured rice (Oryza sativa L.) cells. Two class-1 ns-Hb genes, ORYsa GLBla and ORYsa GLBlb, were strongly induced by nitrate, nitrite and nitric oxide (NO) donors, S-nitroso-N-acetylpenicillamine and sodium nitroprusside. The rapid and transient accumulation of ORYsa GLBla and ORYsa GLBlb transcripts in response to nitrate, nitrite and NO donors was similar to that of nial, which encodes NADH-nitrate reductase (NR), although repression by glutamine and asparagines was significant only for nial. In the mutants defective in NR mRNA expression, nitrate, nitrite and NO donors failed to induce not only nial but also ORYsa GLBla and ORYsa GLBlb transcripts, indicating that the induction of ns-Hb genes is closely associated with that of the NR gene. Although the kinetics of induction by nitrate, nitrite and NO donors are similar for the two ns-Hb genes, an inhibitor study demonstrated that de novo synthesis of the protein in cytoplasm is essential for inducing ORYsa GLBlb. In contrast, ORYsa GLBla, like nial, can be induced in the primary response to these signals without de novo protein synthesis. The role of nitrate, nitrite and NO in the induction of ns-Hb gene expression in rice cells and the possible cellar function of ns-Hbs were discussed in relation to nitrate reduction pathways.
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