| Budget Amount *help |
¥2,200,000 (Direct Cost: ¥2,200,000)
Fiscal Year 2006: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 2005: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 2004: ¥900,000 (Direct Cost: ¥900,000)
|
|---|
| Research Abstract |
Non-symbiotic hemoglobins are found in all plants although their physiological function remains to be determined. The present study was undertaken to explore the function of non-symbiotic hemoglobins in nitrate assimilation using cultured rice (Oryza sativa L.) cells. Two class-1 non-symbiotic hemoglobin genes, ORYsa GLB1a and ORYsa GLB1b, were strongly induced by nitrate, nitrite and nitric oxide (NO) donors in cultured rice cells. The rapid and transient accumulation of ORYsa GLB1a and ORYsa GLB1b 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 nialbut also ORYsa GLB1a and ORYsa GLB1b transcripts, indicating that the induction of non-symbiotic hemoglobin 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 non-symbiotic hemoglobin genes, an inhibitor study demonstrated that de novo synthesis of the protein in cytoplasm is essential for inducing ORYsa GLB1b. By contrast, ORYsa GLB1a, like nia1, can be induced in the primary response to these signals without de novo protein synthesis. Transformed rice cells under-expressing non-symbiotic hemoglobin had reduced ability of metabolize nitrate. These results suggested that the non-symbiotic hemoglobin has a cellar function in nitrate reduction in plants.
|
