Abstract
Non-symbiotic hemoglobins (nsHbs) are ubiquitous in plants. Dicots are known to have two distinct classes of nsHb genes whereas monocots may have one class. Recent microarray work indicated that class 1 nsHb genes are inducible by nitrate in Arabidopsis, though the factors associated with induction of nsHbs by nitrate have not been examined in detail. Expression of two class 1 nsHb genes, ORYsaGLB1a and ORYsaGLB1b, was induced in nitrate treated rice cells in a manner similar to that of the induction of nitrate reductase (NR) activity. When nitrate-treated cells were grown in a medium containing tungstate, an inhibitor for NR activity, the expression of ORYsaGLB1a and ORYsaGLB1b was repressed. Furthermore, mutants defective in NR activity were impaired in the induction of ORYsaGLB1a and ORYsaGLB1b by nitrate. These results suggest that NR activity may be essential for the induction of nsHbs by nitrate in cultured rice cells.
