Abstract
Nitrate-independent activity of nitrate reductase (NR) is generally found in legume root nodules. Therefore, effects of nitrate on the levels of plant NR activity and mRNA were investigated in root nodules of Lotus japonicus. NR activity and mRNA were enhanced by the addition of nitrate in roots and root nodules. They were also detected in root nodules without nitrate while they were undetectable in roots. Southern blot analysis indicated that NR was a single gene. These results indicate that inducible-type NR could be expressed in root nodules without nitrate. The activation state of the nitrate-independent activity of NR was as high as that of nitrate-induced activity of NR. mRNA expressed independently of nitrate in root nodules was localized in the infected region of root nodules. Thus the expression could be related to specific structure and environment of root nodules.
