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Appl Environ Microbiol. 1980 March; 39(3): 554-558

Fixation of Dinitrogen-15 Associated with Rice Plants

Osamu Ito, Delfin Cabrera and Iwao Watanabe

The International Rice Research Institute, Los Baños, Laguna, Philippines

ABSTRACT

Rice plants (IR26 and Latisail) obtained at near heading stage from a wetland field were transferred to water culture and exposed to ¹⁵N₂ in a gas-tight growth chamber for 7 days to measure N₂-fixing activities associated with the rice. The activities measured varied from 6.5 to 11.6 µmol of N₂ fixed per hill per day. The outer leaf sheath had about 2.5 times higher N₂-fixing activities per unit weight than the root. Slight activities were also found in the basal node and inner leaf sheath. Wrapping basal parts of the stem with aluminum foil did not decrease the activities of N₂ fixation in these parts. Thus, the outer leaf sheath as well as the root are N₂-fixing sites in rice plants. N₂ fixation found in above-ground parts is not due to photoautotrophic organisms. Less than 10% of the fixed nitrogen was translocated from the fixing sites to the leaf blades and the young panicles.

Present address: Charles F. Kettering Research Laboratory, Yellow Springs, OH 45387.