Crop Science Journal of Natural Resources and Life Sciences Education
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Published in Crop Sci 22:944-948 (1982)
© 1982 Crop Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
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Location of Nitrate Reduction in Different Soybean Cultivars1

W. J. Hunter, C. J. Fahring, S. R. Olsen and L. K. Porter2

The amount of NO3- in xylem sap from 11 soybean (Glycine max L. Merr.) cultlvars was examined to determine if nitrate was being reduced in the shoot or root. Rhizobium free plants were grown hydroponically in the greenhouse with NO3- as a sole N source. In one study using 5-week-old plants, NO3-—N in the sap was found to vary with cultivar, with NO3- accounting for 42 to 79% of the sap N. Presumably a high proportion of NO3- in the sap indicates a high reduction of NO3- in the shoot. In another study, weekly sap analysis with ‘Tracy’ showed that shoot reduction of the N in the xylem sap dominated in young plants ( 4 to 6 weeks of age), but root reduction dominated in older plants (7 to 14 weeks). A different pattern was seen with ‘Swift’ in which root and shoot NO3-reduction were about equal in younger plants (4 to 6 weeks), but root reduction dominated in older plants (7 to 13 weeks). A comparison of nitrate reductase enzyme activities in older plants (7 to 13 weeks) showed Swift to have a large amount of activity in the shoot and Tracy to have a large amount in roots. These studies suggested that soybean cultivars differ in the location of nitrate reduction.

Key Words: Glycine max L. Merr. • Photosynthesis • Nitrogen fixation • Xylem sap

1 Contribution of USDA-SEA-AR, in cooperation with Colorado State Univ. Exp. Stn., Scientific J. Ser. No. 2657.

2 Research microbiologist, biological laboratory technician, and supervisory soil scientists, USDA-SEA-AR, P.O. Box E, Fort Collins, CO 80522.

Received for publication July 17, 1981.




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