Alterations in nitrogen assimilation and partitioning in nitrogen stressed plants |
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Authors: | Thomas W Rufty Jr Charles T MacKown Richard J Volk |
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Institution: | USDA-ARS, Dept of Crop Science, North Carolina-State Univ., Raleigh, NC27695-7620, USA;USDA-ARS, Dept of Agron., Univ. of Kentucky, Lexington, KY 40546-0091, USA;Dept of Soil Science, North Carolina State Univ., Raleigh, NC 27695, USA. |
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Abstract: | Although nutrient stress is known to alter partitioning between shoots and roots, the physiological basis for the phenomenon is unresolved. Experiments were conducted to examine assimilation of 15NO3 by N-stressed plants and to determine whether apparent changes in assimilation in the root contributed to alterations in whole-plant partitioning of reduced-N. Tobacco plants (Nicotiana tabacum L. cv. NC 2326) were exposed to a low concentration of NO3? in solution (80 μM) for 9 days to effect a N-stress response. Exposure of plants to 1000 μM15NO3? for 12 h on selected days revealed that roots of N-stressed plants developed an increased capacity to absorb NO3?, and accumulation of reduced-15N in the root increased to an even greater extent. When plants were exposed to 80 or 1000 μM15NO3? in steady-state, 15NO3? uptake over a 12 h period was noticeably restricted at the lower concentration, but a larger proportion of the absorbed 15N still accumulated as reduced-15N in the root. The alteration in reduced-15N partitioning was maintained in N-stressed plants during the subsequent 3-day “chase” period when formation of insoluble reduced-15N in the root was quantitatively related to the disappearance of 15NO3? and soluble reduced-15N. The results indicate that increased assimilation of absorbed NO3?, in the root may contribute significantly to the altered reduced-N partitioning which occurs in N-stressed plants. |
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Keywords: | 15N nitrate assimilation nitrogen cycling shoot to root ratio |
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