Translocation of N to and from barley roots: its dependence on local nitrate supply in split-root culture |
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Authors: | David Agrell Petter Oscarson Carl-Magnus Larsson |
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Affiliation: | D. Agrell (corresponding author), Dept of Botany, Stockholm Univ., S-106 91 Stockholm. Sweden;P. Oscarson, Dept of Crap Genetics and Breeding, The Swedish Univ. of Agricultural Sciences, S-268 00 Svalöv, Sweden;C.-M. Larsson. The Swedish Radiation Protection Institute, S-171 16 Stockholm, Sweden. |
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Abstract: | The relationship between availability of external nitrate and N translocation between root and shoot was studied in N-limited barley ( Hordeum vulgare L. cv. Golf). Nitrate-N was added at a relative rate (i.e. N added per unit time and unit N in plant biomass) of (1.09 da-1, and distributed between the subroots at ratios of 50:50 or 80:20. The plants were grown for 13 days under these conditions of nitrate nutrition, and for another three days with the nitrate distribution reversed from 80:20 to 20:80. The nitrale-N doses thus experienced by individual subroots ranged from 2 to 11 mg N g-1 root dry weight day-1 . 15N-Nitrate labellings were performed after 2 to 3 and 12 to 13 days of nitrate nutrition. and 2 to 3 days after reversal of nitrate additions. For all treatments, between 60 and 82% of the absorbed label initially left the root, and between 25 and 55% of the label recovered in roots had been supplied (cycled) via the shoot. Labelling of xylem N at the end of the 24-h labelling period ranged from to 36 to 46% indicating that a substantial fraction of the N in the xylem had been absorbed by the plant prior to labelling. It is concluded that cycling of N to roots, and cycling of N in the plant as a whole, is substantial also during N-limited growth. N allocation to roots increased with external nitrate dose. An increased utilization of non-translocated N as well as an increased translocation of N from the shoot contributed to this effect. Thus, the results indicate that increased external availability of N also increased the sink strength of the root for cycling N. |
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Keywords: | Barley Hordeum vulgare nitrate nitrogen root translocation |
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