A ¹⁵N study of the effects of nitrate, ammonium and nitrate plus ammonium nutrition on nitrogen assimilation in Hordeum vulgare
Master Thesis
1985
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University of Cape Town
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Abstract
A review of the recent literature concerning the assimilation and utilisation of nitrate and ammonium nitrogen within plants has been presented. Barley plants (Hordeum vulgare L.cv. Clipper) were grown hydroponically under controlled environmental conditions. The aerated nutrient solutions contained 2mM inorganic ¹⁴N supplied as either nitrate alone, ammonium alone, a 1:1 nitrate plus ammonium mixture or a 3:1 nitrate plus ammonium mixture. After 20 days of growth ¹⁵N nutrient solutions were substituted. The plant material was harvested four and eight hours after the commencement of the ¹⁵N feeding experiment and prepared for analysis. Xylem sap was also collected for a period of one hour beginning half an hour before each harvest and continuing for half an hour after harvesting. Separate batches of plants were used for harvesting and sap collection. In nitrate-fed plants the shoot was shown to be the main organ of nitrate assimilation. Xylem sap analysis indicated that 66% of the ¹⁵N supply to the shoot was in the form of nitrate and the majority of the absorbed and assimilated ¹⁵N was located in this region. In ammonium-fed plants, however, ¹⁵N-ammonium accumulated in the root with only a very small amount detectable in the xylem sap. Some 93% of the ¹⁵N exported from root to shoot in the xylem stream was in the form of organic nitrogen (mainly glutamine). This indicated that the root was the major organ of ammonium assimilation and that the shoot was the main destination of root assimilated nitrogen.
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Bibliography: pages 98-112.
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Chadwick, S. 1985. A ¹⁵N study of the effects of nitrate, ammonium and nitrate plus ammonium nutrition on nitrogen assimilation in Hordeum vulgare. University of Cape Town.