Journal
ENVIRONMENTAL AND EXPERIMENTAL BOTANY
Volume 74, Issue -, Pages 237-244Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.envexpbot.2011.06.005
Keywords
Hordeum vulgare; Soil fertilization; Nitrate reductase; Nitrite reductase; Asparagine
Categories
Funding
- DAAD (Deutscher Akademischer Austausch Dienst), Germany
- CNPq (National Council for Scientific and Technological Development), Brazil
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Combined nitrogen (N) and sulfur (S) fertilization positively influences yield and quality in cereal crops, and S additions can enhance N use efficiency. Previous studies showed that S deficiency leads to a particular strong decrease in nitrate reductase activity and in nitrate uptake relative to ammonium. We therefore tested the hypothesis whether N fertilization in the form of urea improves N utilization under S deficiency. When barley plants were grown on a S-deficient soil for seven weeks, N additions increased biomass and S concentrations in shoots of nitrate- and urea-supplied plants to the same extent. Under S deficiency nitrate-supplied plants accumulated more N in the form of nitrate and asparagine than urea-supplied plants. This supported the view that asparagine synthesis under S deficiency is induced under supply of nitrate but not or much less by urea. Hydroponically grown plants were then assayed for their nitrate and nitrite reductase activities in response to S supply. Nitrate reductase activity sharply decreased under limiting S supply, while nitrite reductase activity did not respond to S supply, indicating that nitrate reduction rather than nitrite reduction represents the S-limited assimilatory process. Thus, although nitrate reduction is particularly sensitive to S deficiency, urea supply did not improve growth and N efficiency under limited S availability but rather prevented an excess accumulation of asparagine. (C) 2011 Elsevier B.V. All rights reserved.
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