Abstract
The relative effects of ammonium on nitrate uptake and partitioning during induction were compared among decapitated seedlings of three corn (Zea mays L.) genotypes at two developmental stages. This study tested the hypothesis that root systems efficient at translocating products of ammonium assimilation away from sites of nitrate uptake or reduction would exhibit less inhibition of nitrate uptake by ammonium compared to root systems with inefficient N translocation efficiency. Inhibition of nitrate uptake by ammonium was relatively slight at day 5 ranging from 0% to 20% among the three genotypes, as compared to greater inhibition, from 20% to 37%, at day 8. Five-day-old roots exhibited negligible xylem translocation capacity in comparison with those grown for 8 days. Thus, although the capability to translocate ammonium assimilates out of the root increased between days 5 and 8, inhibitory effects of ammonium also increased. In the absence of ammonium, nitrate uptake per unit root mass increased between days 5 and 8. This increased activity of the uptake system was proportionally more sensitive to ammonium.
Partitioning of entering nitrate into the reduction process was positively correlated with lateral root development of the inbred root systems at 5 and 8 days. This is supportive of a localization of a major portion of nitrate reduction occurring in root apical regions. Nitrate reduction was the partitioning process most severely inhibited by ammonium in all cases, ranging from 39% to 55% inhibition. In contrast, ammonium-inhibition of nitrate accumulation in the root tissue and translocation via xylem vessels varied with genotype and root age.
Two mechanisms of ammonium-inhibition of nitrate are implicated, one which directly affects nitrate reduction and the uptake system associated with it, and another which may involve potassium as an intermediate regulator of nitrate accumulation in the root tissue and nitrate translocation out of the root tissue.
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Selected References
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- Butz R. G., Long R. C. l-Malate as an Essential Component of the Xylem Fluid of Corn Seedling Roots. Plant Physiol. 1979 Nov;64(5):684–689. doi: 10.1104/pp.64.5.684. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Deane-Drummond C. E., Glass A. D. Short Term Studies of Nitrate Uptake into Barley Plants Using Ion-Specific Electrodes and ClO(3): II. Regulation of NO(3) Efflux by NH(4). Plant Physiol. 1983 Sep;73(1):105–110. doi: 10.1104/pp.73.1.105. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Ezeta F. N., Jackson W. A. Nitrate translocation by detopped corn seedlings. Plant Physiol. 1975 Jul;56(1):148–156. doi: 10.1104/pp.56.1.148. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Harvey P H. Hereditary Variation in Plant Nutrition. Genetics. 1939 Jun;24(4):437–461. doi: 10.1093/genetics/24.4.437. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Mackown C. T., Jackson W. A., Volk R. J. Restricted nitrate influx and reduction in corn seedlings exposed to ammonium. Plant Physiol. 1982 Feb;69(2):353–359. doi: 10.1104/pp.69.2.353. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Oaks A., Aslam M., Boesel I. Ammonium and amino acids as regulators of nitrate reductase in corn roots. Plant Physiol. 1977 Mar;59(3):391–394. doi: 10.1104/pp.59.3.391. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Pace G. M., Mackown C. T., Volk R. J. Minimizing Nitrate Reduction during Kjeldahl Digestion of Plant Tissue Extracts and Stem Exudates : APPLICATION TO N STUDIES. Plant Physiol. 1982 Jan;69(1):32–36. doi: 10.1104/pp.69.1.32. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Radin J. W. Differential regulation of nitrate reductase induction in roots and shoots of cotton plants. Plant Physiol. 1975 Feb;55(2):178–182. doi: 10.1104/pp.55.2.178. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Volk R. J., Pearson C. J., Jackson W. A. Reduction of plant tissue nitrate to nitric oxide for mass spectrometric 15N analysis. Anal Biochem. 1979 Aug;97(1):131–135. doi: 10.1016/0003-2697(79)90336-1. [DOI] [PubMed] [Google Scholar]