Rapid, Reversible Inhibition of Nitrate Influx in Barley by Ammonium
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The rate of influx of nitrate into the roots of intact barley plants was measured over a period of 3–5 min from external nitrate concentrations of 1–150 mmol m−3, using 13N-labelled nitrate as tracer. Ammonium at external concentrations of 0.005–50 mol m−3 inhibited nitrate influx in a manner which did not conform to a simple kinetic model but increased approximately as the logarithm of the ammonium concentration. At any particular ammonium concentration, inhibition of nitrate influx reached its full extent within 3 min of the ammonium being supplied and was not made more severe by up to 17 min pre-treatment with ammonium. On removing the external ammonium, nitrate influx returned to its original rate within about 3 min. Potassium at 0.005–50 mol m−3 did not reproduce the rapid effect of ammonium on nitrate influx. Net uptake of nitrate also decreased when ammonium was supplied, over a similar timescale and to a similar extent as nitrate influx. The decrease in nitrate influx caused by ammonium was sufficient to account for the observed reduction in net uptake, without necessitating any acceleration of nitrate efflux.Keywords:
Ammonium nitrate
A flowing nutrient culture system permitted relatively rapid determination of the steady-state net nitrogen influx by an intact barley (Hardeum vulgare L. cv Kombar and Olli) plant. Ion-selective electrodes monitored the depletion of ammonium and nitrate from a nutrient solution after a single pass through a root cuvette. Influx at concentrations as low as 4 micromolar was measured. Standard errors for a sample size of three plants were typically less than 10% of the mean.When grown under identical conditions, a variety of barley bred for cold soils had higher nitrogen influx rates at low concentrations and low temperatures than one bred for warm soils, whereas the one bred for warm soils had higher influx rates at high concentrations and high temperatures. Ammonium was more readily absorbed than nitrate by both varieties at all concentrations and temperatures tested. Ammonium and nitrate influx in both varieties were equally inhibited by low temperatures.
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Active extracts of nitrate reductase were prepared from the roots of apple seedlings c.v. Granny Smith which were grown in nutrient solution under controlled enviromental conditions. The nutrient solutions contained various ratios of nitrate and ammonium ions but all the treatments contained a total of 112 ppm nitrogen. Maximum nitrate reductase activity in the roots was obtained when plants were supplied with nitrate as the sole source of nitrogen. Roots grown in solution containing only ammonium nitrogen had little or no activity. When plants were supplied with both forms of nitrogen in the nutrient solution, the presence of ammonium ions markedly lowered the activity of nitrate reductase in the roots. Plants supplied with 98 ppm nitrate nitrogen plus 14 ppm ammonium nitrogen had activities only half those of plants grown in nitrate alone. Plants supplied with equal amounts of ammonium and nitrate nitrogen had activities less than one sixth those of plants grown in nitrate alone.
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The solution culture experiment was conducted in order to investigate the relatively uptake capacity of lettuce,rape,soybean and wheat to nitrate and ammonium,as well as the influence of 3 different nitrogen sources on growth and development of these four crops.The obtained results showed that:(1) When the distilled water was supplied as the growth medium in the nutrient solution,different nitrogen sources greatly affected on the growth and development of lettuce,rape,soybean and wheat.When nitrate was solely supplied,all of these crops growed very well;when the same amount of nitrate and ammonium was supplied as nitrogen source,to some extent the growth amount of lettuce decreased;While ammonium was solely supplied,the growth amounts of these crops decreased greatly except rape,lettuce and soybean were very sensitive to NH + 4-N,and withering took place at late growing stage.(2) During the water culture,the total nitrogen uptake amount of the tested crops had close relation to the nitrogen source.To lettuce,the nitrogen uptake amount as nitrate supplied was significantly higher than that when the same amount of nitrate and ammonium was supplied,if comparing the same amount of NO - 3+NH + 4 treatment with solely supplying nitrate nitrogen treatment,and the nitrogen uptake amounts of lettuce and wheat were almost same;While supplying the same amount of NO - 3+NH + 4,the nitrogen uptake amount of soybean and rape was the largest,when solely supplying nitrate it greatly decreased.When ammounium was supplied,except rape the nitrogen uptake amount of other crops was the lowerest.(3) The tested crops had apparent preference on the uptake of nitrate and ammonium.When the same amount of ammonium and nitrate was supplied,the uptaked nitrate by rape and wheat was larger than ammonium,but the lettuce was vice verse,and the absorped nitroten of two forms by soybean were almost the same.The preference had characteristics of stage,generally speaking,the crop which prefer to nitrate maybe show property of favours ammonium.
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Abstract No yield differences in tops or roots were measured between ammonium and nitrate nitrogen sources in flow ‘United 108’ grown for 14 or 28 days in constant flow culture solution. There was a greater uptake of N from the nitrate source but approximately 25% of the total uptake remained as nitrate within the plant. Higher plant levels of phosphorus and sulphur were measured in the ammonium treatment and higher Ca ++ and Mg ++ in the nitrate treatment indicating a predominately cation‐anion balance effect.
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Abstract Soybean plants (Glycine max, cv. Akisengoku) were water-grown in a greenhouse with a low concentration of nitrate in the culture solution. Under these conditions root nodulation mostly on primary roots was profuse. At the vegetative and pod-filling stages, plants were fed 15N-labeled dinitrogen, nitrate, or ammonium for 7 to 8 hr in the daytime. Partitioning of the 15N from the three nitrogen sources showed distinct characteristics. The nitrogen (N) from dinitrogen preferentially distributed to the developing organs, young leaves, and developing pods, in comparison with N from nitrate. N from ammonium showed distribution pattern similar to that of N from dinitrogen. The nodule N was supplied by both directly fixed-N and transferred nitrogen, and fixedN was inferred to play a major role in this process. The pro tein N in the roots could be furnished by the recycled N of dinitrogen and nitrate through the shoots along with direct incorporation of amino acids produced in the roots from nitrate
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Abstract A portion of the binary phase diagram for the system ammonium nitrate‐potassium nitrate has been determined from − 55 °C to 185 °C. Results are presented for the ammonium‐nitrate‐rich end of the system up to 30 wt% potassium nitrate.
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Abstract Apple seedlings, Pyrus malus L., were grown in complete nutrient solutions containing nitrate, ammonium, or ammonium plus nitrate as the nitrogen source. Uptake of nitrogen was calculated from depletion measurements of the nutrient solutions and by using 15 N labelled nitrate and ammonium salts. If the plants received nitrogen as ammonium only or as nitrate only, the amounts of nitrogen taken up were similar. However, if the seedlings were supplied with ammonium nitrate, the amount of nitrate‐nitrogen assimilated was only half that of ammonium. Nevertheless, if ammonium and nitrate were supplied to a plant with a split‐root system, with each root half receiving a different ion, the uptakes were similar. The possibility of independent inhibition by ammonium of both nitrate uptake and reduction in the roots is discussed.
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Abstract Literature review indicates that higher crop yields may be obtained with a mixture of nitrate and ammonium than with either source alone. An adequate supply of potassium enhances ammonium utilization and thus improves yields, when a mixed ammonium‐nitrate nitrogen nutrition is applied. Nitrate reduction in plant tissues consumes either chemical energy and organic acids, or competes for products of photolysis. When ammonium is applied to the roots, high concentrations of it may accumulate having a strong toxic effect. Potassium activates plant enzymes functioning in ammonium assimilation and transport of amino acids. A summary of the experiments performed by the authors indicates that a mixed ammonium, nitrate and potassium nutrition affects especially N uptake and thus production of organic nitrogen compounds.
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