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Deposition of ammonium and nitrate in the roots of maize seedlings supplied with different nitrogen salts.

Bloom AJ, Randall L, Taylor AR, Silk WK - J. Exp. Bot. (2012)

Bottom Line: In contrast, net root NO(3)(-) influx under NH(4)NO(3) was less than the local deposition rate in the growth zone, indicating that additional NO(3)(-) was imported or metabolically produced.The profile of NO(3)(-) deposition rate in the growth zone, however, was similar for the plants receiving Ca(NO(3))(2) or NH(4)NO(3).These results suggest that NO(3)(-) may serve a major role as an osmoticant for supporting root elongation in the basal part of the growth zone and maintaining root function in the young mature tissues.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant Sciences, University of California, Davis, CA 95616, USA. ajbloom@ucdavis.edu

ABSTRACT
This study measured total osmolarity and concentrations of NH(4)(+), NO(3)(-), K(+), soluble carbohydrates, and organic acids in maize seminal roots as a function of distance from the apex, and NH(4)(+) and NO(3)(-) in xylem sap for plants receiving NH(4)(+) or NO(3)(-) as a sole N-source, NH(4)(+) plus NO(3)(-), or no nitrogen at all. The disparity between net deposition rates and net exogenous influx of NH(4)(+) indicated that growing cells imported NH(4)(+) from more mature tissue, whereas more mature root tissues assimilated or translocated a portion of the NH(4)(+) absorbed. Net root NO(3)(-) influx under Ca(NO(3))(2) nutrition was adequate to account for pools found in the growth zone and provided twice as much as was deposited locally throughout the non-growing tissue. In contrast, net root NO(3)(-) influx under NH(4)NO(3) was less than the local deposition rate in the growth zone, indicating that additional NO(3)(-) was imported or metabolically produced. The profile of NO(3)(-) deposition rate in the growth zone, however, was similar for the plants receiving Ca(NO(3))(2) or NH(4)NO(3). These results suggest that NO(3)(-) may serve a major role as an osmoticant for supporting root elongation in the basal part of the growth zone and maintaining root function in the young mature tissues.

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Models of NO3– content (nmol mm−1) and relative element length as a function of the time (bottom axis) or distance (top axis) that a root tissue element is displaced from the base of the growth zone. (A) Model results of potential NO3– uptake assuming influx with no translocation or assimilation. This is a material specification in which a material (real) tissue element is followed through time and space. The case of influx restricted to the apical 3 mm is given by the dotted line, and the case of influx throughout the root is shown by the dashed line. The solid line shows the length of the tissue element during the time of its displacement through and beyond the growth zone. (B) Material specification in which the potential uptake and observed content of NO3– in a material (real) tissue element is followed through time and space.
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fig9: Models of NO3– content (nmol mm−1) and relative element length as a function of the time (bottom axis) or distance (top axis) that a root tissue element is displaced from the base of the growth zone. (A) Model results of potential NO3– uptake assuming influx with no translocation or assimilation. This is a material specification in which a material (real) tissue element is followed through time and space. The case of influx restricted to the apical 3 mm is given by the dotted line, and the case of influx throughout the root is shown by the dashed line. The solid line shows the length of the tissue element during the time of its displacement through and beyond the growth zone. (B) Material specification in which the potential uptake and observed content of NO3– in a material (real) tissue element is followed through time and space.

Mentions: During its development, an individual tissue element is displaced from the root meristem through and then beyond the growth zone. The position of the basal and apical ends of the segment can be tracked to find the location and length of the segment over time. The growth trajectory gives the time course of the element position (distance from the root apex) and can be calculated by integrating the displacement velocity over time (Silk and Erickson, 1979) or (if growth and cell division are steady) by counting the number of cells to the position of interest and multiplying by the ratio of mature cell length to root elongation rate (Silk et al., 1989). This paper is interested in calculating the total uptake of NO3– into the tissue element as it expands and moves farther from the apex. To model the ‘potential uptake’ of NO3– that results from influx, this study assumes no assimilation or translocation and then considers what the NO3– content would be in the moving tissue element. Before calculating the total uptake in the developing tissue element, two extreme cases are considered: (1) localized influx only in the apical 3 mm; and (2) uniform influx along the growth zone. In the first case, with influx occurring only near the apex (dotted line in Fig. 9A), then the NO3– content would first increase (where uptake is faster than growth-associated dilution) and then decrease (at 2–3 mm where growth is faster than influx). Where growth continues after influx ceases, then NO3– would decrease more rapidly with position. Where influx and growth have both stopped, NO3– would remain uniform (constant with position) in the absence of assimilation and translocation. Therefore, if influx is restricted to the apical 3 mm, the potential uptake into the older root segment would be quite small. In the second case, with influx occurring throughout the root, then the potential uptake would increase slowly as the element moves through the growth zone and more rapidly after growth has ceased in the tissue element (dashed line in Fig. 9A). NO3– is in fact taken up throughout the root (Taylor and Bloom, 1998). Fig. 9B shows that the total NO3– uptake slightly exceeds the observed content while the tissue element is moving through in the growth zone, and the total uptake vastly exceeds the content when the tissue element is in the 10–20 mm region.


Deposition of ammonium and nitrate in the roots of maize seedlings supplied with different nitrogen salts.

Bloom AJ, Randall L, Taylor AR, Silk WK - J. Exp. Bot. (2012)

Models of NO3– content (nmol mm−1) and relative element length as a function of the time (bottom axis) or distance (top axis) that a root tissue element is displaced from the base of the growth zone. (A) Model results of potential NO3– uptake assuming influx with no translocation or assimilation. This is a material specification in which a material (real) tissue element is followed through time and space. The case of influx restricted to the apical 3 mm is given by the dotted line, and the case of influx throughout the root is shown by the dashed line. The solid line shows the length of the tissue element during the time of its displacement through and beyond the growth zone. (B) Material specification in which the potential uptake and observed content of NO3– in a material (real) tissue element is followed through time and space.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC3295394&req=5

fig9: Models of NO3– content (nmol mm−1) and relative element length as a function of the time (bottom axis) or distance (top axis) that a root tissue element is displaced from the base of the growth zone. (A) Model results of potential NO3– uptake assuming influx with no translocation or assimilation. This is a material specification in which a material (real) tissue element is followed through time and space. The case of influx restricted to the apical 3 mm is given by the dotted line, and the case of influx throughout the root is shown by the dashed line. The solid line shows the length of the tissue element during the time of its displacement through and beyond the growth zone. (B) Material specification in which the potential uptake and observed content of NO3– in a material (real) tissue element is followed through time and space.
Mentions: During its development, an individual tissue element is displaced from the root meristem through and then beyond the growth zone. The position of the basal and apical ends of the segment can be tracked to find the location and length of the segment over time. The growth trajectory gives the time course of the element position (distance from the root apex) and can be calculated by integrating the displacement velocity over time (Silk and Erickson, 1979) or (if growth and cell division are steady) by counting the number of cells to the position of interest and multiplying by the ratio of mature cell length to root elongation rate (Silk et al., 1989). This paper is interested in calculating the total uptake of NO3– into the tissue element as it expands and moves farther from the apex. To model the ‘potential uptake’ of NO3– that results from influx, this study assumes no assimilation or translocation and then considers what the NO3– content would be in the moving tissue element. Before calculating the total uptake in the developing tissue element, two extreme cases are considered: (1) localized influx only in the apical 3 mm; and (2) uniform influx along the growth zone. In the first case, with influx occurring only near the apex (dotted line in Fig. 9A), then the NO3– content would first increase (where uptake is faster than growth-associated dilution) and then decrease (at 2–3 mm where growth is faster than influx). Where growth continues after influx ceases, then NO3– would decrease more rapidly with position. Where influx and growth have both stopped, NO3– would remain uniform (constant with position) in the absence of assimilation and translocation. Therefore, if influx is restricted to the apical 3 mm, the potential uptake into the older root segment would be quite small. In the second case, with influx occurring throughout the root, then the potential uptake would increase slowly as the element moves through the growth zone and more rapidly after growth has ceased in the tissue element (dashed line in Fig. 9A). NO3– is in fact taken up throughout the root (Taylor and Bloom, 1998). Fig. 9B shows that the total NO3– uptake slightly exceeds the observed content while the tissue element is moving through in the growth zone, and the total uptake vastly exceeds the content when the tissue element is in the 10–20 mm region.

Bottom Line: In contrast, net root NO(3)(-) influx under NH(4)NO(3) was less than the local deposition rate in the growth zone, indicating that additional NO(3)(-) was imported or metabolically produced.The profile of NO(3)(-) deposition rate in the growth zone, however, was similar for the plants receiving Ca(NO(3))(2) or NH(4)NO(3).These results suggest that NO(3)(-) may serve a major role as an osmoticant for supporting root elongation in the basal part of the growth zone and maintaining root function in the young mature tissues.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant Sciences, University of California, Davis, CA 95616, USA. ajbloom@ucdavis.edu

ABSTRACT
This study measured total osmolarity and concentrations of NH(4)(+), NO(3)(-), K(+), soluble carbohydrates, and organic acids in maize seminal roots as a function of distance from the apex, and NH(4)(+) and NO(3)(-) in xylem sap for plants receiving NH(4)(+) or NO(3)(-) as a sole N-source, NH(4)(+) plus NO(3)(-), or no nitrogen at all. The disparity between net deposition rates and net exogenous influx of NH(4)(+) indicated that growing cells imported NH(4)(+) from more mature tissue, whereas more mature root tissues assimilated or translocated a portion of the NH(4)(+) absorbed. Net root NO(3)(-) influx under Ca(NO(3))(2) nutrition was adequate to account for pools found in the growth zone and provided twice as much as was deposited locally throughout the non-growing tissue. In contrast, net root NO(3)(-) influx under NH(4)NO(3) was less than the local deposition rate in the growth zone, indicating that additional NO(3)(-) was imported or metabolically produced. The profile of NO(3)(-) deposition rate in the growth zone, however, was similar for the plants receiving Ca(NO(3))(2) or NH(4)NO(3). These results suggest that NO(3)(-) may serve a major role as an osmoticant for supporting root elongation in the basal part of the growth zone and maintaining root function in the young mature tissues.

Show MeSH