VezinaLavoieJoyEtAl1993

Reference

Vezina, L.P., Lavoie, N., Joy, K.W., Margolis, H.A. (1993) The fate of newly absorbed ammonium and nitrate ions in roots of jack pine-seedlings. Journal of Plant Physiology, 141(1):61-67.

Abstract

To examine the metabolic basis of the inability of boreal conifers to use nitrate efficiently, the assimilation and partitioning of N-15 from (NO3-)-N-15 and (NH4+)-N-15 was investigated in young jack pine seedlings (Pinus banksiana Lamb.) grown with either ammonium or nitrate nitrogen. N-15 partitioning was also followed after exposure to enzymatic inhibitors for GS, GOGAT and aminotransferases. The accumulation patterns of N-15 in roots indicated that newly absorbed ammonium ions were assimilated by the action of GS, and that GDH played only a very minor role. Results also demonstrated that ammonium incorporated into glutamine by GS was subsequently transferred to glutamate by the activity of GOGAT. When GOGAT was inhibited, glutamine formation by GS also decreased and N-15 accumulated in ammonium. Rapid accumulation of N-15 in asparagine suggested that AS may play a role in the assimilation of free ammonium via glutamine. Rates of label incorporation were lower in nitrate-fed plants, and the inhibitors further reduced the amount of N-15 in roots relative to the controls. The assimilation kinetics of N-15 from (NO3-)-N-15 showed that at least part of the incorporated N-15 flowed through the GS/GOGAT cycle, as in ammonium-fed plants. This indicated that nitrate reduction takes place in root cells of jack pine. However, the response of nitrate-fed plants to GS and GOGAT inhibitors is atypical of nitrophilous plants. Exposure of nitrate-fed plants to MSO and azaserine resulted in a decrease in overall recovery of label in Gln, Glu, Asp and Asn with no significant modification of the distribution pattern. These results suggest either that: (1) part of the incorporated (N-NO3)-N-15 was assimilated through an alternative route, (2) nitrate absorption or nitrate reduction were inhibited by GS or GOGAT inhibitors or (3) the GS inhibitor did not inhibit GS activity at the site where nitrate was reduced.

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@ARTICLE { VezinaLavoieJoyEtAl1993,
    AUTHOR = { Vezina, L.P. and Lavoie, N. and Joy, K.W. and Margolis, H.A. },
    TITLE = { The fate of newly absorbed ammonium and nitrate ions in roots of jack pine-seedlings },
    JOURNAL = { Journal of Plant Physiology },
    YEAR = { 1993 },
    VOLUME = { 141 },
    PAGES = { 61-67 },
    NUMBER = { 1 },
    NOTE = { Times Cited: 0 },
    ABSTRACT = { To examine the metabolic basis of the inability of boreal conifers to use nitrate efficiently, the assimilation and partitioning of N-15 from (NO3-)-N-15 and (NH4+)-N-15 was investigated in young jack pine seedlings (Pinus banksiana Lamb.) grown with either ammonium or nitrate nitrogen. N-15 partitioning was also followed after exposure to enzymatic inhibitors for GS, GOGAT and aminotransferases. The accumulation patterns of N-15 in roots indicated that newly absorbed ammonium ions were assimilated by the action of GS, and that GDH played only a very minor role. Results also demonstrated that ammonium incorporated into glutamine by GS was subsequently transferred to glutamate by the activity of GOGAT. When GOGAT was inhibited, glutamine formation by GS also decreased and N-15 accumulated in ammonium. Rapid accumulation of N-15 in asparagine suggested that AS may play a role in the assimilation of free ammonium via glutamine. Rates of label incorporation were lower in nitrate-fed plants, and the inhibitors further reduced the amount of N-15 in roots relative to the controls. The assimilation kinetics of N-15 from (NO3-)-N-15 showed that at least part of the incorporated N-15 flowed through the GS/GOGAT cycle, as in ammonium-fed plants. This indicated that nitrate reduction takes place in root cells of jack pine. However, the response of nitrate-fed plants to GS and GOGAT inhibitors is atypical of nitrophilous plants. Exposure of nitrate-fed plants to MSO and azaserine resulted in a decrease in overall recovery of label in Gln, Glu, Asp and Asn with no significant modification of the distribution pattern. These results suggest either that: (1) part of the incorporated (N-NO3)-N-15 was assimilated through an alternative route, (2) nitrate absorption or nitrate reduction were inhibited by GS or GOGAT inhibitors or (3) the GS inhibitor did not inhibit GS activity at the site where nitrate was reduced. },
    KEYWORDS = { PINUS-BANKSIANA LAMB; NITRATE ASSIMILATION; AMMONIUM ASSIMILATION QUEBEC FOREST PLANTATIONS; WHEAT-STRAW MULCHES; GLUTAMINE-SYNTHETASE; AMINO-ACID; NITROGEN; ENZYMES; ASSIMILATION; METABOLISM; REDUCTASE; LOCATION },
    OWNER = { brugerolles },
    TIMESTAMP = { 2007.12.05 },
}

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