Direct acquisition of organic N by white clover even in the presence of inorganic N
PLANT AND SOIL 2016, 407 (1-2):91-107
Czaban W, Jamtgard S, Nasholm T, Rasmussen J, Nicolaisen M, Fomsgaard IS

Abstract
This study was conducted to answer the question of whether clover can absorb asparagine in the presence and absence of inorganic nitrogen, as well as to determine the resulting concentration of post-uptake compounds closely involved in asparagine metabolism.

Clover was grown at two asparagine concentrations (10 mu M and 1 mM) supplied in both the absence and presence of ammonium nitrate. Using dual-labeled (CN)-C-13-N-15-asparagine, the uptake rate was analyzed via bulk N-15 and C-13 excess and the detection of intact (CN)-C-13-N-15-asparagine in white clover.

The results from the two methods indicated greater utilization of (CN)-C-13-N-15-asparagine in the 10 mu M treatment than in the 1 mM treatment. The (CN)-C-13-N-15-asparagine uptake rate was higher when (CN)-C-13-N-15-asparagine was provided alone than when it was supplemented with inorganic nitrogen. Up to nine times lower uptake rates were obtained when intact (CN)-C-13-N-15-asparagine was measured than when bulk N-15 and C-13 excess were analyzed. The labeled amino acids that are closely related to (CN)-C-13-N-15-asparagine metabolism (aspartic acid, glutamic acid and glutamine) were detected in clover roots and shoots.

Using two different methods, white clover's potential to absorb intact asparagine, even in the presence of inorganic nitrogen, was confirmed. The dual-methodology approach employed in this study demonstrates how the post-uptake metabolism can affect quantification of amino acid uptake.

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