Direct acquisition of organic N by white clover even in the presence of inorganic N

Aim

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.

Methods

Clover was grown at two asparagine concentrations (10 μM and 1 mM) supplied in both the absence and presence of ammonium nitrate. Using dual-labeled ¹³C¹⁵N-asparagine, the uptake rate was analyzed via bulk ¹⁵N and ¹³C excess and the detection of intact ¹³C¹⁵N-asparagine in white clover.

Results

The results from the two methods indicated greater utilization of ¹³C¹⁵N-asparagine in the 10 μM treatment than in the 1 mM treatment. The ¹³C¹⁵N-asparagine uptake rate was higher when ¹³C¹⁵N-asparagine was provided alone than when it was supplemented with inorganic nitrogen. Up to nine times lower uptake rates were obtained when intact ¹³C¹⁵N-asparagine was measured than when bulk ¹⁵N and ¹³C excess were analyzed. The labeled amino acids that are closely related to ¹³C¹⁵N-asparagine metabolism (aspartic acid, glutamic acid and glutamine) were detected in clover roots and shoots.

Conclusions

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.