Ohlund J, Nasholm T
Regulation of organic and inorganic nitrogen uptake in Scots pine (Pinus sylvestris) seedlings
Tree Physiology: 2004 24:1397-1402
Plants possess regulatory mechanisms that enhance nitrogen (N) uptake under conditions of spatial and temporal variation in N availabilily. Study of regulatory mechanisms has focused almost exclusively on the uptake of inorganic N sources (i.e., ammonium (NH4+), nitrate (NO3-)). Several lines of evidence, however, suggest that amino acids may constitute a potential source of N for a number of plant species, including conifers. In the present study, we investigated the uptake of amino acids and inorganic N in Scots pine (Pinus sylvestris L.) seedlings grown at different N concentrations. We compared the uptake rate of the individual N sources using U-[C-13(2)], [N-15]-glycine, U-[C-13(6)], [N-15(4)]-arginine,(NH4)-N-15, or (NO3)-N-15, and tested the short-term effect of N supply on the uptake rate of glycine, arginine and NH4+ in field-grown Scots pine seedlings. Our data indicate that Scots pine seedlings can absorb substantial amounts of N in the form of intact arginine and glycine molecules. The data also suggest that Scots pine seedlings down-regulate their uptake of NH4+-N and arginine-N, but not of glycine-N in response to increased endogenous N concentrations.
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