© 1993 Heron Publishing—Victoria, Canada
Free amino acids and protein in Scots pine seedlings cultivated at different nutrient availabilities
Kerstin Gezelius (1) and Torgny Näsholm (2)
1. Department of Plant Physiology, University of Umeå, S-901 87 Umeå, Sweden / 2. Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences S-901 83 Umeå, Sweden / Received July 13, 1992
Summary
Scots pine (Pinus sylvestris L.) seedlings of a provenance from northern Sweden were cultivated hydroponically for 7 weeks in a climate chamber. The nutrient
solution contained either 2.5 (low-N) or 50 (high-N) mg N l–1 with other essential elements added in a fixed optimal proportion to the nitrogen. After 5 and 7 weeks, the seedlings were
analyzed for growth, total nitrogen and other essential nutrients, protein and free amino acids.
Low-N seedlings grew more slowly and had higher root/shoot ratios than high-N seedlings. With respect to total nitrogen, the
effect of the lower nutrient supply was mainly on the nitrogen content of the whole plant and the allocation of nitrogen among
tissues, not on tissue nitrogen concentration. This was also the case for potassium, phosphorus, calcium and magnesium. The
proportions by weight among these macronutrients in the whole seedlings were similar in both nutrient regimes. The proportion
and concentration of sulfur were significantly lower in low-N seedlings than in high-N seedlings, because of a lower net uptake
of sulfur than of other macronutrients.
The shoot, needles and stem of low-N seedlings had higher concentrations of free amino acids and lower concentrations of protein
than the shoot, needles and stem of high-N seedlings. Arginine dominated the pool of free amino acids in the low-N seedlings,
whereas glutamine predominated in the high-N
seedlings. We conclude that Scots pine seedlings accumulated soluble nitrogen as arginine when net protein synthesis was limited
by factors other than nitrogen availability. Nutritional imbalance, as revealed by growth characteristics and a suboptimal
proportion and concentration of sulfur in the seedlings, probably affected synthesis of S-amino acids, resulting in the diversion
of assimilated nitrogen to arginine instead of protein.
Keywords:
arginine, glutamine, growth, macronutrients, micronutrients, nitrogen, nitrate, nutrient availability, Pinus sylvestris, sulfur.
