Arginine and the shade tolerance of white spruce saplings entering winter dormancy

Abstract

Shade-tolerant white spruce saplings grown at 100, 45, 25, and 13% natural light for four years, and entering winter dormancy, modified their growth habit and redistributed the total soluble N among needles, roots, and stems with buds mainly to arginine N. Most free amino acid N was found in roots in saplings at full light, and the least at 13% light. Glutamate, glutamine, and aspartate N contributed to the accumulation of soluble arginine N. Arginine-derived γ-guanidinobutyric acid, agmatine and an unidentified guanidino compound accumulated mainly in stems with buds at 25 and 13% light. The profiling N metabolism and arginine-derived guanidino compounds extend models for shade tolerance based mainly on photosynthesis, respiration and carbon gain.