Foliar nutrition and growth in red pine: the fate of photoassimilated carbon in a seedling tree

Abstract

A 2- to 3-year-old red pine seedling was allowed to assimilate 14CO2 for 3 hours at 2000 ft-c and left under the same illumination for 6 days, then divided into segments and analyzed. Ethanol extracts were resolved by chromatography, insoluble residues by chemical methods. The radioactivity in various components was determined for all segments. Autoradiographs were made from stem sections at four levels.Radioactivity was found in all parts of the plant. Per unit mass of tissue, it was more or less uniformly apportioned among root, stem, and leaves, but the expanding terminal bud contained 5 times as much activity per gram of tissue. Overall, about one-third of the radioactivity was in insoluble compounds, mainly in cell wall constituents. In localities where conspicuous growth had occurred the proportion was higher. Autoradiographs of stem sections showed that 14C was concentrated in newly differentiated tracheids, and was still being incorporated after 6 days. About one-third of the activity in the ethanol extract was chloroform soluble, two-thirds water soluble. In the latter fraction, activity was largely in sugars and organic acids, little in amino acids. Activity in sugars, per unit weight of tissue, was more or less uniform throughout the plant, but activity in organic acids varied greatly. It was lowest in the stem, highest in the bud, where organic acids, almost exclusively quinic and shikimic, carried 75% of the label in the ethanol and water-soluble fraction, and 23% of all the activity in the bud.