Abstract:
Roots are considered to be the major production site of amino acids that appear in the xylem sap of conifers. The carbon skeleton of amino acids is derived from photosynthetically reduced carbon dioxide while the nitrogen is derived from the inorganic forms taken up by the roots. An experiment was conducted to determine the
extent of amino acid synthesis from the products of photosynthesis and root assimilated nitrogen. Douglas-fir seedlings were exposed to ¹⁴CO₂ in the atmosphere
and ¹⁵NO₃ in both a solution and a soil rooting medium during a 24-hour period; 12 hours of light followed by 12 hours of dark.
Amino acids were extracted from the xylem sap of both roots and stems. The N-TFAA n-butyl esters of the amino acids were
formed to allow the separation and quantification of individual amino acids by gas-liquid chromatography. A gas-liquid
chromatograph-ionization chamber system was designed to determine the ¹⁴C specific activity of individual amino acids eluting from a GLC column. The percent enrichment of ¹⁵N was determined with a mass spectrometer.
Of the xylem sap amino acids analyzed, ¹⁴C was found to be present in only one amino acid, believed to be proline. The only
significant ¹⁵N enrichment occurred in alanine. The majority of amino acids showed a diurnal fluctuation in their concentration
with a maximum that occurred at the end of the 12-hour light period and a low that occurred at the end of the following 12-hour
dark period.
