Uptake of glycine by non-mycorrhizal Lolium perenne

Abstract

Plants of Lolium perenne were grown in sterile solution culture. 15N-labelled glycine (Gly) coupled with gas chromatograph mass spectrometry was used to prove that non-mycorrhizal plants of L. perenne are capable of acquiring N in the form of intact Gly. It was estimated that a minimum of 80% of Gly-N uptake, over a 3 h period, was as intact Gly, though possible processes resulting in deviation from this estimate are discussed. The relative incorporation of 15N derived from Gly uptake into serine (Ser) compared with other amino acids in the root amino acid pool suggested the enzyme serine:glyoxylate aminotransferase was at least partly responsible for the synthesis of Ser from Gly. Defoliation was shown to reduce Gly uptake by L. perenne. The addition of either 25 mol x m(-3) sucrose or 50 mol x m(-3) glucose to the uptake solution of defoliated plants increased Gly-N uptake compared with both defoliated plants without sugars and with undefoliated plants. Addition of a glucose analogue, 3-O-methyl-D-glucopyranose, that is absorbed but not metabolized by plants, did not affect Gly uptake by defoliated plants. Increasing pH from 3.5 to 9.2 caused a reduction in Gly uptake. Results of the effects of defoliation and pH are consistent with Gly uptake by L. perenne being by an energy-dependent proton symport. When either or Gly were supplied to plants at equimolar concentrations, uptake was five times greater than that of Gly at pH 6 and 13 times greater at pH 9.