Reversal of glyphosate inhibition of Sandersonia aurantiaca flower senescence with aromatic amino acids

Glyphosate (N-(phosphonomethyl) glycine) is a broad spectrum post-emergence herbicide. This herbicide inhibits the shikimate pathway enzyme EPSP synth ase (5-enol pyruvylshikimate 3-phosphate synthase), thereby interfering wit h aromatic amino acid metabolism. During preliminary investigations with in hibitors of protein and amino acid biosynthesis, we noticed that vase solut ions containing glyphosate altered the normal pattern of Sandersonia aurant iaca flower senescence. Further studies showed that although glyphosate (2 mM) was toxic to all green tissue on the flower stem, the senescence of mat ure flowers (no green tissue) was delayed. Glyphosate-treated flowers did n ot fade but stayed a bright orange colour and the compressive strength of t he flowers was greater (the flowers were less wilted) than the control flow ers that were held in water. Treatment of flowers with vase solutions of ph enylalanine (2 mM) and tyrosine (2 mM) in the presence of glyphosate revers ed the beneficial effect that glyphosate treatment had on flower senescence . The data indicate that a lack of aromatic amino acids may be the cause of delayed fading and wilting of glyphosate-treated sandersonia flowers. (C) 2000 Elsevier Science B.V. All rights reserved.