Amino Acid Content of Leaves in Mycorrhizal and Non-mycorrhizal Citrus Rootstocks

Nitrogen status was examined in leaves of sour orange and roughlemon citrus rootstocks grown in a low phosphorus sand inoculatedwith Glomus etunicatus, in sand amended with superphosphateat a rate of 2240 kg ha^–1, and in a sand control leftuntreated. Sour orange was 3.1- and 3.5-fold taller and roughlemon was 1.8- and 2.0-fold taller than the controls in theinoculated and phosphorus treatments, respectively. In the controls,leaf N was up to 2.5-fold higher than in the other treatments.Both total and free amino acids accumulated in leaves of bothrootstocks to higher levels in the control than in the othertreatments. Most total amino acids in the control were lowerthan in the treatments, with the exceptions of arginine (upto 12-fold increase), proline (up to 1.8-fold increase), lysine,and free ammonia. Twenty-two free amino acids, urea, and ammoniawere detected. Both rootstocks grown in control sand had significantincreases in citrulline, ornithine, lysine, histidine, arginineand ammonia. Levels of total and most free amino acids in theinoculated and phosphorus treatments were similar to one another.It is suggested that mineral deficiency caused by the absenceof G. etunicatus causes a reorganization of N-metabolism witha shift to a greater synthesis of ornithine cycle intermediates. Citrus aurantium L., Citrus limon (L.) Burm, amino acid content, citrus rootstocks, mycorrhiza, nitrogen metabolism