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

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Abstract
Nitrogen status was examined in leaves of sour orange and rough lemon citrus rootstocks grown in a low phosphorus sand inoculated with Glomus etunicatus, in sand amended with superphosphate at a rate of 2240 kg ha−1, and in a sand control left untreated. Sour orange was 3.1- and 3.5-fold taller and rough lemon was 1.8- and 2.0-fold taller than the controls in the inoculated 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 both rootstocks to higher levels in the control than in the other treatments. Most total amino acids in the control were lower than in the treatments, with the exceptions of arginine (up to 12-fold increase), proline (up to 1.8-fold increase), lysine, and free ammonia. Twenty-two free amino acids, urea, and ammonia were detected. Both rootstocks grown in control sand had significant increases in citrulline, ornithine, lysine, histidine, arginine and ammonia. Levels of total and most free amino acids in the inoculated and phosphorus treatments were similar to one another. It is suggested that mineral deficiency caused by the absence of G. etunicatus causes a reorganization of N-metabolism with a shift to a greater synthesis of ornithine cycle intermediates.