Metabolic Pathway of alpha-Ketoglutarate in Citrus Leaves as Affected by Phosphorus Nutrition

The uptake and metabolism of alpha-[5-(14)C]ketoglutarate by phosphorus-deficient and full nutrient (control) lemon (Citrus limon) leaves were studied over various time intervals. After 45 minutes in P-deficient leaves, the bulk of incorporated (14)C appeared in organic acids and much less in amino acids, while in the control leaves, the (14)C contents of organic and amino acids were equal. In P-deficient leaves, after longer incubation times the (14)C content of organic acids and amino acids increased, while that of CO(2) and residue fractions remained low. In full nutrient leaves the (14)C content of amino acids and organic acids decreased after longer incubation time and increased in the insoluble residue and CO(2). In full nutrient leaves the organic and amino acid metabolism were closely related and accompanied by protein synthesis and CO(2) release, while in P-deficient leaves an accelerating accumulation of arginine and citric acid was linked together with inhibition of protein synthesis and CO(2) liberation.