EFFECT OF POTASSIUM, MAGNESIUM, AND CALCIUM DEFICIENCIES ON CARBOHYDRATE POOLS AND METABOLISM IN CITRUS LEAVES

Carbohydrate content and related enzyme activities were determined in leaves of rough-lemon (Citrus volkameriana Ten. and Pasq) plants grown under K, Mg, and Ca deficiencies. Starch content was lower and soluble sugar significantly higher in K-deficient than in control leaves, Magnesium- and Ca-deficient leaves, on the other hand, accumulated large amounts of starch, Electron micrographs also showed a reduction in the number and size of starch grains in chloroplasts of K-deficient leaves, while those of Mg- and Ca-deficient leaves were filled with large starch grains. Total amylase activity increased 3- to 7-fold in K-deficient leaves, with maltose as the major product and small amounts of maltotriose. Electrophoretic separation of amylase isozymes on native gels containing starch or amylopectin showed higher band intensities in K-deficient leaves. Examination of the capacity of leaf extracts to use amylopectin vs. P-limit dextrin indicated that mainly B-amylase was involved, Acid invertase activity increased 7-fold in K-deficient leaves, while alkaline invertase showed little change.