Carbohydrate content and related enzyme activities were determined in leaves of rough-lemon (Citrus volkameriana Ten. & 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. β-limit dextrin indicated that mainly 8-amylase was involved. Acid invertase activity increased 7-fold in K-deficient leaves, while alkaline invertase showed little change.
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