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Biochemical basis for effects of K-deficiency on assimilate export rate and accumulation of soluble sugars in soybean leaves
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The effects of K-deficiency on carbon exchange rates (CER), photosynthate partitioning, export rate and activities of key enzymes involved in sucrose metabolism were studied in soybean [Glycine max (L.) Merr.] leaves. Recently expanded leaves had the highest concentration of K, and imposition of K-stress at any stage of leaf expansion resulted in decreased K concentrations relative to control plants (10 millimolar K). A reduction in CER, relative to control plants, was only observed in leaves that expanded during the K-stress. Assimilate export rate from K-deficient leaves was reduced but relative export, calculated as a percentage of CER, was similar to control leaves. Export rate was correlated positively with both CER and activity of sucrose phosphate synthase in leaf extracts. K-deficient leaves had higher concentrations of sucrose and hexose sugars. Accumulation of hexose sugars was associated with increased activities of acid invertase. Neutral invertase activity was low and unaffected by K-nutrition. It is concluded that decreased rates of assimilate export are associated with decreased activities of sucrose phosphate synthase, a key enzyme involved in sucrose formation, and that accumulation of hexose sugars may occur because of increased hydrolysis of sucrose in K-deficient leaves. [AS/SS]
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 Record created 1985-05-31, last modified 2019-03-04

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