Biochemical basis for effects of K-deficiency on assimilate export rate and accumulation of soluble sugars in soybean leaves

TY - JOUR

T1 - Biochemical basis for effects of K-deficiency on assimilate export rate and accumulation of soluble sugars in soybean leaves

AU - Huber, Steven C.

PY - 1984/1/1

Y1 - 1984/1/1

N2 - 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. The different parameters were monitored in mature leaves that had expanded prior to, or during, imposition of a complete K-deficiency (plants received K-free nutrition solution). In general, 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. Stomatal conductance also declined, but this was not the primary cause of the decrease in carbon fixation because internal CO2 concentration was unaffected by 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. Over all the data, 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.

AB - 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. The different parameters were monitored in mature leaves that had expanded prior to, or during, imposition of a complete K-deficiency (plants received K-free nutrition solution). In general, 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. Stomatal conductance also declined, but this was not the primary cause of the decrease in carbon fixation because internal CO2 concentration was unaffected by 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. Over all the data, 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.

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U2 - 10.1104/pp.76.2.424

DO - 10.1104/pp.76.2.424

M3 - Article

AN - SCOPUS:0000643767

VL - 76

SP - 424

EP - 430

JO - Plant Physiology

JF - Plant Physiology

SN - 0032-0889

IS - 2

ER -