Effects of canopy defoliation in the dark on the activity of sucrose phosphate synthase

The use of elasticity coefficients and flux-control coefficients in a quantitative treatment of control is discussed, with photosynthetic sucrose synthesis as an example. Experimental values for elasticities for the cytosolic fructose 1,6-bisphosphatase and sucrose phosphate synthase are derived from their in vitro properties, and from an analysis of the in vivo relation between fluxes and metabolite levels. An empirical factor α , describing the response of the fructose 2,6-bisphosphate regulator cycle to fructose 6-phosphate is described, and an expression is derived relating α to the elasticities of the enzymes involved in this regulator cycle. The in vivo values for elasticities and α are then used in a modified form of the connectivity theorem to estimate the flux control coefficients of the cytosolic fructose 1,6-bisphosphatase and sucrose phosphate synthase during rapid photosynthetic sucrose synthesis.

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Effect of Photoperiod on Photosynthate Partitioning and Diurnal Rhythms in Sucrose Phosphate Synthase Activity in Leaves of Soybean (Glycine max L. [Merr.]) and Tobacco (Nicotiana tabacum L.)

PLANT PHYSIOLOGY ◽

10.1104/pp.75.4.1080 ◽

1984 ◽

Vol 75 (4) ◽

pp. 1080-1084 ◽

Cited By ~ 30

Author(s):

Steven C. Huber ◽

Thomas W. Rufty ◽

Phillip S. Kerr

Keyword(s):

Glycine Max ◽

Nicotiana Tabacum ◽

Sucrose Phosphate Synthase ◽

Diurnal Rhythms ◽

Photosynthate Partitioning ◽

Nicotiana Tabacum L ◽

Glycine Max L ◽

Sucrose Phosphate ◽

Phosphate Synthase

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Site-specific serine phosphorylation of spinach leaf sucrose-phosphate synthase

Biochemical Journal ◽

10.1042/bj2830877 ◽

1992 ◽

Vol 283 (3) ◽

pp. 877-882 ◽

Cited By ~ 38

Author(s):

J L A Huber ◽

S C Huber

Keyword(s):

Okadaic Acid ◽

Spinacia Oleracea ◽

Sucrose Phosphate Synthase ◽

Serine Phosphorylation ◽

Spinacia Oleracea L ◽

Spinach Leaf ◽

Sucrose Phosphate ◽

Phosphate Synthase

We recently reported [Huber, Huber & Nielsen (1989) Arch. Biochem. Biophys. 270, 681-690] that spinach (Spinacia oleracea L.) sucrose-phosphate synthase (SPS; EC 2.4.1.14) was phosphorylated in vivo when leaves were fed [32P]Pi. In vitro the enzyme was phosphorylated and inactivated by using [gamma-32P]ATP. We now report that SPS is phosphorylated both in vivo and in vitro on serine residues. The protein is phosphorylated at multiple sites both in vivo and in vitro as indicated by two-dimensional peptide maps of the immunopurified SPS protein. After being fed with radiolabel, leaves were illuminated or given mannose (which activates the enzyme), in the presence or absence of okadaic acid. Feeding okadaic acid to leaves decreased the SPS activation state in the dark and light and in leaves fed mannose. Across all the treatments, the activation state of SPS in situ was inversely related to the labelling of two phosphopeptides (designated phosphopeptides 5 and 7). These two phosphopeptides are phosphorylated when SPS is inactivated in vitro with [gamma-32P]ATP, and thus are designated as regulatory (inhibitory) sites [Huber & Huber (1991) Biochim. Biophys. Acta 1091, 393-400]. Okadaic acid increased the total 32P-labelling of SPS and in particular increased labelling of the two regulatory sites, which explains the decline in activation state. In the presence of okadaic acid, two cryptic phosphorylation sites became labelled in vivo that were not apparent in the absence of the inhibitor. Overall, the results suggest that light/dark regulation of SPS activity occurs as a result of regulatory serine phosphorylation. Multiple sites are phosphorylated in vivo, but two sites in particular appear to regulate activity and dephosphorylation of these sites in vivo is sensitive to okadaic acid.

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Carbohydrate Storage and Mobilisation by the Culm of Wheat Between Heading and Grain Maturity: the Relation to Sucrose Synthase and Sucrose-Phosphate Synthase

Functional Plant Biology ◽

10.1071/pp9940255 ◽

1994 ◽

Vol 21 (3) ◽

pp. 255 ◽

Cited By ~ 66

Author(s):

IF Wardlaw ◽

J Willenbrink

Keyword(s):

Sucrose Synthase ◽

Flag Leaf ◽

Sucrose Phosphate Synthase ◽

Leaf Sheath ◽

Water Soluble ◽

Soluble Carbohydrates ◽

Carbohydrate Storage ◽

Stem Reserves ◽

Sucrose Phosphate ◽

Phosphate Synthase

Wheat plants grown under non-stress conditions at a dayhight temperature of 18/13�C under glasshouse conditions from head emergence to maturity showed a maximum accumulation of water-soluble, non-structural carbohydrates 20-25 days after anthesis. This storage was largely as fructans with the timing and amount of storage and mobilisation varying between cultivars, although the maximum concentration (fructose equivalents per unit stem fresh weight) was similar in all cultivars. The main storage in the culm was located in the lower part of the peduncle enclosed by the flag leaf sheath, in the penultimate internode and for one cultivar also in the flag leaf sheath. 14CO2 pulse-chase studies showed that there was a considerable delay in the incorporation of flag leaf assimilates into stem fructans, a delay probably associated with transfer and metabolic processes in the stem itself. At anthesis, when soluble carbohydrates were rapidly accumulating in the culm, the level of activity of sucrose synthase (SS) in the penultimate internode was much greater than that of sucrose phosphate synthase (SPS). The activity of SS declined rapidly as active storage ceased. This pattern was the reverse of that found in the leaf where SPS, rather than SS, was initially high and declined towards maturity. These changes are discussed in relation to the possible role of sucrose synthesising enzymes, particularly SS, in the accumulation and mobilisation of stem reserves in wheat.

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