Synthesis sucrose

Sucrose synthesis in the cytosol and starch synthesis in the chloroplast are the major pathways by which the excess triose phosphate from photosynthesis is harvested. Sucrose synthesis (described below) releases four Pi molecules from the four triose phosphates required to make sucrose. For every molecule of triose phosphate removed from the chloroplast, one Pj is transported into the chloroplast, providing the ninth Pj mentioned above, to be used in regenerating ATP. If this exchange were blocked, triose phosphate synthesis would quickly deplete the available Pj in the chloroplast, slowing ATP synthesis and suppressing assimilation of C02 into starch. 

UDP-Glucose Is the Substrate for Sucrose Synthesis in the Cytosol of Leaf Cells... 

FIGURE 20-25 Sucrose synthesis. Sucrose is synthesized from UDP-glucose and fructose 6-phosphate, which are synthesized from triose phosphates in the plant cell cytosol by pathways shown in Figures 15-7 and 20-9. The sucrose 6-phosphate synthase of most plant species is allosterically regulated by glucose 6-phosphate and P,. 

The partitioning of triose phosphates between sucrose synthesis and starch synthesis is regulated by fructose 2,6-bisphosphate (F2,6BP), an allosteric effector of the enzymes that determine the level of fructose 6-phosphate. F2,6BP concentration varies inversely with the rate of photosynthesis, and F2,6BP inhibits the synthesis of fructose 6-phosphate, the precursor to sucrose. 

Regulation of Starch and Sucrose Synthesis Sucrose synthesis occurs in the cytosol and starch synthesis in the chloroplast stroma, yet the two processes are intricately balanced. What factors shift the reactions in favor of (a) starch synthesis and (b) sucrose synthesis ... 

Regulation of Sucrose Synthesis In the regulation of sucrose synthesis from the triose phosphates produced during photosynthesis, 3-phosphoglycerate and P, play critical roles (see Fig. 20-26). Explain why the concentrations of these two regulators reflect the rate of photosynthesis. 

The photosynthetic block precedes sucrose synthesis, and sucrose partially reverses the inhibition caused by the lack of fixation of carbon dioxide. D-Fructose disappears first, after treatment, followed by sucrose, and then u-glucose.188 It is likely that other metabolic systems are involved as well, since the amino acid distributions were not identical to the I4C02 dark-fixation products.189 Uptake of sucrose-14C increased some acids (as-... 

C. Chauvin, K. Baczko, and D. Plusquellec, New highly regioselective reactions of unprotected sucrose. Synthesis of 2-O-acylsucroses and 2-0-(A-alkylcarbamoyl)sucroses, J. Org. Chem., 58 (1993) 2291-2295. 

K. M. Taba, R. Koster, and W. V. Dahlhoff, Organoboron-disaccharides. 2. 2,6-Anhydro-/ -n-fructofuranosc by O-ethylboron-induced cleavage of sucrose, Synthesis, (1983) 1036-1037. 

D-fructose, reaction occurred in the same manner as with the sucrose synthesis and the resulting disaccharides, a-D-glucopyranosyl a-L-sorbo-furanoside89 and a-D-glucopyranosyl /3-D-xyloketofuranoside,40 were isolated. 

Indane-l,2-dioI, cis- and trans-, effect on conductivity of boric acid, IV, 192 Inhibition, of phosphorylation and sucrose synthesis by iodoacetate, V, 33 Inorganic compounds, biochemical reduction of, IV, 95... 

Iodoacetate, inhibitor of phosphorylation and sucrose synthesis, V, 33 Iodoform, III, 139 Iretol, III, 64... 

Noel, G.M. and Pontis, H.G., Involvement of sucrose synthase in sucrose synthesis during mobilization of fructans in dormant Jerusalem artichoke tubers, Plant Sci., 159, 191-195, 2000. 

During the day, the rates of starch and sucrose synthesis and the rate of photosynthetic carbon assimilation must be coordinated. There is a clear need to determine how much assimilated carbon can be diverted into sucrose and starch synthesis without decreasing too much the amount that returns to the RPPP. Conversely, when sucrose accumulates in the cytosol because the rate of export diminishes (and/or photosynthesis increases), starch begins to accumulate inside the chloroplast. During the night, the... 

Furbank, R. T., Stitt, M., and Foyer, C. H. 1985. Intercellular compartmentation of sucrose synthesis in leaves of Zea mays. Planta. 164,172-178. 

Robinson, S. P and Walker, D. A. 1979. The site of sucrose synthesis in isolated leaf protoplasts. FEBS Lett. 107, 295-299. 

Stitt, M., and Heldt, H. W. 1985. Control of photosynthetic sucrose synthesis by fructose-2,6 bisphosphate. Planta 164, 179-188. 

After glucose synthesis in photosynthesis, the disaccharide sucrose (a-D-Glc(l —> 2)(3-D-Fru) is used as a readily transportable sugar. Sucrose synthesis successively involves the following UDP-glucose + fructose-6-phosphate —> sucrose-6-phosphate + UDP [via sucrose phosphate synthase] sucrose-6-phosphate + H20 —> sucrose + P [via sucrose-6-phosphatase]. 

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