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Antal Szőke, Erzsébet Kiss, László Heszky, Ildikó Kerepesi, and Ottó Toldi

In all eukaryotic cells, fructose 2,6-bisphosphate (fru 2,6P 2 ) is an important regulator of carbohydrate metabolism ( Okar and Lange, 1999 ). In plants, this molecule coordinates the rate of CO 2 assimilation and carbon partitioning between

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Zhimin Yang, Lixin Xu, Jingjin Yu, Michelle DaCosta, and Bingru Huang

). Responses of carbohydrate metabolism to drought stress vary with forms of carbohydrates, plant species, and stress duration or severity. Decline in sucrose and starch content with short-term drought stress and increases in sucrose and starch have been

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Lisha He and J.S. Burris

Sweet corn (Zea mays var. rugosa L.) seed with the endosperm mutant shrunken-2 (sh2) often exhibit low seed vigor and poor field emergence. Seed respiration and carbohydrate metabolism during germination of supersweet `Jubilee' (sh2) and sugary sweet `Jubilee' (Sh2) were studied. There were no significant vigor differences expressed by isolated embryos from sh2 and sugary (Sh2) seeds, indicating similar embryo physiology. Respiration rates were higher in the sh2 genotype during early stages of germination (24 hours) while they declined later. The available sucrose originating from the endosperm reserves was depleted by day 4. This insufficiency of a sustained energy source due to rapid consumption and minimal stored reserves may limit subsequent seedling growth in the sh2 genotype.

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Nihal C. Rajapakse and John W. Kelly

The interaction of light quality and growing season on growth and carbohydrate metabolism of chrysanthemum was evaluated using 6% CuSO4 and water as spectral filters. Light transmitted through the CuSO4 filter significantly reduced plant height and internode length compared to control plants regardless of the season. Light transmitted through CuSO4 filters delayed flowering. Total number of flowers was not affected but plants grown under CuSO4 filter had smaller flowers than those grown under the control filter. Light transmitted through CuSO4 filter reduced leaf and stem soluble sugar and starch concentrations regardless of the growing season. However, me magnitude of reduction was greater in spring than in fall-grown plants. Stems of fall-grown plants had mom starch deposition than spring-grown plants under both filters. The reduction of leaf and stem carbohydrate content (per organ basis) was greater than that of concentrations due to reduced stem elongation and total dry matter accumulation. Filters with specific spectral characteristics can be used as alternative means of controlling height and producing compact plants in the greenhouses regardless of the growing season. However, flowering should be evaluated with individual flower crops as flowering response may interact with the quality of light and growing season.

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Lingyun Yuan, Yujie Yuan, Shan Liu, Jie Wang, Shidong Zhu, Guohu Chen, Jinfeng Hou, and Chenggang Wang

-tolerant ‘xd’. Conclusions HT considerably hampered the photosynthetic process in NHCC by altering the chlorophyll pigments content, chloroplast ultrastructure, antioxidative capacity of chloroplast, and carbohydrate metabolism homeostasis, resulting in plant

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Robert W. Blenkinsop, Leslie J. Copp, Alejandro G. Marangoni, and Rickey Y. Yada

Following exposure to low temperatures (i.e., <10 °C), potato tubers undergo low-temperature sweetening (LTS), the conversion of starch to sugars. This phenomenon is of great importance to potato chip processors because high levels of reducing sugars lead to undesirable nonenzymatic browning during potato chip frying operations. The purpose of this study was to elucidate the biochemical differences in carbohydrate metabolism between a tolerant (ND 860-2) and a sensitive (Novachip) cultivar during 4 °C storage. On chilling, there was an increase in the levels of sucrose, fructose, and glucose in both cultivars, with levels being at least 2-fold higher in the sensitive cultivar. Increased levels of ATP and NADH, along with a higher respiratory rate observed in the tolerant tubers, collectively indicate a higher metabolic rate in the LTS-tolerant cultivar. ATP- and pyrophosphate-dependent phosphofructokinase activity was similar in both cultivars. Higher levels of ethanol and lactate were also observed in ND 860-2, suggesting a greater flux of sugars via anaerobic respiration. No significant differences were observed in enzymatic activities in the oxidative pentose phosphate pathway (PPP) or in levels of NADPH, thereby suggesting that the PPP does not play a role in conferring LTS tolerance. Therefore, we propose that LTS-tolerant potatoes may maintain low tissue sugar concentrations via an overall increased metabolism, rather than differing in one specific metabolic step. This increased metabolic rate does not appear to be due to greater enzyme expression (i.e., coarse control) but, rather, to a greater overall flux of carbohydrates through glycolysis and respiration.

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Mark J. Howieson and Nick Edward Christians

. However, steady-state labeling experiments and assays of carbohydrate metabolism enzyme rates would be needed to confirm this hypothesis. Mowing reduced efficiency of PSII and resulted in transient decreases in the levels of fructan and glucose in

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Jinmin Fu and Peter H. Dernoeden

first sign of leaf wilt to replenish the root zone with water ( Fry and Huang, 2004 ). DI irrigation generally is recommended for maintaining cool-season grasses in summer ( Beard, 1973 ; Fry and Huang, 2004 ). Carbohydrate metabolism in leaves and

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Li-Song Chen and Lailiang Cheng*

To determine the cause of zonal chlorosis of `Honeycrisp' apple leaves, we compared CO2 assimilation, carbohydrate metabolism, xanthophyll cycle and the antioxidant system between chlorotic leaves and normal leaves. Chlorotic leaves accumulated higher levels of non-structural carbohydrates, particularly starch, sorbitol, sucrose, and fructose at both dusk and predawn, and no difference was found in total non-structural carbohydrates between predawn and dusk. CO2 assimilation and the key enzymes in the Calvin cycle, ribulose 1,5-bisphosphate carboxylase/oxygenase, NADP-glyceraldehyde-3-phosphate dehydrogenase, phosphoribulokinase, stromal fructose-1,6-bisphosphatase, and enzymes in starch and sorbitol synthesis, ADP-glucose pyrophosphorylase, cytosolic fructose-1,6-bisphosphatase, and aldose 6-phosphate reductase were significantly lower in chlorotic leaves than in normal leaves. However, sucrose phosphate synthase activity was higher in chlorotic leaves. Thermal dissipation of excitation energy was enhanced in chlorotic leaves under full sun, lowering the efficiency of excitation energy transfer to PSII reaction centers. This was accompanied by a corresponding increase in both xanthophyll cycle pool size (on a chlorophyll basis) and conversion of violaxanthin to antheraxanthin and zeaxanthin. The antioxidant system was up-regulated in chlorotic leaves in response to the increased generation of reactive oxygen species. These findings support the hypothesis that phloem loading and/or transport is partially or completely blocked in chlorotic leaves, and that excessive accumulation of non-structural carbohydrates may cause feedback suppression of CO2 assimilation via direct interference with chloroplast function and/or indirect repression of photosynthetic enzymes.

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Rui Zhou and Bruno Quebedeaux

Photosynthesis and carbohydrate metabolism in apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] source leaves were monitored during a 7-day period after source-sink manipulations by girdling or partial defoliation treatments. In the girdling treatment, sorbitol, sucrose, glucose, and starch accumulated in leaves, and net photosynthetic rates (Pn) at 350 μL·L-1 CO2 decreased during a 7-day period. Pn measured at 1000 μL·L-1 [CO2] was also decreased but the changes were less. Stomatal conductance and intracellular CO2 concentration decreased markedly in leaves of girdled shoots. When shoots were partially defoliated, starch and glucose concentrations in remaining source leaves declined steadily during the 7-day study period. Sorbitol and sucrose concentrations decreased during the first 2 days after defoliation, then increased the following 5 days. Pn of the remaining leaves measured at ambient and elevated CO2 levels were enhanced markedly. Aldose-6-phosphate reductase activity in source leaves increased markedly from 27.5 to 39.2 μmol·h-1·g-1 fresh weight (FW) after partial defoliation but remained unchanged in leaves after girdling. Selective and maximum sucrose phosphate synthase (SPS) activities increased following partial defoliation and decreased following girdling. ADP-glucose pyrophosphorylase activity remained relatively unchanged in the partial defoliation treatments but increased markedly in the girdled-shoot leaves. These results suggested that girdling-induced photosynthetic inhibition is mainly due to stomatal limitation, however, the photosynthesis enhancement by partial defoliation may be due primarily to acceleration of photosynthetic capacity per se. These studies showed that the metabolism of sorbitol, sucrose and starch, three photosynthetic end products in mature apple leaves, was coordinately regulated in source leaves in response to source-sink manipulations.