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Johan M.H. Stoop and David M. Pharr

The fleshy parenchyma tissue of celery [Apium graveolens L. var. dulce (Mill.) Pers.] petioles is the major storage tissue for the sugar alcohol mannitol and for the hexoses, glucose and fructose. In this study, we found that plants grown in the soilless mixture, Promix, fertilized weekly with a nutrient solution, or grown in a hydroponic container culture, differed in carbohydrate composition. However, plant growth was not affected. Higher mannitol and lower hexose concentrations were present in petioles from plants grown hydroponically. This was true in petioles that did not differ in total soluble carbohydrate concentration. The ratio of mannitol to hexose concentration in petioles was ≈2-fold higher for hydroponically grown plants compared to Promix-grown plants, and the higher ratio was maintained during the entire 12-week experimental period. Carbohydrate partitioning was also affected by petiole development within the plant. Sucrose and hexose concentrations were highest in mature petioles, whereas mannitol was relatively high in all petioles except the oldest ones. Because the mineral solution applied to the Promix-grown plants had a lower total salt concentration compared to hydroponically grown plants, we postulated that the salt concentration of the mineral solution might be an important factor affecting C partitioning in celery petioles. When plants were grown hydroponically at two different salt concentrations [electrical conductivity (EC) = 2.7 and 6.0 mS·cm-1], high mannitol-to-hexose ratios were observed in celery petioles of plants grown at high salt concentration (EC = 6.0 mS·cm-1), a result supporting the hypothesis that the salt environment might alter mannitol and hexose concentrations in a coordinated way. These data are consistent with the hypothesis that elevated mannitol levels may be a significant component of plant adjustment to salt stress, possibly adding osmotic adjustment and preventing inactivation of metabolic processes.

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Matthew W. Fidelibus, Karen E. Koch and Frederick S. Davies

sugars, especially hexoses, on downregulation of genes encoding chlorophyll and photosynthetic enzymes ( Koch, 1996 ; Pourtau et al., 2006 ; Price et al., 2004 ; Rolland et al., 2006 ). Gibberellic acid can be applied to citrus fruit in the late

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O. Ayari, M. Dorais and A. Gosselin

Daily and seasonal variations of photosynthetic activity, chlorophyll a (Chl-a) fluorescence and foliar carbohydrate content were studied in situ on greenhouse tomato (Lycopersicon esculentum Mill. `Trust') plants grown under CO2 enrichment and supplemental lighting. The objective of this study was to assess the effect of seasonal variation of the photosynthetic photon flux (PPF) on photosynthetic efficiency of tomato plants and to determine the presence or absence of photosynthetic down-regulation under greenhouse growing conditions prevailing in northern latitudes. During winter, the fifth and the tenth leaves of tomato plants showed low, constant daily photosynthetic activity suggesting a source limitation under low PPF. In winter, the ratio of variable to maximum Chl-a fluorescence in dark adapted state (Fv/Fm) remained constant during the day indicating no photoinhibition occurred. In February, an increase in photosynthetic activity was followed by a decline during March, April, and May accompanied by an increase in sucrose and daily starch concentrations and constant but high hexose level. This accumulation was a long-term response to high PPF and CO2 enrichment which would be caused by a sink limitation. Thus, in spring we observed an in situ downregulation of photosynthesis. The ratio Fv/Fm decreased in spring compared to winter in response to increasing PPF. The daily decline of Fv/Fm was observed particularly as a midday depression followed by a recovery towards the end of the day. This indicated that tomato leaves were subject to a reversible inhibition in spring. Fv/Fm was lower in March than in April and May even though PPF was higher in April and May than in March. These results suggest that tomato plants develop an adaptive and protective strategy as PPF increases in spring.

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Badrane M. Erhioui, André Gosselin, Xiuming Hao, Athanasios P. Papadopoulos and Martine Dorais

A study was conducted in mini-greenhouses covered with single-glass (glass), double inflated polyethylene film (D-poly), or rigid twin acrylic panels (acrylic) to determine the effects of covering materials and supplemental lighting (SL) (65 μmol·m-2·s-1 at 1 m from the ground, providing a 16-hour photoperiod) on growth, yield, photosynthesis, and leaf carbohydrate concentration of `Trust' greenhouse tomato plants (Lycopersicon esculentum Mill.). Regardless of the light treatment, the marketable yield (kg·m-2) and the number of fruit per square meter in D-poly houses were higher (P ≤ 0.05) by 15% to 16% and 13% to 17%, respectively, than in glasshouses. Under supplemental lighting (SL), similar results were observed in acrylic houses compared to glasshouses. Covering materials had no significant effect on photosynthesis and leaf chlorophyll (chl) concentration. SL increased the number of leaves (March) by 15% (P ≤ 0.05) in glasshouses, marketable fruit yield by 23% (P ≤ 0.01) in acrylic houses, leaf specific weight by 19% to 33% (P ≤ 0.05) in all houses, total chl concentration by 10% to 14% (P ≤ 0.01) in acrylic houses, and photosynthetic rate (March) by 22% (P ≤ 0.01) in glasshouses. Under nonsupplemental lighting (nonSL, daily solar radiation of 8.42 MJ·m-2), plant height in acrylic houses was significantly higher (P ≤ 0.05) than in glasshouses. Neither covering materials nor SL affected (P ≤ 0.05) dry matter allocation to the fruit. Results suggest that D-poly and acrylic houses with SL provide the best environment for the early yield (February to March) under southwestern Ontario growing conditions. The photosynthetic rate decreased (P ≤ 0.05) by 18% in acrylic, and 15% in D-poly and glasshouses after 2 months of growth under nonSL. Conversely, the decrease in carbon exchange rate was not significant in D-poly houses and glasshouses under SL. As a result, the photosynthesis decline observed in the present study could not be explained by leaf starch accumulation in March.

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Sven Verlinden, Silvanda M. Silva, Robert C. Herner and Randolph M. Beaudry

sections of the spear and may act as a carbohydrate source for the more apical sections of the spear. The objective of this research was to establish the carbon balance between respiration and hexose catabolism as a function of the longitudinal position of

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

phosphorylation of hexoses to hexose monophosphates—were not altered significantly in any transgenic plant lines compared with the wild types ( Table 1 ). Carbohydrates and phosphorylated intermediates. Reduced fru 2,6P 2 levels stimulated the activity of

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Gerhard C. Rossouw, Jason P. Smith, Celia Barril, Alain Deloire and Bruno P. Holzapfel

, ( C ) glucose, and ( D ) total hexose concentration dry weight per vine. Time after veraison refers to the different destructive harvest dates [V (veraison), V + 14 (14 d after V), V + 29 (29 d after V), V + 42 (42 d after V), and V + 56 (56 d after V

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He Lisi, Su Jiale, Liu Xiaoqing, Li Chang and Chen Shangping

, catalyzing the hydrolysis of sucrose into hexose monomers, is thought to play a key role in regulating sugar content to contribute to all aspects of plant growth and development ( Jain et al., 2008 ; Roitsch and Gonzalez, 2004 ). Early studies suggested that

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Thomas E. Marler

concentrations of four free sugars (the hexoses fructose and glucose, and the disaccharides sucrose and maltose) were determined using HPLC-RI (Thermo Scientific RI-150, AS3000 autosampler, P2000 pump; Thermo Scientific, Waltham, MA). Starch was quantified using

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Anil P. Ranwala and William B. Miller

Easter lily flower buds at five stages of development (stage 1, 3–4 cm in length; stage 2, 6–7 cm; stage 3, 9–10 cm; stage 4, unopened buds, 13–14 cm; and stage 5, open flower one day after anthesis) were harvested, and flower organs were dissected for carbohydrate analysis. Extracting soluble sugars in distilled water at 70°C gave the optimum yield of soluble sugars among the several extraction methods tested including 80% ethanol, and distilled water at various temperatures. Separation of the extracted soluble sugars by alkaline high performance anion exchange chromatography revealed the presence of glucose, fructose, sucrose, and two other sugars of unknown identity. Glucose and fructose concentrations increased remarkably during the flower development in sepal (about 15-fold), style (about 10-fold), and filament (about 5-fold), while sucrose levels remained constant at low concentrations. In stigma, sucrose levels increased parallel to the increase of hexose sugars during development. Ovary had high sucrose levels relative to hexoses that remained constant while hexoses increased gradually. In anther, hexose concentrations increased at the stage 2 and then dropped at stage 3 and 4. Sucrose levels were higher than hexoses in anther, and it increased from stage 1 to stage 2, then dropped at stage 3, and increased thereafter. In addition to these sugars, anthers at stages 2 and 3 had a series of late eluting oligosaccharides. These oligosaccharides could be hydrolyzed to glucose with hot 1 m H2SO4 or with amyloglucosidase.