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Aude Tixier, Adele Amico Roxas, Jessie Godfrey, Sebastian Saa, Dani Lightle, Pauline Maillard, Bruce Lampinen and Maciej A. Zwieniecki

were collected at different positions from the apical bud for NSC measurements (starch and SC). Bark was removed from the wood immediately and the samples were then dried at 70 °C for 48 h before grinding into a fine and homogeneous powder. SCs were

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Rebecca L. Darnell and Keith B. Birkhold

Rabbiteye blueberry (Vaccinium ashei Reade) cultivars differ in timing of floral and vegetative budbreak and in final fruit size. For example, `Bonita' exhibits concomitant floral and vegetative budbreak and has relatively large fruit size, while floral budbreak precedes vegetative budbreak in `Climax' and fruit size is smaller. Mobilization of carbohydrate before and during fruit development in `Bonita' and `Climax' rabbiteye blueberries was examined to determine if differences in carbohydrate availability between these two cultivars were correlated with differences in fruit size. Root dry mass (DM) of both cultivars decreased from dormancy (31 days before anthesis) through fruit development. Sugar concentrations in roots and stems of both cultivars decreased significantly between dormancy and anthesis, then remained relatively steady throughout fruit development. Starch concentrations in roots and stems of `Bonita' decreased significantly between dormancy and anthesis. The extent of total starch depletion in `Climax' was similar; however, the decrease was more gradual, extending from dormancy to 28 days after anthesis (DAA); at which time, vegetative budbreak in `Climax' occurred. Thus, although total reserve carbohydrate pool sizes were similar between the two cultivars, remobilization patterns were different, resulting in increased starch mobilization in `Bonita' compared to `Climax' in the period leading up to anthesis. Concentration of 14C from reserve carbon sources was similar in flowers of both cultivars at anthesis. These values declined throughout fruit development as a result of dilution of the labeled carbon by unlabeled carbon from current photosynthesis. There was a sharper decline in 14C concentration of `Bonita' fruit compared to `Climax' fruit between anthesis and 51 DAA. This, coupled with differences in timing of vegetative budbreak between the two cultivars, suggests that `Bonita' fruit were accessing current (unlabeled) assimilate earlier (i.e., before 51 DAA) than `Climax' fruit. Smaller fruit size in `Climax' compared to `Bonita' may be a consequence of a decrease in reserve carbohydrate mobilization to `Climax' flower buds before anthesis relative to `Bonita', as well as a delay or reduction in the availability of current carbohydrates to developing `Climax' fruit between anthesis and 51 DAA.

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C.P. Sharma and Sandhya Singh

Cauliflower [Brassica oleracea (Botrytis Group) cv. Pusi] grown in refined sand with 0.01 normal K supply had lower dry matter and tissue concentration of K than the controls and developed visible symptoms characteristic of K deficiency. Compared with control plants, the laminae of K-deficient plants contained significantly higher concentrations of sugars and nonprotein N and significantly lower concentrations of starch and protein N. However, the midribs of K-deficient leaves contained more protein N than leaves of control plants. Substitution of K by Na resulted in increased Na concentrations in leaves and recovery from the K-deficiency effect on the carbohydrate and N fractions. Maximum response to sodium was found in the intercoastal-lamina of K-deficient plants.

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X. Deng, S.A. Weinbaum, T.M. DeJong and T.T. Muraoka

Abortion of distillate flowers (PFA) in a protandrous cultivar of walnut (Juglans regia L. cv. Serr) was increased by N deficiency. Starch and N concentrations in wood of 2-year-old twigs decreased to minimal levels during abortion of distillate flowers. Nitrogen reserves in woody tissues were reduced by foliar N deficiency, as were concentrations of sugars and N in vacuum-extracted xylem sap. Abortive distillate flowers ceased growth before spur leaves reached 50% of full expansion. PFA may result from transient deficiencies of C and N during the spring flush of growth. Depletion of storage C and N was accentuated before maturation of distillate flowers in this cultivar by the metabolic demands of many catkins, spur growth, and leaf expansion.

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Annick Moing, Christel Renaud, Monique Gaudillère, Philippe Raymond, Philippe Roudeillac and Béatrice Denoyes-Rothan

As genetic factors affect strawberry (Fragaria ×ananassa Duch.) fruit development and quality, changes in metabolite concentrations were studied during fruit development of four strawberry cultivars grown in the field: three commercial cultivars (Capitola, Elsanta and Dover) and a genotype from Centre Interrégional de Recherche et d'Expérimentation de la Fraise, France (`CF1116'). Major and minor metabolites changed with development. The two strawberry cultivars with the highest starch content at early stages, `Capitola' and `Elsanta', also had the highest fruit weight at harvest. There was no correlation between strawberry weight and osmolarity. At maturity, significant differences were observed among cultivars for most of the metabolites studied. `Capitola' and `Elsanta' responded similarly for most measured variables. `CF1116' was characterized by high juice osmolarity and high sucrose, inositol, glutamine, arginine and alanine concentrations, and low citrate and malate concentrations. `Dover' was characterized by a high galactose concentration and low asparagine and alanine concentrations. Organic acid differences among cultivars appeared early during development, while differences in soluble sugars appeared during maturation. The developmental pattern of each amino acid varied among cultivars. Timing of the biochemical differences observed among cultivars provides some information on their metabolic origin.

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Avinoam Nerd and Yosef Mizrahi

Changes occurring during fruit ripening and duration of fruit development were studied in Selenicereus megalanthus (Scum. ex Vaupel) Moran (yellow pitaya), a climbing cactus grown in protected structures at three sites in the Israeli Negev desert. During ripening, peel color turned from green to yellow, fruit dimensions slightly changed, and pulp content markedly increased. Total soluble solids and soluble sugars in the pulp increased, while starch content decreased. Acidity decreased at the last stage of ripening. Fruit in which most of the peel area had turned yellow (stage 4) were given the highest taste grade by a panel of tasters. Measurements of ethylene and CO2 evolution indicated that fruit was nonclimacteric. The mean number of days from anthesis to fruit of stage 4 was negatively correlated with the mean of the maximum and the minimum temperatures during the growth period. Daily accumulation of heat units (HUs) was calculated as the difference between daily mean temperature and a base temperature of 7 °C. Sum of HUs for the period from anthesis to ripening was 1558±12 HUs.

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Christopher M. Menzel and Lindsay Smith

substances such as starch (storage sugar) and soluble sugars, which do not form part of the cell structures such as the cell wall ( Da Silveira et al., 1978 ). These carbohydrates are then available for cell metabolism, whereas carbohydrates in the cell wall

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B.E. Maust, J.G. Williamson and R.L. Darnell

Vegetative budbreak, leaf area development, and fruit size in southern highbush blueberry (Vaccinium corymbosum L. interspecific hybrids) decrease as flower bud density increases. The effect on fruit size has been attributed to both insufficient carbohydrate reserves and reductions in current photoassimilates caused by decreased vegetative growth. Experiments were conducted with two southern highbush blueberry cultivars, `Misty' and `Sharpblue', to test the hypothesis that increased carbohydrate reserve concentrations can overcome the detrimental effects of high flower bud density by increasing vegetative budbreak, shoot development, and whole-canopy net CO2 exchange rate (NCER), which in turn will increase fruit size. Fully foliated plants were placed in greenhouses with either ambient (AMB) CO2 levels (≈360 μmol·mol-1) or enriched (ENR) CO2 levels (≈700 μmol·mol-1) for 38 d during fall. Plants were then moved outdoors, hand defoliated, and flower bud density (flower buds/cm cane length) adjusted to range from 0.07 to 0.31. Root starch and whole plant carbohydrate concentrations increased in ENR compared with AMB plants of both cultivars. Vegetative budbreak (number per centimeter cane length), leaf area, and whole-canopy NCER decreased as flower bud density increased in AMB and ENR plants of both cultivars; however, ENR `Sharpblue' plants had significantly greater vegetative growth and wholecanopy NCER at a given flower bud density compared with AMB `Sharpblue'. Concomitant with this was an increase in fruit fresh weight in ENR compared to AMB `Sharpblue'. This was not the case with `Misty', where vegetative development and fruit size were similar in ENR and AMB plants. Thus, the hypothesis that increased carbohydrate reserves will increase vegetative development and subsequent fruit size may be true only in certain cultivars of southern highbush blueberry. Alternatively, the increased carbohydrate reserve concentrations in ENR compared with AMB `Misty' plants may have been insufficient to affect subsequent vegetative or reproductive development.

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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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Margarita R. Villagarcia, Wanda W. Collins and C. David Raper Jr.

Soil N availability is an important component in storage root production of sweetpotato [Ipomoea batata (L.) Lam.]. A controlled-environment experiment was conducted to characterize effects of N availability on patterns of dry matter, nonstructural carbohydrates, and N accumulation, and to determine possible components of N use efficiency that vary between two genotypes of sweetpotato. Rooted cuttings of `Jewel' and MD810 were transplanted into pots filled with sand and kept in a growth chamber for 72 days. Plants were watered during the first 30 days with a complete nutrient solution that contained 14 mm NO3 - and then for the next 42 days with one of three complete nutrient solution that contained either 2, 8, or 14 mm NO3 -. At 30, 44, 58, and 72 days after transplanting, three plants from each cultivar and treatment combination were sampled and separated into leaves, stems plus petioles, fibrous roots, and storage roots. Each plant fraction was freeze-dried, weighed, ground, and analyzed for total N, soluble sugars, and starch. Availability of N in the substrate, which limited dry matter accumulation at 2 mm NO3 -, was nonlimiting at 8 and 14 mm NO3 -. In both genotypes, net assimilation rate, efficiency of N use (i.e., increments of dry matter accumulated per increment of N taken up), and proportion of dry matter allocated to storage roots were greater for N-stressed (2 mm NO3 -) than N-replete (8 and 14 mm NO3 -) plants. For the N-stressed plants, however, efficiency of N use was greater in MD810 than in `Jewel'. Although rate of NO3 - uptake per unit fibrous root mass was similar in the two genotypes under the N stress treatment, MD810 had greater uptake rate than `Jewel' under nonlimiting availability of NO3- in the substrate. The increased rate of uptake under nonlimiting NO3 - supplies apparently was related to enhanced rates of carbohydrate transport from shoots to roots. As tissue concentration of N declined in response to the lowest application of NO3 -, shoot growth was limited prior to, and to a greater extent than, the photosynthetic rate. The resulting relative decline in sink activity of shoots thus presumably increased the availability of carbohydrates for transport to roots.