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balance. This may lead to greater assimilate accumulation in flower buds on defruited compared with fruiting plants, resulting in ovary swelling and fruit deformation. Although ovary swelling is favored by LNT or increased source:sink ratio, the

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) can be estimated using Eq. [7] . The source-to-sink ratio (SSR m_st ; grams per gram) per stem at m DAT was calculated using Eq. [8] : SST m _ st = Σ 0 n ( SSF m _ n ) [7] SSR m _ st = TDM m _ st SST m _ st [8] Wubs et al. (2007 , 2009a

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-shoot correlative inhibition, shoot removal leads to 1) increased light intensity lower in the crop canopy; 2) changes in the light spectrum (higher intensity of red light compared with far-red light, resulting in a higher red:far-red ratio); and 3) changed source:sink

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, 2000 ), which further decreases source (leaves) to sink (fruit) ratio. However, large-sized ‘Gala’ fruit is preferred over small fruit at a significant premium on the market. This has prompted growers to strive for large fruit size. Apple fruit size

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:Y because leaf area is generally correlated with pruning weight. In practice, the objective is to optimize the source to sink ratio with vineyard management practices to sustain vine productivity and achieve ripeness within climatic constraints. Some studies

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to keep the plants balanced in terms of source-to-sink ratio. Plants were drip-irrigated with a standard cucumber and tomato nutrient solution (Supplemental Table 2). Drip irrigation started 2 h after the supplemental lighting was turned on and

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The carbohydrate economy of developing tomato fruit is determined by wholeplant source–sink relationships. However, the fate of the imported photoassimilate partitioned to the fruit sink is controlled by the carbohydrate metabolism of the fruit tissue. Within the Lycopersicon spp. there exists a broad range of genetic variability for fruit carbohydrate metabolism, such as sucrose accumulation and modified ratios of fructose to glucose in the mature fruit and increased starch synthesis in the immature fruit. Metabolic pathways of carbohydrate metabolism in tomatoes, as well as natural genetic variation in the metabolic pathways, will be described. The impact of sink carbohydrate metabolism on fruit non-structural carbohydrate economy will be discussed.

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Light duration alters carbon partitioning among carbohydrates (CHOs) in source leaves. The current experiments were designed to determine how light duration affected the metabolism of newly fixed and reserve CHOs in various organs of apple and whether longer durations favored sorbitol (sor) synthesis. One-year-old `Gala' apple plants that experienced a 1-, 4-, 7-, 10-, or 14-h photoperiod for 7 d were exposed to 14CO2 for 15 min. Individual CHO concentrations and the activity of newly-fi xed [14C]CHOs in leaves, stems, and roots were analyzed during different intervals after labeling. In source leaves, sor increased significantly, whereas sucrose (suc) did not change as light duration increased from 1 to 10 h, resulting in increased sor/suc ratios from 2.6 in the 1-h to 4.3 in the 10-h light duration. The increased sor/suc ratios may be due primarily to the preferential carbon partitioning into sor in longer light durations. Longer light durations enhanced the sor export rate from source leaves, resulting in higher sor in stems and sink tissues. In roots, starch increased significantly over increasing light durations. A major portion of starch in roots may be converted from newly fixed CHO. Our results suggest that light duration alters the metabolism of sor and other CHOs in source and sink tissues of apple and that the changes in CHO concentrations result from different rates of carbon synthesis, partitioning, and export.

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Apple and many other Rosaceae plants translocate sucrose as well as sorbitol. How photosynthates are partitioned between sorbitol and sucrose in the Rosaceae is not understood. This study was designed to examine the effects of elevated air CO2 on partitioning of sorbitol and other soluble sugars in sink and source apple leaves. Young `Gala' apple plants were exposed to the ambient air and 700, 1000, and 1600 μl·liter–1 of CO2 for 8 days under a light intensity of 928 μmol·m–2·s–1 with a 14-h day/10-h night cycle. Sorbitol, sucrose, glucose, and fructose concentration in sink and source leaves were determined by HPLC analysis. In source leaves, sorbitol was significantly increased, while sucrose was decreased as the air CO2 was elevated from 400 to 1600 μl·liter–1. The sorbitol/sucrose ratio varied from 1.31 in air and 2.26 at 1600 μl·liter–1 of CO2. In sink leaves, sorbitol concentration did not vary across the four CO2 levels; however, sucrose was higher at the three super-atmospheric CO2 levels. Our results suggest that increased photosynthesis via elevated CO2 favors photosynthate partitioning into sorbitol rather than sucrose. A mechanism for regulating this partitioning will be discussed.

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1 To whom reprint requests should be addressed at Dept. of Ornamentals, Danish Institute of Agricultural Sciences, Kirstinebjergvej 10, 5792 Aarslev, Denmark; e-mail cwh@afp.sp.dk . This research was conducted at The Pennsylvania State University

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