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Justine E. Vanden Heuvel*

Fruiting and vegetative greenhouse-grown cranberry uprights (Vaccinium macrocarpon Ait.) were subjected to four defoliation levels (0%, 25%, 50%, 75%) on one of three dates during the growing season. Seven days following defoliation, vines were destructively harvested and carbohydrate concentration was quantified using HPLC. Prior to new growth, defoliation did not affect the concentration of total non-structural carbohydrates (TNSC) in the uprights, or the partitioning of water-soluble (i.e., sucrose, glucose, fructose) to ethanol-insoluble (i.e., starch) carbohydrates, even though uprights with lower leaf areas had higher net CO2 assimilation rates (A). At 2 weeks post-bloom, TNSC concentration was reduced in defoliated vines, although A was not affected by defoliation. Prior to harvest, TNSC concentration was reduced in vines subjected to defoliation while A was unaffected, although the positive relationship between soluble carbohydrate concentration and leaf area per upright reached an asymptote, while the direct relationship between starch concentration and leaf area remained linear. Carbohydrate production and partitioning of an upright was unaffected by the presence of a single fruit throughout the experiment. These results suggest that carbohydrate production in cranberry uprights may be sink-limited prior to fruiting, and then becomes source-limited as the growing season progresses.

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Rui Wang, Yuqing Gui, Tiejun Zhao, Masahisa Ishii, Masatake Eguchi, Hui Xu, Tianlai Li, and Yasunaga Iwasaki

; Villalobos and Ritchie, 1992 ). Under heat stress, the whole-plant carbohydrate partitioning of rice at anthesis was changed, and the sugars acted as a signal molecule to mediate the source–sink relationship ( Zhang et al., 2018 ). Under suboptimal light

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Susanna Marchi, Luca Sebastiani, Riccardo Gucci, and Roberto Tognetti

Net photosynthesis, dark respiration, chlorophyll and carbohydrate content, and leaf and shoot growth in plants of evergreen olive (Olea europaea L.) grown under controlled conditions were measured to assess changes in carbon balance during leaf development of the 6th, 12th, and 16th node (from the base, first flush) through expansion to maturity. Shoot and leaves expanded in a sigmoid pattern with differences among nodes. Photosynthesis varied with leaf development; young leaves had low CO2 assimilation rates that were reflected in their chlorophyll concentration. Net daily CO2 assimilation was negative in young expanding leaves. The sink-source transition, defined to be the time when the increase in daily carbohydrate exchange rate exceeds the daily increase in leaf carbohydrate content, occurred before full leaf expansion, between 10% and 30% expansion depending on the node.

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Jingwei Dai and Robert E. Paull

The inflorescence of Protea neriifolia B. Br. was two-thirds of the total cut floral stem fresh weight and significantly influenced blackening of the attached 20 to 30 leaves. Floral stems harvested at five developmental stages were characterized for inflorescence diameter, fresh and dry weights, respiration, and nectar production. Inflorescence diameter and fresh and dry weights increased from stage 1 (very tight bud) to stage 5 (bracts reflexed). Respiration rate was high in stages 1 and 3. Nectar production began at stage 4 (open, cylindrical flower) and increased from 2.7 to 9.8 ml per flower with 15% to 23.5% total soluble solids as the flower opened. Postharvest inflorescence diameter, respiration rate, and nectar production increased and leaf blackening decreased when floral stems were placed in 5% (w/v) sucrose solution. Application of 14C-sucrose to a leaf subtending the inflorescence lead to >50% of the radioactivity being found in the nectar within 24 hours. These data indicate that leaf blackening in protea is the result of depletion of carbohydrate by the inflorescence, and that this depletion is primarily due to the sugar demand for nectar production.

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Gina E. Fernandez and Marvin P. Pritts

Seasonal changes in growth, mean maximal photosynthetic rates, and the temperature and light response curves of `Titan' red raspberry (Rubus idaeus L.) were obtained from potted plants grown under field conditions. Primocane dry weight accumulation increased steadily at the beginning and the end of the season, but growth slowed midseason during fruiting. The slower midseason dry-weight accumulation rate coincided with an increase in root dry weight. Primocane net assimilation rate (NAR) was highest early in the season. Floricane photosynthetic rates (A) were highest during the fruiting period, while primocane A remained steady throughout the season. Primocane and floricane leaflets displayed a midday depression in A under field conditions, with a partial recovery in the late afternoon. Photosynthetic rates of primocane and floricane leaves were very sensitive to temperature, exhibiting a decline from 15 to 40C. Light-response curves differed depending on cane type and time of year. A temporal convergence of sink demand from fruit, primocanes, and roots occurs when plants experience high temperatures. These factors may account for low red raspberry yield.

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G. Fernandez and M. Pritts

Seasonal changes in growth, photosynthetic rates, temperature, and light response curves of `Titan' red raspberry (Rubus idaeus L.) were obtained from potted plants grown under field conditions. Primocane dry weight accumulation underwent two phases of linear growth at the beginning and the end of the season, but growth slowed during fruiting. This slower rate of dry weight accumulation also coincided with an increase in root dry weight. Primocane NAR and SLA were highest early in the season. Light response curves differed depending on cane type and time of year. Floricane photosynthetic rates (A) were high during the fruiting period, while primocane A rates remained steady throughout the season. Both primocane and floricane leaflets displayed a midday drop in A rate, with a partial recovery in late afternoon. Photosynthetic rates of both primocane and floricane leaves were very sensitive to high temperatures. Temporal convergence of sink demand from fruit, primocanes, and roots occurs when plants experience high temperatures. This may account for low realized yields in raspberry and the high level of yield component compensation typical of source-limited plants.

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Sang Gyu Lee* and Chiwon W. Lee

The pattern of C14 carbohydrate translocation and distribution from source leaf to various plant parts in watermelon grown in the greenhouse and field was investigated. Seedling-grown plants were pruned to have two branches with only one of them carrying a fruit. When leaves at four different positions (on fruit-bearing node, on fifth node above and below it, and on fifth node from the base of the non-fruit-bearing stem) were exposed to 14CO, the distribution of C14 2 compounds to different parts (fruit, stem, leaf, root) of the plant varied. In all treatments, the fruit was the strongest sink, followed by stem, leaf and root tissues. The highest percentage of C14 photo-assimilates was transferred out of the source when the leaf borne on the fruit-bearing node was exposed to 14CO2 in both greenhouse and field grown plants. Translocation of C14 compounds from the leaves on the fifth node above and below the first fruit-carrying node was similar. Only 29% of C14 was transferred from the source leaf borne on the fifth node of the non-fruit bearing branch in the greenhouse, as compared to more than 46% of C14 from other source leaves. Accumulation of C14 in the root tissues was highest when source leaves were borne on the non-fruit bearing branch. In general, field-grown plants had higher percentages of C14 translocated as compared to greenhouse-grown plants.

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Ben Hong Wu, Hai Qiang Huang, Pei Ge Fan, Shao Hua Li, and Guo Jie Liu

could exceed 50% of the total dry matter production of a tree at harvest ( Pavel and DeJong, 1993 ). Therefore, removing all or some fruit has often been used to vary the sink–source relationship so as to investigate photosynthetic responses

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Hadi Susilo, Ying-Chun Peng, Shui-Cheng Lee, Yu-Chun Chen, and Yao-Chien Alex Chang

the fate of fertilizer N after application to the roots, and trace the partitioning of fertilizer N at different growth stages to compare the sink-source relationships between the various organs. Materials and Methods Plant materials. Unless otherwise

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Alison L. Reeve, Patricia A. Skinkis, Amanda J. Vance, Katherine R. McLaughlin, Elizabeth Tomasino, Jungmin Lee, and Julie M. Tarara

estimate wine quality. Given the relationships between tissue N and vine growth measures, N was likely a physiological driver of source–sink relationships affecting berry composition. Total soluble solids were best explained by crop load, whereas other