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Victor N. Njiti, Qun Xia, Leonna S. Tyler, Lakeisha D. Stewart, Antione T. Tenner, Chunquan Zhang, Dovi Alipoe, Franklin Chukwuma, and Ming Gao

vegetative and reproductive sinks ( Hicklenton, 1990 ; Williams, 1988 ). Manipulation of sinks capacity may enhance sweetpotato yield through assimilates repartitioning. The sweetpotato is a storage root and a major carbohydrate sink. Suppressing the growth

Open access

Adam D. Karl, Michael G. Brown, Sihui Ma, Ann Sandbrook, Amanda C. Stewart, Lailiang Cheng, Anna Katharine Mansfield, and Gregory M. Peck

division and growth during alcoholic fermentation of fruit juice ( Bell and Henschke, 2005 ). Yeast assimilable nitrogen is composed of free amino nitrogen (FAN), ammonia ions, and some short oligopeptides ( Bell and Henschke, 2005 ). Unlike wine grapes

Open access

Adam D. Karl, Michael G. Brown, Sihui Ma, Ann Sandbrook, Amanda C. Stewart, Lailiang Cheng, Anna Katharine Mansfield, and Gregory M. Peck

this cultivar has a high level of pectin that interfered with this assay. Fig. 1. Yeast assimilable nitrogen (YAN) concentration in ‘Golden Russet’ apple juice from trees with no, low (28 kg·ha –1 ), medium (56 kg·ha –1 ), and high (112 kg·ha –1

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Keith T. Birkhold and Rebecca L. Darnell

The relative contribution of storage and currently assimilated N to reproductive and vegetative growth of `Bonita' and `Climax' rabbiteye blueberry (Vaccinium ashei Reade) was estimated immediately before and during the fruit development period. Total and storage N decreased in roots and shoots of both cultivars during dormancy and early fruit development. The principle N storage form appeared to be protein, as indicated by a significant decline in total shoot and root protein during this same period. Storage N from roots and shoots in both cultivars was remobilized to flowers and/or fruit and new vegetative growth. At anthesis, 90% of the total N present in reproductive organs was estimated to come from storage N. By fruit maturity, ≈ 50% of the accumulated N was derived from storage pools. Storage N contributed 90% of the total N in developing vegetative growth of `Bonita' at leaf budbreak, which is concomitant with floral budbreak for this cultivar. Developing vegetative growth of `Climax' at leaf budbreak, which occurs ≈ 4 weeks after floral budbreak, derived ≈ 65% of its total N from storage and 35% from currently assimilated N. By fruit maturity, contribution of storage N to new vegetative growth had decreased to ≈ 20% in both cultivars, indicating that currently assimilated N became the principal N supply as vegetative growth became more established. Differences in timing of floral and vegetative budbreak between the two cultivars did not appear to affect allocation of either storage or currently assimilated N to new vegetative or reproductive growth.

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Sang Gyu Lee* and Chiwon W. Lee

The relationship between source leaf position and the photo-assimilate translocation and distribution was characterized for tomato (Lycopersicon esculentum Mill.) grown in the greenhouse. Three different positions of source leaf on the stem (first node above or below the first fruit cluster and fifth node above the first fruit cluster) were tested for their influence on 14CO2 assimilation and transfer to different parts of the plant. The leaves at the fifth node above the first fruit cluster transferred the highest (57%) proportion of C14 to other plant parts, followed by leaves borne on the first node below the first fruit cluster (50%), and the first node above the first fruit cluster (39%). In all treatments, fruits served as the strongest sink for C14, followed by stem, leaf, and root tissues. The leaf borne on the fifth node above the first fruit cluster transferred the largest amount of C14 to the second fruit cluster.

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T.W. Tibbitts and W. Cao

A nutrient delivery system developed for plant growth in space provides a unique system for maintaining a constant, slightly-negative water tension for plant research. The system involves the use of multiple porous stainless steel tubes positioned 4 cm apart in shallow trays (44 cm long, 32 cm wide and 8 cm deep), and then covered with a 4 cm layer of fine medium. Nutrient solution is recirculated through the porous tubes under -5 cm (water head) of negative pressure maintained with a siphoning procedure. Potatoes grown with negative pressures were compared to growth in similarly constructed trays that were maintained on a slant and solution added to the upper end of the trays and drained from the lower end. The same nutrient solution was recirculated through the trays of each treatment and maintained at a pH of 5.6. A microcultured plantlet of Norland cv. was transplanted into each tray. The negative pressure produced plants with less total plant dry weight, leaf area, branches, and stolons but increased biomass partitioning into tubers. The data suggest that this small constant negative water pressure regulates assimilate partitioning to encourage production of tubers.

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Chung-Ruey Yen and Karen E. Koch

Distribution of radiolabeled assimilates was examined at various intervals after 1 hour of light or dark 14CO2 fixation by leaves or developing fruit of grapefruit (Citrus paradisi Macf.) so that the fate of assimilates from each source could be assessed at sequential stages of fruit growth. Exported products of both light and dark 14CO2 fixation in leaves were deposited primarily in juice tissues of fruit even during periods of substantial dry weight accumulation by peel. Fruit photosynthesis, however, gave rise to assimilates that remained almost entirely in the peel (flavedo and albedo) even 7 days later, regardless of dry matter increases by other tissues. Products of dark 14CO2 fixation by intact fruit were recovered in all tissues but predominated in the peel of young fruit vs. juice tissues at later stages of growth. Comparison of dry matter gains and 14C-labeled assimilate distribution indicated that fruit photosynthesis likely contributed substantially to development of peel but not juice sacs. Data on dark 14CO2 fixation were consistent with its suggested involvement in organic acid synthesis by juice sacs.

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Theo J. Blom and Brian D. Piott

Four freesia cultivars were exposed to 24 hour·day-1 high-pressure sodium (HPS) lighting during various stages of their development. Upon emergence, freesia plants were exposed to the following four lighting treatments: 1) ambient; 2) ambient until shoot length was 5 to 8 cm followed by HPS lighting until flowering; 3) HPS lighting until shoot length was 5 to 8 cm followed by ambient lighting; and 4) continuous HPS lighting. Supplemental HPS lighting was provided at 37 μmol·m-2·s-1 at plant level in a glasshouse. Continuous lighting or lighting during flower development hastened flowering but reduced the number of flowering stems per corm, as well as stem length and weight. Lighting during the vegetative and flower initiation periods produced minor effects. The main benefit of supplemental lighting was found in total corm weight.

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Beny Aloni, Tamara Pashkar, Lea Karni, and Jaleh Daie

We investigated the effects of N nutrition on growth and carbohydrate partitioning of pepper (Capsicum annuum L., cv. Maor) seedlings in the greenhouse and on their subsequent recovery and development after transplanting. Seedlings received 0, 30, 100, or 200 mg N/liter for 14 days, after which they were transplanted and received 100 mg N/liter. Nitrogen levels below 100 mg·liter−1 inhibited shoot growth and leaf chlorophyll content; both were severely inhibited in the absence of supplemental N. Root growth had a negative relation with N supply; an enhanced root: shoot ratio was observed under low-N regimes. On a unit-leaf-area basis, CO2 fixation was not affected when N was present; however, it was greatly inhibited in the absence of N. Changes in the leaf starch and soluble sugar concentrations occurred as a function of N supply and leaf age. In the roots, low N led to lower sucrose and higher levels of hexose and starch. More sucrose was transported and accumulated into leaf veins of low-N tissue. Exogenously supplied 14C-labeled sucrose was rapidly converted into starch in the low-N tissue. Seedlings that received 100 mg N/liter had the highest post-transplant growth rate and flowered earlier. Carbohydrate status of young pepper seedlings influenced their post-transplant recovery. Optimal N supply is essential for full recovery and development of transplants.

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Rongcai Yuan and Duane W. Greene

BA was applied at 50 or 100 mg·L-1 to `More-Spur McIntosh'/Malling 7 (M.7) apple trees [Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.] at the 10 mm stage of fruit development. BA thinned fruit and increased fruit size. There were two distinguishable peaks of fruit abscission during `June drop'. BA accentuated the naturally occurring waves of fruit abscission, and enhanced translocation of 14C-sorbitol from leaves to fruit when applied directly to the fruit, but not when applied directly to the leaves. Net photosynthesis was decreased and dark respiration was increased when temperature following BA application was high (30 °C), whereas there was no effect when temperature was lower (20 °C). Total nonstructural carbohydrates, total soluble sugars, and starch in the leaves decreased dramatically over the 12- or 13-day observation period, regardless of BA treatment. These carbohydrate concentrations in the leaves were lowered further by BA application. Abscising fruit, based on specific reddening of the pedicel, had higher carbohydrate levels than persisting fruit, regardless of BA application. We conclude that BA thins fruit, at least in part, by increasing dark respiration and decreasing net photosynthesis. Chemical name used: N-(phenylmethyl)-1H-purine-6-amine [benzyladenine (BA)].