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  • Author or Editor: Karen E. Koch x
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Transpiration, respiration, dry weight gain, and water accumulation were measured to quantify the total carbon balance, total water utilization, carbohydrate cost for fruit growth, and water use efficiency in developing fruit of grapefruit (Citrus paradisi Macf). Rate of net carbon loss and net water loss (mg g-1FW hr-1) both decreased during fruit development. On a whole fruit basis, total carbon demand was reduced during the period of peak expansion, then increased rapidly during fruit maturation. In contrast, whole fruit rates of water loss and water utilization (loss plus accumulation) peaked at about 100 days after anthesis, then decreased toward fruit maturation. Carbohydrate cost for fruit growth was greatest (3.49 g sucrose g-1DW) at the early stage of fruit development (immediately following anthesis), whereas water use efficiency peaked (193 mg DM g-1 H2O) at the final stage of fruit development. The thickness of albedo and pectin content in fruit may contribute to the observed water conservation. Total estimated carbon cost of grapefruit development indicates approximately 120 g of sucrose would be necessary for production of a 450 g fruit (77 g DW) at 22 C.

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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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Abstract

The oxalic-acid-accumulating fruit of carambola (Averrhoa carambola L. Oxalidaceae) was examined during development to characterize changes in sugars and acids and to evaluate potential maturity indices. Commercial maturity (color break) occurred 65 and 60 days after fruit set of sweet ‘Arkin’ and tart ‘Golden Star’, respectively. Fruit size at this stage was highly variable (51 to 103 mm long) and not a reliable indicator of maturity. Total soluble sugar concentration, mainly glucose and fructose, was almost 25% greater in the sweet ‘Arkin’ fruit (≈27 mg·g−1 fresh weight) than in the tart ‘Golden Star’ carambolas (22 mg·g−1 fresh weight). At harvest, sucrose made up only 15% to 20% of the total soluble sugars. Oxalic acid was the predominant organic acid in young fruit of both cultivars, but levels differed dramatically between sweet ‘Arkin’ (≈1 mg·g−1 fresh weight) and tart ‘Golden Star’ (≈7 mg·g−1 fresh weight). Malic acid (<1.5 mg·g−1 fresh weight) was also present. Acidity in sweet ‘Arkin’ carambolas declined rapidly during early growth, but remained high during development of tart ‘Golden Star’. Sugar accumulation, acid reduction, and color development continued for at least 7 days after color break if fruit remained on trees, but such fruit were not firm enough for typical commercial handling.

Open Access

Abstract

Postharvest changes in color and compositional characteristics were monitored in ‘Arkin’ and ‘Golden Star’ carambolas (Averrhoa carambola L.) before, immediately following, and 6 days after they were stored for 44 days at 5, 10, or 15C. General commercial practice has been to store this tropical fruit at 10C or higher to avoid possible chilling injury. Results from the present work demonstrated that fruit stored at 5C maintained better appearance, lost less weight, and exhibited less change in soluble sugar (glucose, fructose, and sucrose) or organic acid (oxalic and malic) concentrations than fruit stored at 10C. Rewarming experiments (6 days at 23C) indicated that these fruit had not lost the capacity to ripen normally and did not develop symptoms of chilling injury. Carambolas therefore can be stored most effectively at 5C.

Open Access

Localization of sucrose synthasa (SS), an enzyme Previously shown to be highly active in transport tissues of citrus fruit, was further defined via immunohistochemical analysis of stage II calamondin fruit. Using the indirect immunogold technique, 8 μm sections were first reacted with rabbit anti-SS polyclonal serum followed by incubation with 5 nm gold conjugated goat-anti-rabbit IgG. Little immunolabel was observed in the majority of peel tissues, however an abundant immunoreaction was evident in parenchyma cells directly adjacent to the segment epidermis surrounding juice sacs. Antibody was not associated with this epidermnl layer. Similarly, in juice vesicle stalks (JVS) the internal parenchyma cells showed significant SS localization compared to minimal immunoreaction in the epidermal layers of the JVS. Although the antigen did not appear to be specifically localized within the vascular bundles, an extensive distribution of the enzyme was associated with the parenchymatous cells immediately adjacent to vascular strands.

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Carrizo citrange [Citrus sinensis (L.) Osb. × Poncirus trifoliata (L.) Raf.] seedlings were budded with `Hamlin' orange [Citrus sinensis (L.) Osb.] and subjected to 3 bud forcing treatments: (1) topping [T] by removing the seedling above the bud union; (2) lopping [L] by cutting half way through the seedling above the bud union and breaking the rootstock over; or, (3) bending [B] the seedling top over and tying it to the base of the plant. As scion buds emerged and grew, plants were sacrificed for dry weight measurements; also, the portion of the rootstock seedling above the bud union was exposed to 14CO2 at 3 stages of scion development. Plants with seedling tops attached (B,L) gained more dry weight and fibrous roots than T seedlings. Scion elongation was greater for B plants than for T plants. Plants usually flushed twice regardless of bud forcing treatment. No treatment differences were noted for time of flushing or scion bud emergence. Labeled photosynthate from attached rootstock leaves was translocated to scions during both flushes suggesting that recently fixed C enhanced scion growth for B and L plants.

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We investigated the effect of gibberellic acid (GA3) application before color break on peel color, fruit respiration, and soluble sugars in different tissues of ‘Hamlin’ sweet orange [Citrus sinensis (L.) Osb.] fruit to test the hypothesis that GA3 influence on peel color might be mediated by sugars. Fruit were sprayed with GA3 (45 g·ha−1 a.i.) in early October of 2 consecutive years. Peel color, whole-fruit respiration, and fructose, glucose, and sucrose levels were quantified in flavedo and albedo tissues when nontreated fruit were still green, at precolor break, color break, and when peels were fully yellow. Fruit treated with GA3 remained more green-colored than nontreated fruit, and differences between them were detectable by 12 or 21 days after treatment (Years 1 and 2, respectively). Fruit respiration rates were similar in both groups regardless of peel color. Effects of GA3 on color transition were evident only after significant differences emerged in flavedo glucose (both years) and fructose (second year) levels. Moreover, there was a linear, inverse relationship between green peel color and flavedo fructose (r 2 = 0.68, first year; 0.72, second year) and glucose levels (r 2 = 0.60, first year; 0.50, second year). In contrast, sucrose levels in the flavedo showed a less consistent relationship with peel color. The GA3 treatment maintained a descending sucrose gradient from the albedo to the flavedo that was typical of young, photosynthetically active fruit. This gradient dissipated during peel color change of nontreated fruit. These data support the hypothesis that soluble sugars could be contributing effectors of the GA3-mediated delay in chloroplast-to-chromoplast conversions by the orange flavedo.

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Growth and yield typically increase when tomato plants are grafted to selected interspecific hybrid rootstocks from which distinctive root system morphologies are envisioned to aid nutrient uptake. We assessed these relationships using a range of exogenous nitrogen (N) supplies under field production conditions. This study analyzed the impact of N on growth, root distribution, N uptake, and N use of determinate ‘Florida 47’ tomato plants grafted onto vigorous, interspecific, hybrid tomato rootstocks ‘Multifort’ and ‘Beaufort’. Six N rates, 56, 112, 168, 224, 280, and 336 kg·ha−1, were applied to sandy soil in Live Oak, FL, during Spring 2010 and 2011. During both years, the leaf area index, aboveground biomass, and N accumulation (leaf blade, petiole, stem, and fruit) responded quadratically to the increase in N fertilizer rates. Averaged over the two seasons, the aboveground biomass, N accumulation, N use efficiency (NUE), and N uptake efficiency (NUpE) were ≈29%, 31%, 30%, and 33% greater in grafted plants than in nongrafted controls, respectively. More prominent increases occurred in the root length density (RLD) in the uppermost 15 cm of soil; for grafted plants, RLD values in this upper 15-cm layer were significantly greater than those of nongrafted plants during both years with an average increase of 69% over the two seasons. Across all the grafted and nongrafted plants, the RLD decreased along the soil profile, with ≈60% of the total RLD concentrated in the uppermost 0 to 15 cm of the soil layer. These results demonstrated a clear association between enhanced RLD, especially in the upper 15 cm of soil, and improvements in tomato plant growth, N uptake, and N accumulation with grafting onto vigorous rootstocks.

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Carbon dioxide exchange, dry weight, C, and N content of `Bonita' and `Climax' blueberry (Vaccinium ashei Reade) fruit were measured from anthesis through fruit ripening to quantify developmental changes in amounts of imported C and N required for fruit development. Net photosynthesis occurred in fruit of both rabbiteye cultivars from petal fall through color break. During this time, fruit net photosynthesis declined from 16 μmol CO2/g fresh weight (FW) per hour for `Bonita' and 22 μmol CO2/g FW per hour for `Climax' to 0.2 μmol CO2/g FW per hour for both. Dark respiration for both cultivars declined following petal fall from 16 μmol CO2/g FW per hour to 3 μmol CO2/g FW per hour before increasing at fruit ripening to 9 μmol CO2/g FW per hour. Fruit C content was constant at 0.43 mg C/mg dry weight (DW) throughout development, while N content declined from 0.05 mg N/mg DW at petal fall to 0.01 mg N/mg DW at ripeness. DW accumulation and respiration accounted for 63% and 37%, respectively, of the total C requirement for fruit development. Fruit photosynthesis was estimated to contribute 15% of the total C required for fruit development in both cultivars; however, fruit photosynthesis supplied 50% of the C required during the first 10 days after bloom and 85% during the 5 days after petal fall. This large, early contribution of C from fruit photosynthesis may aid in the establishment of fruit until the current season's vegetative growth can supplement plant carbohydrate reserves in providing C for fruit development.

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