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Anna J. Talcott and William R. Graves

measuring 2 to 5 m in height with trifoliate leaves ( Dirr, 1998 ; McMinn, 1989 ). The fruits are compressed samaras that are broadly winged, indehiscent, and light brown to cream in color ( Dirr, 1998 ). In the center of the fibrous, papery pericarp are

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S.J.R. Underhill and C. Critchley

Mature lychee (Litchi chinensis Sonn.) fruit were heat-treated at 60C for 10 min to study heat-induced pericarp browning. Polyphenol oxidase (EC activity of the pericarp increased immediately, corresponding with rapid anthocyanin degradation, Tissue browning was observed 2 min after heating, with pigmentation distributed uniformly throughout the pericarp. The distribution of brown pigments was different than the highly localized browning observed under ambient desiccation. Although both ambient and heat-induced pericarp browning are visually similar, the anatomical distribution of brown pigmentation is quite distinct. The distribution of brown pigmentation was not consistent with anthocyanin localization. Following ambient desiccation, the mesocarp became colorless even though this represented the greatest concentration of pigment. Browning caused by heating may result from nonselective degradation of a range of compounds, including anthocyanin.

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Paul W. Bosland, Danise Coon, and Peter H. Cooke

fruit locules and is derived from the tissue connecting the placenta to the pericarp ( Esau, 1977 ; Iwai et al., 1979 ; Judd et al., 1999 ). The epidermal cells of the interlocular septum have been implicated in capsaicinoid biosynthesis based on

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Lucianne Braga Oliveira Vilarinho, Derly Jose Henriques da Silva, Ann Greene, Kara Denee Salazar, Cristiane Alves, Molly Eveleth, Ben Nichols, Sana Tehseen, Joseph Kalil Khoury Jr., Jodie V. Johnson, Steven A. Sargent, and Bala Rathinasabapathi

fruit traits in a population derived by crossing two contrasting, open-pollinated heirloom cultivars of C. annuum . This study confirms previous data on inheritance of fruit morphometric parameters and adds new data on the inheritance of pericarp shape

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Hanling Yu and Claude Willemot

We examined the relationship between reduced galactolipid content in tomato fruit at 4C and chilling injury. Galactolipid biosynthesis from 14C-acetate was compared in pericarp discs of cold-tolerant `New York 280' (`NY') and -sensitive `Early Cherry' (`EC') at 4C and 20C. Labeled lipids were separated by 2D-TLC. Labeled monogalactosyldiglyceride (MGDG) molecular species were hydrolyzed using a position-specific lipase; the fatty acids released were hydrogenated and separated according to chain length by reverse-phase TLC. At 4C, the relative amount of radioactivity was reduced in MGDG and enhanced in phosphatidylcholine (PC) in both cultivars, in comparison with labeling at 20C. In discs from fruit chilled for 6 h, labeling was similar in `NY' and `EC'. In fruit held at 4C for 8 days, labeling of MGDG was reduced and that in PC was enhanced to a greater extent in chilling-sensitive `EC' than in `NY'. The proportion of the MGDG label in eukaryotic species (i.e., the ratio in C18/C16 fatty acids in position sn-2), was less in `EC' at 4C than at 20C, even for fruit held at 4C for only 6 h. The ratio was little affected in `NY'. The data indicate that biosynthesis of eukaryotic MGDG was inhibited in tomato fruit at chilling injury-inducing temperatures.

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Celso L. Moretti, Steven A. Sargent, Donald J. Huber, Adonai G. Calbo, and Rolf Puschmann

`Solar Set' tomatoes (Lycopersicon esculentum Mill.) were harvested at the mature-green stage of development and treated with 50 μL·L-1 ethylene at 20 °C. Breaker-stage fruit were dropped from 40 cm onto a solid surface to induce internal bruising and held along with undropped fruit at 20 °C. At the ripe stage, pericarp, locule, and placental tissues were analyzed for soluble sugars, vitamin C, pigments, titratable acidity, soluble solids content, pericarp electrolyte leakage, extractable polygalacturonase activity, and locule tissue consistency. Bruising significantly affected chemical composition and physical properties of pericarp and locule tissues, but not placental tissue. For bruised locule tissue, carotenoids, vitamin C, and titratable acidity were 37%, 15%, and 15%, lower, respectively, than unbruised fruit. For bruised pericarp tissue, vitamin C content was 16% lower than for unbruised tissue, whereas bruising increased electrolyte leakage and extractable polygalacturonase activity by 25% and 33%, respectively. Evidence of abnormal ripening following impact bruising was confined to locule and pericarp tissues and may be related to the disruption of cell structure and altered enzyme activity.

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Glenn M. Ito and James L. Brewbaker

Pericarp thickness in maize (Zea mays L.) was analyzed by generation mean analysis for backcross and F2 populations from eight hybrids, derived from two thin-pericarped sweet corn inbreds—AA8 and 677a (55 and 51 μm)—crossed with four field corn inbreds—B37, B68, H55, and Hi26 (range 82-132 μm). Average heterosis was −12.5% and segregating progeny distributions were skewed toward those of thin-pericarped parents. Narrow-sense heritability was high, averaging 55.2%, and the number of effective factors was low, ranging from 1.4 to 5.9 and averaging 3.3. Epistatic effects were as large as additive or dominance effects in many crosses, urging caution in applying models that exclude gene interactions to determine variance components and heritabilities. The mode of action in reducing pericarp thickness appeared to differ among the two thin parents, with AA8 affecting the differential thickening of germinal vs. abgerminal walls, and 677a reducing the number of pericarp cell layers. All genetic parameters suggested that genetic progress in backcross conversions to thin pericarp in sweet corn breeding would be rapid irrespective of the pericarp thickness of exotic parents.

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Daniel I. Leskovar, Virgil Esensee, and Helen Belefant-Miller

Spinach (Spinacia oleracea L.) seed germination can be inhibited by high temperatures. An understanding of thermoinhibition in spinach is critical in predicting germination and emergence events. The purpose of this study was 3-fold: 1) to determine seed germination percentage and rate of spinach genotypes—`Cascade', `ACX 5044', `Fall Green', and `ARK 88-354'—exposed to constant and alternating temperatures; 2) to determine the nature and extent of inhibition imposed by the pericarp; and 3) to investigate leachate and oligosaccharide involvement in thermoinhibition. Germination inhibition began at >20 °C constant temperature and was totally suppressed at 35 °C. Alternating temperatures at 30/15 °C (12-hour day/12-hour night) resulted in greater germination than a constant 30 °C. The genotype sensitivity to supraoptimal temperatures was in the order of `ARK 88-354' ≤ `Fall Green' < `ACX 5044' < `Cascade', but the highly thermoinhibited `Cascade' seeds retained the ability to germinate when shifted to lower incubation temperatures. The pericarp inhibited germination, since seeds deprived of the pericarp had ≈90% germination at 30 °C. `ACX 5044' and `Cascade' had higher ABA content in the pericarp than `ARK 88-354' and `Fall Green'. Before imbibition at 30 °C, raffinose levels in each genotype were in the order of `ARK 88-354' > `Fall Green' > `Cascade'. After 48 hours of imbibition, sucrose and glucose levels were highest and raffinose levels were lowest in `ARK 88-354' and `Fall Green' seeds, while `Cascade' seeds remained less active metabolically. These data suggest that the pericarp apparently acts as a physical barrier as well as a source of inhibitors during thermoinhibition.

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Cheryl Ann Engelkes, Irvin Widders, and Hugh Price

A field experiment was conducted to quantify the ontogenetic changes in Ca concentration and content of pickling cucumber fruits as influenced by environmental conditions and genotype. Pericarp tissue Ca concentrations (1.1% to 0.7% of dry weight) were higher but declined less rapidly during fruit development than endocarp concentrations (0.8% to 0.2% of dry weight). About 90% of net fruit Ca content accumulated within the pericarp of ≈150 g fresh weight fruit, the rest in the endocarp. The rate of Ca accumulation was highly variable during fruit ontogeny but was closely correlated with growth rate (grams fresh weight/day). Environmental conditions had the largest effect on Ca accumulation rate. Fruit tissue Ca concentrations were affected both by genotype and the cultural environment, especially at the later stages of fruit development. Calcium concentrations (1.5 to ≈3.0% of dry weight) in fully expanded leaf tissue were higher than in rapidly growing fruit tissues on the same plants.

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Mikal Saltveit*

Heat-shock induced chilling tolerance in excised discs of tomato fruit pericarp tissue significantly alter the kinetics of chilling-induced ion leakage from the discs into an aqueous isotonic mannitol solution. Pericarp discs were excised from mature-green tomato fruit, trimmed of locular material to 5-mm thickness, held overnight (ca. 16 h) at 20 °C and then subjected to various heat-shock (45 °C) treatments before being chilled at 2.5 °C for up to 30 days. Two discs were immersed in 20 mL of 0.3 m mannitol in a 50-mL plastic centrifuge tube and the conductivity of the aqueous solution periodically measured. The tube was capped and frozen at -20 °C. Total conductivity was measured once the tube had warmed to 20 °C with shaking. The percent ion leakage was calculated as the percent of total, and subjected to an analysis to partition rates of leakage into symplastic and apoplastic components. The symplastic component was not affected by the heat-shock treatment, while the apoplastic component showed reductions consistent with reduced chilling-induced damage to the cellular membrane. The protective heat-shock treatments also significantly increased the tissues resistance to fungal infection.