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R.E. McDonald, T.G. McCollum, and E.A. Baldwin

The objective of this study was to determine the effects of prestorage heat treatments on chilling tolerance of tomatoes. Mature-green `Agriset' tomato fruit (Lycopersicon esculentum Mill.), either C2H4-treated or not, were immersed in 42C water for 60 min, held in 38C air for 48 hours, or not treated, and then stored at either 2C (chilled) or 13C (nonchilled) for 14 days before ripening at 20C. Heat-treated fruit stored at 2C and transferred to 20C ripened normally while nonheated fruit decayed before reaching red ripe. Color (a*/b* ratio), lycopene content, and internal quality characteristics of fruit were similar at the red-ripe stage irrespective of method of heat treatment. In red-ripe heat-treated fruit, free sterol levels were significantly higher in chilled fruit than in nonchilled fruit. Heating fruit in 38C air resulted in significantly higher levels of some free sterols compared with heating fruit in 42C water. Of the 15 flavor volatiles analyzed, six showed significantly decreased concentrations as a result of C2H4-treatment and seven showed decreased concentrations when stored at 2C before ripening. Some volatiles were decreased by the heat treatments. Prestorage short- and long-term heat treatments could allow for storage of mature-green tomatoes at lower temperatures with little loss of their ability to ripen normally.

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S.V. Overton, L.D. Moore, and O.K. Miller

Ultrastructural observations were made of leaves of apple (Malus domestics Borkh. cv. Red Delicious) 12, 24, and 72 hours following a single foliar application of the sterol-inhibiting fungicide bitertanol. Thylakoids of chloroplasts from treated leaves were swollen and irregular and chloroplasts had lost their integrity within 12 hours after treatment. Occasionally, mitochondria looked washed out, although no other changes in membrane or organelle structures were observed. Within 24 to 72 hours, moreover, thylakoids of chloroplasts from treated leaves returned to a state similar to that of the controls. However, the numbers of starch granules in the chloroplasts of treated leaves appeared to increase throughout the 72 hours and remained somewhat higher than levels in controls. Thus, bitertanol does not appear to have a lasting effect on apple leaves. Chemical name used: ß-([1,1′-biplenyl]-4-yloxy)-α-(1,1-dimethylethyl)-1H-1,2,4-trizole-1-ethanol (bitertanol).

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Shiow Y. Wang and Miklos Faust

The glycolipids, phospholipids, and sterols were determined in normal and watercore-affected apple (Malus domestica Borkh. cv. Delicious). Fruit with watercore contained higher amounts of glycolipids, phospholipids, and sterols. The ratios of unsaturated to saturated fatty acids and (18:3) to (18:1 + 18:2) were lower in watercore-affected tissue than in normal tissue. The ratio of free sterols to phospholipids was higher, whereas the ratio of phosphatidylcholine to phosphatidylethanolamine was lower in watercore-affected apple. Membrane lipids were altered in watercore-affected fruit.

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Shiow Y. Wang and Miklos Faust

Composition changes in galactolipids, phospholipids, and sterols in apple shoots (Malus domestica Borkh. cv. Red Delicious) from August to April were determined. The predominant fatty acids in the membrane lipids of apple shoots were palmitic acid (C16:0), linoleic acid (C18:2), and linolenic acid (C18:3). The major galactolipid components in apple shoots were monogalactosyl diglyceride (MGDG) and digalactosyl diglyceride (DGDG). The amount of MGDG and DGDG increased from autumn to spring. Galactolipids contained highly unsaturated fatty adds, mainly linoleic (18:2) and linolenic (18:3) acid. The major individual phospholipids were phosphatidylcholine (PC) and phosphatidylethaeolamine (PE). β -Sitosterol and sitosteryl ester were the predominant sterols. The phloem contained higher amounts of galactolipids, phospholipids, and sterols than did the xylem tissue. There was a significant increase in the content of galactolipids and phospholipids and onsaturation of their fatty acids during cold acclimation. A decrease in the ratio of free sterols to phospholipids also occurred in apple shoots toward cold winter months. Composition changes in galactolipids, phospholipids, and sterols that were associated with growth cessation, defoliation and cold acclimation from fall to winter, were mostly reversed following deacclimation in spring.

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Shiow Y. Wang and Miklos Faust

The changes of membrane lipids in apple (Malus domestics Borkh. cv. Delicious) auxillary and terminal buds from August to April were determined. The predominant lipids were monogalactosyl diglyceride (MGDG), digalactosyl diglyceride (DGDG), phosphatidylcholine (PC), and phosphatidylethanolamine (PE). An increase in membrane polar lipids was associated with budbreak and bud growth from August to April. Linolenic acid was the predominant fatty acid in MGDG, DGDG, and PC, while linoleic acid was predominant in PE. Phosphatidylglycerol (PG) and phosphatidylinositol (PI) contained a high amount of palmitic acid. The ratio of (18:2 + 18:3) to 18:1 fatty acids in galactolipids in apple buds increased from August to April. ß-Sitosterol and sitosteryl ester were the predominant sterols in apple buds. An increase in sitosterol, a decrease in sitosteryl ester, and a decline in the ratio of free sterols to phospholipids occurred during budbreak in spring. A decrease in sitosterol was associated with bud expansion in spring.

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D.A. Rosenberger, T.L. Robinson, J.R. Schupp, C.A. Engle-Ahlers, and F.W. Meyer

Effects of three sterol-demethylation inhibiting (DMI) fungicides and a contact fungicide were compared over two years at each of two locations to determine if fungicide treatments had differential effects on productivity, fruit size and shape, or gross returns for `Empire' apples (Malus ×domestica Borkh.). Treatments were applied four to five times per year during the primary apple scab season. Effects of treatments were assessed by comparing fruit set efficiencies, number of fruit per tree, total harvested fruit weight, and fruit length: diameter ratios at harvest. No significant differences were noted among individual treatments in any of the four trials. However, when treatments were contrasted by grouping individual treatments, significantly larger fruit size was noted for triflumizole treatments vs. combined fenarimol and myclobutanil treatments in one of the four trials and for captan or mancozeb compared to fenarimol and myclobutanil treatments in two trials. None of the DMI fungicides compared in these trials had any consistent adverse affect on fruit size, total yield, or estimated gross return per hectare. We conclude that the plant growth regulator effects of DMI fungicides are inconsistent and are unlikely to have significant economic impact on commercial apple production.

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R.E. McDonald, W.R. Miller, and T.G. McCollum

Irradiation is being evaluated as a quarantine treatment of grapefruit (Citrus paradisi Macf. `Marsh'), but it can cause damage to the fruit. Research was conducted to determine if preirradiation heat treatments would improve fruit tolerance to irradiation as they improve tolerance to low temperature injury and to determine if canopy position influenced fruit tolerance to irradiation. Initially, grapefruit were irradiated at 0 or 2.0 kGy at a dose rate of 0.14 kGy·min-1 and selected biochemical changes were monitored over time. There was a marked increase in phenylalanine ammonia-lyase (PAL) activity following irradiation. Maximum activity (≈18-fold increase) was attained 24 hours after irradiation. Subsequently, grapefruit were harvested from interior and exterior canopy positions and irradiated at 0 or 1.0 kGy at a dose rate of 0.15 kGy·min-1 before storage for 4 weeks at 10 °C. Following storage, pitting of flavedo was the most evident condition defect noted as a result of irradiation. Pitting was observed on 27% and 15% of irradiated exterior and interior canopy fruit, respectively, whereas there was no pitting on nonirradiated fruit. Heat treatment before irradiation decreased susceptibility of fruit to damage. Pitting was 26%, 19%, and 17% when fruit were held 2 hours at 20 (ambient), 38 or 42 °C, respectively. Irradiation-induced PAL activity was reduced by temperature conditioning at 38 or 42 °C. Exterior canopy fruit flavedo contained higher levels of total phenols, including flavanols and coumarins compared with interior canopy fruit. Deposition of lignin was not related to canopy position. Neither irradiation nor heat treatment had an effect on total phenols or lignin deposition. Generally, cholesterol, campesterol, stigmasterol, β-sitosterol, and isofucosterol were found to be higher in four steryl lipid fractions in exterior canopy fruit compared with interior canopy fruit. Irradiation increased campesterol in the free sterol and steryl glycoside fractions and decreased isofucosterol in the free sterol fraction. Heat treatments had no effect on individual sterol levels. It seems that irradiation causes a stress condition in the fruit, which leads to pitting of peel tissue. Heat treatment before irradiation reduced damaging effects of irradiation.

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Gene Lester

Using an aqueous polymer two-phase [polyethylene glycol (PEG) 3400/dextran T500, 6.2%: 6.2%, w/w] partitioning procedure combined with isopycnic fractionation, plasma membranes derived from muskmelon (Cucumis melo L. var. reticulates Naud.) leaf blades have been isolated and examined for marker enzyme activity, density, and molecular composition. After aqueous polymer partitioning, plasma membranes were centrifuged on a linear sucrose density gradient, and a single band was found at the 31% (w/w) sucrose (1.13 g-cm-3). Identification of plasma membranes was performed by the combination of K+-stimulated ATPase, pH 6.5, vanadate inhibition of ATPase and KNO3-insensitive ATPase activity. Plasma membranes from seedling leaves grown for 5 days at 15C had the highest concentration of total phospholipids, the lowest concentration of proteins, and a total sterol concentration not significantly different from leaves grown at 30C. The total sterol to total phospholipid ratio of the plasma membrane from leaves grown for 5 days at 15C was ≈1:1; from leaves grown for 10 days at 15C or 5 days at 30C the ratio was ≈2:1; and from leaves grown for 10 days at 30C the ratio was ≈3:1. The plasma membrane phospholipid saturated to unsaturated fatty acid ratio from leaves grown for 5 days at 15C was ≈0.8:1.0; from leaves grown for 10 days at 15C or 5 days at 30C the ratio was ≈1.0:1.0; and from leaves grown for 10 days at 30C it was 1.4:1.0.

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Gene Lester

Hybrid honey dew muskmelon (Cucumis melo L. var. inodorus Naud.) fruit physiological maturity, the period of maximized or greatest compositional changes, occurs by 40 days after anthesis (DAA). Fruit maturity was determined by major changes in quality attributes: glucose, fructose, sucrose, and moisture content, firmness, mass, volume, and hypodermal-mesocarp plasma membrane specific H+-ATPase (E.C. 3.6.1.3) activity. Fruit ripening occurs by 50 DAA, as determined by additional changes in the mentioned quality attributes, and by fruit abscission at 50 DAA. Fruit senescence begins with decreases in almost all quality attributes, H+-ATPase activity, protein content, by the largest increase in the total free sterol : total phospholipid (FS:PL) ratio, and in hypodermal-mesocarp lipoxygenase (E.C. 1.13.11.12) activity. Physicochemical profiles of hybrid honey dew muskmelon fruit during growth and maturation should be useful to schedule commercial harvest of mature fruit, which is necessary for maximum honey dew fruit quality, extended shelf-life, and enhanced consumer satisfaction.

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Shiow Y. Wang, Miklos Faust, and Michael J. Line

The effect of IAA on apical dominance in apple buds was examined in relation to changes in proton density (free water) and membrane lipid composition in lateral buds. Decapitation induced budbreak and enhanced lateral bud growth. IAA replaced apical control of lateral buds and maintained paradormancy. Maximal inhibition was obtained when IAA was applied immediately after the apical bud was removed; delaying application reduced the effect of IAA. An increase in proton density in lateral buds was observed 2 days after decapitation, whereas the change in membrane lipid composition occurred 4 days later. Removing the terminal bud increased membrane galacto- and phospholipids and the ratio of unsaturated to corresponding saturated fatty acids. Decapitation also decreased the ratio of free sterols to phospholipids in lateral buds. Applying thidiazuron to lateral buds of decapitated shoots enhanced these effects, whereas applying IAA to the terminal end of decapitated shoots inhibited the increase of proton density and prevented changes in membrane lipid composition in lateral buds. These results suggest that change in water movement alters membrane lipid composition and then induces lateral bud growth. IAA, presumably produced by the terminal bud, restricts the movement of water to lateral buds and inhibits their growth in apple.