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Abbreviations: EER, ethane: ethylene ratio; EL, electrolyte leakage. 1 Graduate Assistant. 2 Associate Professor. To whom reprint requests should be addressed. Journal article no. 6121 of the Agr. Expt. Sta., Oklahoma State Univ., Stillwater

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Three years ago we established a long-term cryogenic storage project for apple germplasm and utilized grafting of buds obtained from stored dormant shoot sections as the major viability assay. Grafting, however, is time consuming and requires considerable skill. Electrolyte leakage and oxidative browning tests were used as alternative viability assays. Using leakage from individual buds in a multiwell analyzer, we examined modifications of the electrolyte leakage test and analyzed the kinetics of leakage in an attempt to determine whether the test can predict grafting success. The results suggest that more buds were viable than were estimated by the grafting test. In vitro culture is being examined to test this and to determine if practical recovery is feasible for diversity within the germplasm collection.

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Respiration, C2H4 production, lipid composition, and electrolyte leakage were monitored during ripening of two nonnetted muskmelon (Cucumis melo L.) varieties differing in their storage life: `Clipper' (a long-storage-life variety) and `Jerac', which was used as a control. Respiration rates were comparable in both varieties. Although `Jerac' exhibited normal climacteric C2H4 production, `Clipper' continued to produce significant amounts of C2H4 until senescence. Electrolyte leakage increased with ripening and was always higher in `Jerac'. The loss of membrane integrity seems to be related to changes in the lipid composition due to a breakdown of phospholipids, an increase of sterol synthesis, and an increase in fatty acid saturation. On the contrary, in `Clipper', the absence of a major change in sterol and phospholipids content and the high level of fatty acid unsaturation suggest that membrane permeability is not greatly affected during ripening. This is consistent with the low loss of solutes measured and may delay senescence in `Clipper' fruit.

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Abstract

Ethylene and ethane production and electrolyte leakage were determined during water stress of leaves of asceptically-cultured plum (Prunus insititia L. cv. Pixy). Ethylene production increased to a maximum at about 50% leaf water loss and decreased as water deficit increased. Ethane production and electrolyte leakage were highly correlated, increasing only after 50% water loss to a maximum at about 72% water loss, indicating an increase in cell injury and death.

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Abstract

Electrolyte leakage from tissue discs and internal conductivity of intact fruit of peach (Prunus persica (L.) Batsch) were determined during storage at 1°C and after transferring to 21°. Both methods produced similar results, however, the method used for measuring internal conductivity was rapid, nondestructive, and seemed to be more sensitive. Electrolyte leakage remained fairly constant while internal conductivity tended to decline during 5 weeks of chilling. Electrolyte leakage and internal conductivity increased when fruits were transferred to 21°. At 21° fruits which had been chilled for 2 weeks had enhanced leakage while conductivity was enhanced in fruits chilled for 1 and 2 weeks. In fruits transferred to 21° after 3 or more weeks of chilling, leakage and internal conductance declined and woolliness was concomitantly detected. The binding of free ions appears to be closely associated with woolliness in peaches.

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Abstract

Mature-green tomato fruit from 2 chilling-sensitive cultivars and 2 chilling-tolerant breeding lines, all derived from Lycopersicon esculentum Mill., were harvested and chilled at 5°C for 0, 2, 7, and 15 days. Mature-green fruit analyzed immediately after chilling showed higher electrolyte leakage in chilling-sensitive than chilling-tolerant lines. However, electrolyte leakage from chilled fruit that were ripened before analysis was higher in normal-sized than in cherry cultivars and seemed to be a function of fruit type rather than of chilling sensitivity. Unchilled field samples of these cultivars harvested at the mature-green, turning, and full-ripe stages and analyzed immediately showed an electrolyte leakage pattern similar to that found for comparable chilled mature-green fruit. No significant differences were found in calcium content (total, bound, or soluble) or in pectinase activity between chilling-sensitive or -tolerant cultivars.

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Storage of `Marsh' white seedless grapefruit (Citrus paradisi Macf.) for 2 weeks at 5C resulted in the development of chilling injury (CI). Electrolyte leakage from chilled fruit did not increase significantly until CI had become severe, and was therefore considered to be of limited value as an early indicator of CI. In contrast to electrolyte leakage, respiration and ethylene evolution were significantly higher in chilled than in nonchilled fruit, even before the onset of visual symptoms of CI. Respiration rates ranged from ≈8 to 11 and 5 to 7 ml CO2/kg per hour in chilled and nonchilled fruit, respectively. Ethylene evolution was not detected from nonchilled fruit, whereas chilled fruit produced from 45 to 250 nl ethylene/kg per hour. Results of this study indicate that electrolyte leakage does not increase until visible pitting of the flavedo has occurred, whereas stimulation of respiration and ethylene evolution occur early in the development of CI.

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Abstract

Seeds of 2 cultivars of muskmelon (Cucumis melo L.) were subjected to accelerated aging at 45°C and 100% relative humidity (RH) for periods up to 288 hours. In general, longer periods of aging resulted in greater declines in seed quality as measured by laboratory, greenhouse, and field emergence and germination. Seeds of ‘Iroquois’ were more sensitive to aging than ‘Hale’s Best #36’. Significant declines in germination occurred prior to any significant increases in electrolytic leakage from decorticated seeds indicating that electrolytic leakage is not a suitable test for seed quality with muskmelon.

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Abstract

Exposure of muskmelon (Cucumis melo L. Group reticulatus) fruit to high temperatures at harvest causes sunbuming, decreases firmness, lessens overall quality (2), and may accelerate fresh weight loss. The purpose of this study was to examine the effect of high prestorage temperatures on muskmelon fresh weight loss and on relative storage life measured as electrolyte leakage of shrink-film wrapped and nonwrapped fruit.

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Abstract

Studies were conducted to investigate the influence of 50 μl·liter−1 ethylene on the cell wall, polygalacturonase (PG) activity, and electrolyte leakage of harvested watermelon [Citrullus lanatus (thunb) Matsum and Nakai] fruit. Electrolyte leakage was significantly increased in tissues from ethylene-treated fruit. The highest leakage occurred in distilled water, although the net effect of ethylene was less dramatic due to high leakage from control fruit. Leakage was greatly reduced but the ethylene effect more apparent compared to the control when tissues were incubated in an isotonic medium of mannitol or in isotonic medium containing CaCl2. Polygalacturonase activity increased markedly in ethylene-treated fruit, showing a > 10-fold rise during the first 6 days of treatment. Little change in PG activity occurred in melons stored in air, even in fruit stored for as long as 120 days. Cell walls of fruit exposed to ethylene exhibited acute ultrastructural damage. The decline in placental tissue firmness and the development of watersoaking symptoms observed by the third day of 50 μl·liter−1 ethylene treatment were apparently due, in part, to the PG-mediated cell wall breakdown resulting in cell rupture. Additionally, ethylene appeared to enhance membrane permeability.

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