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Geeta K. Nanaiah and Jeffrey A. Anderson

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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Leigh E. Towill, John W. Waddell and Philip L. Forsline

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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Dominique Lacan and J.C. Baccou

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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T.G. McCollum and R.E. McDonald

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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Tomasz Anisko, Cynthia L. Haynes and Orville M. Lindstrom

Freeze tests were performed on stem sections of Fraxinus americana, Lagerstroemia indica Magnolia gradiflora, Rhododendron `Red Ruffle', Zelkova serrata, and leaves of Magnolia grandiflora and Rhododendron `Red Ruffle' in the tinter and summer of 1993. Freeze injury was quantified using electrolyte and phenolic leakage techniques and compared to the lethal temperature range determined by visual method assisted by differential thermal analysis. Richards function was fitted to the electrolyte and phenolic leakage data by the modified Gauss-Newton method. The inflection point of the Richards function coincided with the lethal injury range for non-acclimated leaves, but overestimated the freeze tolerance for acclimated leaves and for both acclimated and non-acclimated stems. A proposed interception point of the lower asymptote and a line tangential to the curve inflection point provided an improved estimate of the lethal injury range in most of the species.

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Kurt D. Nolte, Eugene A. Nothnagel and Charles W. Coggins Jr.

Studies were conducted to determine whether certain physiological effects of gibberellic acid (GA3) on the peel of citrus fruits may be attributed to GA3 interaction with cellular membranes. Excised mesocarp tissue from pummelo [Citrus maxima (Burm.) Merrill] fruits was analyzed for electrolyte and K+ release over time in varying concentrations of GA3. Electrolyte leakage and K+ efflux was significantly reduced (up to 30%) when tissue was incubated in the presence of GA3. GA3 improved the viability of mechanically isolated protoplasts during 72 hr of storage at 7C, as shown by the use of fluorescein diacetate. These results suggest that some of the GA3-elicited responses in citrus fruits may be membrane related.

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Leena Lindén, Pauliina Palonen and Mikael Lindén

Seasonal cold hardiness of red raspberry (Rubus idaeus L.) canes was measured by freeze-induced electrolyte leakage test and visual rating of injury. Leakage data were transformed to percentage-adjusted injury values and related to lethal temperature by graphical interpolation and by the midpoint (T50) and inflection point (Tmax) estimates derived from three sigmoid (the logistic, Richards, and Gompertz) functions. Tmax estimates produced by Richards and Gompertz functions were corrected further using two different procedures. The 10 leakage-based hardiness indices, thus derived, were compared to lethal-temperature estimates based on visual rating. Graphical interpolation and Tmax of the logistic or T50 of the Gompertz function yielded lethal-temperature estimates closest to those obtained visually. Also, Tmax values of the Gompertz function were well correlated with visual hardiness indices. The Richards function yielded hardiness estimates deviating largely from visual rating. In addition, the Richards function displayed a considerable lack of fit in several data sets. The Gompertz function was preferred to the logistic one as it allows for asymmetry in leakage response. Percentage-adjusted injury data transformation facilitated curve-fitting and enabled calculation of T50 estimates.

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Chon C. Lim, Rajeev Arora and Edwin C. Townsend

Seasonal patterns in freezing tolerance of five Rhododendron cultivars that vary in feezing tolerance were estimated. Electrolyte leakage was used, and raw leakage data were transformed to percent leakage, percent injury, and percent adjusted injury. These data were compared with visual estimates of injury. Percent adjusted injury was highly correlated (0.753) to visual estimates. Two asymmetric sigmoid functions—Richards and Gompertz—were fitted to the seasonal percent adjusted injury data for all cultivars. Two quantitative measures of leaf freezing tolerance—Lt50 and Tmax (temperature at maximum rate of injury)—were estimated from the fitted sigmoidal curves. When compared to the General Linear Model, the Gompertz function had a better fit (lower mean error sum of squares) than Richards function. Correlation analysis of all freezing tolerance estimates made by Gompertz and Richards functions with visual LT50 revealed similar closeness (0.77 to 0.79). However, the Gompertz function and Tmax were selected as the criteria for comparing relative freezing tolerance among cultivars due to the better data fitting of Gompertz function (than Richards) and more descriptive physiological representation of Tmax (than LT50). Based on the Tmax (°C) values at maximum cold acclimation of respective cultivars, we ranked `Autumn Gold' and `Grumpy Yellow' in the relatively tender group, `Vulcan's Flame' in intermediate group, and `Chionoides' and `Roseum Elegans' in the hardy group. These relative rankings are consistent with midwinter bud hardiness values reported by nurseries.

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John M. Ruter

Membrane thermostability of `Needlepoint' Chinese holly (Ilex cornuta Lindl. & Paxt.), `Albo-marginata' English holly (Ilex aquifolium L.), and `Nellie R. Stevens', an Ilex aquifolium × Ilex cornuta hybrid, was determined by measuring electrolyte leakage in excised leaves and roots. The critical midpoint heat-killing temperature (T,) after a 30-min exposure was 54.4 ± 0.4C for `Nellie R. Stevens' leaves and was ≈ lC higher than that for Chinese (52.9 ± 0.3C) or English holly (52.9 ± 0.4C). The Tm for English holly roots (53.9 ±_ 1.5C) was higher than that for either `Nellie R. Stevens' (51.7 ± 0.3C) or Chinese holly (50.1 ± 0.3C). The results of this study suggest that English holly and `Nellie R. Stevens' leaves and roots can withstand direct heat injury equal to or greater than that of Chinese holly.

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F.P. Maier, N.S. Lang and J.D. Fry

Stolons of `Raleigh', `Floratam', and FX-332 St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] were sampled from the field between October and March in two consecutive years to evaluate accuracy of an electrolyte leakage (EL) method for predicting freezing tolerance. Lethal temperatures of stolons estimated using EL were compared to those obtained by regrowth tests in the greenhouse. Mean lethal low temperatures for regrowth and EL methods over 12 sampling dates were `Floratam', –4.5C (regrowth) vs. –4.4C (EL); FX-332, –4.2C (regrowth) vs. –4.9C (EL); and `Raleigh', –6.0C (regrowth) vs. –5.4C (EL). A positive correlation (r = 0.81) was observed between EL-predicted and regrowth lethal temperatures for `Raleigh', which exhibited some acclimation during the first sampling year. The EL technique consistently predicted a lower lethal temperature for `Raleigh' than for `Floratam', which corroborates field observations concerning freezing tolerance of these two cultivars.