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Jeffrey A. Anderson

`Early Calwonder' pepper (Capsicum annuum L.) and `Jubilee' corn (Zea mays L.) leaf disks exposed to high temperature stress produced ethylene, ethane, methanol, acetaldehyde, and ethanol based on comparison of retention times during gas chromatography to authentic standards. Methanol, ethanol, and acetaldehyde were also identified by mass spectroscopy. Corn leaf disks produced lower levels of ethylene, ethane, and methanol, but more acetaldehyde and ethanol than pepper. Production of ethane, a by-product of lipid peroxidation, coincided with an increase in electrolyte leakage (EL) in pepper but not in corn. Compared with controls, pepper leaf disks infiltrated with linolenic acid evolved significantly greater amounts of ethane, acetaldehyde, and methanol and similar levels of ethanol. EL and volatile hydrocarbon production were not affected by fatty acid infiltration in corn. Infiltration of pepper leaves with buffers increasing in pH from 5.5 to 9.5 increased methanol production.

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Elizabeth A. Baldwin and Myrna O. Nisperos-Carriedo

Edible lipid and composite films were tested for their ability to retain flavor volatiles in `Pineapple' orange fruits stored at 21° using a headspace analysis technique. Volatiles, considered to be important to fresh orange flavor, were quantified and acetaldehyde, ethyl acetate, ethyl butyrate and methyl butyrate increased progressively during storage in coated fruits. Acetaldehyde increased by the second day of storage in uncoated fruits but declined thereafter, `Sunny' tomato fruits were harvested at the green or breaker stage of maturity and ripened at 32.5, 21.0 and 12.9°C. Some fruit from the higher and lower storage temperatures were moved to 21° after one week. In most cases major or important flavor volatiles were highest in fruit transferred to or continuously stored at 21.0°C followed by 12.9 and 32.5°C. Fruit harvested at the breaker stage generally had higher volatile levels compared to those harvested green.

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Tonda Bardwell, Huang Jin Xing, J. O. Garner, and J. L. Silva

Storage roots of `Jewel', `Centennial' and `Beauregard' were chilled at 5C for 0, 10, 20, 30 or 40 days. After chilling, the roots were placed at 21C for two days to allow hardcore development. Hardcore was measured as weight of root that remain hard after boiling for 45 minutes. Hardcore and fatty acid composition of total lipids were compared for the three cultivars. Hardcore was present at 10 days in both `Jewel ' and `Centennial' and at 20 days for `Beauregard'. Severity of hardcore increased with time of chilling. Linoleic acid content of 'Beauregard ' was higher for the 0, 10, and 20 day sampling periods, and decreased to a level equal to that found in 'Jewel ' and `Centennial'.

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Sharon Sowa and Eric E. Roos

Infrared spectroscopy was used to measure biochemical changes during bean (Phaseolus vulgaris L.) seed imbibition. Transmission spectroscopy of excised embryonic axes revealed changes in lipid phase (gel to liquid crystalline) and protein secondary structure within the first 15 min of hydration. Spectral changes in seed coats, cotyledons, and axes during the first 2 hr of imbibition (measured in vivo) were detected using photoacoustic sensing. Onset of seed respiration could be detected as early as 15 min after addition of water. CO2 production, demonstrated by the appearance of a double peak centered at 2350 cm-1, increased with time of imbibition. Infrared photoacoustic spectroscopy of intact seeds holds promise as a method for non-invasive viability assessment.

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Abha Upadhyaya, Tim D. Davis, and Narendra Sankhla

Seeds of moth bean (Vigna aconitifolia Jacqu. Marechal cv. Jaadia) were germinated in the presence of 0, 0.1, 1, or 2 μm 24-epibrassinolide (EBL). After 72 h, cotyledons were excised and the seedlings exposed to 22 or 48 °C for 90 min. At 48 °C EBL increased total electrolyte, K+, and sugar leakage relative to the untreated control. Following exposure to 48 °C, EBL-treated seedlings had higher malondialdehyde concentrations than controls indicating that EBL enhanced high temperature-induced lipid peroxidation. At 48 °C, EBL increased ascorbic acid oxidase activity and decreased superoxide dismutase activity relative to the control. Taken together, these data do not support the hypothesis that brassinosteroids confer thermotolerance to plants. On the contrary, EBL increased high temperature-induced damage and reduced the activity of some antioxidant systems that may protect against stress-induced cellular damage.

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Benjamin Jeyaretnam, Hazel Y. Wetzstein, Sharad C. Phatak, and Russel W. Carlson

Changes in lipid and total protein content of somatic embryos of pecan (Carya illinoinensis) were estimated during maturation, cold treatment alone (3, 5, or 8 weeks) or cold followed by dessication (3, 5, or 7 days). Triglyceride was estimated colorimetrically and methyl esters of fatty acids were analyzed by GC-MS. Total protein was extracted from the same tissue with 2% SDS in Tris·HCL buffer. Triglyceride content of enlarged somatic embryos was significantly lower than zygotic embryos and further declined after 5 weeks cold treatment. An even greater decline was observed during the desiccation treatment. The most abundant fatty acids in small and enlarged somatic embryos are linolenic > palmitic > oleic > stearic acid. However, the molar ratio of linolenic to oleic reached 1:1 after 5 weeks of cold treatment. During enlargement, protein content increased to levels found in zygotic embryos, with desiccation resulting in further elevation.

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Darlene M. Cowart and Robert L. Shewfelt

-Lipid peroxidation has been proposed as an important factor in chilling injury of susceptible fruits and vegetables. The effect of in vitro peroxidative challenge on H+ATPase activity in intact plasma membrane vesicles and solubilized enzyme was determined by incubation with (1) deionized water (control), (2) Fe3+-ascorbate, and (3) lipoxygenase (LOX) + phospholipase A2(PLA2) for 0, 30, and 60 min. Enzyme activity increased throughout the incubation period with no accumulation of thiobarbituric acid-reactive substances (TBA-RS) in the control, but vesicles challenged by the peroxidative systems showed significant increases in TBA-RS and decreases in membrane-bound H+ATPase activity. Greater losses in H+ATPase activity were observed in solubilized enzyme than in intact vesicles. The results indicate that loss of H+ATPase activity due to chemical modification of the protein rather than changes in membrane fluidity and suggest that modification is away from the active site.

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Dehua Liu, Miklos Faust, Helen A. Norman, Merle Millard, and Garry W. Stutte

Membrane lipids and cellular water states were studied in endodormant and paradormant apple buds. Paradormancy was overcome by thidiazuron while endodormant buds were forced to break after a certain period of chilling. Nuclear magnetic resonance imaging was used to determine water states in buds of different stages of dormancy. In endodormant buds, the changes in water states from a more tightly-bound to a more free form were correlated with changes in membrane fatty acid composition. The ratio of saturated/unsaturated fatty acids decreased with chilling, especially in C18:l/C18:3 molecular species of phosphatidylcholine and phosphatidylethanolamine. Bud lipase activity, which was assayed by in vitro hydrolysis of triglycerides, showed an abrupt increase after chilling treatments.

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Steven F. Vaughn

Localization of enzymes in specific plant tissues is crucial to understanding their role in processes such as differentiation and disease resistance. The oxidative enzymes lipoxygenase (LOX; EC 1.13.11.12), peroxidase (PER, EC 1.11.1.7) and polyphenol oxidase (PPO; EC 1.10.3.1) have all been implicated as playing critical roles in plant disease resistance. The histochemical localization of all three enzymes in potato tuber slices was accomplished either directly on the tissue slices (for LOX) or by blotting of the tissue onto nitrocellulose membranes (for PER and PPO). LOX was visualized in specific tissues by the oxidation of KI to I2 via lipid peroxides and the subsequent reaction of I2 and endogenous starch to form a colored, insoluble complex. PER and PPO activities were visualized with 4-methoxy-α-naphthol and 3,4-dihydroxy-phenylalanine, respectively. Fractionation of the slices and determination of enzyme activities in the fractions confirmed the reliability of these techniques.

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Jeffrey A. Anderson, Niels O. Maness, and Robert E. Stall

Bell pepper (Capsicum anuum L.) leaves inoculated with Race 1 of Xanthomonas campestris pv. vesicatoria (XCV) produced more ethylene and methanol than water-infiltrated controls in studies with leaves attached or detached during inoculation and dissipation of water-soaking. `Early Calwonder 20R'. a pepper genotype resistant to Race 1 of XCV, evolved more ethylene and methanol than `Early Calwonder 10R' (susceptible) following syringe inoculation of detached leaves with ≈ 7 × 107 cells/ml. A light intensity of ≈ 500 μmol· m-2·s-1 during dissipation of water-soaking of attached leaves triggered more ethylene and methanol than covering inoculated leaves with aluminum foil. Volatile hydrocarbon production from leaves infiltrated with distilled water was not significantly affected by light intensity during dissipation of water-soaking. The lipid peroxidation products, ethane and pentane, were not detected by headspace sampling following bacterial inoculation.