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Bruce D. Whitaker

MG tomato fruit were stored for four or 12 days at chilling (2C) or nonchilling (15C) temperature. Fruits stored 12 days at 15C ripened to the turning stage, whereas fruits at 2C did not ripen. Lipids of microsomes and plastids from pericarp tissue were analyzed at harvest and after four or 12 days of storage. After 12 days at either 15C or 2C, the ratio of phospholipid (PL) to protein in microsomes declined, with a concomitant increase in the ratio of total membrane sterols (TMS) to PL. The TMS/PL ratio also increased in crude plastids. In both microsomes and plastids, free sterols (FS) increased more at 2C than at 15C, and thus accounted for a larger percentage of the TMS. The ratio of stigmasterol to sitosterol in steryl lipids, particularly in FS, increased more at 15C than at 2C. The unsaturation index of fatty acids in PL and galactolipids generally increased slightly during storage at both 15C and 2C. The ratio of phosphatidylethanolamine to P-choline increased in both membrane fractions at both temperatures. In plastids, the ratio of mono- to digalactosyldiacylglycerol declined substantially at 2C but not at 15C.

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Bruce D. Whitaker

Plastids and microsomal membranes were isolated from pericarp tissue of mature green and red-ripe tell pepper fruit harvested from greenhouse and field grown plants. The lipid composition of these membrane fractions changed far more with ripening of field grown than greenhouse grown fruit. Also, the phospholipid (PL), free sterol (FS), steryl glycoside (SG) and acylated steryl glycoside (ASG) content of microsomes and plastids from both green and red fruit were very different under the two growing conditions. Total steryl lipids (TSL = FS + SG + ASG), and the TSL/PL ratio, increased in microsomes and decreased in plastids with ripening. These changes were much greater in field grown fruit. The ASG/SG ratio decreased with ripening in both membrane fractions, under both growing conditions. Ripening and growth conditions affected the phospholipid and sterol composition in plastids much more than in microsomes. Lipid changes associated with the chloroplast – chromoplast transformation were similar in field and greenhouse grown fruit, including an increase in the galactolipid/PL ratio. Future studies will assess how differences in membrane lipid composition affect postharvest storage life of the fruit.

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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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Gene Lester

Hypodermal mesocarp disks from abscised muskmelon fruits (Cucumis melo L. var. reticulatus Naud.) were floated in 0.00, 0.04 or 0.16 M CaCl2 plus 0.35 M mannitol at ′20C in the dark for 10 days. Changes in chlorophyll, protein and total phospholipids all indicators of membrane senescence were assayed. The catabolism, percent retention, of chlorophyll, protein and total phospholipids was delayed by 0.04 M Ca, but accelerated by 0.16 M compared to no Ca. Loss of membrane integridity, increased free sterol: total phospholipid (umol./umol.), was delayed by 0.04 M Ca, hut accelerated by 0.16 M compared to no Ca. The degree of lipid saturation was inconclusive between Ca treatments. Muskmelon fruit disks membrane lipid degradation is slowed by 0.04 M Ca but accelerated by supraoptimal 0.16 M Ca treatment.

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Monte L. Nesbitt, J. Benton Storey, D. Lyda, and L.J. Grauke

Rootstock resistance to soil-borne phytopathogenic fungi, such as Phymatotrichum omnivorum (Shear) Duggar, is an important factor in disease control. Measurement of natural rootstock resistance is often based on plant survival/mortality percentage, and /or growth data. Fungal colonization of host roots in disease screening experiments may not be uniform for many reasons, causing variability in host response. Quantification of fungal colonization is needed in order to better understand rootstock performance. Ergosterol, a structural sterol in cell membranes of fungi, is not found in higher plants, and can thus be a measure of fungal colonization. Ergosterol was extracted from roots of pecan seedlings artificially inoculated with P. omnivorum and grown in an environmental growth chamber. Analysis of extracts with HPLC revealed that seedlings which were killed in screening, or had low root performance ratings, had increased levels of ergosterol. Non-inoculated controls also contained Ergosterol. indicating contamination and possible competition by other fungi.

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

The effect of Indole-3-acetic acid (IAA) on apical dominance in apple (Malus domestica Borkh.) buds was examined by studying 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 bud paradormancy. Maximal inhibition was obtained when IAA was applied immediately after the apical bud was removed. Delaying this application weakens the effect of IAA. An increase in proton density in lateral buds was observable 2 days after decapitation, whereas the change in membrane lipid composition occurred 4 days later. Decapitating the terminal bud induced an increase in membrane galacto- and phospholipids. and the ratio of unsaturated to corresponding saturated fatty acids. Decapitation also induced a decrease in the ratio of free sterols to phospholipids in lateral buds. Application of IAA to the terminal end of decapitated shoots inhibited the increase of proton density and prevented changes in the membrane lipid composition of lateral buds.

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Gene Lester

Hybrid, non-netted, green-fl esh, honeydew muskmelon fruit physiological maturity occurred by 40 days after anthesis (DAA). Fruit maturity was determined by major increases in quality attributes: moisture content, firmness, soluble solids concentration, weight, volume, and qualitative and quantitative changes in glucose, fructose, and sucrose content. Fruit ripening occurred between 40 and 50 DAA as determined by maximized changes in the aforementioned quality attributes, and by fruit abscission at 50 DAA. Fruit senescence begins with decreases in: quality attributes, hypodermal-mesocarp plasma membrane H+-ATPase (E.C. 3.6.1.3) activity, and protein content, and by increases in: the total free sterol: total phospholipid ratio, and hypodermal-mesocarp lipoxygenase (E.C. 1.13.11.12) activity. Delineated growth and maturation physicochemical data of hybrid honeydew muskmelon fruit should be beneficial to the commercial harvest of mature fruits, which is necessary for maximizing honeydew fruit quality, extending shelf-life, and enhancing consumer satisfaction.

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

Mature-green `Sunbeam' tomatoes (Lycopersicon esculentum Mill.) were treated in varying order with C2H4, 42 °C water for 1 hour, 38 °C air for 2days, held 2 days at 20 °C (partial ripening), or not treated and then stored at 2 °C (chilled) for 14 days before ripening at 20 °C. Heat-treated fruit stored at 2 °C and transferred to 20 °C ripened normally, while 63% of nonheated fruit decayed before reaching the red-ripe stage. Partially ripened fruit developed more chilling injury, were firmer, were lighter, and were less red in color than fruit not partially ripened. Lycopene content and internal quality characteristics of fruit were similar at the red-ripe stage irrespective of sequence of C2H4 exposure, heat treatment, or a partial ripening period. Of the 15 flavor volatiles analyzed, 10 were reduced by storage at 2 °C, Exposure to C2H4 before the air heat treatment reduced the levels of four volatiles, while C2H4 application either before or after the water heat treatment had no effect on flavor volatiles. Two volatiles were decreased and two were increased by partial vipening, Storage at 2 °C decreased the level of cholesterol and increased levels of campesterol and isofucosterol in the free sterol pool. Exposure to C2H4 before or following heat treatments, the method of heat treatment, and partial ripening had little effect on free sterols, steryl esters, steryl glycosides, or acylated steryl glycosides in the pericarp of red-ripe fruit. A shortor long-term heat treatment of mature-green tomatoes could permit storage at low temperatures with little loss in their ability to ripen normally, whereas partial ripening did not reduce chilling injury.

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T.G. McCollum, R.E. McDonald, and H.E. Nordby

The objective of this work was to determine if lipid composition of grape fruit flavedo tissue differed with canopy position and if changes in flavedo lipid composition occurred during the development of chilling injury (CI). `Marsh grapefruit were harvested from interior (IN) and exterior (EX) canopy positions and stored at 5C for up to 8 weeks. During storage, EX fruit developed severe CI, whereas IN fruit developed only trace CI. Electrolyte leakage from EX fruit flavedo increased during storage and significantly greater than from IN fruit At the time of harvest, flavedo oleate and linoleate, on a μg % basis, were higher in IN than in EX fruit During storage at 5C, the amount of oleate in IN fruit flavedo decreased and was similar to EX fruit after 4 weeks at 5C. The relative amount of flavedo linoleate decreased in IN fruit and increased in EX fruit during storage at 5C and following 8 weeks at 5C was higher in EX fruit than in IN fruit At the time of harvest, total lipid P in flavedo was higher in IN fruit than in EX fruit; during storage the amount of flavedo lipid P in IN fruit decreased and was equivalent to EX fruit following 8 weeks at 5C. Total sterols in flavedo did not differ with canopy position and remained constant during storage.

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Susan Lurie and Joshua D. Klein

Mature-green tomato (Lycopersicon esculentum Mill.) fruit, when kept for 3 days at 36, 38, or 40C before being kept at 2C for 3 weeks, did not develop chilling injury, while unheated fruit placed at 2C immediately after harvest did. When removed from 2 to 20C, the heated tomatoes had lower levels of K+ leakage and a higher phospholipid content than unheated fruit. Sterol levels were similar in heated and unheated fruit while malonaldehyde concentration was higher in heated fruit at transfer to 20C. The unheated tomatoes remained green, and brown areas developed under the peel; their rate of CO2 evolution was high and decreased sharply, while ethylene evolution was low and increased at 20C. In contrast, the heat-treated tomatoes ripened normally although more slowly than freshly harvested tomatoes: color developed normally, chlorophyll disappeared, and lycopene content increased, CO2, and ethylene evolution increased to a climacteric peak and K+ leakage increased with time. During prestorage heating, heat-stress ethylene production was inhibited, protein synthesis was depressed, and heat-shock proteins accumulated. There appears to be a relationship between the “heat shock response” and the protection of tomato fruit from low-temperature injury.