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Kemin Su, Dale J. Bremer, Richard Jeannotte, Ruth Welti, and Celeste Yang

molecular species in cellular membranes may change in response to environmental stress ( Grover et al., 2000 ; Welti et al., 2002 ). The major categories of plant cellular membrane lipids are glycolipids and phospholipids ( Lea and Leegood, 1993

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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, 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.

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Chana Phromtons and J. O. Garner Jr.

Storage roots of `Beauregard' and Centennial' were analyzed for total fatty acid composition and fatty acid composition by lipid class. The glycolipid, monagalactosyldiglycerol, may have been involved in chilling tolerance of `Beauregard' storage roots. This lipid had over 70 percent low-melting point fatty acids, mostly linoleic acid and linolenic acid. No consistent differences in the composition of phospholipids could be related to the chilling responses of the two sweetpotato cultivars.

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James Q. Garner Jr. and Thammasak Thongket

Proline content, leaf water potential (LWP), and leaf diffusive resistance (LDR) were determined for eight sweetpotato genotypes underwater stress conditions. Changes in fatty acid compositions of leaf polar lipids were determined in two sweetpotato genotypes during declining soil moisture. Proline did not accumulate and LWP did not decrease until soil moisture dropped below 10%, but LDR increased as soil moisture decreased. Genotypic differences in proline accumulation and LWP were found. Changes in fatty acid compositions occurred more in glycolipids than in phospholipids. Fatty acid changes were more pronouned in genotype MS20-2 than in “Vardaman”

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Bruce D. Whitaker

Abbreviations: ASG, acylated steryl glycoside; DGDG, digalactosyldiacylglycerol; FS, free sterols; GL, galactolipids; GlyL, glycolipid; MGDG, monoga-lactosyldiacylglycerol; NL, neutral lipid; PA, phosphatidic acid; PC, phosphatidylcholine; PE

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Dana F. Faubion and Adel A. Kader

California-grown `Hass' avocado fruit were stored at 5C, in air or a controlled atmosphere (CA) of 2% oxygen and 5% carbon dioxide. Fruit were evaluated at 0, 2, 4, 6, 8, 10, and 12 weeks, both immediately upon removal from storage and after ripening at 20C. Severe chilling injury (flesh browning) developed in the airstored fruit after 6 weeks, while only moderate symptoms were observed in CA-stored avocado fruit after 12 weeks. Lipid peroxidation breakdown products increased during storage and ripening in both air and CA treatments. Sterols, steryl esters, steryl glycosides, glycolipids, and phospholipids were analyzed. Quantity of acylated steryl glycoside in ripe fruit changed from 34 nmoles initially, to 51 or 27 nmoles after 6 weeks at 5C in air or CA, respectively. Glycolipid fatty acid unsaturation in air-stored fruit decreased with the development of chilling injury. Fatty acid unsaturation in phospholipids (phosphatidylinositol, phosphatidylcholine, phosphatidylglycerol, and phosphatidylethanolamine) of air-stored avocados decreased with the development of chilling injury. CA storage delayed the development of chilling injury and the loss of fatty acid unsaturation.

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Dana F. Faubion and Adel A. Kader

California grown `Hass' avocado fruit were stored at 5C, in air or a controlled atmosphere (CA) of 2% oxygen and 5% carbon dioxide. Fruit were evaluated at 0, 3, 6, and 10 weeks, both immediately upon removal from storage and after 5 days at 20C. Severe chilling injury developed in the air-stored fruit after six weeks, while only moderate symptoms were observed in CA stored avocado fruit after 10 weeks. Lipid peroxidation breakdown products increased during storage and ripening in both air and CA treatments. Sterols, sterol esters, glycolipids, and phospholipids were analyzed. There was a shift in composition during storage towards increasingly saturated fatty acids. The fatty acid shift was greater in air, than in CA stored fruit. Results will be discussed concerning their relevance to chilling injury development.

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Ehiorobo Izekor and James O. Garner Jr.

Selected physiological and anatomical characteristics of four chilling-tolerant sweetpotato genotypes were evaluated. Although the genotypes were considered highly tolerant to chilling, it was proposed that differences in their mechanism for tolerance existed. A genotype temperature interaction for chlorophyll fluorescence ratio was observed when the plants were exposed to 5 °C. Genotype differences were found for electrolyte leakage and peroxidase activity. There were no differences found for fatty acid percentage composition of the glycolipid or the phospholipid fraction from leaf samples. There were no differences in diffusive resistance and transpiration rate among the genotypes; however, stomata density, leaf shrinkage, and specific leaf weight differed among the genotypes. Differences were also found among the genotypes for percent leaf dry weight, leaf thickness, and cellular structure of the leaf. It was concluded that the basis or mechanism for chilling tolerance was not the same for the four genotypes tested; therefore, combining traits for tolerance could lead to higher tolerance levels.

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Arambage Abesinghe and James O. Garner

Storage roots of `Beauregard' and `Centennial' were used to identify varietal differences in fatty acid composition in plasmalemma lipids during storage conditions. Total plasmalemma fatty acid composition of glycolipids and phospholipids in storage roots of `Beauregard' and `Centennial' did not differ. The fatty acid composition of MGDG and DGDG in storage root plasmalemma was >50% unsaturated fatty acids in `Beauregard'. The high percentage of 18:2 (65.44%) fatty acid compared to `Centennial' (19.70%) and 79.35% total unsaturated fatty acid content in MGDG may contribute to low temperature tolerance in `Beauregard'. The higher percentages of 16:1 and 22:1 fatty acids in `Centennial' compared to `Beauregard' contributed to MGDG fatty acid unsaturation. However, these fatty acids have not been related to chilling tolerance.