The proportion of spurs blooming on `McIntosh' apples (Malus domestica Borkh.) was reduced significantly in 1986 and 1988, but not in 1987, following seasonal programs of six bitertanol or flusilazole treatments applied at two and three rates, respectively. The fungicides were not associated with any visible phytotoxic effect nor was shoot length reduced by any fungicide treatment. In two of three experiments conducted in May and June 1986, transpiration was reduced by the low rate of flusilazole and the high rate of bitertanol relative to both the captan and nonsprayed trees. In all three experiments, flusilazole at 1.4 g a.i./100 liter was associated with transiently reduced transpiration rates, lasting a minimum of 48 hours, relative to the nonsprayed control. Fungicides affected the diffusive resistance of apple leaves in all three experiments; however, there were no consistent treatment effects on diffusive resistance among the three experiments.
Thomas E. Marler and Christopher A. Shaw
). We have been studying the physiology of C. micronesica in relation to a group of sterols and their derived glucosides because of the various issues discussed here. We have chosen these compounds because of the demonstrated epidemiological links
Thomas E. Marler, Vivian Lee, and Christopher A. Shaw
prevalent part of the local diet throughout historic times. We have been studying a group of phytosteryl glucosides and their sterol precursors because they elicit cell death in neural cell cultures and spinal motor neuron loss in mice studies ( Khabazian et
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
G.A. Picchioni, A.E. Watada, W.S. Conway, and B.D. Whitaker
Postharvest Ca infiltration delays senescence and improves storage quality of apple fruit, but the consequences on membrane lipid composition have received little evaluation. We studied changes in galactolipids (mono- and digalactosyl-diacylglycerol; MGDG and DGDG) and sterol conjugates (sterol glycosides and acylated sterol glycosides; SG and ASG) in `Golden Delicious' cortical tissue. Fruit were pressure-infiltrated with CaCl, at harvest (0, 2, or 4% w/v), stored for 6 months at 0C, and evaluated during subsequent exposure to 20C. MGDG, SG and ASG concentrations were greater in Ca-infiltrated fruit (CIF) than in control fruit. A 35-37% increase in ASG occurred during the first 7 days at 20C in CIF, when ASG decreased by 19% in control fruit. Ca infiltration may delay degradation of plastid membranes and increase sterol conjugation during apple fruit ripening.
Bruce D. Whitaker
A previous study of lipids from pericarp tissue of tomato fruit ranging from mature-green to red-ripe showed a large increase in total sterols accompanied by dramatic changes in sterol composition and conjugation with ripening. This study was conducted to determine whether similar changes occur in microsomal membranes derived from tomato fruit pericarp. Acylated steryl glycoside (ASG), the predominant steryl lipid, declined during ripening, with increases in steryl glycoside (SG) and free sterol (FS). Only minor changes in fatty acid composition were associated with the drop in ASG. The stigmasterol:sitosterol ratio increased throughout ripening, but much more in Fs than in SG or ASG. The ratio of FS to phospholipid (PL) increased with ripening. However, FS was never greater than 10 percent of the total membrane sterol (TMS), and TMS:PL actually declined over the middle stages of ripening. It is not known why tomato tissues maintain such high levels of ASG and SG, but sterol conjugation is thought to regulate the physical properties of cell membranes.
Gene E. Lester
Plasma membrane (PM) from hypodermal-mesocarp tissues of muskmelon fruits (Cucumis melo L. var. reticulatus Naud.) were compared to the electrolyte leakage changes of the same tissue during maturation and storage at 4 or 24C. During fruit maturity and storage, leakage of the hypodermal-mesocarp tissue increased, which is coincident with increased total sterol: total phospholipid ratios and increased phospholipid fatty acid saturation index of the PM. ATPase activity, a marker for the PM, indicated that the PM increased in buoyant density from 1.13 g.cm-3 to 1.14 g.cm-3 during maturity and ATPase activity peaked with fruit maturation. ATPase activity decreased with 10 days postharvest storage and was less at 24C vs. 4C, which was coincident with increased hypodermal-mesocarp electrolyte leakage. Biochemical changes within the sterol and phospholipid matrix of the PM are suggested to contain the processes capable of altering fruit membrane permeability and subsequent muskmelon fruit storage life.
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.
Bruce D. Whitaker
Altered metabolism of membrane lipids has been proposed as a mechanism for the beneficial effects of postharvest calcium treatment on apple quality. A previous study showed that after transfer of apples stored 6 months at 0C to 20C, calcium-treated fruit exhibited slower loss of galactolipid and altered levels of sterol conjugates. The present study of lipids in “control” fruit was conducted as a prelude to further in-depth analyses of the effects of postharvest calcium and heat treatments on lipid metabolism in apples during and after cold storage. Neutral lipid, glycolipid (GL), and phospholipid (PL) fractions were obtained by column chromatography followed by TLC separation of GL and PL classes. The major GL were steryl glycosides (SG), acylated steryl glycosides (ASG), cerebrosides (CB), and mono- and digalactosyl diacylglycerols. Phosphatidylcholine (PC) > P-ethanolamine (PE) > P-irositol (PI) were the major PL. The fatty acids of PC and PE were quite similar, whereas those of PI were more saturated. CB included only 2-hydroxy fatty acids. Among the steryl lipids, free sterols > SG > ASG, with beta-sitosterol >90% of the total sterol in each.
Bruce D. Whitaker
Lipid composition and pigment content were determined in pericarp of `Pik Red' tomatoes (Lycopersicon esculentum Mill.) that were harvested when mature-green (MG) then ripened for 1 or 14 days at 20C, chilled for 11 or 21 days at 2C, or chilled for 21 days and transferred to 20C for 4 days (rewarmed). During ripening, chlorophyll fell below a detectable level, carotenes increased 100-fold, phospholipids (PLs) dropped ≈20%, and galactolipids (GLs) dropped ≈35%. Fatty-acid unsaturation decreased slightly. Steryl esters (SEs), more than free sterols (FSs) and steryl glycosides (SGs), increased at the expense of acylated steryl glycosides (ASGs), and in all four steryl lipids, the stigmasterol: sitosterol ratio rose dramatically, whereas the level of isofucosterol fell sharply. During chilling, chlorophyll declined ≈40% and carotenes ≈60%. PL content did not change, whereas GL fell ≈15%. Fatty-acid unsaturation increased slightly. FS, much more than SG and SE, increased at the expense of ASG. The stigmasterol: sitosterol ratio changed little in ASG, SG, and SE but declined in FS. Isofucosterol increased in FS and SE. Rewarming had little effect on the levels of chlorophyll, carotenes, or PL levels, but caused GL to fall another ≈15%. Fatty-acid unsaturation decreased slightly in GL and ASG. The distribution of total sterol in ASG, SG, FS, and SE changed dramatically, yielding proportions close to those in unchilled MG fruit. Also, 4 days after rewarming, the stigmasterol: sitosterol ratio had increased sharply, particularly in FS and SE, and there was a further rise in isofucosterol in all four steryl lipids. These results indicate that chloroplast damage occurs during chilling, but PL-rich cell membranes are not degraded, even upon rewarming. Changes in sterol composition and conjugation during chilling and after rewarming could result in membrane dysfunction.