Fluorescent products (lipofuscin-like compounds) of lipid peroxidation, which accumulate with age, were extracted from `Fuerte' avocado (Persea americana Mill.) peels during ripening. Fractionation and analysis of these fluorescent compounds (FCs) was carried out by an improved method, based on separation of FCs from-chlorophyll by Sep-Pak silica cartridges. A sharp rise in FCs content was found 2 days after harvest in avocado fruits stored at 22C, and ethylene enhanced this rise 3-fold on the 4th day. The accumulation of FCs preceded by at leasts days the onset of climacteric ethylene and respiration and by 2 days the decrease in fruit firmness. Moreover, a 6-foId increase in the FCs concentration occurred during 1 to 2 weeks of storage at SC, but the avocado fruits did not show any other detectable signs of ripening. These results suggest that lipid peroxidation may be regarded as one of the earliest detectable processes occurring during fruit ripening. Thus, an increase of FCs in peel may be employed as a horticultural characteristic for estimating initiation of ripening in avocado fruit.
Abstract
Immature zygotic embryos of Theobroma cacao L. (cacao) were cultured for 46 days in a liquid medium based on Murashige and Skoog (MS) salts and standard vitamins. Embryos at about the 100-day-stage were stimulated to develop toward maturity, based on increased production of anthocyanins, alkaloids, and lipids, when sucrose levels in the medium were increased to 27% (10 days in 3%, 2 days each in 9%, 15%, and 21%, and 30 days in 27% sucrose). Lipid development of embryos in vitro corresponded to that of zygotic embryos in vivo and asexual embryos in vitro. Embryos at the 150-day-stage did not respond to the high sucrose protocol.
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.
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.
Abstract
Four-year-old ‘Marsh’ grapefruit (Citrus paradisi Macf.) trees on trifoliate orange [Poncirus trifoliate (L.) Raf.] were subjected to temperature regimes of 25° to 5°C over 11 weeks in controlled environment facilities. Levels of total fatty acids in the flavedo of tree fruit decreased over this period by ≈50%, regardless of temperature. After 5 weeks, the level of linoleic acid in the flavedo of grapefruit that had been kept at progressively cooler temperatures from 25° to 5° was 76% greater than the level in control fruit at 25°. On rewarming and cooling, the differential for linoleic acid in flavedo was 41%. Increases of linoleic acid in the flavedo of fruit on trees that were treated with lower temperatures occurred in six lipids, with the greatest increases in phosphatidyl choline and wax-sterol esters. Chilling injury in harvested fruit during cold storage occurred slightly earlier in fruit from trees exposed to low temperatures, but was most severe in nonacclimated fruit.
Abstract
The content and sterol composition of free sterols (FS), steryl esters (SE), acylated steryl glycosides (ASG), and steryl glycosides (SG) in pericarp tissue of bell pepper fruit from three cultivars (Capsicum annuum L. cv Gator Bell, Bell Tower, and Lady Bell) were determined at three stages of ripening (mature-green, turning, and red-ripe). In each cultivar, FS were predominant at all stages of ripening, with ≈5- to 20-fold lesser amounts of SE, ASG, and SG. The proportions of the sterol conjugates (SE, ASG, and SG) varied somewhat between cultivars, but there was a consistent increase in the ratio of SG to ASG with ripening. The sterol composition of steryl lipids was quite similar in the three cultivars, and only minor changes occurred with ripening. Sitosterol was always the major sterol, followed by campesterol. Sitosterol plus campesterol comprised 89% to 95% of the total sterols in FS, ASG, and SG, and 74% to 91% in SE. Cholesterol and stigmasterol were always present as minor (1% to 4%) constituents. In general, small increases in stigmasterol and several minor, unidentified sterols occurred with ripening, at the expense of sitosterol and campesterol. These changes were greatest in SE.
Fresh fruit and vegetables are highly perishable because of their active metabolism during the postharvest phase. Previous studies showed that hormic dose of UV cause a delay in the senescence of tomato fruit by about 7 days. The objective of this study was to elucidate whether UV acts on the cell membrane in producing the phenomenon of delayed senescence, since it is known that UV radiation can provoke photooxidation of membrane lipids. Membrane lipid peroxidation was studied in tomato fruit (Lycopersicon esculentum Mill cv. Trust) treated by hormic UV dose, and was followed by assaying products of lipid oxidation during the storage period. We observed the production of lipofuscin-like compounds, malondialdehyde, aldehydes, pentane, ethane, and hydrogen peroxide within few days of the treatment. An increase in the efflux of electrolytes (total, potassium, and calcium) was also observed. An immediate increase in the level of these products of oxidation supports the hypothesis that UV radiation induces membrane lipid peroxidation. However, beyond 5 to 7 days after treatment, the production of oxidation products and electrolyte leakage were lower than the control fruits. Thereafter, the level of products of lipid oxidation associated with senescence was higher in control fruits than in treated ones. Results suggest that the initial oxidation stress by the exposure to UV led to biochemical reactions inducing the production of stress compounds, such as polyamines, which are non specific antioxidants. Consequently, a delay in the senescence was observed.
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.
Degradation of chlorophyll in spinach (Spinacia olearacea L. cv. Hybrid 612) appeared to be regulated through the peroxidase-hydrogen peroxide pathway, which opens the porphyrin ring, thus resulting in a colorless compound. This conclusion was arrived at from the analysis of chlorophylls (Chls) and their metabolizes by HPLC and of enzyme activities catalyzing the degradative reactions. Chls decreased at 25C but not at 1C. The chlorophyll oxidase pathway was not active, as noted by the lack of accumulation of a reaction product named Chl a-1. Lipid peroxidation increased with storage, but the products of the reaction. did not degrade chlorophyll, as noted by the lack of increase in Chl a-1. Chlorophyllase activity increased, but chlorophyllide, the expected product of the reaction, changed minimally during senescence. Ethylene at 10 ppm did not alter the pathway that degraded chlorophyll in spinach.
Abstract
Green and sun-bleached seeds of cultivars ‘G 2’ and ‘Green Fordhook 861’ lima beans (Phaseolus lunatus L.) were analyzed for total chlorophyll in whole seeds, and for soluble protein and rates of synthesis of carbohydrates, proteins, and lipids in excised embryonic axes. Bleached seeds were lower in total chlorophyll than green seeds. Embryonic axes from bleached seeds synthesized less carbohydrates and proteins, but more lipids than embryonic axes from green seeds. When held in water for 3 hours, embryonic axes from ‘G 2’ lima beans had about 65% more soluble protein, and respired 20% faster than embryonic axes from ‘Green Fordhook 861’. Whole ‘G 2’ lima bean seeds also emerged faster than ‘Green Fordhook 861’ seeds. In each cultivar, green seeds had a higher percent emergence than bleached seeds.