Grapefruit Flavedo Research Articles

CHARACTERIZATION OF GRAPEFRUIT FLAVEDO PEROXIDASES

Grapefruit (Citrus paradisi) flavedo is a rich source of peroxidase (POD) (EC 1.11.1.7). Changes in POD have been related to senesence and environmental stress in a variety of plant tissues. However, due to the large number of POD isoenzymes as well as the broad substrate specificity, measurement of POD activity in crude extracts is of limited value for gaining an understanding of the role of POD in vivo. We have begun to purify and characterize POD isoenzymes from grapefruit flavedo. HPLC gel permeation chromatography reveals 2 peaks of POD activity with apparent MW of 66 kD and 30 kD. Native PAGE (8% bis-acrylamide, pH 8.8) followed by activity staining indicates that the PODs differ in Pi; the 30 kD POD migrates anodally, whereas the 66 kD POD does not migrate. Isoelectric focusing has been used to separate flavedo PODs into acid (Pi ca 4.0) and basic (Pi > 8.5) forms. Treatment of grapefruit with ethylene (2 ppm 72 hours) induces a basic POD not present in freshly-harvested fruit or in nonethylene-treated controls.

Comparisons of Cobalt-60 Gamma Irradiation Dose Rates on Grapefruit Flavedo Tissue and on Mexican Fruit Fly Mortality

Percent electrolyte leakage, a measure of membrane integrity, proved to be a good predictor (R2 = 0.99) of cobalt-60 gamma irradiation dose injury on mid-season ‘Ruby Red’ grapefruit Citrus paradisi (Macf.) flavedo tissue (peel). Percent electrolyte leakage on grapefruit peel following a dose-rate of 250 grays/1.0, 2.5, 5.0, and 25.0 min decreased as grays/min (dose-rate) decreased. Total phenols, a biochemical response to irradiation following 250 grays/1.0, 2.5, 5.0, and 25.0 min also decreased as dose-rate decreased, demonstrating that injury to grapefruit peel diminished as 250 grays of gamma irradiation/rate declined. Comparisons of 10 and 20 grays of cobalt-60 gamma irradiation showed that a dose-rate of 10 grays/0.25 min to naked 8-d old Mexican fruit fly Anastrepha ludens (Loew) larvae caused a 90% reduction of adult emergence. Whereas, at 20 grays the reduction was greater than 99% with dose-rates of 20 grays/0.25, 0.5, 1.0, or 100 min. These data show that a gamma irradiation dose capable of reducing fly emergence by >99% will maintain an inhibitory effect even at relatively lower dose-rates. Therefore, once a quarantine security treatment for Mexican fruit fly is established, a lower dose-rate will reduce adult emergence and should impart little damage to grapefruit peel tissue.

Limitation of Alternative Respiratory Pathway Activity in Grapefruit Flavedo Tissue by Oxygen Availability

The capacity of the alternative respiratory pathway increased in the flavedo tissue of ;Marsh' grapefruit (Citrus paradisi Macf.) stored at 5 degrees C for 2 weeks or longer. Elevated O(2) levels during respiratory assays enhanced respiration by the tissue at 20 degrees C but not at 5 degrees C. At 20 degrees C, salicylhydroxamic acid alone was inhibitory to O(2) uptake only in elevated O(2). In conventional Warburg studies, alternative pathway respiration may be limited by the low solubility and/or slow rate of O(2) diffusion into plant tissues, such as grapefruit flavedo, and may be responsible for the apparent low utilization of the alternative pathway potential observed in other studies.

Interactive effects of washing, film wrapping and ethylene concentration on color development in grapefruit flavedo

Film-wrapping has recently developed into a valuable post-harvest technique. If combined with washing before de-greening citrus, decay could be reduced, de-greening could take place at ambient humidities, and shelf life would be increased by permitting ethylene (C 2H 4) application just prior to shipment. Previous reports indicate that pre-washing and wrapping inhibit color development in citrus. Therefore, the present work focused on characterizing the level of inhibition and attempting to overcome the inhibition by manipulation of applied C 2H 4 concentration during degreening. Washing and wrapping grapefruit did greatly inhibit de-greening. By increasing the C 2H 4 concentration to 250 μl l −1, the effect of washing was overcome. However, the combined effect of washing and wrapping was not overcome by increasing exogenous C 2H 4.

Lipids in Peel of Grapefruit and Resistance to Chilling Injury During Cold Storage

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.

Accumulation of Putrescine during Chilling Injury of Fruits

Putrescine (Put) increased 68% in lemon (Citrus limon (L.) Burm. f. cv Bearss) flavedo, 39% in grapefruit (C. paradisi Macf. cv Marsh) flavedo, 49% in grapefruit juice, and 149% in pepper (Capsicum annuum L. cv Early Calwonder) pericarp when fruits were stored at chilling temperatures. In lemon flavedo, the coefficient of correlation (r(2)) between Put concentration with severity of chilling was 0.90 and Put levels almost doubled; the injury index going from 1 to 2 units. Pepper pericarp, which was the most chilling-sensitive tissue tested (injury index going from 1 to 3.8 units), showed the greatest difference in Put accumulation (166 to 413 nanomoles per gram fresh weight) between storage temperatures of 7.2 and 1 degrees C. The least difference (338 to 470 nanomoles per gram fresh weight) was found in grapefruit flavedo between storage temperatures of 15.5 and 4.4 degrees C; the injury index going from 1 to 1.3 units.

Low Temperature Induced Azide-insensitive Oxygen Uptake in Grapefruit Flavedo Tissue

Abstract O2 uptake by tissues of grapefruit (Citrus paradisi Macf.) was measured using manometric Warburg techniques. The highest rate of uptake was by flavedo tissue and the lowest rate was by intact juice vesicles. O2 uptake by flavedo tissue increased exponentially when temperature increased, and the proportion of O2 uptake insensitive to azide (N3), an inhibitor of the cytochrome path, was greater at low temperatures than at high temperatures. Salicylhydroxamic acid (SHAM), an inhibitor of the alternative path, was only marginally inhibitory at all temperatures. Arrhenius-type plots of O2 uptake showed discontinuities at 12°C in the presence and absence of respiratory inhibitors. O2 uptake increased in flavedo tissue of grapefruit during the low temperature hardening of young trees. The increase was primarily in the N3-insensitive component. Low temperatures also induced N3-insensitivity in detached stored fruit, and induction was greater in chilling-resistant interior canopy fruit than in chilling-susceptible exterior fruit. Thus, N3-insensitive O2 uptake may be related to chilling resistance of sensitive fruit.

Ethylene-promoted malonylation of 1-aminocyclopropane-1-carboxylic acid participates in autoinhibition of ethylene synthesis in grapefruit flavedo discs

The increase in ethylene formation and in 1-aminocyclopropane-1-carboxylic acid (ACC) content in flavedo tissue of grapefruit (Citrus paradisi Macfad. cv. Ruby Red) in response to excision was markedly inhibited by exogenous ethylene. Ethylene treatment inhibited the synthesis of ACC, but increased the tissue's capability to malonylate ACC to N-malonyl-ACC, resulting in further reduction in the endogenous ACC content. The development of extractable ACC-malonyl-transferase activity in the tissue was markedly promoted by treatment with exogenous ethylene. These results indicate that the autoinhibition of ethylene production in this tissue results not only from suppression of ACC synthesis, but also from promotion of ACC malonylation; both processes reduce the availability of ACC for ethylene synthesis.

Low temperature induction of invertase activity in grapefruit flavedo tissue

Invertase activity increased in the flavedo tissue of ‘Marsh’ grapefruit ( Citrus paradisi Macf.) when trees were exposed to cold hardening temperatures and decreased at dehardening temperatures. Invertase activity also increased in the flavedo of detached fruit stored at 5δ. Reducing sugar levels paralleled invertase activity while sucrose levels were inversely related to invertase levels. The mechanism by which low temperatures induce invertase activity in grapefruit flavedo tissue was not determined. However, results indicated that a proteinaceous inhibitor, similar to the one found in potato tubers, is not involved in the regulation of invertase activity in flavedo tissue of grapefruit.

Sugar and Proline Accumulation in Grapefruit Flavedo and Leaves during Cold Hardening of Young Trees1

Abstract Four-year-old ‘Marsh’ grapefruit (Citrus paradisi Macf.) trees on trifoliate orange [Poncirus trifoliata (L.) Raf.] rootstock were temperature acclimated to 5°C in controlled environment facilities with approximately 400 μeinsteins m−2s−1 PAR. Total soluble carbohydrates and proline increased in both leaves and fruit flavedo as temperatures were progressively decreased. Maximum accumulation of carbohydrates occurred in leaves and flavedo at 10° ambient air. Both sucrose and reducing sugars increased in leaves at all acclimating temperatures, but only reducing sugars increased in the flavedo at temperatures below 15°. The concentration of proline was the greatest in the leaves and flavedo at 5°. Both total soluble carbohydrates and proline decreased during temperature deacclimation at 25°.

Respiration of Grapefruit and Orange Flavedo Tissue in Relation to Chilling and Non-chilling Temperatures and Respiratory Inhibitors1

Abstract One theory on the mechanism of chilling injury of tropical and subtropical fruits is that aerobic respiration is impaired at chilling temperatures and injury occurs from consequent accumulation of fermentation products. Therefore, O2 uptake and CO2 evolution by the flavedo (colored portion of peel) of chill-sensitive grapefruit (Citrus paradisi Macf.) and chill-resistant orange (Citrus sinensis (L.) Osbeck) tissue were measured by a manometric Warburg technique over a range of chilling and non-chilling temperatures to see if there were differences in respiratory activities of the 2 tissues. A break in the Arrhenius plot of CO2 evolution and O2 uptake by grapefruit tissues occurred at 12°C but no break was apparent in similar plots for orange tissue. Respiratory quotients for both orange and grapefruit were lower at chilling than non-chilling temperatures. When O2 uptake was determined in the presence of maximal inhibitory levels of cyanide and salicylhydroxamic acid, a large residual O2 uptake remained. At chilling temperatures, in the absence of cyanide, salicylhydroxamic acid reduced O2 uptake by grapefruit flavedo tissue by 30% but had no effect on O2 uptake by orange flavedo tissue in the absence of cyanide. The results indicate that extra-mitochondrial oxidases may have a role in chilling injury of grapefruit flavedo.

Phytochemical arrestants for the leaf-cutting ants,Atta cephalotes(L.) andAcromyrmex octospinosus(Reich), with some notes on the ants' response

Albedo (the inner, white part of the rind) of the grapefruit (Citrus parodisi) and the flowers of the garden hibiscus (Hibiscus rosa-sinensis) were analysed for the presence of chemo-stimulants for the leaf-cutting antsAtta cephalotes(L.) andAcromyrmex octospinosus(Reich). Two distinct types of chemical substances in grapefruit albedo (unabsorbed sapids from a cation-exchange resin I.R. 120, and the total lipid fraction) were significant arrestants forAtta cephalotes, whilst five types of chemical substances (absorbate on the cation-exchange resin I.R. 120, unabsorbed sapids from the same resin, the total lipid fraction, absorbate on a polyamide resin, and neohesperidosides) arrestedAcromyrmex octospinosus. For both ant species, the unabsorbed sapids from the polyamide resin appeared to be the most attractive of the relatively refined fractions. A preliminary analysis showed a similar situation for hibiscus flowers.Both ant species preferred young to older grapefruit leaves. There appears to be a chemical basis for this, and in the case ofA. octospinosusthere was evidence of the existence of repellents in the older leaves and in grapefruit flavedo (the outer, yellow part of the rind).Substantial heterogeneity in preferences was detected in a given nest from day to day, between different nests of the same species, and between the two species. It is suggested that this is attributable to social phenomena evolved by the ants.