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At least 19 recordsLinked to original sources
PubMed1987

Regulation of climacteric respiration in ripening avocado fruit.

Ripening of avocado fruit is associated with a dramatic increase in respiration. In vivo(31)P nuclear magnetic resonance spectroscopy revealed large increases in ATP levels accompanying the increase in respiration. Both glycolytic enzymes, phosphofructokinase, and pyrophosphate: fructose-6-phosphate phosphotransferase were present in avocado fruit with the latter activity being highly stimulated by fructose 2,6-bisphosphate. Fructose 2,6-bisphosphate levels increased approximately 90% at the onset of ripening, suggesting that the respiratory increase in ripening avocado fruit may be regulated by the activation of pyrophosphate:fructose-6-phosphate phosphotransferase by an increase in fructose 2,6-bisphosphate.

Journal Article↗
PubMed1986

Synthesis and processing of cellulase from ripening avocado fruit.

The biosynthesis and processing of cellulase from ripening avocado fruit was studied. The mature protein is a glycoprotein, as judged by concanavalin A binding, with a molecular weight of 54,200. Upon complete deglycosylation by treatment with trifluoromethane sulfonic acid the mature protein has a molecular weight of 52,800 whereas the immunoprecipitated in vitro translation product has a molecular weight of 54,000. This result indicates that cellulase is synthesized as a large molecular weight precursor, which presumably possesses a short-lived signal peptide. A membrane-associated and heavily glycosylated form of the protein was also identified. This putative secretory precursor was enzymically active and the carbohydrate side chains were sensitive to endoglycosidase H cleavage. Results of partial endoglycosidase H digestion suggest that this precursor form of the mature glycoprotein possesses two high-mannose oligosaccharide side chains. The oligosaccharide chains of the mature protein were insensitive to endoglycosidase H cleavage, indicating that transport of the membrane-associated cellulase to the cell wall was accompanied by modification of the oligosaccharide side chains. The presence of a large pool of endoglycosidase H-sensitive membrane-associated cellulase (relative to an endoglycosidase H-insensitive form) suggest that transit of this protein through the Golgi is rapid relative to transit through the endoplasmic reticulum.

Journal Article↗
PubMed2025

Cultivar-Specific Differences in C6 and C7 Sugar Metabolism During Avocado Ripening: Comparative Insights from Bacon, Fuerte, and Hass.

Avocado is a unique fruit in which of seven-carbon (C7) sugars (notably D-mannoheptulose and perseitol) dominate the carbohydrate profile at harvest. Despite growing interest in sugar-mediated ripening processes, limited comparative data exist across cultivars. This work characterises the dynamic changes in non-structural carbohydrates in the mesotecarp of three commercially relevant avocado varieties-Bacon, Fuerte, and Hass-across four defined ripening stages, from unripe to overripe, with five biological replicates per stage. Using a validated hydrophilic interaction liquid chromatography-mass spectrometry (HILIC-MS) method, we quantified five key sugars and assessed their evolution through ripening. Concentrations varied among the studied samples within the following ranges: D-mannoheptulose, 0.4-49 mg/g dry weight (DW); perseitol, 0.5-23 mg/g DW; glucose, 0.8-5.3 mg/g DW; fructose, 0.6-4.5 mg/g DW; and sucrose, 0.5-3.4 mg/g DW. C7 sugar levels consistently declined, while C6 sugars increased-primarily between the intermediate and ready-to-eat stages-with distinct cultivar-specific patterns. Bacon maintained elevated C7 concentrations for a longer period; Fuerte exhibited a rapid transition from C7 to C6 sugars; and Hass displayed a more gradual and balanced shift. Multivariate analysis (partial least squares discriminant analysis, PLS-DA) effectively discriminated between cultivars at each ripening stage, confirming cultivar-specific metabolic signatures. These findings offer new insights into avocado carbohydrate metabolism, emphasising variety-dependent pathways that could inform breeding strategies, optimise postharvest ripening protocols, and support the nutritional characterisation of different avocado cultivars.

Persea americana↗
PubMed1991

Involvement of wound and climacteric ethylene in ripening avocado discs.

Avocado (Persea americana Mill. cv Hass) discs (3 mm thick) ripened in approximately 72 hours when maintained in a flow of moist air and resembled ripe fruit in texture and taste. Ethylene evolution by discs of early and midseason fruit was characterized by two distinct components, viz. wound ethylene, peaking at approximately 18 hours, and climacteric ethylene, rising to a peak at approximately 72 hours. A commensurate respiratory stimulation accompanied each ethylene peak. Aminoethoxyvinyl glycine (AVG) given consecutively, at once and at 24 hours following disc preparation, prevented wound and climacteric respiration peaks, virtually all ethylene production, and ripening. When AVG was administered for the first 24 hours only, respiratory stimulation and softening (ripening) were retarded by at least a day. When AVG was added solely after the first 24 hours, ripening proceeded as in untreated discs, although climacteric ethylene and respiration were diminished. Propylene given together with AVG led to ripening under all circumstances. 2,5-Norbornadiene given continuously stimulated wound ethylene production, and it inhibited climacteric ethylene evolution, the augmentation of ethylene-forming enzyme activity normally associated with climacteric ethylene, and ripening. 2,5-Norbornadiene given at 24 hours fully inhibited ripening. When intact fruit were pulsed with ethylene for 24 hours before discs were prepared therefrom, the respiration rate, ethylene-forming enzyme activity buildup, and rate of ethylene production were all subsequently enhanced. The evidence suggests that ethylene is involved in all phases of disc ripening. In this view, wound ethylene in discs accelerates events that normally take place over an extended period throughout the lag phase in intact fruit, and climacteric ethylene serves the same ripening function in discs and intact fruit alike.

Journal Article↗
PubMed1993

Ethylene and Wound-Induced Gene Expression in the Preclimacteric Phase of Ripening Avocado Fruit and Mesocarp Discs.

Whereas intact postharvest avocado (Persea americana Mill.) fruit may take 1 or more weeks to ripen, ripening is hastened by pulsing fruit for 24 h with ethylene or propylene and is initiated promptly by cutting slices, or discs, of mesocarp tissue. Because the preclimacteric lag period constitutes the extended and variable component of the ripening syndrome, we postulated that selective gene expression during the lag period leads to the triggering of the climacteric. Accordingly, we sought to identify genes that are expressed gradually in the course of the lag period in intact fruit, are turned on sooner in response to a pulse, and are induced promptly in response to wounding (i.e. slicing). To this end, a mixed cDNA library was constructed from mRNA from untreated fruit, pulsed fruit, and aged slices, and the library was screened for genes induced by wounding or by pulsing and/or wounding. The time course of induction of genes encoding selected clones was established by probing northern blots of mRNA from tissues variously treated over a period of time. Four previously identified ripening-associated genes encoding cellulase, polygalacturonase (PG), cytochrome P-450 oxidase (P-450), and ethylene-forming enzyme (EFE, or 1-aminocyclopropane-1-carboxylic acid synthase), respectively, were studied in the same way. Whereas cellulase, PG, and EFE were ruled out as having a role in the initiation of the climacteric, the time course of P-450 induction, as well as the response of same to pulsing and wounding met the criteria[mdash]together with several clones from the mixed library[mdash]for a gene potentially involved in preclimacteric events leading to the onset of the climacteric. Further, it was established that the continuous presence of ethylene is required for persisting induction, and it is suggested that in selected cases wounding may exert a synergistic effect on ethylene action.

Journal Article↗
PubMed1993

Ethylene-Mediated Posttranscriptional Regulation in Ripening Avocado (Persea americana) Mesocarp Discs.

Discs of avocado (Persea americana) fruit (15 x 3 mm thick) kept in a stream of moist air ripen within 72 h. Following cutting, a modest evolution of wound ethylene that dissipates in 24 h is followed by a burst of autocatalytic ethylene production associated with a respiratory climacteric, much as in the intact fruit. Aminoethoxyvinylglycine (AVG), an inhibitor of ethylene synthesis, and 2,5-norbornadiene (NBD) and Ag+, inhibitors of ethylene action, inhibit disc ripening, as does 2,4-dichlorophenoxyacetic acid (2,4-D), a synthetic auxin. On the other hand, none of the foregoing agents except Ag+, at concentrations that delay or prevent ripening, suppress the induction of four ripening-related genes encoding cellulase, polygalacturonase (PG), cytochrome P-450 oxidase (P-450), and ethylene-forming enzyme (EFE, or 1-aminopropane-1-carboxylic acid oxidase), respectively. Whereas Ag+ fully inhibits the production of cellulase and PG mRNAs, it has little effect on the induction of EFE and P-450 mRNAs. Cellulase and PG enzyme activities are absent in extracts of discs treated with AVG, NBD, or 2,4-D, as are antigenically detectable cellulase and PG proteins. The strong appearance of ripening-related mRNAs in discs inhibited from softening by ethylene antagonists suggests posttranscriptional control by ethylene. Similarly, inhibition of ripening by 2,4-D without suppression of mRNA induction suggests translational control. Whether ethylene inhibits transcription or postttranscriptional events or both depends on its concentration.

Journal Article↗
PubMed1989

Hydrolytic Enzyme Activities and Protein Pattern of Avocado Fruit Ripened in Air and in Low Oxygen, with and without Ethylene.

The effect of 2.5% O(2) atmosphere with and without ethylene on the activities of hydrolytic enzymes associated with cell walls, and total protein profile during ripening of avocado fruits (Persea americana Mill., cv Hass) were investigated. The low 2.5% O(2) atmosphere prevented the rise in the activities of cellulase, polygalacturonase, and acid phosphatase in avocado fruits whose ripening was initiated with ethylene. Addition of 100 microliters per liter ethylene to low O(2) atmosphere did not alter these suppressive effects of 2.5% O(2). Furthermore, 2.5% O(2) atmosphere delayed the development of a number of polypeptides that appear during ripening of avocado fruits while at the same time new polypeptides accumulated. The composition of the extraction buffer and its pH greatly affected the recovery of cellulase activity and its total immunoreactive protein.

Journal Article↗
PubMed1974

The effect of tonicity and metabolic inhibitors on respiration and ripening of avocado fruit slices.

The ripening of avocado (Persea americana Mill.) fruit slices was inhibited whether they were floated in water or in buffered aqueous 0.3 m mannitol, 0.25 m KCl, and sucrose. There was no evidence to support the contention that ripening occurred when the tonicity of the bathing medium was increased. Decreased gaseous exchange is considered to be a major cause of this inhibition because by utilizing a technique that afforded better aeration, slices could be water infiltrated and still ripen normally. Metabolic studies on the ripening of slices using this method indicated that several metabolic inhibitors, malonate, cyanide, acetaldehyde, dinitrophenol, and fluoride did not prevent ripening, but that their effect on the respiration pattern was marked. This technique provides a suitable way to study control of ripening at the tissue level.

Journal Article↗
PubMed1993

Polyuronides in Avocado (Persea americana) and Tomato (Lycopersicon esculentum) Fruits Exhibit Markedly Different Patterns of Molecular Weight Downshifts during Ripening.

Avocado (Persea americana) fruit experience a rapid and extensive loss of firmness during ripening. In this study, we examined whether the chelator solubility and molecular weight of avocado polyuronides paralleled the accumulation of polygalacturonase (PG) activity and loss in fruit firmness. Polyuronides were derived from ethanolic precipitates of avocado mesocarp prepared using a procedure to rapidly inactivate endogenous enzymes. During ripening, chelator (cyclohexane-trans-1,2-diamine tetraacetic acid [CDTA])-soluble polyuronides increased from approximately 30 to 40 [mu]g of galacturonic acid equivalents (mg alcohol-insoluble solids)-1 in preripe fruit to 150 to 170 [mu]g mg-1 in postclimacteric fruit. In preripe fruit, chelator-extractable polyuronides were of high molecular weight and were partially excluded from Sepharose CL- 2B-300 gel filtration media. Avocado polyuronides exhibited marked downshifts in molecular weight during ripening. At the postclimacteric stage, nearly all chelator-extractable polyuronides, which constituted from 75 to 90% of total cell wall uronic acid content, eluted near the total volume of the filtration media. Rechromatography of low molecular weight polyuronides on Bio-Gel P-4 disclosed that oligomeric uronic acids are produced in vivo during avocado ripening. The gel filtration behavior and pattern of depolymerization of avocado polyuronides were not influenced by the polyuronide extraction protocol (imidazole versus CDTA) or by chromatographic conditions designed to minimize interpolymeric aggregation. Polyuronides from ripening tomato (Lycopersicon esculentum) fruit extracted and chromatographed under conditions identical with those used for avocado polyuronides exhibited markedly less rapid and less extensive downshifts in molecular weight during the transition from mature-green to fully ripe. Even during a 9-d period beyond the fully ripe stage, tomato fruit polyuronides exhibited limited additional depolymerization and did not include oligomeric species. A comparison of the data for the avocado and tomato fruit indicates that downshifts in polyuronide molecular weight are a prominent feature of avocado ripening and may also explain why molecular down-regulation of PG (EC 3.2.1.15) in tomato fruit has resulted in minimal effects on fruit performance until the terminal stages of ripening.

Journal Article↗
PubMed1986

Regulation of Ethylene Biosynthesis in Avocado Fruit during Ripening.

Preclimacteric avocado (Persea americana Mill.) fruits produced very little ethylene and had only a trace amount of l-aminocyclopropane-1-carboxylic acid (ACC) and a very low activity of ACC synthase. In contrast, a significant amount of l-(malonylamino)cyclopropane-1-carboxylic acid (MACC) was detected during the preclimacteric stage. In harvested fruits, both ACC synthase activity and the level of ACC increased markedly during the climacteric rise reaching a peak shortly before the climacteric peak. The level of MACC also increased at the climacteric stage. Cycloheximide and cordycepin inhibited the synthesis of ACC synthase in discs excised from preclimacteric fruits. A low but measurable ethylene forming enzyme (EFE) activity was detected during the preclimacteric stage. During ripening, EFE activity increased only at the beginning of the climacteric rise. ACC synthase and EFE activities and the ACC level declined rapidly after the climacteric peak. Application of ACC to attached or detached fruits resulted in increased ethylene production and ripening of the fruits. Exogenous ethylene stimulated EFE activity in intact fruits prior to the increase in ethylene production. The data suggest that conversion of S-adenosylmethionine to ACC is the major factor limiting ethylene production during the preclimacteric stage. ACC synthase is first synthesized during ripening and this leads to the production of ethylene which in turn induces an additional increase in ACC synthase activity. Only when ethylene reaches a certain level does it induce increased EFE activity.

Journal Article↗
PubMed1992

Expression of a Ripening-Related Avocado (Persea americana) Cytochrome P450 in Yeast.

One of the mRNAs that accumulates during the ripening of avocado (Persea americana Mill. cv Hass) has been previously identified as a cytochrome P450 (P450) monooxygenase and the corresponding gene designated CYP71A1. In this report we demonstrate that during ripening the accumulation of antigenically detected CYP71A1 gene product (CYP71A1) correlates with increases in total P450 and two P450-dependent enzyme activities: para-chloro-N-methylaniline demethylase, and trans-cinnamic acid hydroxylase (tCAH). To determine whether both of these activities are derived from CYP71A1, we have expressed this protein in yeast (Saccharomyces cerevisiae) using a galactose-inducible yeast promoter. Following induction, the microsomal fraction of transformed yeast cells undergoes a large increase in P450 level, attributable almost exclusively to the plant CYP71A1 protein. These membranes exhibit NADPH-dependent para-chloro-N-methylaniline demethylase activity at a rate comparable to that in avocado microsomes but have no detectable tCAH. These results demonstrate both that the CYP71A1 protein is not a tCAH and that a plant P450 is fully functional upon heterologous expression in yeast. These findings also indicate that the heterologous P450 protein can interact with the yeast NADPH:P450 reductase to produce a functional complex.

Journal Article↗
PubMed1975

The Effect of Indole-3-acetic Acid and Other Growth Regulators on the Ripening of Avocado Fruits.

Observations were made of the effects of several plant regulators, indole-3-acetic acid, kinetin, abscisic acid, and gibberellic acid, as well as of extracts prepared from leaves and fruit stalks on the respiration pattern, ethylene production, and the number of days to ripen of avocado fruits (Persea americana Mill.). These substances were vacuum infiltrated to insure good penetration and distribution. Kinetin, abscisic acid, gibberellic acid, and the extracts had no effect on either ripening time or on the respiration pattern and ethylene production of the fruits. Indoleacetic acid, however, had a marked effect on ripening. At high concentrations (100 and 1000 mum), indoleacetic acid stimulated respiration and induced preclimacteric ethylene production, resulting in accelerated ripening of the fruits. At the low concentrations (1 and 10 mum), it delayed ripening of fruits and suppressed the climacteric respiration and ethylene production. The results reinforce several previous observations with other fruits that auxins may largely constitute ;resistance to ripening' and may be responsible for the lack of ripening shown by unpicked fruits.

Journal Article↗
PubMed1978

Respiratory Contribution of the Alternate Path during Various Stages of Ripening in Avocado and Banana Fruits.

The respiration of fresh slices of preclimacteric avocado (Persea americana Mill. var. Hass) and banana (Musa cavendishii var. Valery) fruits is stimulated by cyanide and antimycin. The respiration is sensitive to m-chlorobenzhydroxamic acid in the presence of cyanide but much less so in the presence of antimycin. In the absence of cyanide the contribution of the cyanide-resistant pathway to the coupled preclimacteric respiration is zero. In uncoupled slices, by contrast, the alternate path is engaged and utilized fully in avocado, and extensively in banana. Midclimacteric and peak climacteric slices are also cyanide-resistant and, in the presence of cyanide, sensitive to m-chlorobenzhydroxamic acid. In the absence of uncoupler there is no contribution by the alternate path in either tissue. In uncoupled midclimacteric avocado slices the alternate path is fully engaged. Midclimacteric banana slices, however, do not respond to uncouplers, and the alternate path is not engaged. Avocado and banana slices at the climacteric peak neither respond to uncouplers nor utilize the alternate path in the presence or absence of uncoupler.The maximal capacities of the cytochrome and alternate paths, V(cyt) and V(alt), respectively, have been estimated in slices from preclimacteric and climacteric avocado fruit and found to remain unchanged. The total respiratory capacity in preclimacteric and climacteric slices exceeds the respiratory rise which attends fruit ripening. In banana V(alt) decreases slightly with ripening.The aging of thin preclimacteric avocado slices in moist air results in ripening with an accompanying climacteric rise. In this case the alternate path is fully engaged at the climacteric peak, and the respiration represents the total potential respiratory capacity present in preclimacteric tissue. The respiratory climacteric in intact avocado and banana fruits is cytochrome path-mediated, whereas the respiratory climacteric of ripened thin avocado slices comprises the alternate as well as the cytochrome path. The ripening of intact fruits is seemingly independent of the nature of the electron transport path.Uncouplers are thought to stimulate glycolysis to the point where the glycolytic flux exceeds the oxidative capacity of the cytochrome path, with the result that the alternate path is engaged.

Journal Article↗
PubMed1975

Acid Phosphatase Development during Ripening of Avocado.

The activity and subcellular distribution of acid phosphatase were assayed during ethylene-induced ripening of whole fruit or thick slices of avocado (Persea americana Mill. var. Fuerte and Hass). The activity increased up to 30-fold during ripening in both the supernatant fraction and the Triton X-100 extract of the precipitate of a 30,000g centrifugation of tissue homogenates from whole fruit or slices ripening in moist air. Enzyme activity in the residual precipitate after Triton extraction remained constant. The development of acid phosphatase in thick slices ripened in moist air was similar to that in intact fruit, except that enzyme development and ripening were accelerated about 24 hours in the slices. The increase in enzyme activity that occurs in slices ripening in moist air was inhibited when tissue sections were infiltrated with solutions, by aspiration for 2 minutes or by soaking for 2 hours, anytime 22 hours or more after addition of ethylene. This inhibition was independent of the presence or absence of cycloheximide or sucrose (0.3-0.5m). However, the large decline in enzyme activity in the presence of cycloheximide, as compared with the controls, indicated that synthesis of acid phosphatase was occurring at all stages of ripening.

Journal Article↗
PubMed1990

Isolation and characterization of a cellulase gene family member expressed during avocado fruit ripening.

We present in this paper the structural analysis of two members of a small cellulase gene family, designated cel1 and cel2, from avocado. These genes were isolated by screening a lambda EMBL3 genomic library with a ripening-induced cellulase cDNA. Restriction endonuclease and Southern blot analyses showed that the cel1 gene is highly homologous to the cellulase cDNA and thus represents a ripening-related cellulase gene. The other cellulase gene, cel2, is closely related to cel1, but is divergent at its 5' end. The nucleotide sequence of a 5 kb region encompassing the cel1 gene was determined. Four previously characterized cellulase cDNAs from ripe fruit are identical to the eight exons of the cel1 gene. RNase protection and primer extension analyses were used to define the transcription start site of cel1 and to quantitate cel1 transcripts in ripening fruit. The cel1 mRNA was present at a low level in unripe fruit and increased 37-fold during ripening. Partial DNA sequence analysis of cel2 and comparison to the cel1 sequence revealed a high degree of similarity both at the DNA and deduced amino acid sequence levels. No characterized cellulase cDNAs derived from ripe fruit represent cel2 transcripts. These data suggest that the cel1 gene is responsible for a major portion, if not all, of the cellulase transcripts in ripe fruit. The DNA sequence of 1.4 kb of 5' flanking DNA of the cel1 gene was compared to the upstream sequence of other ethylene-regulated genes. Several interesting upstream sequence motifs were identified and are discussed.

Amino Acid Sequence↗
PubMed1974

Similarities between the Actions of Ethylene and Cyanide in Initiating the Climacteric and Ripening of Avocados.

A continuous exposure of intact avocados (Persea americana) to 400 mul/l of cyanide results in a rapid increase in the rate of respiration, followed by a rise in ethylene production, and eventual ripening. The pattern of changes in the glycolytic intermediates glucose 6-phosphate, fructose diphosphate, 3-phosphoglyceric acid, and phosphoenolpyruvate during the rapid rise in respiration in both ethylene and cyanide-treated fruits is similar to that found in fruits made anaerobic where a 2.3- to 3-fold increase in the rate of glycolysis is observed. It is suggested that both during the climacteric and in response to cyanide, glycolysis is enhanced. It is proposed that cyanide implements the diversion of electrons to the cyanide-resistant electron path through structural alterations which are independent of the simultaneous inhibition of cytochrome oxidase.

Journal Article↗
PubMed1974

Water-deficit Stress, Ethylene Production, and Ripening in Avocado Fruits.

Differential rates of water loss were achieved in picked avocado (Persea americana Mill.) fruits, either by controlling the evaporation rate or by supplying water through the fruit stalk. A negative linear correlation was found between the daily rate of water loss from fruits and their ripening, as determined by the time from harvest to peak of ethylene production. Ripening rate was hastened by 40% in fruits which had lost water at rate of 2.9% fresh weight per day, compared with those which lost only 0.5% per day.

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