Post-climacteric Stage Research Articles

Genome-wide characterization and expression analysis of SAUR gene family in Melon (Cucumis melo L.).

We identified 66 melon SAUR genes by bioinformatic analyses. CmSAUR19, 38, 58, 62 genes are specifically expressed in different stages of fruit growth, suggesting their participation in regulating fruit development. Auxin plays a crucial role in plant growth by regulating the multiple auxin response genes. However, in melon (Cucumis melo L.), the functions of the auxin early response gene family SAUR (Small auxin up RNA) genes in fruit development are still poorly understood. Through genome-wide characterization of CmSAUR family in melon, we identified a total of 66 CmSAUR genes. The open reading frames of the CmSAUR genes ranged from 234 to 525bp, containing only one exon and lacking introns. Chromosomal position and phylogenetic tree analyses found that the two gene clusters in the melon chromosome are highly homologous in the Cucurbitaceae plants. Among the four conserved motifs in CmSAUR proteins, motif 1, motif 2, and motif 3 located in most of the family protein sequences, and motif 4 showed a close correlation with the two gene clusters. The CmSAUR28 and CmSAUR58 genes have auxin response elements located in the promoters, suggesting they may be involved in the auxin signaling pathway to regulate fruit development. Through transcriptomic profiling in the four developmental stages of fruit and different lateral organs, we selected 16 differentially-expressed SAUR genes for performing further expression analyses. qRT-PCR results showed that five SAUR genes are specifically expressed in flower organs and ovaries. CmSAUR19 and CmSAUR58 were significantly accumulated in the early developmental stage of the fruit. CmSAUR38 and CmAUR62 showed high expression in the climacteric and post-climacteric stages, suggesting their specific role in controlling fruit ripening. This work provides a foundation for further exploring the function of the SAUR gene in fruit development.

Fruit Quality Evaluation in The Maturation Process of Blueberries Using Image Processing

Blueberries' quality does not change uniformly during ripeness. Blueberries should be harvested fully ripened at the post-climacteric stage with an excellent indicator including consistent color, taste, and ease of removal from plant as excellent indicators. Therefore, the blueberries are not harvested until it has the desired blue color. The reliance on human perception on the fruit's taste and appearance might cause inconsistency and inaccurate judgment of the fruit maturation. This study aimed to develop an image processing algorithm capable of classifying blueberry maturity stages. The Bluecrop Northern highbush blueberry was harvested at five different stages of maturity based on visual grading of the fruit color (green, green-red, red, red-blue, and blue) from various fruit positions on the tree. Image processing with discriminant analysis accurately classified maturity stages at 98.3% accuracy. The image quality attributes of blueberries changed significantly at different maturity stages. Overall, most image quality attributes correlated strongly with well-performed blueberry physicochemical properties. This study showed that image processing during the blueberry maturation process could be a reliable and comprehensible method for estimating changes in color, shape, weight, and ultimately changes in specific physicochemical properties. This study also provided a practical evaluation of the maturity stages and physicochemical properties, which were predicted using image processing.

Avocado Fruit Pulp Transcriptomes in the after-Ripening Process

Avocado is an important tropical fruit whose after-ripening process is still poorly understood. The fatty acid, phenolics, flavonoids, and tannins were analyzed in ‘Lisa’ avocado (Persea americana Mill. ‘Lisa’) fruit pulp during after-ripening. The transcriptome was analyzed to screen for transcripts associated with the aforementioned after-ripening parameters. The results showed that there were no significant differences in the total fatty acid content among the preclimacteric, climacteric, and postclimacteric stages. Nevertheless, the concentrations of C18:3 (α-linolenic acid) were significantly higher in the climacteric and postclimacteric stages than the preclimacteric stage. RNAseq generated 235,082 transcripts and 151,545 unigenes. In addition, 4,324 DEGs were produced among the three stages. KEGG analysis of the DEGs suggested the pathways about “α-linolenic acid metabolism, unsaturated fatty acid biosynthesis”, “fatty acid degradation”, “linoleic acid metabolism and fatty acid biosynthesis”, “linoleic acid metabolism and fatty acid elongation”, and “fatty acid elongation” may all contribute to the C18:3 variations in ‘Lisa’ avocado fruit pulp. Several transcription factors, including the ethylene-related transcription factors, such as NAC, MYB, bHLH, and WRKY, were also identified in the DEGs database. This study generated transcript data and screened the transcription factors involved in the avocado after-ripening process. This information could be used to control after-ripening in avocado and maintain fruit quality during storage.

Isolation and characterization of ripening related pectin methylesterase inhibitor gene from banana fruit

Identification of ethylene-regulated and ripening-related genes from banana (Musa acuminata Var. Harichaal) fruits using DDRT-PCR led to the isolation of differentially expressed partial cDNA of pectin methylesterase inhibitor (MaPMEI) gene. Its full-length cDNA sequence consisted of a 567bp ORF, encoding a protein of 189 aa with deduced molecular mass 19.6 kDa. Expression pattern of MaPMEI gene revealed that upon ethylene treatment, this gene is up-regulated initially giving maximum expression in post-climacteric stage then decreases slightly in later stages of ripening. 1-MCP, a known ethylene perception inhibitor, inhibits both fruit ripening as well as the transcript level of this gene. Also, the transcripts of MaPMEI gene were not detected during the short time ethylene treatment suggesting this gene appears to be not directly induced by ethylene. Interestingly, MaPMEI gene showed fruit specific expression that indicates its possible role in the regulations of PMEs in fruits. In silico analysis revealed a predicted signal peptide sequence necessary for localization of MaPMEI in the cell wall. Furthermore, the four Cys residues involved in disulfide bridges are conserved in MaPMEI similar to other PMEIs and invertase inhibitors. Phylogenetic analysis further suggests that the MaPMEI identified in this study is more closely related to PMEIs than to invertase inhibitors.

Role of Brassinosteroids, Ethylene, Abscisic Acid, and Indole-3-Acetic Acid in Mango Fruit Ripening

Rapid ripening of mango fruit limits its distribution to distant markets. To better understand and perhaps manipulate this process, we investigated the role of plant hormones in modulating climacteric ripening of ‘Kensington Pride’ mango fruits. Changes in endogenous levels of brassinosteroids (BRs), abscisic acid (ABA), indole-3-acetic acid (IAA), and ethylene and the respiration rate, pulp firmness, and skin color were determined at 2-day intervals during an 8-day ripening period at ambient temperature (21 ± 1°C). We also investigated the effects of exogenously applied epibrassinolide (Epi-BL), (+)-cis, trans-abscisic acid (ABA), and an inhibitor of ABA biosynthesis, nordihydroguaiaretic acid (NDGA), on fruit-ripening parameters such as respiration, ethylene production, fruit softening, and color. Climacteric ethylene production and the respiration peak occurred on the fourth day of ripening. Castasterone and brassinolide were present in only trace amounts in fruit pulp throughout the ripening period. However, the exogenous application of Epi-BL (45 and 60 ng g−1 FW) advanced the onset of the climacteric peaks of ethylene production and respiration rate by 2 and 1 day, respectively, and accelerated fruit color development and softening during the fruit-ripening period. The endogenous level of ABA rose during the climacteric rise stage on the second day of ripening and peaked on the fourth day of ripening. Exogenous ABA promoted fruit color development and softening during ripening compared with the control and the trend was reversed in NDGA-treated fruit. The endogenous IAA level in the fruit pulp was higher during the preclimacteric minimum stage and declined during the climacteric and postclimacteric stages. We speculate that higher levels of endogenous IAA in fruit pulp during the preclimacteric stage and the accumulation of ABA prior to the climacteric stage might switch on ethylene production that triggers fruit ripening. Whilst exogenous Epi-BL promoted fruit ripening, endogenous measurements suggest that changes in BRs levels are unlikely to modulate mango fruit ripening.

Rabbiteye Blueberry Postharvest Fruit Quality and Stimulation of Ethylene Production by 1-Methylcyclopropene

A postharvest 1-methylcyclopropene (1-MCP) treatment was evaluated for its ability to maintain firmness and delay the ripening of rabbiteye blueberries. Three cultivars, Austin, Brightwell, and Premier, were harvested by hand from the UGA Alapaha Blueberry Farm and treated overnight with 1 μL·L−1 1-MCP as field heat was being removed [0 to 1 °C, 90% to 95% relative humidity (RH)]. Fruit were evaluated for firmness, total soluble solids (TSS), total acidity (TA), ethylene production, and other quality attributes at 0, 1, and 2 weeks after harvest as well as 1 or 4 days post-removal evaluations at room temperature (≈21 °C). In general, the 1-MCP treatment resulted in the stimulation of ethylene production in all three cultivars but had minimal effect on TSS and TA content. Furthermore, the treatment resulted in an accelerated loss of firmness in ‘Brightwell’. The lack of inhibition of fruit ripening likely related to the fact that blueberries were harvested, and subsequently treated with 1-MCP, at a post-climacteric stage of development. Based on current results, more information is required regarding ethylene production during rabbiteye blueberry fruit maturation before establishing a 1-MCP treatment recommendation for use by the rabbiteye blueberry industry.

1-Methylcyclopropene delays arazá ripening and improves postharvest fruit quality

Six different experiments were conducted to give some practical recommendation to apply 1-MCP during the postharvest handling chain of arazá fruit ( Eugenia stipitata McVaugh). Fruit were harvested in three stages of maturity (mature-green primarily, turning and mature) and treated for 1 to 12 h with 0 (control in air) or 1 μL L −1 1-Methylcyclopropene (1-MCP) at 20 °C. The mature-green fruit were subjected to different storage conditions (7, 10, 12, 13, 20 or 27 °C). The treatment of mature-green fruit with 1-MCP for 1 h, and storage at 12 °C for up to 2 weeks prolonged the shelf-life about one week by delaying or reducing the respiration and ethylene production rates, skin colour changes, the loss of organic acids, and softening, with or without a further shelf-life period of 3 days at 20 °C. At 7 °C, 1-MCP also reduced mature-green fruit weight loss and shrivelling. Extending 1-MCP treatment periods at 20 °C to 6 or 12 h caused partial and uneven ripeness. Treating fruit in their post-climacteric stage of maturity had little effect on ripening compared with the mature-green stage. 1-MCP increased the respiration rate and/or the ethylene production in certain combinations of advanced harvest maturities and/or unfavourable storage temperatures. Recommendations for maintaining postharvest quality are harvesting at the mature-green stage, treatment with 1 μL L −1 of 1-MCP for 1 h, and storage at 12 °C for up to 2 weeks.

Postharvest respiratory activity and changes in some chemical constituents during maturation of yellow mombin (Spondias mombin) fruit

Mature fruit from the yellow mombin (Spondias mombin) was monitored for its respiration activity. Mature green fruit from the yellow mombin was stored in closed glass chambers and the concentration of oxygen and carbon dioxide at the end of a six hour respiration period was determined. At the same interval of time, the lid of the chamber was opened for air renewal. The increase in carbon dioxide and decrease in oxygen concentration demonstrated that the fruit was climacteric. The maximum liberation of CO2 54.2 mL Kg -1 h-1 and maximum absorption of O2 49.0 mL Kg -1 h-1 occurred 186 hours after the harvest which, obviously, represented the optimum fruit quality after the senescence process started. The respiratory quotient of fruit at a climacteric maximum was 1.11 representing the oxidation of carbohydrates. Total soluble solids increased from 9.1 °Brix (initial) to 13.7 °Brix (climacteric maximum) during maturation, while the total number of acids in the fruit decreased during maturation i.e. from 1.55% initially to 1.40% at pre-climacteric, 1.0% at climacteric maximum and 0.8% in the post-climacteric stage. A similar behaviour was observed in the case of ascorbic acid. There was a continuous decrease in chlorophyll and a continuous increase in the carotenoid content of fruit during maturation.

Interaction of Water Loss and Fruit Ripening Promote Postharvest Cluster Tomato Fruit Abscission

Abscission of cluster tomatoes commonly limits product marketability in the retail environment. Ripening and exogenous ethylene exposure are assumed to play important roles in cluster tomato fruit abscission. `Clarance' and `DRW7229' fruit harvested at either mature green or partially ripened stages did not abscise during storage for 2 weeks at 20 °C and 95% to 100% relative humidity (RH), although respiration and ethylene production indicated that all fruit reached the postclimacteric stage. Exogenous ethylene (1 or 10 ppm) exposure for 8 days at 20 °C and 95% to 100% RH also did not induce fruit abscission for either cultivar, although pedicel and sepal yellowing were observed. Fruit from clusters stored at 20 °C and 20% or 50% RH abscised if sepal shrivel became noticeable before the fruit reached the full red ripeness stage, while no abscission occurred in fruit that reached the full red stage prior to the appearance of sepal shrivel; no fruit stored in 95% to 100% RH abscised. Fruit that ripened prior to the appearance of sepal shrivel were “plugged” (i.e., tissue underlying the stem scar was pulled out) if manual fruit detachment from the pedicel was attempted. These results indicate that there is an interaction of water loss and fruit ripening in promoting abscission zone development in cluster tomatoes.

Aerobic-Anaerobic Metabolic Transition in ‘Hass’ Avocado Fruits

The aim of this work was to determine the anaerobic compensation point (ACP) in ‘Hass’ avocado fruits as a function of temperature and the advance in ripening. Controlled atmosphere treatments with oxygen in a range from 0 to 4%, with two temperature levels, 5.5 and 20°C, applied to fruits of three firmness levels which included the pre-climacteric, the mid-zone of the climacteric rise and the post-climacteric phase. Mean ACP values of 1.44% and 1.81% were found for 5.5°C and 20°C, respectively. These values increased with ripening. The production of fermentative metabolites was not exclusive of O2 concentrations below to ACP, and temperature affected the accumulation of these compounds, with values of 10.7 mol/100mL at 5.5°C and 101.3 mol/100mL at 20°C. The production of those metabolites significantly increased with ripening and the values were, in the post-climacteric stage, 20 and 39 times greater than in the pre-climacteric one, at 5.5°C and 20°C, respectively. Results obtained here could be used to define adequate storage conditions for ‘Hass’ avocado fruits in modified atmosphere systems.

Xanthoxin, abscisic acid and its metabolite levels associated with apple fruit development

A suitable internal standard for the measurement of natural xanthoxin (XAN) was developed. Endogenous XAN, abscisic acid (ABA), phaseic acid (PA), dihydrophaseic acid (DPA), and epi-dihydrophaseic acid (epi-DPA) concentrations were quantified in the pulp and seeds of apples in various stages of fruit development. The relative amounts of ABA in the pulp increased toward fruit maturation. On a molar basis, the amount of total XAN (cis, trans-XAN and trans, trans-XAN) in immature fruit was equal to the amount of ABA. However during the fruit ripening process, the total XAN levels markedly decreased in proportion with increases in the levels of ABA. At the climacteric rise and postclimacteric stage ABA concentrations were higher than the total amount of XAN. The low levels of XAN in a ripening apple may be caused by its rapid turnover. The total XAN concentrations was high in immature seeds but decreased toward seed maturation. The opposite tendency was observed in the case of ABA concentration. Thus, decreases of total XAN correlated with increases in the ABA levels; this tendency was observed in both the pulp and seeds, and was consistent with the role of XAN as an ABA precursor. In the pulp, PA concentrations changed in a manner similar to those of ABA. The maximum epi-DPA concentration was 67% of the maximum ABA concentration, but the maximum DPA concentration was only 11% of the maximum ABA concentration. Therefore, epi-DPA may be a major metabolite of PA in the pulp. In contrast, DPA appeared to be the major metabolite of ABA in apple seeds, because the levels of DPA were higher than those of PA and epi-DPA.

Interactions between Jasmonates and Abscisic Acid in Apple Fruit, and Stimulative Effect of Jasmonates on Anthocyanin Accumulation.

The interactions between jasmonates [jasmonic acid (JA) and methyl jasmonate (MeJA)] and abscisic acid (ABA) were investigated in 'Tsugaru' apple (Malus pumila Mill. var. domestica Schneid.). In Exp. 1, discs from pulp excised 93 days after full bloom (DAFB)(preclimacteric), 112 DAFB (climacteric), and 133 DAFB (postclimacteric) were collected and placed in petri dishes containing a solution of 0.4 M mannitol with a combination of MeJA, ABA, and aminoethoxyvinylglycine (AVG). Jasmonates, ABA, and ethylene levels in the discs were measured at 0, 24, 48, and 72 hr after the initiation of treatment. At the climacteric and postclimacteric stages, the ABA treatment increased endogenous JA concentration and decreased it when combined with AVG. This result suggests that ethylene may be related to the induction of endogenous JA by ABA. MeJA treatment decreased endogenous ABA concentration from 93 to 133 DAFB, whereas AVG had no influence. This result also demonstrates that jasmonates may influence endogenous ABA synthesis independently from ethylene. In Exp. 2 when discs with skins from the apple pulp samples from preclimacteric, climacteric, and postclimacteric stages were excised, cultured for 7 days under light on B5 media containing MeJA, and the combination of MeJA and AVG was investigated, MeJA and MeJA combined with AVG stimulated greater anthocyanin accumulation in both sampling stages compared to the untreated control ; the combination of MeJA and AVG resulted in a lower concentration of anthocyanin than that of only MeJA at the preclimacteric and postclimacteric stages. Therefore, in most cases, jasmonates may be related to anthocyanin formation in apples in the presence and absence of ethylene.

Lipid evolution during development and ripening of peach fruits

Changes in the phospholipid, glycolipid, diacyl and triacylglycerol, free fatty acid and free sterol classes were examined during the development and ripening of Prunus persica cv. Redhaven peach fruit. Total lipid and lipid class contents decreased until 100 days after full bloom (AFB). While phospholipids and glycolipids decreased in the following stages, diacyl- and triacylglycerols increased. The analysis of each lipid class showed that the predominant fatty acids were 16:0 and 18:2. The double bond index showed, in each class, a general increase during maturation. The free sterol content continuously declined during maturation with the exception of samples at 100 days AFB, which showed an increase in the free sterol to phospholipid molar ratio. The main changes observed in lipids occurred mostly between the climacteric and postclimacteric stages.

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.

Cyanide Metabolism in Relation to Ethylene Production and Cyanide Insensitive Respiration in Climacteric and Non-Climacteric Fruits

In a climacteric fruit such as apple, ethylene synthesis increases during ripening and cyanide is stoichiometrically produced with ethylene. β-cyanoalanine synthase (CAS) activity was found to increase in ripening apple from the preclimacteric to climacteric and to decrease in the post-climacteric stage. In the non-climacteric fruit pepper, ethylene production and CAS activity was 250 fold and 30 fold lower, respectively, than in preclimacteric apples. Treating peppers with ethylene induced a transient increase in ethylene production and a longer lasting rise in CAS activity. Both fruits evidenced cyanide insensitive respiration, apple at all stages of ripeness and pepper from the turning stage onward. The results are discussed with regard to mechanisms in fruit that protect tissue function against increasing amounts of cyanide.

Beyond Sixty-Five: The Dilemma of Old Age in America's Past

1. Classifying Society's Superannuated 2. Aging in Colonial America 3. Social Realities and Perceptions of Old Age in the Nineteenth Century 4. Medical Models of Growing Old 5. Treating the Postclimacteric Stage 6. Institutionalizing the Elderly 7. The Pension Barrier 8. Old Age in a Bureaucratic Society.

Postharvest Changes in Fruit Composition of Annona atemoya during Ripening and Effects of Storage Temperature on Ripening

Abstract Respiration and ethylene production were determined daily on fruit of A. atemoya Hort. stored at 20°C from preclimacteric to postclimacteric stages. At 5 stages, fruit were analyzed for water, sugars, starch, organic acids, Vitamin C, thiamin, titratable acidity, pH, and total soluble solids. The major changes during ripening were a continuous decrease in starch, a continuous increase in fructose and glucose, an increase in sucrose to a maximum at the climacteric, an increase in malic acid early in the climacteric rise, and a decrease in Vitamin C after the climacteric. Eating quality was optimal 2 days after the climacteric and the levels of protein, fat, dietary fiber, ash, sodium, potassium, iron, calcium, magnesium, zinc, riboflavin, niacin, α-carotene, β-carotene, cryptoxanathin, energy content, and edible portion were determined at this stage. Fruit were stored at temperatures from 0° to 25°. The safe range of storage temperature was between 15° and 25° with 20° being the optimum for the development of eating quality but with 15° giving the longest delay in ripening. Storage at lower temperatures gave rise to symptoms typical of chilling injury.

Microsomal Membrane Changes during the Ripening of Apple Fruit

The changes in leakage and viscosity of microsomal membranes from apples (Malus sylvestris cv Calville de San Sauveur) at different stages of ripening were examined. These changes were correlated with those in the lipid composition of the membranes, sterols, phospholipids, and fatty acids of the phospholipids. The greatest changes in membrane properties occurred as the fruit reached its climacteric and this corresponded with a change in the sterol:phospholipid ratio in the membranes. Changes were also found in fatty acid unsaturation level, but primarily in the postclimacteric stage of ripening.

Effect of low oxygen and high carbon dioxide on the levels of ethylene and 1-aminocyclopropane-1-carboxylic acid in ripening apple fruits

The association of the level of ACC and the ethylene concentration in ripening apple fruit (Malus sylvestris Mill, var. Ben Davis) was studied. Preclimacteric apple contained small amounts of ACC and ethylene. With the onset of the climacteric and a concomitant decrease in flesh firmness, the level of ACC and ethylene concentration both increased markedly. During the postclimacteric period, ethylene concentration started to decline, but the level of ACC continued to increase. Ethylene production and loss of flesh firmness of fruits during ripening were greatly suppressed by treatments with low O2 (O2 1–3%, CO2 O%) or high CO2 (CO2 20–30%, O2 15–20%) at the preclimacteric stage. However, after 4 weeks an accumulation of ACC was observed in treated fruits when control fruit was at the postclimacteric stage. Treatment of fruit with either low O2 or high CO2 at the climacteric stage resulted in a decrease of ethylene production. However, the ACC level in fruit treated with low O2 was much higher than both control and high CO2 treated fruit; it appears that low O2 inhibits only the conversion of ACC to ethylene, resulting in an accumulation of ACC. Since CO2 inhibits ethylene production but does not result in an accumulation of ACC, it appears that high CO2 inhibits both the conversion of ACC to ethylene and the formation of ACC.

Postharvest Variation in Cell Wall-Degrading Enzymes of Papaya (Carica papaya L.) during Fruit Ripening

Pectin methylesterase (PME), polygalacturonase (PG), xylanase, cellulase, and proteinase activity were determined and related to respiration, ethylene evolution, and changes in skin color of papaya (Carica papaya L.) fruit from harvest through to the start of fruit breakdown. PME gradually increased from the start of the climacteric rise reaching a peak 2 days after the respiratory peak. PG and xylanase were not detectable in the preclimacteric stage but increased during the climacteric: during the post climacteric stage, the PG declined to a level one-quarter of peak activity with xylanase activity returning to zero. Cellulase activity gradually increased 3-fold after harvest to peak at the same time as PME, 2 days after the edible stage. Proteinase declined throughout the climacteric and postclimacteric phases. A close relationship exists between PG and xylanase and the rise in respiration, ethylene evolution, and softening. Cultivar differences in postclimacteric levels of enzymic activity were not detected.An inhibitor of cellulase activity was detected in preclimacteric fruit. The inhibitor was not benzyl isothiocyanate (BITC). BITC did inhibit PG activity, though no inhibitor of PG activity was detected in preclimacteric homogenates when BITC was highest. The results indicate that inhibitors did not play a direct role in controlling wall softening.