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Donald J Huber - One of the best experts on this subject based on the ideXlab platform.

  • suppression of avocado persea americana mill fruit softening and changes in cell wall matrix polysaccharides and enzyme activities differential responses to 1 mcp and delayed ethylene application
    Journal of the American Society for Horticultural Science, 2004
    Co-Authors: Jiwon Jeong, Donald J Huber
    Abstract:

    Pre-ripe ʻBooth 7ʼ avocado (Persea americana Mill.) fruit, a cross of West Indian and Guatemalan strains, were treated with 0.9 µL·L -1 1-methylcyclopropene (1-MCP) for 12 hours at 20 °C. After storage for 18 days in air at 13 °C, at which time whole fruit fi rmness values averaged about 83 N, half of the 1-MCP-treated fruit were treated with 100 µL·L -1 ethylene for 12 hours and then transferred to 20 °C. 1-MCP delayed softening, and fruit treated with 1-MCP retained more green color than air-treated fruit when full ripe (fi rmness 10 to 15 N). 1-MCP affected the activities of pectinmethylesterase (EC 3.2.1.11), α- (EC 3.2.1.22) and β-galactosidases (EC 3.2.1.23), and endo-β-1,4-glucanase (EC 3.2.1.4). The appearance of polygalacturonase (EC 3.2.1.15) activity was completely suppressed in 1-MCP-treated fruit for up to 24 days, at which time the fi rmness of 1-MCP-treated fruit had declined nearly 80% compared with initial values. The effect of exogenous ethylene applied to partially ripened 1-MCP-treated fruit differed for different ripen- ing parameters. Ethylene applied to mid-ripe avocado exerted no effect on the on-going rate or fi nal extent of soften- ing of 1-MCP-treated fruit, even though polygalacturonase and endo-1,4-β-glucanase activities increased in response to ethylene. β-galactosidase decreased in 1-MCP-treated fruit in response to ethylene treatment. 1-MCP delayed the increase in solubility and depolymerization of water- and CDTA (1,2-cyclohexylenedinitrilotetraacetic acid)-soluble Polyuronides, likely due to reduced polygalacturonase activity. At the full-ripe stage, the levels of arabinose, galactose, glucose, mannose, rhamnose, and xylose associated with the CDTA-soluble polyuronide fraction were similar among all treatments. In contrast, the galactose levels of water-soluble Polyuronides declined 40% and 17% in control and 1-MCP treated fruit, respectively. Hemicellulose neutral sugar composition was unaffected by 1-MCP or ethylene treat- ment. The data indicate that the capacity of avocado fruit to recover from 1-MCP-mediated suppression of ripening can be only partially amended through short-term ethylene application and differs signifi cantly for different ripening parameters.

  • activities of several membrane and cell wall hydrolases ethylene biosynthetic enzymes and cell wall polyuronide degradation during low temperature storage of intact and fresh cut papaya carica papaya fruit
    Postharvest Biology and Technology, 2003
    Co-Authors: Yasar Karakurt, Donald J Huber
    Abstract:

    Abstract Fresh-cut fruit tissue deteriorates more rapidly than its intact counterpart. A study was conducted to determine changes in firmness, cell-wall Polyuronides, and the activities of cell-wall and membrane hydrolases and ethylene biosynthetic enzymes in intact and fresh-cut papaya fruit during storage at 5 °C. Processing of papaya fruit was performed under sanitized conditions at 5 °C, and fruit pieces were stored for 8 days at 5 °C. Levels of total and CDTA-soluble Polyuronides in intact fruit did not change during storage, but water-soluble Polyuronides increased significantly by day 8 (15%). In contrast, total polyuronide content of fresh-cut papaya decreased (9.5%), whereas levels of CDTA- and water-soluble Polyuronides increased 45 and 30%, respectively. Firmness and mol mass of Polyuronides decreased more rapidly in fresh-cut fruit than in intact fruit. The activities of polygalacturonase (EC 3.2.1.15), alpha- (EC 3.2.1.22) and beta-galactosidases (EC 3.2.1.23), lipoxygenase (EC 1.13.11.12), phospholipase D (EC 3.1.4.4), and ACC synthase (EC 4.4.1.14) and ACC oxidase increased within 24 h in fresh-cut fruit, and remained significantly higher compared with levels in intact fruit throughout the storage period. Pectin methyl esterase (EC 3.2.1.11), and phospholipase C (EC 3.1.4.3) activities showed no consistent differences between fresh-cut and intact fruit. The data suggest that a wound-induced increase in enzymes targeting cell walls and membranes contributes to the rapid deterioration of fresh-cut fruit. The significantly less pronounced changes observed for intact fruit stored under identical conditions indicate that the enhanced deterioration of fresh-cut fruit does not reflect low-temperature injury.

  • methyl de esterification as a major factor regulating the extent of pectin depolymerization during fruit ripening a comparison of the action of avocado persea americana and tomato lycopersicon esculentum polygalacturonases
    Journal of Plant Physiology, 2003
    Co-Authors: Kazuyuki Wakabayashi, Takayuki Hoson, Donald J Huber
    Abstract:

    Pectinmethylesterase (PME, EC 3.2.1.11) and polygalacturonase (PG, EC 3.2.1.15) are known to operate in tandem to degrade methylesterified Polyuronides. In this study, PGs purified from tomato and avocado fruit were compared in terms of their capacity to hydrolyze water-soluble Polyuronides from avocado before and following enzymic or chemical de-esterification. When assayed using polygalacturonic acid or Polyuronides from avocado fruit, the activity of PG from tomato fruit was 3-4 times higher than that from avocado fruit. High molecular mass, low methylesterified (33%) water-soluble Polyuronides (WSP) from pre-ripe avocado fruit (day 0) were partially depolymerized upon incubation with purified avocado and tomato PGs. In contrast, middle molecular mass, highly methylesterified (74%) WSP from day 2 fruit were largely resistant to the action of both PGs. PME or weak alkali treatment of highly methylesterified WSP decreased the methylesterification values to 11 and 4.5%, respectively. Treatment of de-esterified WSP with either avocado or tomato PGs caused extensive molecular mass downshifts, paralleling those observed during avocado fruit ripening. Although PME and PG are found in many fruits, the pattern of depolymerization of native Polyuronides indicates that the degree of cooperativity between these enzymes in vivo differs dramatically among fruits. The contribution of PME to patterns of polyuronide depolymerization observed during ripening compared with physically compromised fruit tissues is discussed.

  • cell wall degrading enzymes and pectin solubility and depolymerization in immature and ripe watermelon citrullus lanatus fruit in response to exogenous ethylene
    Physiologia Plantarum, 2002
    Co-Authors: Yasar Karakurt, Donald J Huber
    Abstract:

    Watermelon fruit have been shown to be extremely sensitive to exogenous ethylene, exhibiting acute symptoms of whole-fruit softening and placental-tissue water-soaking following short periods of exposure to the gas. This study addressed the firmness, specific activities of cell wall hydrolases, and solubility and molecular mass properties of Polyuronides in placental tissue in response to treatment of intact fruit with ethylene. Watermelon fruit were harvested at the immature and full-ripe stages and exposed to 50 μl l -1 ethylene for 6 days at 20°C. The firmness of placental tissue from ethylene-treated ripe and immature fruit decreased nearly 80% during 6 days of ethylene exposure, whereas the firmness of placental tissue from fruit maintained in air remained relatively constant up to day 3 and then decreased slightly (12%) during the following 3 days of storage. Although ethylene treatment in some cases influenced the levels of extractable placental-tissue polygalacturonase (EC 3.2.1.15), pectinmethylesterase (EC 3.2.1.11), and α-(EC 3.2.1.22) and β-galactosidase (EC 3.2.1.23) specific activities, these effects were not observed for fruit of both developmental stages and appeared not to be directly involved in the water-soaking syndrome. Symptoms of water-soaking were accompanied by increases in the levels of water- and CDTA (trans-1,2-cyclohexanediamine-N,N,N',N'-tetraacetic acid)-soluble Polyuronides and significant molecular mass downshifts in Polyuronides in both immature and ripe watermelon fruit. Polyuronide depolymerization in ethylene-treated ripe fruit was extensive. The parallel trends of enzyme changes in ethylene- compared with air-treated fruit indicate that extractable enzyme levels are not associated with development of the water-soaking disorder. The potential involvement of membrane dysfunction in the water-soaking phenomenon is discussed.

  • influence of 1 methylcyclopropene 1 mcp on ripening and cell wall matrix polysaccharides of avocado persea americana fruit
    Postharvest Biology and Technology, 2002
    Co-Authors: Jiwon Jeong, Donald J Huber, Steven A Sargent
    Abstract:

    Abstract West Indian-type avocado (Persea americana Mill. cv. ‘Simmonds’) fruit were treated with two different concentrations (0.09 and 0.45 μl l−1) of 1-methylcyclopropene (1-MCP) for three exposure times (6, 12, and 24 h) at 20 °C. The fruit were then stored at 20 °C in ethylene-free air for ripening assessment. Firmness, weight loss, respiration and C2H4 production, peel color, cell-wall enzymes (polygalacturonase (PG), pectinmethylesterase, α-,β-galactosidase, and Cx-cellulase) and cell-wall matrix polysaccharides (Polyuronides and hemicellulose) were monitored during storage. 1-MCP treatment at 0.45 μl l−1 for 24 h at 20 °C delayed the ripening of avocado fruit by 4 days at 20 °C. This delay was characterized by a significant reduction in the rate of fruit softening and in the timing and intensity of the ethylene and respiratory climacterics. Avocado treated with 1-MCP (0.45 μl l−1) for 24 h at 20 °C also showed significantly less weight loss and retained more green color than control fruit at the full-ripe stage (10–20 N). The delay in avocado ripening was influenced by 1-MCP concentration, exposure duration, and exposure temperature. 1-MCP treatment affected the activity trends of all cell-wall enzymes measured and completely suppressed increases in PG activity for up to 12 days. Consistent with the activity trends of PG, Polyuronides from 1-MCP treated fruit when fully ripe exhibited less extensive molecular mass downshifts compared with the control fruit. The data indicate that the primary phase of avocado fruit softening occurs in the absence of appreciable PG activity. 1-MCP treatment also delayed and slightly reduced the depolymerization of 4 M alkali-soluble hemicelluloses, including xyloglucan.

Ariel Roberto Vicente - One of the best experts on this subject based on the ideXlab platform.

  • phytochemical content antioxidants and cell wall metabolism of two loquat eriobotrya japonica cultivars under different storage regimes
    Food Chemistry, 2014
    Co-Authors: Vlasios Goulas, Ioannis S Minas, Panayiotis M Kourdoulas, Ariel Roberto Vicente, George A Manganaris
    Abstract:

    Changes in quality, phytochemical content and cell wall metabolism of two loquat cultivars (Eriobotrya japonica cvs. ‘Morphitiki’, ‘Karantoki’) under different storage regimes were studied. The fruit were harvested at commercial maturity stage and analyzed after 1, 3, 5, 7, and 11 days maintenance at room temperature (RT, 20 C) or after cold storage (14 days at 4 C) and additional ripening at RT for 1, 3 and 5 days, respectively. Compositional analysis revealed substantial cultivar differences; the ‘Morphitiki’ fruit was more acidic and showed higher contents of total phenolics, flavonoids and hydroxycinnamic acid-derivatives as well as greater antioxidant potency. Although firmness did not change markedly during storage, the cell wall exhibited extensive remodeling. Greater changes were observed in the pectin backbones than in polyuronide side chains and cross-linking glycans. Polygalacturonase (PG) showed better association with cell wall solubilization at RT than the enzymes involved in arabinan or galactan disassembly. During postharvest ripening after harvest, ‘Karantoki’ showed more extensive pectin solubilization than ‘Morphitiki’. Interestingly, cold storage inhibited the cell wall disassembly in ‘Karantoki’ but not in ‘Morphitiki’, suggesting that the cultivars may differ in their susceptibility to chilling-related wall disorders. Low temperature-induced alterations in wall disassembly may impact juice and phytochemical release upon consumption.

  • benzyl aminopurine bap treatments delay cell wall degradation and softening improving quality maintenance of refrigerated summer squash
    Postharvest Biology and Technology, 2014
    Co-Authors: Juan Facundo Massolo, Ariel Roberto Vicente, Analia Concellon, Maria Laura Lemoine, Alicia R Chaves
    Abstract:

    Abstract Round summer squash are harvested before reaching full maturity and even though they are highly perishable, fruit postharvest handling is mostly based on storage at non-chilling temperatures. Finding complementary treatments minimizing deterioration and reducing postharvest losses would be extremely useful. In this work we evaluated the effect of postharvest cytokinin (CK) treatments on refrigerated round soft rind squash. Fruit were harvested at commercial maturity and sprayed with 1 mmol L −1 benzylaminopurine (BAP) or water (control) prior to storage at 5 °C for 0, 13 or 25 days. Quality was assessed upon removal from cold storage as well as after a 2 day shelf-life period at 20 °C. CK-treated fruit showed slower deterioration and dehydration and remained firmer than the control. BAP sprays did not affect color, respiration or sugar-acid balance. The treatments prevented phenolic compound accumulation, and decreased pectin solubilization. By the end of the storage period BAP-treated squash had higher levels (45%) of tightly-bound Polyuronides than untreated controls, indicating a substantial delay in cell wall dismantling. CK sprays also reduced neutral sugar solubilization from pectin-rich fractions, but no changes were found in the cross-linking glycans or cellulose. To our knowledge, this is the first work showing that CK can regulate pectin disassembly in developing fruit. Postharvest BAP sprays preventing texture deterioration may be a simple treatment to complement refrigeration of round, soft rind, summer squash.

  • effect of short term ozone treatments on tomato solanum lycopersicum l fruit quality and cell wall degradation
    Journal of Agricultural and Food Chemistry, 2010
    Co-Authors: Luis Maria Rodoni, Natalia Casadei, Analia Concellon, Alicia Chaves R Alicia, Ariel Roberto Vicente
    Abstract:

    We evaluated the effect of short-term gaseous ozone treatment (10 μL/L; 10 min) on tomato fruit quality and cell wall degradation. The treatments did not modify fruit color, sugar content, acidity, or antioxidant capacity but reduced fruit damage and weight loss and induced the accumulation of phenolic compounds. In addition, softening was delayed in ozone-treated fruit. Cell wall analysis showed that exposure to ozone decreased pectin but not hemicellulose solubilization. Polyuronide depolymerization was also reduced in ozone-treated fruit. While the treatments did not alter the activity of the pectin-degrading enzymes polygalacturonase (PG) and β-Galactosidase (β-Gal), a clear decrease in pectin methyl esterase (PME) was found. Results show that short-term ozone treatments might be useful to reduce fruit damage and excessive softening, two of the main factors limiting tomato postharvest life, without negatively affecting other quality attributes. The impact of the treatments on fruit softening might be ...

Shigeru Yamanaka - One of the best experts on this subject based on the ideXlab platform.

  • physicochemical characteristics of rapidly dried onion powder and its anti atherogenic effect on rats fed high fat diet
    Food Chemistry, 2011
    Co-Authors: Yasunori Hamauzu, Toshiya Nosaka, Fuyu Ito, Takanori Suzuki, Shuichi Torisu, Miyoko Hashida, Akira Fukuzawa, Masakatsu Ohguchi, Shigeru Yamanaka
    Abstract:

    Abstract Rapidly dried onion (Allium cepa L. cv. Momiji No. 3) powder (OP) prepared from the outer layers (from second to fourth scale leaves from the surface) of onion bulbs was analysed for its quercetin and polyuronide contents, the effects of enzymatic treatment and the anti-atherogenic effect on rats fed a high-fat diet. Quercetin 4′-glucoside (50%), free quercetin (30%) and quercetin 3,4′-diglucoside (20%) were identified as quercetin derivatives, and boiling-water extraction was effective in extracting these compounds. OP contained 12.9% of Polyuronides, the basic skeleton of pectin. Enzymatic degradation (cellulase and pectinase, 50 °C for 12 h, pH 6.0) of OP was effective in obtaining a slurry of smaller particle sizes. The free quercetin increased and the glucosides decreased with enzyme treatment. In Wistar rats fed an OP-added high-fat diet, the total cholesterol, HDL-cholesterol and triglyceride concentrations were not significantly different from the rats fed a high-fat diet without OP. However, the atherogenic index (AI) of Wistar rats fed an OP-added high-fat diet was lower (AI = 3.3) than rats fed the diet without OP (AI = 4.1). The incremental elastic modulus (IEM) of the aorta from rats fed the OP-added diet was also significantly lower than that of the rats fed the diet without OP. The AI and IEM values of the rats fed the OP-added diet were quite similar to the values of rats fed the diet without OP but were allowed spontaneous exercise. These results suggest that OP intake is effective for decreasing the risk of arteriosclerosis.

John M Labavitch - One of the best experts on this subject based on the ideXlab platform.

  • cell wall metabolism during the development of chilling injury in cold stored peach fruit association of mealiness with arrested disassembly of cell wall pectins
    Journal of Experimental Botany, 2004
    Co-Authors: David A Brummell, Carlos H Crisosto, Susan Lurie, John M Labavitch
    Abstract:

    Partially tree-ripened ripe fruit of peach (Prunus persica L.) were stored for 1–4 weeks at 5 8C and then ripened at 20 8C for 3 d to induce chilling injury. With increasing cold storage the incidence and severity of mealiness symptoms increased progressively, manifested as reduced quantities of free juice and internal flesh browning. Relative to juicy fruit, tissue of mealy fruit showed altered intercellular adhesion when examined by microscopy and, upon crushing, a higher proportion of cells remained intact and did not release cellular contents. Substantial alterations in the metabolism of cell wall polysaccharides were observed. Chelator-soluble Polyuronides from mealy fruit were partially depolymerized during cold storage in a manner dissimilar to that in unripe or ripe juicy fruit, and were not depolymerized further during the ripening period. The solubility of these high molecular weight pectins remained low, and did not show the increase characteristic of juicy fruit. Furthermore, in mealy fruit the dramatic decline in the polymeric Ara content of base-soluble, matrix glycan-enriched fractions occurring during normal ripening was absent, indicating diminished disassembly of an arabinan-rich polysaccharide firmly attached to cellulose. A corresponding rise in the polymeric Ara content of the most soluble

  • cell wall metabolism during maturation ripening and senescence of peach fruit
    Journal of Experimental Botany, 2004
    Co-Authors: David A Brummell, Carlos H Crisosto, John M Labavitch
    Abstract:

    Cell wall changes were examined in fruit of a melting flesh peach (Prunus persica L.) allowed to ripen on the tree. Three phases to softening were noted, the first of which began prior to the completion of flesh colour change and an increase in ethylene evolution. Softening in young mature fruit, prior to ripening, was associated with a depolymerization of matrix glycans both loosely and tightly attached to cellulose and a loss of Gal from all cell wall fractions. After the initiation of ripening, but before the melting stage, softening was associated with continuing, progressive depolymerization of matrix glycans. A massive loss of Ara from the loosely bound matrix glycan fraction was observed, probably from side chains of glucuronoarabinoxylan, pectin, or possibly arabinogalactan protein firmly bound into the wall and solubilized in this extract. An increase in the solubilization of Polyuronides also occurred during this period, when softening was already well advanced. The extensive softening of the melting period was marked by substantial depolymerization of both loosely and tightly bound matrix glycans, including a loss of Ara from the latter, an increase in matrix glycan extractability, and a dramatic depolymerization of chelator-soluble Polyuronides which continued during senescence. Depolymerization of chelator-soluble Polyuronides thus occurred substantially after the increase in their solubilization. Ripening-related increases were observed in the activities of exo- and endo-polygalacturonase (EC 3.2.1.67; EC 3.2.1.15), pectin methylesterase (EC 3.1.1.11), endo1,4-b-glucanase (EC 3.2.1.4), endo-1,4-b-mannanase (EC 3.2.1.78), a-arabinosidase (EC 3.2.1.55), and b-galactosidase (EC 3.2.1.23), but the timing and extent of the increases differed between enzymes and was not necessarily related to ethylene evolution. Fruit softening in peach is a continuous process and correlated closely with the depolymerization of matrix glycans, which proceeded throughout development. However, numerous other cell wall changes also took place, such as the deglycosylation of particular polymers and the solubilization and depolymerization of chelator-soluble Polyuronides, but these were transient and occurred only at specific phases of the softening process. Fruit softening and other textural changes in peach appear to have a number of stages, each involving a different set of cell wall modifications.

  • temporal sequence of cell wall disassembly in rapidly ripening melon fruit
    Plant Physiology, 1998
    Co-Authors: Jocelyn K C Rose, Kristen A Hadfield, John M Labavitch, Alan B Bennett
    Abstract:

    The Charentais variety of melon (Cucumis melo cv Reticulatus F1 Alpha) was observed to undergo very rapid ripening, with the transition from the preripe to overripe stage occurring within 24 to 48 h. During this time, the flesh first softened and then exhibited substantial disintegration, suggesting that Charentais may represent a useful model system to examine the temporal sequence of changes in cell wall composition that typically take place in softening fruit. The total amount of pectin in the cell wall showed little reduction during ripening but its solubility changed substantially. Initial changes in pectin solubility coincided with a loss of galactose from tightly bound pectins, but preceded the expression of polygalacturonase (PG) mRNAs, suggesting early, PG-independent modification of pectin structure. Depolymerization of Polyuronides occurred predominantly in the later ripening stages, and after the appearance of PG mRNAs, suggesting the existence of PG-dependent pectin degradation in later stages. Depolymerization of hemicelluloses was observed throughout ripening, and degradation of a tightly bound xyloglucan fraction was detected at the early onset of softening. Thus, metabolism of xyloglucan that may be closely associated with cellulose microfibrils may contribute to the initial stages of fruit softening. A model is presented of the temporal sequence of cell wall changes during cell wall disassembly in ripening Charentais melon.

David A Brummell - One of the best experts on this subject based on the ideXlab platform.

  • cell wall metabolism during the development of chilling injury in cold stored peach fruit association of mealiness with arrested disassembly of cell wall pectins
    Journal of Experimental Botany, 2004
    Co-Authors: David A Brummell, Carlos H Crisosto, Susan Lurie, John M Labavitch
    Abstract:

    Partially tree-ripened ripe fruit of peach (Prunus persica L.) were stored for 1–4 weeks at 5 8C and then ripened at 20 8C for 3 d to induce chilling injury. With increasing cold storage the incidence and severity of mealiness symptoms increased progressively, manifested as reduced quantities of free juice and internal flesh browning. Relative to juicy fruit, tissue of mealy fruit showed altered intercellular adhesion when examined by microscopy and, upon crushing, a higher proportion of cells remained intact and did not release cellular contents. Substantial alterations in the metabolism of cell wall polysaccharides were observed. Chelator-soluble Polyuronides from mealy fruit were partially depolymerized during cold storage in a manner dissimilar to that in unripe or ripe juicy fruit, and were not depolymerized further during the ripening period. The solubility of these high molecular weight pectins remained low, and did not show the increase characteristic of juicy fruit. Furthermore, in mealy fruit the dramatic decline in the polymeric Ara content of base-soluble, matrix glycan-enriched fractions occurring during normal ripening was absent, indicating diminished disassembly of an arabinan-rich polysaccharide firmly attached to cellulose. A corresponding rise in the polymeric Ara content of the most soluble

  • cell wall metabolism during maturation ripening and senescence of peach fruit
    Journal of Experimental Botany, 2004
    Co-Authors: David A Brummell, Carlos H Crisosto, John M Labavitch
    Abstract:

    Cell wall changes were examined in fruit of a melting flesh peach (Prunus persica L.) allowed to ripen on the tree. Three phases to softening were noted, the first of which began prior to the completion of flesh colour change and an increase in ethylene evolution. Softening in young mature fruit, prior to ripening, was associated with a depolymerization of matrix glycans both loosely and tightly attached to cellulose and a loss of Gal from all cell wall fractions. After the initiation of ripening, but before the melting stage, softening was associated with continuing, progressive depolymerization of matrix glycans. A massive loss of Ara from the loosely bound matrix glycan fraction was observed, probably from side chains of glucuronoarabinoxylan, pectin, or possibly arabinogalactan protein firmly bound into the wall and solubilized in this extract. An increase in the solubilization of Polyuronides also occurred during this period, when softening was already well advanced. The extensive softening of the melting period was marked by substantial depolymerization of both loosely and tightly bound matrix glycans, including a loss of Ara from the latter, an increase in matrix glycan extractability, and a dramatic depolymerization of chelator-soluble Polyuronides which continued during senescence. Depolymerization of chelator-soluble Polyuronides thus occurred substantially after the increase in their solubilization. Ripening-related increases were observed in the activities of exo- and endo-polygalacturonase (EC 3.2.1.67; EC 3.2.1.15), pectin methylesterase (EC 3.1.1.11), endo1,4-b-glucanase (EC 3.2.1.4), endo-1,4-b-mannanase (EC 3.2.1.78), a-arabinosidase (EC 3.2.1.55), and b-galactosidase (EC 3.2.1.23), but the timing and extent of the increases differed between enzymes and was not necessarily related to ethylene evolution. Fruit softening in peach is a continuous process and correlated closely with the depolymerization of matrix glycans, which proceeded throughout development. However, numerous other cell wall changes also took place, such as the deglycosylation of particular polymers and the solubilization and depolymerization of chelator-soluble Polyuronides, but these were transient and occurred only at specific phases of the softening process. Fruit softening and other textural changes in peach appear to have a number of stages, each involving a different set of cell wall modifications.

  • modification of expansin protein abundance in tomato fruit alters softening and cell wall polymer metabolism during ripening
    The Plant Cell, 1999
    Co-Authors: David A Brummell, Alan B Bennett, Mark H Harpster, Pedro Marcos Civello, Joseph M Palys, Pamela Dunsmuir
    Abstract:

    The role of the ripening-specific expansin Exp1 protein in fruit softening and cell wall metabolism was investigated by suppression and overexpression of Exp1 in transgenic tomato plants. Fruit in which Exp1 protein accumulation was suppressed to 3% that of wild-type levels were firmer than controls throughout ripening. Suppression of Exp1 protein also substantially inhibited polyuronide depolymerization late in ripening but did not prevent the breakdown of structurally important hemicelluloses, a major contributor to softening. In contrast, fruit overexpressing high levels of recombinant Exp1 protein were much softer than controls, even in mature green fruit before ripening commenced. This softening was correlated with the precocious and extensive depolymerization of structural hemicelluloses, whereas polyuronide depolymerization was not altered. These data are consistent with there being at least three components to fruit softening and textural changes. One component is a relaxation of the wall directly mediated by Exp1, which indirectly limits part of a second component due to polyuronide depolymerization late in ripening, perhaps by controlling access of a pectinase to its substrate. The third component is caused by depolymerization of hemicelluloses, which occurs independently of or requires only very small amounts of Exp1 protein.