Cell Wall Enzyme Activities Research Articles

New insights into the heterogeneous ripening in Hass avocado via LC–MS/MS proteomics

Hass avocado postharvest ripening heterogeneity creates several logistics problems at destination markets. Although several approaches mainly based on targeted analysis have been undertaken to broaden our understanding of the potential causes of this postharvest ripening heterogeneity, still the secret is not yet unveiled. In this study biopsies from individual fruit displaying contrasting ripening behavior (slow vs fast) and subjected to different storage conditions (immediately after harvest, 30 d regular air at 5°C and 30 d at 5°C and 4kPa O2 and 6kPa CO2) were analyzed for targeted fatty acid analysis and cell wall enzyme activity combined with a more integrative approach based on gel free proteomics LC–MS/MS. The high throughput proteomics was capable of discriminating between slow and fast ripening avocado fruit. Proteins that were mainly less abundant in the slow ripening phenotype were annotated to correct protein folding, translation and de novo synthesis and higher abundant proteins were annotated to amino sugar and nucleotide metabolism, detoxification and stress response and proteolysis. Our study opens new insights into the causes of heterogeneous ripening and may provide new markers for avocado ripening at harvest and after prolonged storage.

A transcriptomics-based kinetic model for enzyme-induced pectin degradation in apple (Malus × domestica) fruit

Modifications of cell wall pectin during apple softening involve the concerted action of several enzymes. A mathematical model was developed to describe the action of cell wall hydrolases resulting in specific modifications in cell wall pectin polysaccharides during softening of ‘Jonagold’ apple. A conceptual model of enzyme-induced pectin breakdown was formulated based on current knowledge. Activities of different cell wall enzymes were considered to be directly correlated to the expression levels of the respective genes. The first pectin modification to occur was assumed to be cleavage of side chain neutral sugars from the polymer backbone, by the action of side chain debranching enzymes, beta-galactosidase and alpha-l-arabinofuranosidase. It was considered that this increases cell wall porosity, facilitating the action of pectin methyl esterase, which de-methylates pectin polysaccharides, providing a substrate for polygalacturonase. Polygalacturonase degrades the de-methylated pectin chain, producing smaller pectin fragments which are easily solubilised in water. Coupled differential equations were written based on these reactions. The model was calibrated using data on expression of cell wall-related genes, activities of enzymes encoded by these genes, and the associated modifications in pectin polysaccharides during softening in ‘Jonagold’ apples stored at 1°C under regular atmosphere or controlled atmosphere. The model could explain 79% of the variation in the data. Using the model, in silico investigations on the impact of downregulation of different key cell wall-related genes on softening were carried out, and the results were compared successfully with currently available literature data.

Xyloglucan Metabolism Differentially Impacts the Cell Wall Characteristics of the Endosperm and Embryo during Arabidopsis Seed Germination

Cell wall remodeling is an essential mechanism for the regulation of plant growth and architecture, and xyloglucans (XyGs), the major hemicellulose, are often considered as spacers of cellulose microfibrils during growth. In the seed, the activity of cell wall enzymes plays a critical role in germination by enabling embryo cell expansion leading to radicle protrusion, as well as endosperm weakening prior to its rupture. A screen for Arabidopsis (Arabidopsis thaliana) mutants affected in the hormonal control of germination identified a mutant, xyl1, able to germinate on paclobutrazol, an inhibitor of gibberellin biosynthesis. This mutant also exhibited reduced dormancy and increased resistance to high temperature. The XYL1 locus encodes an α-xylosidase required for XyG maturation through the trimming of Xyl. The xyl1 mutant phenotypes were associated with modifications to endosperm cell wall composition that likely impact on its resistance, as further demonstrated by the restoration of normal germination characteristics by endosperm-specific XYL1 expression. The absence of phenotypes in mutants defective for other glycosidases, which trim Gal or Fuc, suggests that XYL1 plays the major role in this process. Finally, the decreased XyG abundance in hypocotyl longitudinal cell walls of germinating embryos indicates a potential role in cell wall loosening and anisotropic growth together with pectin de-methylesterification.

Cell wall metabolism and related gene expression inMalus domesticaBorkh. during fruit growth and softening

Introduction. Pre-harvest fruit development of apple can have a great effect on its storable quality. However, little research has focused on fruit metabolism during growth. Our objective was to study cell wall metabolism during the various stages of fruit growth and softening to gain more insight into the nature of fruit development and ripening. Materials and methods. Apple varieties Fuji and Golden Delicious (GD) were used to investigate cell wall metabolism and related gene expression during fruit growth and softening. Results and discussion. During fruit growth, cell wall components underwent similar changes in the two cultivars although the covalent soluble pectin (CSP) content in Fuji fruit was much higher than that in GD fruit. The activities of cell wall enzymes and the related gene expression indicated that cell wall degradation was involved in fruit growth. However, these changes showed significant differences between the two cultivars during storage. The water soluble pectin (WSP) content increased more rapidly and the content of CSP and hemi-cellulose decreased more obviously, showing a more significant correlation with firmness loss in GD fruit than with Fuji. Accordingly, the activities of cell wall enzymes and the related gene expression were significantly higher in the GD fruit. Conclusion. Cell wall metabolism and the related gene expression showed significant differences between Fuji and GD fruit during growth and softening. Both acted on fruit growth and enlargement but revealed a significant cultivar-dependency with regards to fruit softening.

Effect of Temperature on Activities of Cell Wall Enzymes of Kiwifruit during the Shelf Life

Taking kiwifruits stored 60 days at 0°C as material, studied on the effect of three temperature treatments on hardness and cell wall enzymes activity during the shelf life. The results indicated that the time of firmness decreased to 3 kg·cm-2 at 0°C extended 17 days and 29 days than at 10°Cand at 20°C respectively. Low temperature treatments could effectively inhibited PG, Cx and PE activities, thus extended shelf life. The time of PG activity reached the peak at 0°C was 28 days, later than at10°C and at 20°C by 16 days and 20 days respectively . The Cx activity peak at 0°C was 1.31×103 μg/h·g and much smaller than at 10°C 1.77×103μg/h·g and at 20°C 1.95×103μg/h·g. PE activity of 0°C has remained the lowest state after three days. So The best treatment was 0°C.

Role of putrescine in regulating fruit softening and antioxidative enzyme systems in ‘Samar Bahisht Chaunsa’ mango

The role of putrescine (PUT) in regulating fruit softening, antioxidative enzymes and biochemical changes in fruit quality was investigated during ripening and cold storage of mango (Mangifera indica cv. Samar Bahisht Chaunsa). Fruit were treated with various PUT concentrations (0.0, 0.1, 1.0 and 2.0mM) and were allowed to ripen at 32±2°C for 7 days, or stored at 11±1°C for up to 28 days. Respiration rate and ethylene production were measured daily during ripening and cold storage. Cell wall degrading enzymes such as exo-polygalacturonase (exo-PG), endo-polygalacturonase (endo-PG), pectin esterase (PE), endo-1,4-β-d-glucanase (EGase), antioxidative enzymes including superoxide dismutase (SOD), peroxidase (POX), and catalase (CAT), fruit firmness as well as biochemical fruit quality characteristics were estimated during ripening and cold storage at 2 and 7 day intervals, respectively. PUT treatments reduced respiration rate, ethylene production and maintained higher fruit firmness during ripening as well as cold storage. PUT-treated fruit exhibited significantly suppressed activities of cell wall enzymes (exo-, endo-PG and EGase), but retained higher PE activity during ripening and cold storage. Total phenolic and antioxidant contents were significantly higher in PUT-treated fruit during ripening as well in the cold storage period than in the controls. Activities of antioxidative enzymes (CAT, POX and SOD) were also significantly higher in PUT-treated fruit during ripening as well as cold storage. SSC and SSC:TA were lower in PUT-treated fruit, while TA and ascorbic acid content showed the reverse trend. In conclusion, pre-storage 2.0mM PUT treatment inhibited ethylene production and suppressed the activities of cell wall enzymes, while resulting in higher activities of antioxidative enzymes and maintaining better fruit quality during ripening and cold storage.

Potency Of Bacteriocin For Animal Health And Food Safety

The emergence of antibiotic resistance in many bacteria related to animal and public health stresses the importance of decreasing the use of antibiotics in animal production. The reduction of antibiotic application in livestock can only be achieved if alternative antimicrobial strategies are available. A number of strategies have been explored to control microbial pathogens and to improve growth and feed efficiency in livestock without the use of antibiotics. Bacteriocins have been more extensively studied and proposed as potential alternatives to conventional antibiotics in animal husbandry. Bacteriocins are antimicrobial peptides ribosomally synthesized by many species of Bacteria and some strains of Archaea. In general, bacteriocins just exhibited bactericidal or bacteriostatic activity against other bacteria that are closely related to the producing strain. The main mechanisms of bacteriocin activity vary from pore formation in cytoplasmic membranes to the inhibition of cell wall biosynthesis and enzyme activities (RNAse or DNAse) in target cells. The use of bacteriocins in probiotic applications, as preservatives, and most excitingly as alternatives to conventional antibiotics is being broadly explored and studied. This review will describe the bacteriocins potency for animal health and food safety, as well as the results of bacteriocin study that had been conducted in Indonesia.Key words: Bacteriocin, animal health, food safety

Transcriptome dynamics during fibre development in contrasting genotypes of Gossypium hirsutum L.

Understanding the contribution of genetic background in fibre quality traits is important for the development of future cotton varieties with superior fibre quality. We used Affymetrix microarray (Santa Clara, CA) and Roche 454 GSFLX (Branford, CT) for comparative transcriptome analysis between two superior and three inferior genotypes at six fibre developmental stages. Microarray-based analysis of variance (ANOVA) for 89 microarrays encompassing five contrasting genotypes and six developmental stages suggests that the stages of the fibre development have a more pronounced effect on the differentially expressed genes (DEGs) than the genetic background of genotypes. Superior genotypes showed enriched activity of cell wall enzymes, such as pectin methyl esterase, at early elongation stage, enriched metabolic activities such as lipid, amino acid and ribosomal protein subunits at peak elongation, and prolonged combinatorial regulation of brassinosteroid and auxin at later stages. Our efforts on transcriptome sequencing were focused on changes in gene expression at 25 DPA. Transcriptome sequencing resulted in the generation of 475 658 and 429 408 high-quality reads from superior and inferior genotypes, respectively. A total of 24 609 novel transcripts were identified manually for Gossypium hirsutum with no hits in NCBI 'nr' database. Gene ontology analyses showed that the genes for ribosome biogenesis, protein transport and fatty acid biosynthesis were over-represented in superior genotype, whereas salt stress, abscisic acid stimuli and water deprivation leading to the increased proteolytic activity were more pronounced in inferior genotype.

Cell wall enzymes and changes in sugar content in pollinated orchids treated with ethylene inhibitors and sugars

The pollinated flowers of Dendrobium Pompadour orchids exhibited rapid morphological changes, which resulted in full flower closure. In contrast, unpollinated flowers remained fresh and turgid during the identical time period. The aim of this study was to examine the pollination-induced changes in the cell wall enzyme activity and sugar content. Cell wall hydrolase assays showed that pollination induces significant increases in polygalacturonase, pectate lyase and cellulase activity, whereas pectin methyl esterase showed insignificant changes in activity. Membrane leakage was rapid in pollinated flowers. The total and reducing sugar content increased in the pollinated flowers and was most profound in the column of the flowers. Treatment with ethylene inhibitors and sugars suppressed cell wall hydrolase activity and membrane leakage to a varying extent. The sugar content was more stable in the treated flowers. Altogether, the results show that ethylene inhibitors effectively delay pollination-induced floral destruction.

THE ROLE OF CALCIUM IN PLANTS' SALT TOLERANCE

High concentrations of sodium (Na) are toxic to most plant species, making soil salinity a major abiotic stress in plant productivity world wide. It has been shown that, calcium (Ca2+) is an important determinant for plant salt tolerance and confers protective effects on plants under growing in sodic soils. Calcium plays an essential role in processes that preserve the structural and functional integrity of plant cell membranes, stabilizes cell wall structures, regulates ion transport and selectivity, and controls ion-exchange behavior as well as cell wall enzyme activities. The nature of these responses will vary depending on the plant genotype. One of the essential functions of Ca2+ is acting as a second messenger in stress signaling. Genetic evidence suggests that perception of salt stress leads to a cytosolic calcium-signal that activates the calcium sensor protein SOS3. SOS3 binds to and activates a ser/thr protein kinase SOS2. The activated SOS2 kinase regulates the activities of SOS1, a plasma membrane Na+/H+ antiporter, and NHX1, a tonoplast Na+/H+ antiporter. This results in either Na+ efflux out of cytosol or its compartmentation in vacuole.

The carbohydrate-binding module of Fragaria × ananassa expansin 2 (CBM-FaExp2) binds to cell wall polysaccharides and decreases cell wall enzyme activities “in vitro”

A putative carbohydrate binding module (CBM) from strawberry (Fragaria×ananassa Duch.) expansin 2 (CBM-FaExp2) was cloned and the encoding protein was over-expressed in Escherichia coli and purified in order to evaluate its capacity to bind different cell wall polysaccharides "in vitro". The protein CBM-FaExp2 bound to microcrystalline cellulose, xylan and pectin with different affinities (K(ad)=33.6±0.44mLg(-1), K(ad)=11.37±0.87mLg(-1), K(ad)=10.4±0.19mLg(-1), respectively). According to "in vitro" enzyme assays, this CBM is able to decrease the activity of cell wall degrading enzymes such as polygalacturonase, endo-glucanase, pectinase and xylanase, probably because the binding of CBM-FaExp2 to the different substrates interferes with enzyme activity. The results suggest that expansins would bind not only cellulose but also a wide range of cell wall polymers.

Axial changes in apoplast properties in the elongation zone of maize mesocotyl

Changes in extensibility of cell walls and composition of apoplastic solution along the elongation zone were studied in mesocotyls of etiolated seedlings of maize (Zea mays L.). It was found that plastic and elastic extensibility of cell walls was much greater in the cells with a high rate of elongation. Basipetal decrease in hydrogen peroxide concentration in the apoplast (from 5.1 to 2.0 μM) was detected. We determined the activity of cell wall enzymes participating in H2O2 metabolism and found that in basal direction, potential ability of these enzymes to decompose H2O2 rises stronger than the ability to produce it. We found a basipetal decrease in polyamine oxidase activity, an increase in oxalate oxidase activity, and a rise in the ratio between peroxidase and NADH-oxidase activities of peroxidases. IAA (10−6 M) promoted elongation of mesocotyl segments, induced a steady elevation of H2O2 content in the apoplast, an increase in NADH-oxidase activity of peroxidases, and a transient decrease in oxalate oxidase activity. Treatment with ABA (10−4 M) suppressed elongation of mesocotyl segments, induced a transient elevation of H2O2 content in the apoplast, and a decrease in oxalate oxidase activity. It was shown that the main metabolites of apoplastic solution are glucose (20–30 mM), fructose (6–7 mM), malic acid (3 mM), and amino acids, namely, Asp, Glu, Asn, Gln, Ala, Val, Ser, Thr, and Phe. In basal direction, we observed a decrease in the content of glucose (from 30 to 20 mM), inositol (from 0.24 to 0.08 mM), and total amino acids (from 5.5 to 3.3 mM), whereas concentration of orthophosphate (3 mM) and malate (3 mM) did not change significantly. A relationship between the detected changes in the apoplast composition and basipetal decrease in the elongation rate of mesocotyl cells is discussed.

Molecular analysis of softening and ethylene synthesis and signaling pathways in a non-softening apple cultivar, ‘Honeycrisp’ and a rapidly softening cultivar, ‘McIntosh’

A feature of ‘Honeycrisp’ apples [ Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.] is that they maintain flesh firmness over extended storage. The objective of this study was to elucidate molecular mechanisms that are responsible for slow softening of ‘Honeycrisp’ as compared with a rapidly softening cultivar, ‘McIntosh’. Fruit from both cultivars were picked during the normal harvest period and stored at 20 °C for 10 d. Internal ethylene concentrations (IECs) in ‘Honeycrisp’ fruit were lower than in ‘McIntosh’, but at climacteric levels of ethylene ‘Honeycrisp’ fruit maintained their firmness over this period, while ‘McIntosh’ softened rapidly. Concentrations of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) were higher in ‘Honeycrisp’ than in ‘McIntosh’ apples. qRT-PCR analysis was carried out for genes involved in ethylene biosynthesis, perception and signaling [ACC synthase ( MdACS); ACC oxidase ( MdACO); ethylene receptors ( MdETR and MdERS); constitutive triple response ( MdCTR); ethylene response factor ( MdERF)], as well as those involved in cell wall metabolism [polygalacturonase ( MdPG); xyloglucan endotransglucosylase ( MdXTH); expansin ( MdEXP); β-galactosidase ( Md β- GS); arabinofuranosidase ( MdAFase); pectate lyase ( MdPL)]. At comparable IECs, the expression of genes involved in ethylene synthesis, ethylene perception and signal transduction was generally much higher in ‘Honeycrisp’ than in ‘McIntosh’ fruit. However, the expression of MdAFase and MdEXP3 was generally lower in ‘Honeycrisp’ than in ‘McIntosh’, while that of MdPG and MdPL was extremely low in ‘Honeycrisp’. Expression of MdPG1 was very low, even though IECs were at climacteric levels. Absence of fruit softening in ‘Honeycrisp’ is probably associated with restricted cell wall enzyme activity. The lower maximum IECs found in ‘Honeycrisp’ compared with ‘McIntosh’ do not appear to be related to expression of genes involved in ethylene biosynthesis.

Postharvest ethylene treatment affects berry dehydration, polyphenol and anthocyanin content by increasing the activity of cell wall enzymes in Aleatico wine grape

Ethylene is known to induce cell wall degradation by acting on cell wall enzymes. Thus, the objective of this experimental study was to evaluate the effect of ethylene on weight loss in Aleatico wine grape during dehydration and whether this effect was due to cell wall enzyme activation. Moreover, the effect on polyphenol, anthocyanin content, and volatile compounds was studied. Aleatico red grapes (Vitis vinifera L, cv Aleatico) were treated with 1,000 μL/L of ethylene in air for 48 h at 20 °C and high relative humidity (RH). Control grapes were untreated. After 48 h, grape clusters were placed at 45% RH, 20 °C, and 1 m/sec air flow (dehydration treatment) to dehydrate until reaching 40% of weight loss (wl). Pectin methylesterase (PME), polygalacturonase (PG), α galactosidase, and β glucosidase were analyzed during dehydration treatment. Weight loss in ethylene-treated berries was about 6% higher than in control grapes, and PME, PG, galactosidase, and glucosidase activities had increased. During dehydration, the concentration of polyphenols and anthocyanins in ethylene-treated grape was higher than in untreated grape. Geraniol and citronellol peak areas rose slightly in ethylene-treated grapes following the pattern of β glucosidase, but the total peak area of terpene alcohols decreased. Ethylene increased the concentration of anthocyanins and polyphenols during dehydration.

The effect of antifungal hot-water treatments on papaya postharvest quality and activity of pectinmethylesterase and polygalacturonase

The effect of antifungal hot-water treatments (AHWT) at 55°C for 0, 3, 6 and 9min on quality attributes and cell-wall enzymatic activity during storage at 25°C was investigated in papaya fruit. The total soluble solids (TSS), pH, titratable acidity (TA), firmness and fresh weight loss were not affected, whereas color on skin was negatively affected by the treatments of 6- and 9-min. However, the skin color was not different between the 3-min treated fruit and the untreated fruit during the storage. Decay was delayed and reduced by AHWT. We observed that the 3-min treatment of 55°C did not affect softening and quality of papaya cv Maradol when applied as a pesticide-free treatment at color-break stage of papaya. PME (Pectinmethylesterase) and PG (Polygalacturonase) activities were not significantly affected by AHWT. We concluded that the AHWT did not affect the softening process from papaya pulp since the cell-wall enzyme activity (PME and PG) was not altered by treatments.

Genetic variability for leaf growth rate and duration under water deficit in sunflower: analysis of responses at cell, organ, and plant level

Plants under water deficit reduce leaf growth, thereby reducing transpiration rate at the expense of reduced photosynthesis. The objective of this work was to analyse the response of leaf growth to water deficit in several sunflower genotypes in order to identify and quantitatively describe sources of genetic variability for this trait that could be used to develop crop varieties adapted to specific scenarios. The genetic variability of the response of leaf growth to water deficit was assessed among 18 sunflower (Helianthus annuus L.) inbred lines representing a broad range of genetic diversity. Plants were subjected to long-term, constant-level, water-deficit treatments, and the response to water deficit quantified by means of growth models at cell-, leaf-, and plant-scale. Significant variation among lines was found for the response of leaf expansion rate and of leaf growth duration, with an equal contribution of these responses to the variability in the reduction of leaf area. Increased leaf growth duration under water deficit is usually suggested to be caused by changes in the activity of cell-wall enzymes, but the present results suggest that the duration of epidermal cell division plays a key role in this response. Intrinsic genotypic responses of rate and duration at a cellular scale were linked to genotypic differences in whole-plant leaf area profile to water deficit. The results suggest that rate and duration responses are the result of different physiological mechanisms, and therefore capable of being combined to increase the variability in leaf area response to water deficit.

Cell wall metabolism during durian fruit dehiscence

Changes in cell wall composition and enzyme activities were studied during durian fruit dehiscence. Water-soluble pectin concentrations remained constant for 2 days in both the husk and the dehiscence zone (DZ), and then increased in the DZ toward the end of storage. Chelator-soluble pectin was higher in the DZ at harvest and throughout storage. This pectin fraction increased steadily in both tissues. Na 2CO 3-soluble pectin content was about the same in the husk and the DZ, but slightly decreased during the dehiscence process. Hemicellulose (1 and 4 M KOH-soluble fractions) slowly decreased in the husk and the DZ during storage. The molecular size distribution of the three pectin fractions shifted from a larger molecular size to a smaller size, during durian dehiscence. The DZ was found to contain smaller pectin molecules than the husk. There was no change in molecular size in the 1 M KOH fraction and only a minor change toward the smaller molecular size in the 4 M KOH fraction during the later period of durian dehiscence. Pectin methyl esterase activity, both in the husk and in the DZ, was the same at the beginning of storage. However, differences were observed by the time storage had ended. Polygalacturonase activity slowly increased in both tissues during 8 days of storage, with the activity always being higher in the DZ than in the husk, especially at late dehiscence. β-1,4-Endoglucanase activity increased more in the DZ than in the husk during the dehiscence process. β-Galactosidase activity increased during the first half of fruit ripening, and then declined. The results suggested that the durian dehiscence process mainly involved degradation of chelator-soluble pectin by polygalacturonase.

Temperature Effect on Skin Adhesion, Cell Wall Enzyme Activity, Lignin Content, Anthocyanins, Growth Parameters, and Periderm Histochemistry of Sweetpotato

Sweetpotatoes [Ipomoea batatas (L.) Lam.] often experience significant epidermal loss during harvest and postharvest handling. Skin loss causes weight loss, shriveling of the root surface, and increased susceptibility to pathogen attack as well as poor appearance. It is not known if sweetpotatoes show variation in skin adhesion, cell wall enzyme activity and components, and growth parameters with growth temperature or if skin loss can be explained on the basis of variation among these variables. Skin adhesion, polygalacturonase (PG) and pectin methylesterase (PME) activity, lignin, anthocyanin, and dry matter content were measured in the periderm of ‘Beauregard’ roots grown at various temperatures under controlled conditions. Biomass dry matter content, storage root yield, root length, diameter, and weight at harvest were recorded. Histochemical and anatomical characteristics of periderm of roots were studied. Growth temperature affected skin adhesion, PG and PME activity, periderm and biomass dry matter content, yield, storage root weight, and diameter. High temperatures (34/31 °C day/night) yielded roots that were smaller and more resistant to skin loss. These roots had a periderm composed of more cell layers with a lower dry matter content than roots grown at lower and intermediate temperatures (27/24 °C and 20/17 °C). In cured roots, the correlation between skin adhesion and PG activity was negative (r = 0.544, P = 0.0006) and positive between skin adhesion and PME (r = 0.319, P = 0.05). For most of the variables studied, the interaction between growing temperature and curing was significant. Curing improved skin adhesion, but the effect of curing was dependent on the root growth temperature. The periderm of roots grown at higher temperatures was thicker and had more layers than that of roots grown at lower temperatures. Histochemical studies of the periderm of sweetpotato showed that the anatomical and structural composition of the cell walls differ depending on growth temperature.

Eating quality of ‘Flor de Invierno’ pears: chemical and structural aspects

SummaryThe eating quality of ‘Flor de Invierno’ pears in ambient conditions was studied. The samples were stored for 7 months in refrigeration and then for different periods (0, 7, 14 and 20 days) at 20 °C without atmosphere control. The samples were analysed using various different techniques: instrumental texture (penetration), microstructure (Cryo‐SEM and LM), image analysis, acidity, soluble solids, cell wall enzyme activity (PME, Endo‐PG), and consumer acceptance/rejection. The acceptance percentage of the pear samples fell with storage time at 20 °C, from more than 80% on day 0, to 30% for 14 and 20‐day samples. This drop in acceptability was related to losses in texture (softer and less crisp fruits) and lower acid/sugar ratio, as well as to a loss of cell wall integrity observed at a microscopic level as a result of the activation of the PME and PG enzymes during ripening.

Why are Chloris gayana leaves shorter in salt-affected plants? Analyses in the elongation zone

Reduced hydraulic conductance calculated from growth data was suggested to be the main reason for reduced leaf expansion in salt-stressed Chloris gayana (Rhodes grass). In this work, xylem vessel cross-sections and wall enzyme activities were analysed to re-examine the effects of salinity on leaf growth in this species. Maximal segmental growth rates were 20% lower and the growth zone was 23% shorter in leaves from salinized plants than in controls; however, growth rates between 0 mm and 15 mm from the ligule were similar in both types of leaves. Xylem cross-sectional areas in this region were about 65% smaller in leaves of salinized plants, suggesting that hydraulic restrictions in the leaves of salinized plants were much higher than overall growth reductions. Extractable xyloglucan endotransglucosylase activity in this zone was twice as high in leaves of salinized plants as in leaves of controls. Nevertheless, the activity of the extracted enzyme was not affected by up to 1 M NaCl added to the reaction medium. Therefore, increased xyloglucan endotransglucosylase activity under salinity may be due to a promotion of transcription of XTH (xyloglucan endotransglucosylase/hydrolases) genes and/or translation of preformed transcripts. These results suggest that, as in drought stress, increased activity of cell wall enzymes associated with wall loosening may contribute to the maintenance of growth under saline conditions despite hydraulic restrictions.