Climacteric Rise Research Articles

Differential expression of α-l-arabinofuranosidase and α-l-arabinofuranosidase/β-d-xylosidase genes during peach growth and ripening

Arabinose is the major neutral sugar in peach (Prunus persica (L.) Batsch) cell walls and substantial changes in arabinose content take place not only during peach melting, when a rapid-softening-related depolymerizing activity may be expected, but also at the onset of peach ripening. A full-length cDNA clone sequence referred to as PpARF1 (GenBank accession no. DQ486870) was obtained and determined by bioinformatics' analysis to be a peach alpha-l-arabinofuranosidase homologue. The deduced PpARF1 translation product is 677 amino acids in length while the mature protein has a predicted molecular mass of 71.6 kD and a theoretical pI of 4.94. Semi-quantitative RT-PCR reactions were conducted to evaluate the expression of both PpARF1 and PpARF/XYL (GenBank accession no. AB264280), the latter encoding a putative bifunctional protein displaying both alpha-l-arabinofuranosidase and beta-d-xylosidase activities. In peach fruit, the PpARF1 gene expression was detected at every developmental stage with a maximum during S2 (lag phase of development) and a subsequent decrease towards S4 (maximal fruit size). In contrast, PpARF/XYL transcript levels were relatively high at the end of S1 (fruit set) and at S3-E (beginning of the cell expansion). Substantial increases in PpARF1 mRNA levels were found at the beginning and end of the climacteric rise and also in melting fruit. In contrast, PpARF/XYL transcripts reached a maximum when fruit firmness was 22-26 N, with a slight decline during the melting stage. PpARF/XYL and PpARF1 were expressed differently in three fruit tissue types as well as in other plant tissues. Ethylene is regarded as the main regulator of peach ripening and the accumulation of PpARF/XYL and PpARF1 transcripts is coincident with the autocatalytic ethylene production during ripening. On the hand, other factors may also play a role in PpARF1 and PpARF/XYL expression, since transcripts accumulate at different developmental times and organs even when ethylene biosynthesis is barely detectable.

The mitochondrial elongation factor LeEF-Ts mt is regulated during tomato fruit ripening and upon wounding and ethylene treatment

A gene encoding an elongation factor LeEF-Ts mt that participates in the protein synthesis process in mitochondria shows strong expression in ripening fruit as compared to other organs. It is strongly up-regulated during the first stages of the ripening process in parallel with the climacteric rise in respiration. LeEF-Ts mt expression is stimulated by ethylene, wounding and high temperature but ethylene-insensitive mutants exhibit normal expression. Transgenic fruit have been generated in which LeEF-Ts mt has been constitutively up- and down-regulated. Surprisingly, altering the expression of the gene by genetic transformation with antisense and sense LeEF-Ts mt constructs did not affect the pattern of respiration and ethylene production during ripening and upon wounding. In addition, expression of the alternative oxidase gene which is known to play an important role in respiratory climacteric was not affected. Possible reasons for the absence of effect on respiration of variations of LeEF-Ts mt gene expression are discussed.

PpEG4 is a peach endo-β-1,4-glucanase gene whose expression in climacteric peaches does not follow a climacteric pattern*

In peach (Prunus persica L. Batsch.) the degradation of the pectic compounds of the cell wall is considered to be the principal component responsible for fruit softening. Many genes encoding enzymes acting on the different polymers of the pectic matrix have been shown to be highly expressed during the late phases of softening, with polygalacturonase being the most important. Nevertheless, it is known that softening starts well before the ethylene climacteric rise which occurs concomitant with the maximal expression of the pectolytic enzymes. The cloning and characterization of PpEG4, an endo-beta-1,4-glucanase (EGase) gene preferentially expressed in preclimacteric fruits, are presented here. PpEG4 belongs to the group of EGases containing, at their carboxy-terminus, a peptide similar to the cellulose binding domain of microbial origin. This EGase is also expressed during abscission of both leaves and fruits. The effect of exogenous ethylene treatments on PpEG4 transcription is null in young fruits and negative in preclimacteric ones, while it is positive in abscission zones. Thus, the expression of PpEG4 seems to be more dependent on the type of separation process rather than being influenced by a direct hormone action. The ability of the PpEG4 regulatory sequences to drive transcription in cells undergoing separation events is also maintained in tomato, where about 3 kb of the gene promoter could drive the expression of gusA in preclimacteric fruits and in the fruit abscission zones.

Apple Scald Development and Regulation

We have studied scald development by comparing changes in gene expression, C2H4 evolution, and α-farnesene and conjugated trienol contents in scald-resistant cultivars, i.e., `Gala' and `Braeburn', and scald-sensitive cultivars, i.e., `Red Delicious' and `Granny Smith'. We also carried out similar comparisons between controls and treatments that diminished scald symptoms in sensitive cultivars. The data show that scald development is critically dependent on the initiation of the climacteric rise in C2H4 evolution, since treatments that suppress the latter inhibit scald development at low temperatures coincident with a suppression of α-farnesene and conjugated trienols. However, in scald-resistant cultivars, there is an increase in α-farnesene and conjugated trienols, although to a lower degree than in the sensitive cultivars. This indicates that factors other than the auto-oxidation of α-farnesene are also involved in scald development. Analytical data show that malonyl dialdehyde (MDA) increases only in scalded areas, which, in turn, suggests that oxidative reactions are involved in scald development. Storage of `Granny Smith' at temperatures above 7 °C prevents the development of scald without affecting the accumulation of α-farnesene and conjugated trienols. This in turn suggests that chilling temperatures induce as yet unknown enzymes that contribute to scald development. In short, the data show that in addition to cultivars, low temperature stress and the induction of the C2H4 climacteric play a crucial role in scald development. Preliminary data show that treatment of `Granny Smith' apples with olive oil emulsions suppress scald development symptoms.

Postharvest responses of Chinese bayberry fruit

The postharvest responses of Chinese bayberry ( Myrica rubra Sieb. & Zucc.) at 20 °C were investigated using three red cultivars, ‘Biqi’, ‘Hunanzhong’ and ‘Wuzhong’. Fruit from a single harvest for each cultivar were divided into three categories according to fruit colour, designated as ‘immature’, ‘mature’ and ‘ripe’. Respiration rate, ethylene production, total soluble solids (TSS), titratable acidity (TA), fructose, glucose, sucrose and individual organic acids contents were determined over 48 h at 20 °C after harvest. Immature and mature fruit of all three cultivars underwent typical climacteric respiratory and ethylene behaviour, while ripe fruit did not exhibit any climacteric rise. TSS, TA, sugar and organic acid contents of all three cultivars substantially declined over the 48 h; changes in the ratios of TSS/TA and SS/organic acids indicated that acid content decreased more rapidly than sugar content. Citric, malic, oxalic and tartaric acids were the principle organic acids detected, and sugars were mainly sucrose, glucose and fructose. ‘Biqi’ and ‘Hunanzhong’ cultivars had very similar levels of sugars and acids, whereas the ‘Wuzhong’ cultivar had lower levels of both components. Postharvest life could be extended for up to 7 days by storage at 0 °C, but with only a short subsequent shelf life because of rot development. Chinese bayberry fruit should be classified as a climacteric fruit, and our results show the importance of fruit maturity in terms of postharvest response, and similar patterns of response among the three cultivars.

EFFECT OF HARVEST DATE AND STORAGE ON ANTIOXIDANT SYSTEMS IN PEARS

In many fruits the ripening process is characterised by an increase in oxygen consumption related to the climacteric rise. The enhanced oxidative metabolism could generate an excess in Active Oxygen Species (AOS) that, if not effectively detoxified by the cell defence systems, leads to a peroxidation of biomembranes, to a damage of cell compartmentation and, ultimately, to tissue senescence and general disorders. Studies on some components of the system of enzymatic and non enzymatic antioxidants involved in the protection of cells from oxidative damage, are reported. Pears (Pyrus communis 'Passa Crassana') were picked at 3 different stages of ripening: immature, commercial ripe and fully ripe. Commercially ripe fruits were stored for 3 and 4 months at normal atmosphere (T: 1.5°C; R.H.: 95%). Ethylene production rates were measured and the activity of the scavenging enzyme ascorbate peroxidase (APX) was evaluated. The levels of the antioxidant ascorbic acid (AA) and of malondialdehyde (MDA), a marker of lipid peroxidation, were also determined. Ethylene levels were barely detectable at all 3 harvest dates and increase progressively during storage. APX activity was positively affected by the ripening stage, whereas decreased significantly during cold storage. AA reached the highest level in commercial ripe fruits. Furthermore, storage had a negative effect on AA content and caused a gradual, marked decrease. MDA did not change in fruits of different ripening stages, while after storage the levels were significantly higher. These results suggest that, during cold storage of pears, defense mechanisms against AOS fail to provide adequate protection, thus oxidative stress occurs.

The climacteric-like behaviour of young, mature and wounded citrus leaves

Although leaves and other vegetative tissues are generally considered as non-climacteric, citrus leaves show a climacteric system II behaviour after detachment. Upon harvest, young, fully expanded 'Valencia' orange (Citrus sinensis) leaves ( approximately 60-d-old) exhibited two phases of ethylene production. The first phase, up to 6 d after detachment, was characterized by a low and constant ethylene production (system I pathway), associated with a constitutive expression of ACC synthase 2 (CsACS2), CsERS1, and CsETR1. ACC synthase 1 (CsACS1) was not expressed during this phase and autoinhibition of ethylene production was apparent following treatment with exogenous ethylene or propylene. The second phase, 7-12 d after detachment, was characterized by a climacteric rise in ethylene production, preceded by the induction of CsACS1 and ACC oxidase 1 (CsACO1) gene expression in the system II pathway. This induction was accelerated and augmented by exogenous ethylene or propylene, indicating an autocatalytic system II ethylene biosynthesis. Mature leaves (6-8-months-old) behaved similarly, except that the climacteric peak in ethylene production occurred earlier (day 5). Young and mature leaves varied in the timing of the climacteric ethylene rise and CsACS1 and CsACO1 induction. The two phases of ethylene production, system I and system II, were also detected in wounded leaf discs of both young and mature leaves. The first phase peaked 15 min after excision and the second phase peaked after 6 h.

Changes during the ripening of the very late season Spanish peach cultivar Calanda: Feasibility of using CIELAB coordinates as maturity indices

Physiological maturity of peach at harvest greatly influences the post-harvest quality. Changes in colour during the last ripening stages of a very late and firm peach cultivar [ Prunus persica (L.) Batsch cv. Calanda] have been studied to assess the feasibility of using reflectance colour references as non-destructive indices of maturity. The respiratory peak was simultaneous to the ethylene rise, and both induced important changes in the peaches. The physiological changes brought about a rise in polyphenoloxidase and peroxidase enzyme activity. The amount of carotenoids increased as maturity advanced and more markedly at the climacteric rise. Reflectance spectra and CIELAB coordinates reflected changes in skin and pulp colour and a * and h ab evolved nearly in a near linear way. Values of the b * coordinate show changes as well. These findings agree with and extend previous results that reflectance changes can be used as reliable indices to establish the time of physiological maturity in Calanda peaches.

Preharvest application of aminoethoxyvinylglycine (AVG) modifies harvest maturity and cool storage life of ‘Arctic Snow’ nectarines

Abstract The aims were to determine whether preharvest application of aminoethoxyvinylglycine (AVG) adversely affects the cool storage life of ‘Arctic Snow’ nectarines ( Prunus salicina ), and if so whether application of ethylene during storage could counteract these effects. AVG (as ReTain ® Plant Growth Regulator) was applied at 125 mg L −1 to 6-year-old trees in a commercial orchard 7 days before anticipated commercial harvest. First pick fruit were used for this study and untreated (UTC) fruit were harvested at commercial maturity based on changes in skin ground colour and flesh firmness. Two harvest criteria were used for AVG-treated fruit. ReTA fruit were harvested when the colour of the fruit was identical to the UTC (3 days after UTC first pick) and ReTB fruit were harvested when the fruit firmness had declined to the same level as the UTC (7 days after UTC first pick). Fruit were stored for 5 weeks at 1.0–1.5 °C with and without continuous ventilation with 30 μL L −1 ethylene. All fruit had similarly low rates of ethylene production when received and ethylene production remained low in all AVG-treated fruit but exhibited a climacteric rise in untreated fruit. The fruit were assessed weekly for changes in flesh firmness and storage disorders (internal bleeding and percentage juice recovery) 6 days after transfer from cool storage to 20 °C. AVG-treated fruit remained firmer than untreated fruit after 6 days of ripening following harvest but this difference was absent in fruit ripened after 1 week of cool storage. Internal bleeding was detected after 2 weeks of air storage in ReTA and ReTB fruit but not until 3 weeks in UTC fruit. A decrease in percentage juice recovery was found in all treatments after 3 weeks of air storage but ReTA fruit were the most affected. A loss of ability to soften normally was found in all treatments after 4 weeks of storage in air but the continuous application of ethylene during storage maintained normal softening except in ReTA fruit. UTC and ReTB fruit started to go ‘mealy’ ( 20 N firmness, loss of juice). The addition of ethylene resulted in fruit softening more normally and changed the chilling injury from predominantly leatheriness to predominantly mealiness. ReTA fruit tended to go leathery and the addition of ethylene did not change this.

TOWARDS UNDERSTANDING THE ONSET OF PETAL SENESCENCE: ANALYSIS OF ETHYLENE PRODUCTION IN THE LONG-LASTING CARNATION CV. WHITE CANDLE

In senescing carnation (Dianthus caryophyllus L.) flowers, ethylene is produced from the gynoecium, and acts as a diffusible signal received by petals to induce the expression of 1-aminocyclopropane-1-carboxylate (ACC) synthase (DC-ACS1) and ACC oxidase (DC-ACO1) genes in the petals. This results in autocatalytic ethylene production in the petals. We investigated ethylene production in cut flowers of cv. White Candle, which produce ethylene only in trace amounts and have a long vase life. The low ethylene production in these flowers was due to low ethylene production in the gynoecium, accompanied by low accumulation of ACC synthase transcripts. These findings further support the importance of ethylene production from the gynoecium in the senescence of carnation flowers. Cv. White Candle flowers had water relations that were different from those in cv. Light Pink Barbara, a cultivar that showed the normal climacteric rise of ethylene production during senescence. We discuss a factor that possibly induces ethylene production in the carnation gynoecium.

Characterization of tomato fruit ripening and analysis of gene expression in F1 hybrids of the ripening inhibitor (rin) mutant

The ripening inhibitor (rin) mutation of tomato yields non‐ripening fruit, and the gene corresponding to RIN, LeMADS‐RIN, is known to encode a transcriptional factor that controls ripening‐related genes. In this study, to evaluate the heterozygosity effect of rin on fruit ripening, we developed eight F1 hybrid lines of the rin mutant from various crosses between the lines of the rin mutant and wild type. In the fruit of these F1 hybrid lines, the shelf‐life was improved, but both the shelf‐life and colouring varied between the lines. We then chose one line of the F1 hybrids and investigated the physiological and transcriptional properties of the fruit. Compared with the wild‐type parent, this F1 line showed about half the lycopene content, lower fruit softening and lower mRNA accumulation of the genes that encode phytoene synthase (Psy), polygalacturonase (PG), β‐galactosidase (TBG4) and expansin (LeEXP1). The characteristic climacteric rise in ethylene production typically observed in the wild‐type parent during fruit maturation was not observed in the fruit of this F1 line. The genes that encode ethylene biosynthetic enzymes, namely 1‐aminocyclopropane‐1‐carboxylic acid (ACC) synthase (ACS2 and ACS4) and ACC oxidase (ACO1), were, however, significantly expressed in the F1 hybrid, suggesting that the post‐transcriptional regulator for activating these enzymes is affected by LeMADS‐RIN. These results suggest that the heterologous effect of LeMADS‐RIN in F1 hybrids affects the gene transcription and activation of ripening‐related factors, resulting in changes in fruit properties, including the extension of the shelf‐life.

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.

Ripening of mountain papaya (Vasconcellea pubescens) and ethylene dependence of some ripening events

The first noticeable event during the ripening of mountain papaya ( Vasconcellea pubescens ) is the rapid degreening of the skin, followed by climacteric ethylene and flesh softening. When ethylene perception is blocked by 1-methylcyclopropene (1-MCP, 0.3 μl l −1 for 16 h at 20 °C), the increase in ethylene evolution is avoided, and softening and color development are partially delayed. This indicates that ethylene perception is an absolute requirement for ethylene production during ripening and that softening and color development are only partially dependent on ethylene. Our data also suggest that the changes in pH, titratable acidity, and soluble solids are not dependent on ethylene. Mountain papaya fruit displayed the typical climacteric rise in ethylene production, reaching maximum values of 1.8–3.2 μmol kg −1 h −1 , and so confirmed the climacteric nature of the fruit. The activity of ACC oxidase paralleled changes in ethylene production. Nevertheless, when 1-MCP treated fruit recover ethylene sensitivity, a big increase in ACC oxidase activity is observed followed by a further increase, but at a reduced level, of ethylene; the reduced ACC content suggests that in these fruit the availability of ACC is limiting ethylene biosynthesis. Finally, our results indicate that treatment of mountain papaya with 1-MCP delays the onset of the climacteric phase, and therefore can be used commercially to extend effectively the short shelf life of this fruit.

Temporary Relationship Between C2 H4 Evolution and C2 H4 Recptor Genes

`Granny Smith' apples were stored at 1 °C, 5 °C and 20 °C, then treated at the preclimacteric stage with 2 ppm MCP, various O2 concentrations, and MCP + low O2. All the treatments greatly retarded the onset of the C2 H4 climacteric, and hence ripening. MCP + low O2 was much more effective than were the applications of MCP and low O2 singly. Even at 20 °C, 4.04 kPa O2 inhibited the rise in C2 H4 evolution for 145 d. Neither low O2 nor MCP inhibited the System 1 C2 H4 evolution. The suppression of the climacteric rise in C2 H4 evolution was accompanied by a strong inhibition of the accumulation of ERS1 C2 H4 receptor and ACS transcripts. On the other hand, ETR1 receptor was constitutively expressed. When climacteric fruits were treated with MCP, and with low O2 + MCP the rate of C2 H4 evolution decreased sharply. This occurred simultaneously with a decrease in ERS1 mRNA. Moreover, the decrease in ERS1 mRNA paralleled the decrease in C2 H4 evolution. The data thus indicate that the initiation and sustainment of the C2 H4 climacteric requires the presence of functional C2 H4 receptors. The expression of ETR2 and ERS2 is also under investigation.

Endogenous Free Polyamines of Mangos in Relation to Development and Ripening

Changes in endogenous free polyamines (putrescine, spermidine, spermine) were monitored from fruit set (fruit diameter 4.6 ± 0.5 mm, wt 0.09 ± 0.05 g) until 1 week before the expected harvest time in `Kensington Pride' and `Glen' to examine their role during mango (Mangifera indica L.) fruit development. Polyamines (PAs) in the pericarp tissues (exocarp and mesocarp) were estimated throughout the fruit development period, while estimations from growing ovules were started from 41 days after fruit set (DAFS). During fruit ripening, ethylene production and endogenous free PAs in skin and pulp of `Kensington Pride' mango were also monitored. PA contents of pericarp declined between fruit set and maturity from 788 to 101 nmol·g-1 fresh weight (FW) in `Kensington Pride' and from 736.6 to 89.6 nmol·g-1 FW in `Glen' during fruit development. Spermidine (SPD) and spermine (SPM) were higher than putrescine (PUT) during the initial phase of fruit growth. The highest levels of free PAs, especially SPD and SPM, at the initial stages of fruit growth suggest a potential role during the cell division phase and not in subsequent fruit development. Ovule seems to be a rich source of PAs as evident from 2.3- and 2.7-fold higher total PAs than pericarp tissues in `Kensington Pride' and `Glen', respectively. During fruit ripening of `Kensington Pride', total PAs increased in skin and pulp tissues along with the climacteric rise of ethylene, and reached maximum levels (skin 796, pulp 314 nmol·g-1 FW) on day 4 of ripening. Skin exhibited 55.8% higher mean free PAs than the pulp. PUT dominated both in skin and pulp tissues. The simultaneous increase of ethylene and free PAs during fruit ripening suggests that their biosynthesis may not be competitive, and free PAs may have evolved as a response to increased biosynthesis of ethylene.

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.

Fatty acids as precursors for aroma volatile biosynthesis in pre-climacteric and climacteric apple fruit

Abstract Changes in the concentration of free fatty acids (FA) and FA as constituents of neutral and polar lipids were determined during the course of ripening in the peel of ‘Golden Delicious’ apple fruit. The concentration of these FA was then related to previously examined volatile aroma substances in order to evaluate a possible quantitative relationship between both variables. In particular, the concentrations of the C18:1 and C18:2 FA in the free FA fraction were low in pre-climacteric fruit but rapidly increased three- to fourfold during the climacteric rise. Changes in FA concentrations during maturation were less pronounced in the neutral lipid fraction and almost absent in the polar lipid fraction. Treatment of immature fruit (harvested almost 5 weeks before the climacteric rise) with 100 μl l−1 ethylene increased the concentration of FA in the free and neutral lipid fraction but not in polar lipids. The increase in the free and ‘neutral lipid’ 18:2 FA after ethylene treatment in immature apples exceeded the concentration of this FA found in mature climacteric fruit. A hypothesis is discussed linking the examined dynamic changes of FA with previous results of ATP and aroma volatiles in an attempt to explain deficiencies in aroma volatile production in unripe and long-term stored apple fruit.

A cell wall-oriented genomic approach reveals a new and unexpected complexity of the softening in peaches.

During ripening, fleshy fruits undergo textural changes that lead to loss of tissue firmness and consequent softening. It is a common idea that this process is the consequence of cell wall dismantling carried out by different and orderly expressed enzymes. For this purpose, by using a single enzyme family approach many enzymes and related genes have been characterized in different fruits. In this work, the softening of the climacteric peach fruits (Prunus persica (L.) Batsch.) has been studied by using a genomic approach, and the results obtained are novel and partly unexpected. The genes analysed encode proteins involved in the main metabolic aspects of a primary cell wall: degradation, synthesis, structure. In addition, some genes encoding cell-wall-related proteins with an unknown function have been studied. The gene expression profiles show that the softening actually begins well before the climacteric rise and continues thereafter. Genes whose expression starts before the climacteric rise are mostly down-regulated by ethylene, while genes with a ripening-specific expression are mostly up-regulated by the hormone. A few other genes are apparently insensitive to ethylene. Besides the expected parietal degradation, the softening that results from this study also comprises some repairing of the cell wall performed by enzymes involved in the synthesis of parietal polysaccharides and, especially, by proteins with structural functions. The newly synthesized polysaccharides and the structural proteins would thus help to hold together the fruit cell wall while not preventing the softening.

The role of salicylic acid in postharvest ripening of kiwifruit

During postharvest ripening and softening of kiwifruit ( Actinidia deliciosa (A. Chev.) C.F. Liang and A.R. Ferguson cv. Bruno) at 20 °C, the levels of salicylic acid (SA) in fruit tissues declined. Concurrently, lipoxygenase (LOX) activity increased, and this was associated with climacteric ethylene release. In fruit stored at 0 °C with a reduced rate of softening, SA concentrations remained at relatively high levels. Application of acetylsalicylic acid (ASA) to ripening kiwifruit resulted in substantially higher SA levels than in control fruit. ASA treatment slowed down the increase in LOX activity and superoxide free radical production, and suppressed ACC synthase and ACC oxidase activities and biosynthesis of ethylene, and hence retarded the climacteric rise in ethylene production. Fruit ripening and senescence were also delayed. A close relationship was found to exist between change in SA levels in the fruit tissues and the extent of fruit ripening and softening.

Respiration rate, ethylene production and biochemical changes during fruit development and maturation of jujube (Ziziphus mauritiana Lamk)

AbstractJujube fruits (Ziziphus mauritiana Lamk) of cv Zaytoni were harvested from fruit set until maturity to study some physiological and biochemical changes. Jujube fruit cv Zaytoni displayed a double‐sigmoid growth curve with a very short second stage (2 weeks). Changes in respiration rate and ethylene production during fruit development were typical of climacteric fruits, the peak of ethylene production coinciding with the climacteric rise in respiration. As for chemical constituents, reducing sugars were dominant and sucrose was absent in ripe fruit. Total soluble solid content was low during the early stages of growth, then increased to a peak in ripe fruit. Titratable acidity was low initially, but increased to a peak in physiologically mature fruit and declined rapidly in ripe fruit. The pattern of changes in protein content was typical of that characterising climacteric fruits.© 2002 Society of Chemical Industry