F. Romojaro

Differential rind and pulp ripening of transgenic antisense ACC oxidase melon

1-Aminocyclopropane-1-carboxylic acid (ACC) oxidase (ACO) antisense Cantaloupe melons (Cucumis melo var. cantalupensis Naud.) unable to produce ethylene were used to identify the characteristic physiological processes occurring during ethylene-dependent ripening and to determine which tissue (pulp or rind) was most affected by this plant hormone. The antisense fruits were compared with untransformed fruits, which were used as controls. The most pronounced differences were observed in the rind when the untransformed melons entered in the climacteric respiratory stage. The major pigments, chlorophylls and carotenoids, remained undegraded, while sucrose and citric acid were accumulated continuously in antisense fruit rind. No big differences in the ripening parameters tested were observed in the pulp, except for those regarding the citric acid content and ripening index. The hypothesis of a differential ripening between pulp and rind in Cantaloupe melon is proposed.

Transcriptomic Events Involved in Melon Mature-Fruit Abscission Comprise the Sequential Induction of Cell-Wall Degrading Genes Coupled to a Stimulation of Endo and Exocytosis

Background Mature-fruit abscission (MFA) in fleshy-fruit is a genetically controlled process with mechanisms that, contrary to immature-fruit abscission, has not been fully characterized. Here, we use pyrosequencing to characterize the transcriptomes of melon abscission zone (AZ) at three stages during AZ-cell separation in order to understand MFA control at an early stage of AZ-activation. Principal Findings The results show that by early induction of MFA, the melon AZ exhibits major gene induction, while by late induction of MFA, melon AZ shows major gene repression. Although some genes displayed similar regulation in both early and late induction of abscission, such as EXT1-EXT4, EGase1, IAA2, ERF1, AP2D15, FLC, MADS2, ERAF17, SAP5 and SCL13 genes, the majority had different expression patterns. This implies that time-specific events occur during MFA, and emphasizes the value of characterizing multiple time-specific abscission transcriptomes. Analysis of gene-expression from these AZs reveal that a sequential induction of cell-wall-degrading genes is associated with the upregulation of genes involved in endo and exocytosis, and a shift in plant-hormone metabolism and signaling genes during MFA. This is accompanied by transcriptional activity of small-GTPases and synthaxins together with tubulins, dynamins, V-type ATPases and kinesin-like proteins potentially involved in MFA signaling. Early events are potentially controlled by down-regulation of MADS-box, AP2/ERF and Aux/IAA transcription-factors, and up-regulation of homeobox, zinc finger, bZIP, and WRKY transcription-factors, while late events may be controlled by up-regulation of MYB transcription-factors. Significance Overall, the data provide a comprehensive view on MFA in fleshy-fruit, identifying candidate genes and pathways associated with early induction of MFA. Our comprehensive gene-expression profile will be very useful for elucidating gene regulatory networks of the MFA in fleshy-fruit.

Pectic enzymes in fresh fruit processing: optimization of enzymic peeling of oranges

Abstract An enzymic technique for peeling oranges has been optimized. The process is based on the vacuum infusion of a commercial glycohydrolase preparation (pectinases and cellulases) (Rohament PC) allowing the removal of the orange peel to obtain peeled whole fruit and segments. The influence of the different parameters of the process, such as the vacuum conditions necessary for infusing the enzyme preparation, enzyme concentration, pH, temperature and enzyme solution reusability, have been studied. To improve the enzymes action, several cuts were made in the orange peel to facilitate the introduction of the enzyme solution, and substantial differences in peeling quality were obtained as a function of the different cutting patterns assayed. The optimal processing conditions for peeling whole oranges made it possible to reuse the enzyme solution for 8 days without any significant loss in enzyme activity or peeling efficiency. This is obviously of interest for any industrial application.

NON-INVOLVEMENT OF ACC AND ACC OXIDASE ACTIVITY IN PEPPER FRUIT RIPENING

Abstract Pepper of the variety California shows sigmoid-type growth curves and changes of colour, which are characteristic of the fruit reaching maturity, when it has practically reached full size. Respiratory activity is high a few days after fruit-set and then falls progressively. Ethylene production and 1-aminocyclopropane-1-carboxylic acid (ACC) levels remain low throughout fruit development and maturation, while ethylene-forming enzyme (EFE) activity gradually falls throughout the development. We show that treatment with propylene has no effect on the post-harvest maturation of pepper, although treatment with silver thiosulphate (STS) increases respiratory intensity and ethylene production due to the stress caused which, in turn, causes an increase in ACC levels after treatment. All these results lead to the conclusion that pepper behaves like a non-climacteric fruit during maturation, and that maturation is not regulated by ethylene.

Understanding the mechanisms of chilling injury in bell pepper fruits using the proteomic approach.

In order to advance in the understanding of CI in pepper fruits, the cell ultrastructure alterations induced by CI and the physiological and metabolic changes have been studied along with the proteomic study. When stored at low temperatures bell pepper (Capsicum annuum) fruits exhibited visual CI symptoms and important alterations within the cell ultrastructure, since peroxisomes and starch grains were not detected and the structure of the chloroplast was seriously damaged in chilled tissues. Physiological and metabolic disorders were also observed in chilled fruits, such as higher ethylene production, increased MDA content, changes in sugar and organic acids and enzymatic activities. The comparative proteomic analysis between control and chilled fruits reveals that the main alterations induced by CI in bell pepper fruits are linked to redox homeostasis and carbohydrate metabolism. Thus, protein abundance in the ascorbate-glutathione cycle is altered and catalase is down-regulated. Key proteins from glycolysis, Calvin cycle and Krebs cycle are also inhibited in chilled fruits. Enolase and GAPDH are revealed as proteins that may play a key role in the development of chilling injury. This study also provides the first evidence at the protein level that cytosolic MDH is involved in abiotic stress.

Ethylene biosynthesis and physico-chemical changes during fruit ripening of cherimoya (Annona cherimola, Mill)

This work indicates that cherimoya behaves like a climacteric fruit after harvesting, because it shows respiration and ethylene crises connected with its ripening. The increase in ethylene production is caused by an increase in the activities of ACC-synthase and ethylene-forming enzyme (EFE), which are very low in the freshly picked fruit, but increase rapidly over the second day, reaching a maximum on the third day. During the climacteric there is also a low amount of 1-aminocyclopropane-l-carboxylic acid (ACC) in its conjugated form. Skin browning increases after harvesting, but this is not related to a decrease of chlorophyll, since the chlorophyll level remains stable throughout the entire post-harvest period. The level of browning shows a good correlation (r=0.947) with the L parameter of colour of reflection. There is a temporal coincidence between the onset of ethylene production, the degradation of starch, the loss of firmness and the build up of total sugars.

A cross-flow reactor with immobilized pectolytic enzymes for juice clarification

SummaryA new system for continuous juices clarification is presented. The bioreactor combines microporous plates commercially available and industrial pectinases immobilized on nylon membranes in a cross-flow configuration. The kinetic behaviour of the reactor for different recirculation flow rates has been determined. Fresh apricot juice has been continuously clarified in the bioreactor with excellent results.

Levels of ACC and physical and chemical parameters in peach development

SummaryThe state of maturity of peach fruits (Prunus persica, L.) was determined in terms of different physical and chemical attributes at different stages of fruit development. It was shown that the onset of softening coincided with an increase in red fruit colour, 100 days after fruit set. At the same time the rates of respiration and ethylene production reached maxima of 210 mg CO2 kg−1 h−1 and 23 nl ethylene g−1 h−1, respectively. During the first 60 days of development the concentration of conjugate ACC was about 40 times higher than that of free ACC. A subsequent fall in conjugate and free ACC was succeeded by a rapid increase in both conjugate and free ACC at the time of onset of the respiration climacteric.

Antioxidant Systems from Pepper (Capsicum annuum L.): Involvement in the Response to Temperature Changes in Ripe Fruits

Sweet pepper is susceptible to changes in the environmental conditions, especially temperatures below 15 °C. In this work, two sets of pepper fruits (Capsicum annuum L.) which underwent distinct temperature profiles in planta were investigated. Accordingly, two harvesting times corresponding to each set were established: Harvest 1, whose fruits developed and ripened at 14.9 °C as average temperature; and Harvest 2, with average temperature of 12.4 °C. The oxidative metabolism was analyzed in all fruits. Although total ascorbate content did not vary between Harvests, a shift from the reduced to the oxidized form (dehydroascorbate), accompanied by a higher ascorbate peroxidase activity, was observed in Harvest 2 with respect to Harvest 1. Moreover, a decrease of the ascorbate-generating enzymatic system, the γ-galactono-lactone dehydrogenase, was found at Harvest 2. The activity values of the NADP-dependent dehydrogenases analyzed seem to indicate that a lower NADPH synthesis may occur in fruits which underwent lower temperature conditions. In spite of the important changes observed in the oxidative metabolism in fruits subjected to lower temperature, no oxidative stress appears to occur, as indicated by the lipid peroxidation and protein oxidation profiles. Thus, the antioxidative systems of pepper fruits seem to be involved in the response against temperature changes.

Influence of fruit ripening stage and harvest period on the antioxidant content of sweet pepper cultivars.

Pepper (Capsicum annuum L.) fruits are highly appreciated by producers and consumers for their economical and nutritional value. Four different cultivars of coloured peppers in immature and mature stages were harvested throughout the spring and examined for their content of phenolic compounds, ascorbic acid and total antioxidant capacity (TAA) as well as for lipid peroxidation and carbonyl proteins as index of oxidative stress. Ripening and harvest period influenced the antioxidants and the development of oxidative processes in the cultivars differently: lipid peroxidation increased in mature peppers except in one cultivar (Y1075), while no changes in protein oxidation or in TAA were produced, except in Y1075 in which both parameters increased. Each cultivar presented differences in antioxidant compounds depending on the harvest period, but we could recommend May as the optimal if all cultivars have to be harvested at the same time, when levels of ascorbate, phenols and TAA were not decreased, fresh weight and proteins were elevated, and levels of oxidation were not as high as in June (except for Y1075). A previous study of the response of each cultivar to different environmental conditions results essential to establish a good program of selection of cultivars with high quality and productivity.