Determination of firmness of field-grown tomatoes during storage in controlled atmosphere or ripened at different temperatures

Durometer readings indicated that although differences in firmness of maturegreen fruits were small, there were large varietal differences in red-ripe fruit after preor post-storage ripening treatment at different temperatures. Such differences were positively related to the performance of the different cultivars in controlled atmosphere storage. Thus the durometer provides a simple means of assessing the firmness of ripe tomato fruits and hence of predicting the long-term storage potential of different cultivars.     

Reevaluation of the changes in polygalacturonases in tomatoes during ripening

A procedure was developed for the differential extraction of polygalacturonases (PG) I and II from tomatoes (Lycopersicon esculentum Mill.). Extraction of pericarp tissue from ripe fruit at conventional conditions of 1.0 M NaCl and pH 6.0 yielded nearly equal amounts of the two enzymes. However, most of the PG activity could be extracted also with water at pH 1.6, and the water extract contained only PG II. Subsequent extraction of the pellet with 1.0 M NaCl at pH 6.0 and 10.0 yielded some PG I and high levels of PG converter, the protein in tomatoes that reacts with PG II to form PG I. Application of this procedure to tomatoes at different stages of ripening showed that PG II appeared as ripening began and then increased during ripening. Much lower levels of PG I than of PG II were extracted at all stages of ripeness. The PG converter was present in unripe fruit and increased during ripening. The results demonstrate that PG I is formed when PG II and PG converter are solubilized simultaneously and that PG II is the only endogenous PG in tomatoes.Abbreviation PG polygalacturonase     

Plastid changes during the conversion of chloroplasts to chromoplasts in ripening tomatoes

Methods were developed for the isolation of plastids from mature green and ripening tomatoes (Lycopersicon esculentum Mill.) and purification by sucrose or Percoll density-gradient centrifugation. Assessment of the purity of preparations involved phase-contrast and electron microscopy, assays for marker enzymes and RNA extraction and analysis. Proteins were extracted from isolated plastids at different ripening stages and separated by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The profiles obtained from chloroplasts and chromoplasts showed many qualitative and quantitative differences. Labelling of proteins with [³⁵S]methionine in vivo showed that there was active protein synthesis throughout ripening, but there was a change in the plastid proteins made as ripening proceeded. The cellular location of synthesis of specific proteins has yet to be established.Abbreviations CS citrate synthase - EDTA ethylenediaminetetraacetic acid,-acetate - GAPDH NADP⁺-glyceraldehyde-3-phosphate dehydrogenase - rRNA ribosomal RNA - SDS sodium dodecyl sulphate - SDS-PAGE SDS-polyacrylamide gel electrophoresis - Tris 2-amino-2(hydroxymethyl)-1,3-propanediol     

Endogenous cytokinins in the fruits of ripening and non-ripening tomatoes

Ripening fruits of a normal strain (Rutgers) of tomato (Lycopersicon esculentum Mill.) were found to contain lower levels of endogenous cytokinins than fruits of a non-ripening mutant rin. The cytokinin content of both strains was high at the light green (breaker) stage and decreased as the fruits senesced. This decrease was more pronounced in the normal fruits. The non-ripening rin not only contained higher levels of the free base cytokinins, zeatin and zeatin riboside, but also high levels of zeatin glucoside, a storage cytokinin. It is suggested that the high levels of endogenous cytokinins in rin fruits are involved in delaying the ripening process.     

Composition of ethanol-insoluble polysaccharides in water extracts of ripening tomatoes

The carbohydrate composition of the 80% ethanol-insoluble polysaccharides (EIP) from water extracts of ‘Rutgers,’ rin (ripening inhibitor) and nor (non-ripening) tomatoes has been determined. The amount of EIP extracted from ‘Rutgers’ fruit increased from 0.34 to 0.61 mg/g fr. wt during ripening little change occurred in rin or nor fruit. The carbohydrate composition (μg/g fr. wt) of EIP from mature green fruit was: galacturonic acid (48); rhamnose (3); arabinose (20); xylose (48); mannose (31); glucose (139); galactose (51). The most obvious changes that accompanied ripening were a 7.4-fold and 4-fold increase in galacturonic acid and rhamnose content, respectively. These changes were attenuated in the ripening mutants. EIP was fractionated into three major peaks by using DEAE-cellulose ion exchange chromatography. The first peak, which was not retained by the column, contained predominantly glucose and mannose, with lower amounts of galacturonic acid and galactose. The two retained peaks which eluted at 0.1 and 0.2 M sodium chloride contained primarily galacturonic acid, xylose, galactose and arabinose. The galacturonic acid content of these two fractions increased substantially during ripening, whereas the other components decreased. No changes were evident in the ripening mutants. No increase in water-soluble polysaccharides high in galactose content was observed during ripening.     

Inheritance and effect on ripening of antisense polygalacturonase genes in transgenic tomatoes

The role of the cell wall hydrolase polygalacturonase (PG) during fruit ripening was investigated using novel mutant tomato lines in which expression of the PG gene has been down regulated by antisense RNA. Tomato plants were transformed with chimaeric genes designed to express anti-PG RNA constitutively. Thirteen transformed lines were obtained of which five were analysed in detail. All contained a single PG antisense gene, the expression of which led to a reduction in PG enzyme activity in ripe fruit to between 5% and 50% that of normal. One line, GR16, showed a reduction to 10% of normal PG activity. The reduction in activity segregated with the PG antisense gene in selfed progeny of GR16. Plants homozygous for the antisense gene showed a reduction of PG enzyme expression of greater than 99%. The PG antisense gene was inherited stably through two generations. In tomato fruit with a residual 1% PG enzyme activity pectin depolymerisation was inhibited, indicating that PG is involved in pectin degradation in vivo. Other ripening parameters, such as ethylene production, lycopene accumulation, polyuronide solubilisation, and invertase activity, together with pectinesterase activity were not affected by the expression of the antisense gene.     

Effect of temperature and ripening stages on membrane integrity of fresh-cut tomatoes

The shelf-life of fresh-cut tomatoes mainly depends on loss of tissue integrity and firmness that occurs also in intact fruits after long-term cold storage due to chilling injury. Round-fruit tomatoes (Solanum lycopersicum L.) cv. Jama were stored in 1.1-L plastic (polyethylene) fresh-cut produce containers as 10.0-mm-thick tomato slices and as intact tomatoes at 4 ± 0.5 °C. The aim of this work was to study the loss of membrane integrity and biochemical processes involved in membrane disruption. Electrolyte leakage and lipid peroxidation were studied at different stages of maturity: mature green, pink (PK), fully ripe and two different storage temperatures: 4 and 15 °C. The tomato slices of PK stage stored at 4 °C did not show changes for both parameters, while significant increase in membrane leakage and lipid peroxidation was observed at 15 °C, especially after 24 h of storage. The enzymes showed a simultaneous increase in their activities with a rise in electrolyte leakage and lipid peroxidation after 7 days of storage. Finally, phospholipase C (PLC) and phospholipase D (PLD) were investigated for intact fruit and tomato slices stored at 4 °C. The PLC had higher activity compared with PLD. In conclusion, the loss of membrane integrity in fresh-cut tomatoes is mainly affected by ripening stages, storage temperature and duration. The wounds enhance the PLC and PLD activities and they play a role late during storage.     

Polygalacturonase-inhibiting proteins in plant fleshy fruits during their ripening and infections

During ripening of fleshy fruits, changes in tissue consistency are largely due to the functioning of the enzyme polygalacturonase (PG) digesting polygalacturonan in cell-wall pectin. Polygalacturonase-inhibiting proteins (PGIP) have been found in plants as proteins interacting with PG, which is secreted by pathogenic microorganisms. PGIP are glycoproteins comprising sequences enriched in leucine repeats. Since PG is one of the main factors of pathogenicity, it is supposed that PGIP are involved in processes hampering plant disease development. PGIP presence in the apoplast of essentially all plant tissues implies their involvement in biochemical processes occurring in the cell walls. This review considers PGIP role in plant fleshy fruits, where the cell-wall composition and structure are of importance for fruit ripening, storage, and resistance to diseases.     

Water-soaked symptom of 'Andesu' netted melon fruit does not develop under anaerobic nitrogen atmospheres during ripening

'Andesu' netted melon fruits (Cucumismelo. L.) were ventilated with pure nitrogen or air for 12 days from35 to 47 DAA or 6 days from 47 to 53 DAA (ripe and over-ripe stages,respectively). Exposure to anaerobic nitrogen atmosphere resulted in higheracetaldehyde and ethanol concentrations, while lower sucrose concentration wasrecorded in the mesocarp compared with air-ventilated fruit. However,water-soaked symptom was not developed under anaerobic nitrogen atmospheres,suggesting that the formation of water-soaking mesocarp tissue does not resultfrom increased alcoholic fermentation and/or decreased soluble sugaraccumulation in the flesh. Anaerobic nitrogen atmospheres also resulted in lowethylene production, high flesh firmness, and inhibition of depolymerisation ofpolyuronides and non-cellulosic neutral sugars in the cell walls. Theimportanceof increased intercellular spaces and membrane permeability on the developmentof water-soaked symptom was suggested.     

The appearance of polygalacturonase mRNA in tomatoes: one of a series of changes in gene expression during development and ripening

Tomato mRNA was extracted from individual fruits at different stages of development and ripening, translated in a rabbit reticulocyte lysate and the protein products analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The results indicate that there are at least two classes of mRNA under separate developmental control. One group of approximately six mRNAs is present during fruit growth and then declines at the mature-green stage. Another group of between four and eight mRNAs increases substantially in amount at the onset of ripening, after the start of enhanced ethylene synthesis by the fruit, and continues to accumulate as ripening progresses. Studies of protein synthesis in vivo show that several new proteins are synthesised by ripening fruits including the fruit-softening enzyme polygalacturonase. One of the ripening-related mRNAs is shown to code for polygalacturonase, by immunoprecipitation with serum from rabbits immunised against the purified tomato enzyme. Polygalacturonase mRNA is not detectable in green fruit but accumulates during ripening. It is proposed that the ripening-related mRNAs are the products of a group of genes that code for enzymes important in the ripening process.Abbreviation SDS sodium dodecyl sulfate     

超声在植物生理学领域的应用

综述了超声在植物生理学研究和实践中的应用。研究涉及超声对植物体呼吸强度、萌发率、生根状况、某些代谢途径的影响以及超声的空化作用对植物体生理学方面的影响。在植物生理学领域中超声的应用主要是利用了超声的空化作用、机械作用和热效应。     

Internal carbon dioxide and ethylene levels in ripening tomato fruit attached to or detached from the plant

The carbon dioxide and ethylene concentrations in tomato fruit ( Lycopersicon esculentum cv. Castelmart) and their stage of ripeness (characteristic external color changes) were periodically measured in fruit attached to and detached from the plant. An external collection apparatus was attached to the surface of individual tomato fruit to permit non-destructive sampling of internal gases. The concentration of carbon dioxide and ethylene in the collection apparatus reached 95% of the concentration in the fruit after 8 h. Gas samples were collected every 24 h. A characteristic climacteric surge in carbon dioxide (2-fold) and ethylene (10-fold) concentration occurred coincident with ripening of detached tomato fruit. Fruit attached to the plant exhibited a climacteric rise in ethylene (20-fold) concentration during ripening, but only a linear increase in carbon dioxide concentration. The carbon dioxide concentration increases in attached fruit during ripening, but the increase is a continuation of the linear increase seen in both attached and detached fruit before ripening and does not exhibit the characteristic pattern normally associated with ripening climacteric fruit. In tomato fruit, it appears that a respiratory climacteric per se, which has been considered intrinsic to the ripening of certain fruit, may not be necessary for the ripening of "climacteric" fruit at all, but instead may be an artifact of using harvested fruit.