ISSN:0114-0671    

DOI:10.1080/01140671.1992.10421902

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The advent of new molecular tools has opened up fresh approaches to some long standing questions concerning the ripening of fruit. These same tools, coupled with transformation and plant regeneration techniques, give promise of the availability of genotypes that may not have been achieved by traditional means. In the latter context, the regulation of ethylene production or perception, colour, disease and insect resistance, and texture have received most emphasis. To have a means of modifying the capacity for ethylene production by a fruit without using inhibitors is an attraction when questions of maturity and ethylene sensitivity are raised. The means may be close at hand. Ethylene production is regulated at two steps: by 1-aminocyclopropane-1-carboxylate reductase, which has a very rapid rate of turnover; and by the ethylene forming enzyme or EFE. Genes for each of these functions have now been located. Also available are some fruit specific promoters and various enhancers. It is already known that down-regulating the EFE gene increases fruit shelf life in tomato, and that exogenous ethylene advances senescence in mutated fruit. The prospect is there to explore the sensitivity of many fruit to exogenous ethylene. There has also been an opportunity to test hypotheses on fruit softening using transgenic tomatoes. A decade or less back, correlation analysis suggested that softening of tomato fruit was regulated by a single factor, the rate of accumulation of the pectin splitting enzyme, endopolygalacturonase. Moreover, the accumulation of the enzyme seemed to depend on contemporaneous gene transcription. So, down-regulation of the gene should inhibit softening, but it did not The hypothesis was disproven and rewoven. Recombinant DNA technology offers other opportunities to explore mechanisms in fruit ripening. Probes for hormone receptors are becoming available and will allow the exploration of the role of receptors in the regulation of maturity and senescence in fruits. Fruit and stage specific promoters offer other opportunities including the further evaluation of the respiratory climacteric that features so prominently in the studies of fruit physiology.

ISSN:0114-0671    

DOI:10.1080/01140671.1992.10421903

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Antisense RNA technology is a powerful tool to study the metabolic role of enzymes and to produce commercially desirable traits in food crops. This is demonstrated here for the study of pectin degradation during tomato (Lycopersicon esculentumMill) fruit ripening. Two enzymes—polygalacturonase (PG) and pectinesterase (PE), have been down regulated using this technique. Reduced PG prevented pectin depolymerisation during ripening and resulted in fruit with improved storage and transport characteristics. The reduction in PE activity resulted in increased pectin esterification throughout ripening but had no apparent effect on fruit physiology. All other aspects of pectin metabolism tested were unaffected in these transgenic fruit.

ISSN:0114-0671    

DOI:10.1080/01140671.1992.10421904

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Softening during fruit ripening may be initiated by an increase in proton pumping across the plasma membrane. This would lower the cell wall pH and loosen acid-labile bonds, as well as displacing Ca2+from load-bearing bonds. The enzyme responsible for proton pumping is the plasma membrane H+-ATPase. The activity of this enzyme in nectarine (Prunus persica(L.) Batsch var.nectarina(Ait.) Maxim., cv. Redgold) mesocarp was studied during 4 days of ripening at 20°C after harvest at commercial maturity. Fruit began to produce significant amounts of ethylene (> 1 µlitre/kg per h) from the second day. Flesh firmness began to decline from the third day, but background skin colour did not change until the fourth day. Plasma membranes were extracted from the fruit by phase partitioning. Initial characterisation of the H+-ATPase activity showed that it was Mg2+-dependent, K+-stimulated, and VO43−-sensitive. The Kmfor MgA TP was 0.19 ± 0.02 mM. The Kivalue for Ca2+was estimated at 100 µMfree Ca2+. The in vitro specific activity of the ATPase did not alter significantly during a 4-day period after commercial harvest. There was a slight decline in ATPase activity with increasing ethylene evolution (R2= 0.25, P < 0.05) but no significant correlation between ATPase activity and firmess or skin colour.

ISSN:0114-0671    

DOI:10.1080/01140671.1992.10421905

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

An experiment on carambola (Averrhoa carambola) cv. ‘B17’ was conducted in the 1989/90 harvest season to investigate the relationships between fruit physical and chemical characteristics and maturation. The physical properties were length, width, weight. and volume and the chemical properties were total soluble solids, pH, total titratable acidity, total sugars, and total ascorbic acid content. Sensory evaluation for sourness, colour, sweelness, texture, and overall acceptability were also carried out. Measurements were made weekly between 9 and 13 weeks after fruit set. Colour was classified as light green, yellowish green, more yellow, than green, more orange than yellow, and full orange. For fresh consumption, harvesting was carried out from Week 11 to Week 13 after fruit set. Chemical and physical characteristics were measured over the harvest season. Total soluble solids, pH, total sugars, and total ascorbic acid content increased whereas total titratable acidity declined. The causal regression relationships of chemical variates on harvest maturity are presented.

ISSN:0114-0671    

DOI:10.1080/01140671.1992.10421906

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The distribution of pectin methyl esterase (PE) and endopolygalacturonase (PG) was studied in tomato (Lycopersicon esculentumMill) fruit. Antibodies were raised in rabbits to the PE2 isoform of PE and the PG2 isoform of PG. The antisera were used to probe PE and PG in sections of mature green and ripening tomato pericarp tissue by immunocytology. PE was detected in the cell wall of green and ripening fruit. A comparison with specific and non-specific sera indicated that the PE antigen was largely confined to the cell wall. PG was detected in the cell wall of ripening but not green tissue. Gold label was observed over both the primary wall and the middle lamella, and also over the cytoplasm. In the wall region, no distinctions could be drawn between the distributions of PE and PG, but PG differed from PE in that a significant proportion of the antigen was in the cytoplasm.

ISSN:0114-0671    

DOI:10.1080/01140671.1992.10421907

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Cauliflower (Brassica oleracea) curds are of better quality, and therefore more marketable, when they are white and free from blemishes. As the production of pigments in plants can be stimulated by exposure to light, cauliflower curds were covered with either their leaves or “Tyvek”, a spunbounded olefin material, during curd growth to minimise the light transmitted. In a spectrophotometer, Tyvek and leaves transmitted <1% of light, as compared to deionised water, over the spectral range 200–800 nm. In a field experiment at Medina, Western Australia. covered curds were whiter and had 20% (Tyvek) or 40% (leaves) of the concentration of flavonoids in the florets (estimated by absorbance at 366 nm) of the curds grown without covers. The carotenoid concentration did not differ significantly (P> 0.05) between covered and uncovered curds. Under the conditions of the field experiment management of curd quality required pre-harvest protection from light to reduce flavonoid production.

ISSN:0114-0671    

DOI:10.1080/01140671.1992.10421908

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Effects of decreased O2partial pressure P(O2) and increased CO2partial pressure p(CO2) on senescence of 7-day-old oat plants or excised leaves (Avena sativaL. cv. Victory) and broccoli miniflorets (Brassica oleraceaL. var.italica) were studied in terms of chlorophyll and protein loss, proteolytic activity, and stomatal behaviour. Senescence in darkness was delayed by decreasing p(O2), an effect which in oat leaves was unaffected by the CO2partial pressure, p(O2). However, increased P(CO2) at low O2levels gave the best colour and flavour retension in broccoli miniflorets. Chlorophyll level increased c. 25% during the first 2–3 days after plants or excised leaves were placed in darkness at a P(O2) of 0.5 kPa. Protein and chlorophyll breakdown were inhibited when p(O2) was 2 kPa or less. Excision of leaves accelerated breakdown when compared to whole plants regardless of p(O2). Modification of ubiquitin conjugates was observed in broccoli miniflorets stored at reduced p(O2). The data indicates ubiquit-independent proteolysis contributed to senescence of broccoli miniflorets.

ISSN:0114-0671    

DOI:10.1080/01140671.1992.10421909

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Fruit-to-fruit impacts on commercial packing lines were simulated in the laboratory for pairs of fresh ‘Gala’, ‘Splendour’, ‘Fuji’, ‘Braeburn’, and ‘Granny Smith’ apples by dropping one apple onto the other from a range of heights. Bruising was generally more severe on one of the two apples, and it was quite common for only one apple to be damaged. Contact areas above 1 cm2were closely related to bruise areas. Below this level bruising rarely occurred. Some bruises produced in apple-to-apple impacts were not visible unless the apple skin was removed. ‘Braeburn’ apples required a greater drop height to produce a significant bruise than other varieties. An Instrumented Sphere (IS), 89 mm in diameter with a mass of 0.336 kg, which recorded acceleration magnitudes above an adjustable pre-programmed threshold, was used to characterise impacts onto fruit. When the results of apple-to-apple and IS-to-apple impacts were compared, it was found that the area of the larger of the two bruises produced in fruit-to-fruit impacts was directly related to the peak acceleration recorded by the IS when it was dropped onto a fruit from the same height. Using this comparison, damage thresholds resulting from fruit-to-fruit impacts were determined by analysing IS output. The implications of these results to the techniques to interpret IS output during field trials on handling systems are discussed. It was concluded that the IS can be used to identify apple-to-apple impacts likely to cause bruising in commercial packing operations, providing care is taken with interpretation of the data.

ISSN:0114-0671    

DOI:10.1080/01140671.1992.10421910

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

After 6 weeks storage at 1°C, the broccoli (Brassica oleracea) heads which were stored in unsealed polyethylene bags in waxed cartons without ice or in polystyrene boxes without the addition of ice (top ice) were still very fresh with green compact heads and no sign of microbial infection. The broccoli which was stored in unsealed polyethylene bags with ice or in polystyrene boxes with ice was not as good as those stored without ice. Ten—15% of broccoli was slightly mouldy and some soft rots were observed in iced treatments. Growth of micro-organisms was associated with the presence of free water in the packages after the melting of the ice. Chlorine treatment (250 ppm) controlled the mould in storage without ice, but had no effect in treatments with ice. The quality of broccoli which was stored in sealed bags (modified atmosphere (MA) storage) was as good as those stored in waxed cartons with unsealed polyethylene bags. The use of a polystyrene box with top ice for broccoli is not necessary if the temperature during storage and transportation can be maintained below 2°C. Irrespective of packaging, all the broccoli turned yellow and became unmarketable after transfer and storage for 2 days at 26°C, 70–75% RH, except those stored in sealed polyethylene bags under MA condition. The broccoli which was stored in sealed high density polyethylene bags was still fresh and green with compact heads and free of offensive odours. However, that stored in sealed low density polyethylene bags was also green, but some rots and off-odours were present.

ISSN:0114-0671    

DOI:10.1080/01140671.1992.10421911

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor