Comparative transcriptomic analysis of plum fruit treated with 1-MCP

Microarray technology has allowed the large scale transcriptomic analysis of fruit ripening. The μPEACH1.0 microarray containing 4,806 probes corresponding to genes expressed in peach fruit tissues has been used in a heterologous fashion in two studies of plums ripening behavior. Gene expression of different cultivars of plums treated with the ethylene antagonist, 1-methylcyclopropene (1-MCP) and stored for short periods at room temperature or for longer periods of cold storage was examined. In the first study, mature fruit of a suppressed ethylene climacteric cultivar 'Shiro' and a cultivar characterized by a typical increase of ethylene production during ripening ('Santa Rosa') were harvested and incubated for 24h in air (control) or 1-MCP and allowed to ripen at room temperature. Different levels of transcripts of genes implicated in cell wall metabolism, hormone (ethylene and auxin) regulation, stress and defense, and in the transcription/translation machinery, as well as others involved with ripening were identified. In the second study, the effects of 1-MCP on gene expression in relation to the development of chilling injury (CI) in the climacteric cultivars 'Ruby Red' (RR) and 'October Sun' (OS) and 'Zee Lady' peaches (ZP) were analyzed. The fruit were treated for 24h at room temperature with 1-MCP prior to storage at 0°C. For RR, there was no significant effect of 1-MCP on the level of CI symptoms, while 1-MCP significantly reduced CI symptoms in OS fruit and an increase of CI in treated ZP fruit. Microarray analysis showed that immediately following treatment, 186, 134 and 56 genes were differentially expressed between the control and 1-MCP-treated fruit of these cultivars, respectively: after 4 weeks cold storage, 311, 52 and 224 genes for RR, OS and ZP, respectively, were differentially expressed between control and treated fruit. Thus, for OS, the number of differentially expressed genes reduced during storage while the number increased in RR and ZP. Comparisons of the data suggest that the transcript profile is altered by 1-MCP more in plums than peaches. These studies, carried out within an international collaborative network, will increase our understanding of the regulation of pathways involved in plum fruit ripening and in metabolic processes related to storage and shelf lif

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Detection of ripening-related proteins in stone fruit

The objective of this research was to identify ripening-related proteins in stone fruit that can be used as an index of ripening and whose expression is not affected by growing conditions. The initial research was conducted with Japanese type plums. Fruit were harvested at several stages during development, including optimum commercial harvest maturity, as determined by changes in skin colour, firmness, titratable acidity, soluble solids concentrations and storage life at 00C. Total proteins were extracted from the fruit and separated by 2-D polyacrylamide gel electrophoresis. Four proteins were detected that are synthesised a few days before ideal commercial maturity. Closely related proteins were also found in extracts of maturing peaches and nectarines. Monoclonal antibodies (mAbs) were raised against conjugated oligopeptides designed from amino acid sequence data from two of the proteins. However, the mAbs could not reliably detect the proteins either in protein extracts or juice samples from fresh fruit. Research is continuing on the properties of the ripening-related proteins that should enable the development of a highly sensitive immunological field test of maturity

Changes in total proteins related to chilling injury of nectarine

Low-temperature disorders in nectarines (Prunus persica) can be delayed by storage in atmospheres containing elevated CO₂; however, this benefit is limited to a few cultivars. The storage of produce at low temperatures itself leads to changes in protein synthesis; therefore, this study examined the applicability of 2-D electrophoresis to assess differences in protein production in cultivars of nectarine that either do ('Arctic Snow') or do not ('Red Gold') respond to elevated CO₂ levels during storage. In addition, the effect of harvest maturity and their response to added ethylene was assessed. Fruit of the two cultivars were either ripened immediately after harvest at 20°C before protein extraction or stored in air, air + CO₂, air + ethylene or air + CO₂ + ethylene then ripened at 20 °C before protein extraction. 2-D PAGE showed that the expression of approximately 30 proteins varied among cultivars and treatments. Two proteins showed clear differences in expression in both cultivars between fruit ripened immediately after harvest and those that had been stored. A second set of differences in protein expression was found in fruit of 'Red Gold' only and involved 12 proteins whose expression was either reduced or increased by storage: these proteins did not vary in expression in 'Arctic Snow'. A third set of differences in protein expression was observed in 'Arctic Snow' only in atmospheres containing ethylene. Several proteins were down-regulated by ethylene and this down-regulation was negated by the addition of CO₂ to the storage atmosphere. Thus, differences in protein expression can be found between cultivars of nectarines that do or do not respond to the addition of CO₂ to the storage atmosphere and in the cultivar that is known to respond to CO₂, this gas was able to antagonise protein changes mediated by ethylene

Application of two-dimensional gel electrophoresis to detect proteins associated with harvest maturity in stonefruit

The correct assessment of harvest maturity stage of stonefruit is an important determinant of their quality when they reach the consumer. However, the current indices of ripening used (e.g. skin colour, firmness and soluble solids concentration) vary with cultivar, rootstock, growing conditions and seasonal climatic factors. To develop an index that is independent of environmental factors, total proteins were extracted from fruit and separated by 2D-PAGE. Four proteins (Z1, Z2, Y and X) that were synthesised in fruit a few days before optimum harvest maturity were identified in Japanese-type plums (Prunus salicina), peaches and nectarines (Prunus persica), and European plums (Prunus domestica). These proteins are first expressed a few days before optimum harvest date and their expression increases as the fruit mature. The N-termini of the three most prominent proteins from plums (Z1, Z2 and Y) were sequenced. There appears to be close homology between these proteins and those from a range of species including almond, grape and rubber. It appears that these proteins belong to a family of allergens common to plants whose function may be to confer some form of protection to the plant during periods of stress. These proteins may be used for the development of a test kit that will assist growers to determine optimum harvest maturity for cultivars of plums, peaches and nectarines

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

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 125mgL−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’ (20N 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

Changes in ACC and conjugated ACC following controlled atmosphere storage of nectarine

Low temperature disorders of nectarines are thought to be expressions of chilling injury. Chilling injury is a form of stress usually associated with increased synthesis of ethylene and its immediate precursor, aminocyclopropane-1-carboxylic acid (ACC). However, other mechanisms for the development of chilling injury have been proposed. To help determine the nature of the processes leading to chilling injury in nectarines (Prunus persica) and how the gaseous composition of the storage atmosphere effects the development of low temperature disorders, levels of ACC and conjugated ACC were measured in fruit of the cv. Arctic Snow. These compounds were measured in fruit ripened at 20°C immediately after harvest, in fruit on removal from cold storage and in fruit ripened at 20°C following cold storage. During storage, fruit were kept at 0°C in the 4 following atmospheres: air; air + 15% CO2; air + 15 µL/L ethylene; and air + 15% CO2 + 15 µL/L ethylene. Concentrations of ACC remained low in all treatments and no significant changes in ACC levels due to added ethylene or CO2 were observed. Concentrations of conjugated ACC were about 10-times that of ACC and again were not influenced by the composition of the storage atmosphere. No significant changes in either ACC or conjugated ACC were observed until after flesh bleeding, the major symptoms of low temperature disorder expressed in these fruit, had begun to appear. It was concluded that disorders in nectarines stored at low temperatures are not a stress response involving a disruption of ethylene metabolism but may be associated with differential changes in the metabolism of enzymes associated with normal ripening

Relationship between production of ethylene and a-farnesene in apples, and how it is influenced by the timing of diphenylamine treatment

The relationship between ethylene and peel α-farnesene concentrations was examined by applying diphenylamine (DPA) and the ethylene analogue, propylene at varying times after harvest to superficial scald (scald) susceptible ‘Granny Smith’ apples (Malus domestica Borkh.) stored at 10°C. Delaying DPA application after harvest had no large effect on ethylene or on peel α-farnesene production. Propylene advanced fruit ripening and promoted an increase in peel α-farnesene concentration before endogenous internal ethylene production, suggesting that ethylene has an important regulatory role in α-farnesene production, but their biosynthetic pathways are controlled independently. The effect of delayed DPA application (4 and 7 days after harvest) on the relationship between ethylene and peel α-farnesene was further examined at both a scald-inducing temperature (0°C) and a non-scald-inducing temperature (10°C) with ‘Granny Smith’ and the scald resistant ‘Crofton’ cultivar. Similarly a delayed DPA application had only minor effects on internal ethylene and peel α-farnesene concentrations. The relationship between internal ethylene and peel α-farnesene concentration was dependent on storage temperature, and the type of relationship was independent of cultivar. However, the magnitude of the relationship between cultivars was significantly different (‘Granny Smith’ produced significantly more α-farnesene than ‘Crofton’) and may be related to scald developmen

Improving the dessert quality of stone fruits

The major postharvest diseases and methods of control are briefly reviewed. Since the application of fungicides is being restricted worldwide, close attention must be given to handling practices that reduce the need for fungicide treatments. These include an initial wash with a hypochlorite solution, the addition of ethanol to hot water and the use of a warm iodine solution. The use of biological control agents has received considerable attention but none has achieved acceptable levels of control. Rapid advances in genomics, proteomics and metabolomics have enabled genes controlling quality traits and to derive molecular markers for others to be identified. Marker production is facilitated by the small genome size of members of the Rosaceae and the lack of major chromosomal rearrangements among species of Prunus. Peach has been selected as the reference species for Prunus and will be the first member of the Rosaceae to have its genome sequenced and a physical map of the genome is nearing completion. A Prunus microarray (PEACH1.0) based on 4806 unigenes is now available. These molecular approaches will allow genetic markers for traits that affect tree and fruit growth, susceptibility to pests and diseases, and dessert and storage qualities to be developed. The major challenge for physiologists is now to determine how to overcome the large variation in fruit composition and hence eating quality that occurs within trees and among batches from the same orchards

Root zone temperature influences growth, partitioning, leaf morphology and physiology of the peach rootstock, Green Leaf Nemaguard

This paper examines the hypothesis that root zone temperature (RZT) affects the growth of stone fruit plants. This hypothesis was tested by growing plants of the peach rootstock, Green Leaf Nemaguard (Prunus persica L. Batsch), at a diurnally variable (26/15°C) or at constant (5, 15, 20°C) RZTs; the plants were either actively growing or emerging from dormancy when the treatments were applied. These trials demonstrated that RZT, independently of air temperature and light intensity, influences growth, dry matter partitioning, leaf morphology and physiological processes. The growth of plants emerging from dormancy was more sensitive to RZT than that of actively growing plants, therefore, phenology can influence sensitivity to RZT. The area, numbers and daily rates of expansion of leaves, correlated positively with RZT for both sets of plants. However, plants exposed to a diurnally variable 26/15°C RZT were smaller with respect to overall growth and aspects of leaf morphology than plants exposed to a constant 20°C RZT, despite the daily mean RZTs for both treatments being similar. This could be due to supraoptimal RZTs during the day and/or suboptimal RZTs at night. Root mass ratio, in both actively growing and plants exiting dormancy was highest at 20° RZT. In contrast, the stem mass ratio of actively growing plants was maximised at 5°C, and for plants exiting dormancy, the stem mass ratio was minimised at this RZT. RZTs influence the rate of leaf expansion, which in turn affects the total number of leaves and leaf area and, along with its effect on CO2 assimilation rates, results in reductions in DM production. This research illustrates the importance of RZTs, particularly in the spring, on growth and leaf development and suggests the need to incorporate RZT into development models for peaches