Treatment of carnation flowers (Dianthus caryophyllus I., cv Elliot's White) with 50 or 100 mM aminotriazole (ATA) for 4 days postharvest results in suppression of the respiratory climacteric and significant extension of vase life. ATA inhibited ethylene evolution and the ethylene climacteric via inhibition of the biosynthesis of ACC synthase. The inhibitory effects of ATA increased with time of exposure and concentration. Flowers treated with 50 or 100 mM ATA for 2 days exhibited a dose dependent climacteric increase in ethylene evolution and increased respiratory activity, in response to application of 10 μL/L exogenous ethylene. Senescence associated morphological changes, increased ACC synthase activity, ACC content, and ethylene evolution were completely inhibited in flowers treated for 4 days with 100 mM ATA. Although treatment with 50 mM ATA for 4 days did not completely inhibit components of the ethylene biosynthetic pathway, applicationof 10 μL/L exogenous ethylene failed to elicit any responses typically associated with carnation senescence, indicating that prolonged ATA treatment inhibited ethylene action. ATA may therefore serve as a useful tool in identifying molecular species involved in the perception or transduction of ethylene action.
In the past three years we have studied the effects of oxygen on the maturation and ripening of `Gala' apples. Fruit-respiration, the onset of the climacteric rise in ethylene evolution and the rate of increase in ethylene production were measured. The effects of oxygen on softening and titrable acidity were also assessed. The delay in the onset of the climacteric rise in ethylene evolution shows enzymatic-type kinetics, with saturation levels of about 8-10% oxygen. Treatment with pure oxygen was highly detrimental; it induced visual symptoms of low-oxygen damage and high levels of ethanol. The slope of the rise in ethylene evolution is also a function of oxygen concentration, with an apparent Km for oxygen lower than that which delays the climacteric onset. The effect of oxygen on respiration is dependent on the physiological state of the fruit. In preclimacteric fruits, levels of oxygen between 2 and 8% eventually decrease respiration. Calculations of internal oxygen levels indicate that the diminution of respiration results from decreased metabolic activity in response to hypoxia.
Aroma production by apple fruit is an important quality criterion and has been found to be a fruit-ripening-related process. 1-Methylcyclopropene (1-MCP), an effective ethylene action inhibitor, was used to study the relationship between volatile biosynthesis, ethylene action, and fruit ripening in `Golden Delicious' apple fruit. Pre-climacteric fruit were treated with 1-MCP vapors at a concentration of 500 parts per billion (v/v) at 23°C. 1-MCP prevented the climacteric rise of ethylene production, respiration, and volatile production, while untreated fruits developed typical climacteric changes in ethylene production, respiration and volatile production. Applying ethylene at 15–20 parts per million for 24 hr 11 days after 1-MCP treatment could not overcome the effect of 1-MCP, suggesting that 1-MCP inhibited ethylene action irreversibly. Interestingly, when 1-MCP-treated tissue were fed butanol and butyric acid, they converted these compounds to their corresponding esters butylacetate and butylbutanoate. Thus precursor supply is apparently limiting and appears to be ethylene-dependent.
Pear trees (Pyrus communis L.), cv. d'Anjou, received foliar applications of X-77 surfactant and 32.3 mm CaCl2 at 55, 85, 125, and 137 days after full bloom (DAFB) and fruit were harvested at 147 DAFB. Samples of fruit were stored in air either at 20 °C continuously or at 5 or 10 °C for several periods, then transferred to 20 °C, to determine the effects of storage temperature and CaCl2 treatments on the development of the ethylene climacteric and flesh firmness loss. Control fruits held continuously at 20 °C required 70 days for the onset of climacteric ethylene production, which commenced when firmness had decreased to ≈20 N. Calcium-sprayed fruit required 80 days at 20 °C before the rise in ethylene and resisted softening for ≈50 days. Regardless of calcium treatment, pears stored at 5 or 10 °C required only 40 days to produce climacteric ethylene; fruit softening and internal ethylene concentration after storage at 10 °C were intermediate between those of fruits stored at 5 and 20 °C. Calcium application did not alter the sequence of ripening events.
AVG applied alone to `Gala' and `Jonagold' apples delayed maturity and the onset of the ethylene climacteric and delayed red color development. AVG followed by ethephon delayed maturity and the onset of the ethylene climacteric, but promoted red color development of both cultivars. Ethephon applied alone advanced maturity, ethylene production, ripening, and red color development compared to AVG alone. In other studies, the ripening-related effects of these treatments were reflected in the storability of fruit in CA storage. AVG - and AVG + ethephon-treated fruit were still at preclimacteric ethylene levels after 6 months in CA storage, with excellent retention of flesh firmness and shelf-life, while ethephon and control fruits had significantly higher ethylene levels and softened more during storage and shelf-life evaluation. Collectively, our results indicate that an ethephon application following AVG treatment may be useful to overcome the delay of red color development of apples treated with AVG only and that this can be achieved without overly stimulating fruit ripening. Thus, a once-over harvest of `Gala' and `Jonagold' apples may be achieved with a significant reduction in harvest costs. We attribute the promotion of red color development of apples receiving AVG treatment with a follow-up application of ethephon to the action of ethylene temporally-released from ethephon stimulating the development of the anthocyanin biosynthetic pathway, while AVG inhibits the development of the endogenous ethylene climacteric. Inhibiting endogenous ethylene production delays fruit from producing their own ethylene. We attribute maturation uniformity to the action of AVG allowing the less mature fruits to gain maturity while slowing maturity development of the more mature fruits. Improved storability of AVG + ethephon-treated fruit is attributed to the same ethylene-related phenomena.
We investigated the differential regulation of two 1-aminocyclopropane-1-carboxylate synthase (ACS) genes, one 1-aminocyclopropane-1-carboxylate oxidase (ACO) gene and one ethylene response sensor (ERS1) ortholog during ripening and in response to wounding in avocados (Persea americana Mill. `Bacon'). The 1-aminocyclopropane-1-carboxylate (ACC) content, ACS activity and detectable expression of PA-ACS1 mRNA increased and reached a maximum prior to the climacteric peak, whereas ACO activity and the PA-ACO mRNA levels increased markedly only at the upsurge of ripening ethylene. A basal level of PA-ERS1 transcript was detected as from harvest, however, PA-ERS1 transcript was hyper-induced at the climacteric peak of ethylene production. 1-Methylcyclopropene (1-MCP) application at thepreclimacteric and the onset of climacteric stages inhibited the ACS and ACO activities, the transcription of PA-ACS1 and suppressed PA-ACO and PA-ERS1 mRNAs to trace levels. Discontinuation of 1-MCP treatment led to super-induction of PA-ACS1, PA-ACO, and PA-ERS1 transcripts. Wound induced ethylene biosynthesis and wound-induced PA-ACS2 mRNA accumulation were enhanced by 1-MCP, whereas wound-induced PA-ACO mRNA accumulation was unaffected by 1-MCP. These results indicate positive feedback regulation of the PA-ACS1 gene and negative feedback regulation of the PA-ACS2 gene by ethylene, while PA-ACO exhibits positive feedback regulation by ethylene and is also induced by wounding. The hyper-induction of PA-ERS1 mRNA at relatively high concentrations of ethylene may be a mechanism of avocados to regulate the ethylene responsiveness of the tissues by dissipation of the gas.
Abstract
Changes in firmness, protein, color, respiration, cellulase, and polygalacturonase were followed during maturation and ripening of tomatoes, Lycopersicon esculentum L., on the plant and in detached fruit allowed to ripen at 20°C. Cellulase activity in the young fruit increased steadily during the maturation period. Cellulase activity in detached fruit ripened at 20°C increased rapidly during the onset of ripening and reached a higher level than in fruit ripened on the plant. Polygalacturonase activity was not detectable in developing fruit until after the fruit had initiated ripening. Polygalacturonase activity in detached fruit ripened at 20°C did not appear until the onset of the climacteric and then increased rapidly. This corresponded to the polygalacturonase activity in fruit allowed to ripen on the plant.
The changes during ripening appeared to follow a pre-determined pattern. Grow-regulating substances only moderately affected the onset of the climacteric rise, but markedly influenced the time interval to reach the climacteric peak. They also markedly affected the rate of the normal sequence of changes during ripening. Such changes as softening, color formation, and enzyme activities of cellulase and polygalacturonase were accelerated by ethephon and SADH and delayed by gibberellic acid and indoleacetic acid. Gibberellic acid suppressed polygalacturonase activity. After 14 days polygalacturonase activity in the control fruit was 25 times greater than in fruit treated with gibberellic acid. Cellulase activity in gibberellic acid treated fruit increased steadily during this period. The loss of firmness in treated fruit suggests that softening is initiated by action of cellulolytic enzymes and that pectinolytic enzymes are involved in subsequent changes in texture.
Abstract
Respiration rate of whole ‘Kerman’ pistachio (Pistacia vera L.) fruit increased progressively during seed growth and development and gradually declined after the completion of seed growth. Blank (seedless) fruit, on the other hand, respired at a constant rate which was 5 to 6 times lower than that of fruit with seeds. There was no indication of a climacteric peak in respiration of fruit with seeds. Ethylene evolution from seeded fruit was not significantly different from that of blank fruit. Constant low levels of ethylene were maintained throughout the period of shell and hull dehiscence, as well as fruit maturation, indicating that this hormone is probably not involved in those processes.
Abstract
Activities of the acidic and basic peroxidases from tomato fruit (Lycopersicon esculentum Mill. cv. Flora Dade) were determined at six ripening stages, from green to red-ripe fruits. Both the acidic and basic peroxidases reached a maximum during the climacteric, at the pink stage, but the relative increase in basic peroxidase activity was much more pronounced. Changes in the peroxidase, IAA oxidase, and ACC oxidase activities of the basic peroxidases paralleled the changes in ethylene production. However, in the presence of calcium, the degree of activation of peroxidase was constant throughout ripening, whereas the IAA and ACC oxidase activities of the basic peroxidases were only activated at the pink stage.
Abstract
Internal atmosphere composition, respiration rate, ethylene production, weight loss, and firmness were monitored during the ripening of waxed and nonwaxed avocado fruit (Persea americana Mill.) during storage at 5°C, and ripening at 20°. Artificial waxing, which usually forms a uniform film over the closely packed platelet structure of the natural wax, was sometimes incomplete. Waxing caused a slight buildup of CO2 and possible reduction in internal O2 concentrations during the preclimacteric of stored fruit, and may have reduced ethylene synthesis during the climacteric. Waxing caused a 1-day delay in fruit softening under extended cold-storage conditions.