Abstract
Fruit detachment and small branch removal before fruit harvest stimulated the rise in the climacteric. Defoliation and removal of the phloem from the fruit pedicels stimulated the rise in only about one-half of the experiments. IAA sprays gave erratic results, with an increase in the time of the respiratory rise in about half of the cases. Sprays of GA had no effect. Fruit dipping after harvest in IAA, GA, ABA, and trachael sap had no effect on subsequent respiration.
Abstract
Difference in optical density (∆OD) of intact ‘Bartlett’ pears (Pyrus communis L.) between wavelengths 690 and 740 nm was measured at harvest and during ripening with a single-beam multiwavelength spectrophotometer. The ∆OD indicated the status of ripeness and detected core breakdown of ‘Bartlett’ pears nondestructively. The ∆OD decreased consistently with ripening and was associated with softening, climacteric rise in respiration, and ethylene production. The ∆OD increased in pears with core breakdown even before external symptoms were visible.
Abstract
Flower petal abscission (shattering) in seed geraniums (Pelargonium X hortorum Bailey) is delayed by low temperature (1-5°C) and ethylene-free air. Naphthaleneacetic acid (NAA) or CO2 (5%) did not delay shattering. Respiration and endogenous ethylene synthesis did not follow a climacteric pattern. A method was devised to test flowers for petal abscission. Variation in petal abscission was found among flowers of 35 cultivars evaluated over a 2-year period.
AVG, as ReTain™, an inhibitor of ethylene biosynthesis, was used alone or with a subsequent application of ethephon (Ethrel™), an ethylene-releasing chemical, to determine if red color development could be enhanced without over-ripening `Gala' and `Jonagold' apples. Treatments included: 1) AVG alone; 2) AVG followed by ethephon; 3) ethephon alone; and 4) control. Silwet L-77 surfactant was included in all treatments. Application of AVG delayed the onset of the ethylene climacteric and red color development of both cultivars. Application of AVG followed by ethephon similarly delayed the onset of the ethylene climacteric, but red color development at the commercial harvest date was only marginally reduced or not affected. The results were similar in both 1998 and 1999, although environmental stress during the growing seasons differed (1998—heat; 1999—moderate temperatures). The delay of fruit maturation and ripening observed at harvest following AVG +/- ethephon treatments improved storability of fruit in controlled atmosphere (CA) storage, as demonstrated by low internal ethylene levels after storage, and high retention of flesh firmness and shelf-life, while control fruit and those treated only with ethephon entered the ethylene climacteric during storage, and flesh firmness subsequently declined during shelf-life evaluation. Chemical name used: aminoethoxyvinylglycine (AVG).
Previous research has shown that subjecting bananas to low O2 treatment during the climacteric rise decreases the rate of sugar accumulation but the fruits eventually ripen. In the present study we applied low O2 in fruits whose ripening had been initiated by exogenous C2H4 and in preclimacteric ones. In preclimacteric fruits low O2 suppressed the climacteric rise during the duration of the experiment (20 days). It completely inhibited the increase in sugars, invertase and sucrose phosphate synthase (SPS) activities while there was a sharp increase in sucrose synthase (SS). In control fruits the increase in sugar content coincides with a sharp increase in invertase, and SPS and a decline in SS. Hypoxia inhibited the increase in invertase and SPS while it induced an increase in SS. Nevertheless, the activities of invertase and SPS in the climacteric hypoxic fruits was higher than in hypoxic preclimacteric ones. The results, thus, indicate that the imposition of low O2 at the preclimacteric stage is much more efficient in delaying banana ripening than when it is applied after the initiation of ripening.
Pawpaw fruit ethylene production, 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS) and ACC oxidase (ACO) activities, and tissue content of the ethylene precursor ACC and conjugate malonyl-ACC (MACC) were measured during postharvest ripening. Fruit were harvested near the advent of the ripening process and were ripened at room temperature. The fruit displayed increases in ethylene production and respiration rate during ripening with maxima for both 3 days after harvest. Mean ethylene maxima on a fresh weight basis were 4.7 and 7.6 μg·kg-1·h-1 and mean respiratory (CO2 production) maxima on a fresh weight basis were 220 and 239 mg·kg-1·h-1 in 1999 and 2001, respectively. The increase in ethylene evolution coincided with an increase in respiration and a rapid decline in fruit firmness. Internal and external fruit firmness declined in a parallel manner. The ethylene climacteric peak occurred after the greatest decline in fruit firmness, indicating that low levels of ethylene may be sufficient to initiate the ripening process. The ethylene climacteric peak also coincided with the highest activities of both ACS and ACO as well as the maximum tissue ACC content. As ACC content increased, MACC content declined, suggesting a regulation of ethylene production via free ACC levels by malonylation of ACC. Thus, the climacteric development of ethylene production may be regulated by an increase of ACS activity and a decrease in ACC malonyltransferase activity, making more free ACC available for the production of ethylene by increased activity of ACO.
The rate of ethylene biosynthesis was monitored throughout the four stages (S1, S2, S3, and S4) of peach (Prunus persica L. Batsch `Springcrest') fruit development. The highest values of ethylene production were detected during the early S1 and at ripening. During S1, the increase in the evolution of ethylene was accompanied by high activity of 1-aminocyclopropane-1-carboxylic acid oxidase (ACO). A weak accumulation of ACO mRNA was detected in developing fruitlets, indicating that ACO may play a specific role in modulating the rate of ethylene biosynthesis during the early growth stage. When fruitlets harvested at S1 were flushed with propylene (500 mL·L-1) for 48 h, a two-fold increase of ethylene biosynthesis and a dramatic induction of ACO activity were observed. Treatment with the ethylene analogue greatly stimulated the expression of ACO gene(s). During ripening, the climacteric occurred when fruit had softened to ≈20 N. This process was preceded by an increase in ACC content and ACO activity in the mesocarp. ACO transcripts began to accumulate before the rise in whole-fruit ethylene biosynthesis with peak levels coincident with the climacteric when the highest values of ACO activity were detected. Propylene greatly enhanced ACO gene expression and stimulated the ripening-associated ethylene climacteric. ACO-related transcripts also accumulated in fruit treated with nitrogen for 72 hours.
Abstract
‘McIntosh’ apples (Malus domestica Borkh.) were harvested on 3 different dates and stored in controlled atmosphere (CA) storage with less than 1, 10 or 500 ppm ethylene. After 5 and 8 months of storage the fruits which had been harvested 5 to 6 days before the onset of the climacteric were less ripe and had less breakdown than fruits harvested after the onset of the climacteric. The fruits harvested at the preclimacteric stage had either comparable or slightly better eating quality but less red color than fruits harvested later. High levels of ethylene had slight but statistically significant negative effects on firmness and acidity of early harvested fruits judged by sensory evaluation after 5-month storage plus 7-day holding and by objective evaluation after 8-month storage plus 1- or 7-day holding at 21°C. An attempt was made to find a method to estimate the physiological age of preclimacteric apples. The minimum treatment time required for 10 ppm ethylene to trigger the onset of the climacteric at 21°C is judged to be promising.
`Bisbee Delicious' apples were harvested in two orchards over a two-month period prior to and after commercial harvest during three consecutive production seasons. Changes in the predominant non-ethylene volatile compounds (NEVs) were characterized using dynamic headspace sampling with subsequent analysis by GC-MS. Alcohols and aldehydes were the predominant qualitative and quantitative NEVs in preclimacteric apples although other compounds were consistently present. The concentration of total NEVs declined to a minimum prior to the onset of the climacteric rise in ethylene synthesis. The increase in total NEVs after this minimum was attributable largely to increased production of esters. Initial detection of major esters associated with ripening `Bisbee Delicious' apples occurred prior to onset of the climacteric, however, amounts approached the limits of detection. The large increase in ester synthesis during ripening was coincident with the onset of the climacteric. Quantitative differences between orchards and production seasons were observed. Differences between harvest dates and orchards carried through storage in air at 0 C or 1% O2/2% CO2 CA storage at 0 C.
The internal concentration of CO2 and C2H4 and the stage of ripeness was periodically measured in tomato fruit (Lycopersicon esculentum cv. Castelmart) attached to and detached from the plant. An external collection apparatus permitted nondestructive sampling of internal gases. The concentration of CO2 and C2H4 in the collection apparatus had equilibrated with the internal gas concentrations after 18 hr. A 20-fold increase in C2H4 during ripening of detached tomato fruit was paralleled by a 3-fold increase in CO2 concentration. Ripening attached fruit exhibited a 100-fold rise in C2H4 during ripening, but lacked a ripening associated climacteric rise in O02. CO2 did increase 2-fold in an erratic fashion during ripening of attached fruit, but the increase did not show any correspondence to increased C2H4 or ripening associated color changes. In tomato fruit, it appears that a CO2 climacteric per se, which has been considered an intrinsic quality of certain ripening fruit, may not be necessary for the ripening of “climacteric” fruit at all, but may instead be an artifact of using harvested fruit.