). According to their respiratory patterns and ethylene production rates during ripening, fruit and vegetables are classified into two major groups, known as “climacteric” and “nonclimacteric” ( Baile, 1964 ). Climacteric fruit are those whose ripening process
R. Porat, B. Weiss, I. Zipori and A. Dag
R. Koslanund, D.D. Archbold and K.W. Pomper
Pawpaw (Asimina triloba L.), the largest tree fruit native to North America, has become the focus of a significant effort to develop its commercial potential. Due to the very short shelf life of the ripe fruit, a critical component of this effort is the establishment of appropriate harvest and postharvest storage techniques. Although it has been reported that the ripening of the fruit is climacteric, there is no published data to support this. Nor are there any reports on the response of the fruit to cold storage. Fruit were harvested and classified as unripe if no softening was evident or as ripe if softening had commenced. Fruit were held at room temperature or were stored at 4 °C for 28 days, then moved to room temperature. Ripe fruit exhibited respiratory and ethylene climacteric peaks within 3 days of harvest and 5 to 7 days after removal from cold storage. Unripe fruit exhibited climacterics 5 days after harvest and after removal from cold storage. A survey of drops indicated that they were postclimacteric. Thus, pawpaw is a climacteric fruit and cold storage delays the start but not the relative rate of ripening.
Respiration (i.e., carbon dioxide production and oxygen consumption) increases as ripening is initiated in a group of harvested fruit called climacteric. This group includes many horticulturally important fruit crops, such as apples, avocados, bananas, melons, peaches, pears, and tomatoes. Other fruit, which includes cherries, citrus, and strawberries, do not exhibit an increase in respiration as they ripen and are called nonclimacteric. Measurements of carbon dioxide production by ripening apples, melons, and tomatoes revealed a well-defined climacteric, but only in harvested fruit. The respiratory climacteric was greatly diminished or absent from these fruit when they ripened while attached to the plant. Fixation of respired carbon dioxide through photosynthesis or into organic acids was insufficient to account for the diminished amount of carbon dioxide evolved from ripening attached climacteric fruit. Unlike the respiratory climacteric, an increase in ethylene production occurred in both attached and harvested climacteric fruit. Ethylene stimulates respiration in most plant tissues. The rapid rise in respiration as soon as attached ripening climacteric fruit were harvested or abscised suggests that an inhibitor of ethylene-stimulated respiration may be translocated from the plant and prevent the climacteric rise in respiration in attached ripening fruit.
Jiwon Jeong, James Lee and Donald J. Huber
Cantaloupe ( Cucumis melo L.) melons of the Reticulatus Group, commonly known as cantaloupes or muskmelons, are climacteric fruits in which ripening is highly coordinated by ethylene and have a relatively short storage life ( Seymour and
Krista C. Shellie and Mikal E. Saltveit Jr.
The CO2 and C2H4 conc in the internal cavity of three melon (Cucumis melo L., var. reticulatus and inodorus Naud.) cultivars was periodically measured in fruit attached to the vine and in fruit harvested 30 days after pollination (DAP). Gas samples were withdrawn through sterile serum stopper sampling ports aseptically installed near the equator of each fruit at ca. 20 DAP. Sampling continued until either 60 DAP or until fruit abscised. Internal CO2 and C2H4 conc increased in harvested fruit as they ripened (i.e., increased percent soluble solids, decreased flesh firmness, characteristic external color change). Fruit allowed to ripen on the vine also exhibited a rise in C2H4, but lacked a ripening associated climacteric rise in respiration, CO2 conc in attached fruit remained constant or declined as the C2H4, conc increased around 40-fold and the fruit ripened. The increase in CO2 conc, so commonly observed in ripening climacteric fruit, was observed in harvested melons, but not in fruit ripening on the vine. In melons, the respiratory climacteric may be an artifact of harvest. Implications of these observations will be discussed.
Donald J. Huber
selective course, focusing on 1-MCP responses in ripening-initiated fruits, nonclimacteric fruits and vegetables, and features of recovery from the effects of the ethylene inhibitor. A perusal of recent literature reveals that climacteric fruit continue to
G.H. Pemberton, Terril A. Nell and James E. Barrett
Senescence of gladiolus flowers, like many geophytes, does not involve a climacteric burst of ethylene. Eleven gladiolus cultivars were screened and all were non-climacteric (NC) for both respiration and ethylene production. Average ethylene levels for individual flowers were 0.5 μl C2H4/kg per h or less. As in other NC flowers, protein synthesis may be linked to senescence. Our goal was to identify specific proteins that were involved in the senescence process that could be used as indicators of postharvest longevity. SDS-PAGE protein profiles of cut gladiolus flowers were determined from a tight bud stage to senescence. Both increases and decreases were observed in major polypeptides that may be connected to postharvest flower longevity. Total protein content of gladiolus flower petals decreased by ≈70% during the profile period. This could explain the relatively short postharvest life of 3 to 5 days for individual gladiolus flowers. Total protein profiles were probed with an ACC synthase antibody to establish the relationship of this enzyme in NC senescence.
M. Serrano, F. Romojaro, J.L. Casas and M. Acosta
We have compared the ethylene and polyamine metabolism of senescing flowers from two cultivars of carnation (Dianthus caryophyllus L.), one showing climacteric (`Arthur') and the other non climacteric behavior (`Killer'). `Arthur' carnations showed the first symptoms of senescence at day 7, coinciding with maximum ethylene and CO2 production, a peak in the ethylene-forming enzyme (EFE) activity, and a 7-fold increase in free ACC content in respect to the initial value. In `Killer' carnations, however, onset of senescence was 15 days after harvest, and no ethylene or CO2 peak was detected. The lack of ethylene production was due to a constantly low level of free ACC and a low EFE activity. Free polyamine distribution was similar in the two cultivars at the preclimacteric stage, with the spermidine content being about three times that of putrescine. But as senescence progressed, this situation was reversed in `Arthur' carnation, with a predominance of putrescine during the senescence, while it was maintained in `Killer', with no significant changes during senescence. No free spermine was found at any stage of senescence in either cultivar. Thus, a correlation exists between ACC level, distribution of polyamides, and longevity of cut carnation flowers. Chemical name used: 1-aminocyclopropane-1-carboxylic acid (ACC).
James R. Gorny and Adel A. Kader
Autocatalytic C2H4 biosynthesis in preclimacteric apple fruit (Malus domestica Borkh. `Golden Delicious') was prevented by storage in atmospheres of 20% CO2-enriched air (17% O2 + 63% N2) or 0.25% O2 (balance N2). In preclimacteric fruit, both treatments inhibited C2H2 biosynthesis by suppressing expression of ACC synthase (ACC-S) at the mRNA level. ACC oxidase (ACC-O) mRNA abundance and in vitro enzyme activity also were impaired by these treatments. However, the conversion of ACC to C2H4 never became the rate limiting step in C2H4 biosynthesis. C2H4 biosynthesis also was effectively inhibited in climacteric apple fruit kept in air + 20% CO2 or 0.25% O2. Climacteric apples also exhibited suppressed expression of ACC-S at the mRNA level, while ACC-O transcript abundance, enzyme activity, and protein abundance were reduced only slightly. ACC-S is the key regulatory enzyme of C2H4 biosynthesis and is the major site at which elevated CO2 and reduced O2 atmospheres inhibit C2H4 biosynthesis, irrespective of fruit physiological maturity. Chemical names used: 1-aminocyclopropane-1-carboxcylic acid (ACC).
Sastry Jayanty, Mauricio Canoles, Alejandra Ferenczi, Jun Song and Randolph Beaudry*
Volatile aroma compounds produced by apple, banana, and tomato are produced throughout development, however, those associated with ripening and edible quality are dependent upon ethylene action. In apple and banana, characteristic aroma is, in large part, dependent upon the formation of volatile esters. In tomato, many of the characteristic aromas are dependent upon tissue disruption and result from aldehydes and alcohols following lipid degradation. For apple and banana, the enzyme alcohol acyl-CoA transferase (AAT, EC 184.108.40.206) is the enzyme responsible for the final reaction in the pathway for ester formation and catalyzes the union of an alcohol and the CoA derivative of fatty acids. In both tissues, AAT gene expression was detected prior to the onset of ester production. In apple, AAT expression was found to be closely tied with the onset of autocatalytic ethylene synthesis. In banana, ethylene synthesis peaked and began to decline well before ester synthesis began. However, the expression of AAT increased as ester production increased for both tissues. Tomato fruit, like apple and banana, produced characteristic aromas following the onset of the ethylene climacteric, suggesting changes in the activity of various components of the lipoxygenase pathway. In all three tissue types, there are continuous, significant shifts in the aroma profile as fruit ripen age, suggesting shifts in specific metabolic pathways associated with precursor synthesis or degradation.