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- Author or Editor: M.E. Saltveit Jr. x
Exposure to acetaldehyde (M) vapors that produced tissue levels of 0.02% AA (w/w) stimulated ripening of `Hayward' kiwifruit (Actinidia deliciosa L.) much more effectively than exposure to ethanol vapors that produced tissue levels of 0.18% ethanol. Tissue levels of 0.02% and 0.18% ethanol stimulated ripening, while the ripening rate of tissue with 0.04% was similar to the controls. Ethylene and CO production from M-treated tissues were, respectively, 23 times and 60% higher than from control tissues. AA induced a rapid softening that was localized in the core tissue and rendered the fruit unmarketable for 7 days after treatment.
Abstract
Tomato fruit (Lycopersicon esculentum Mill., cv. Castlemart) either harvested hot (e.g., 32°C) and chilled for 7 days at 7°, or harvested cool (e.g., 19°) and held in the laboratory at 37° for 7 hr before chilling at 2.5° for 4 days ripened slower (a symptom of chilling injury) than fruit that were either harvested cool (19°) or held at 12.5° for 7 hr before chilling.
Symptoms of chilling injury were reduced by intermittently warming cucumber fruit (Cucumis sativus L. cv. Poinsett 76) from 2.5 to 12.5C for 18 hr every 3 days. Fruit continuously held at 2.5C for 13 days developed severe pitting and decay after 6 days at 20C, while fruit continuously held at 12.5C or intermittently warmed showed no pitting or decay during subsequent holding at 20C. The increased rate of C2H4 production during the first warming period, from 12 nl·(kg·hr)-1 at 2.5C to 201 nl·(kg·hr)-1 at 12.5C, was significantly greater than that during the second or third warming periods, i.e., 53 to 98 and 53 to 55 nl C2H4/(kg·hr), respectively. Respiration increased 3-fold during the initial warming period, but only 2-fold during subsequent warming periods. Leakage of cellular ions from excised disks of mesocarp tissue was around 6% and 10% of the total ion content of the tissue for control and intermittently warmed fruit, respectively, but increased to 17% for fruit that were continuously held at 2.5C for 10 days. After 320 hr (three cycles) of chilling and warming, chilled fruit showed significantIy lower ethylene-forming enzyme activity than the control or intermittently warmed fruit. Fruit held at 12.5C contained 0.09 to 0.34 nmol·g-1 of ACC. ACC levels were 6.23 nmol·g-1 in fruit exposed to 2.5C for 320 hr. In contrast, intermittently warmed fruit only showed 30% and 27% increases in ACC content during the first and second warming periods, respectively. Periodic warming appears to allow chilled fruit to acclimate to subsequent periods of chilling. Chemical names used: 1-aminocyclopropane-1-carboxylic acid (ACC).
Abstract
The degree to which white light stimulated ethylene production in germinating seeds of cucumber (Cucumis sativus L.) was influenced by the length of time the seed had been germinated in the dark before being exposed to light. Maximum stimulation occurred when 24 hour old dark-grown seedlings were exposed to 40 μE m−2 sec−1 light for 24 hours. Ethylene production increased with the duration and intensity of light exposure at all seedling ages. Neither the light or dark rates of ethylene, or carbon dioxide production, nor their ratios, were highly correlated with the sexual phenotype of the 9 cultivars examined.
Relationships between storage quality attributes, such as russet spotting and browning intensity, and physiological attributes, such as soluble phenolic content and polyphenol oxidase (PPO) and phenylalanine ammonia-lyase (PAL) activities, of minimally processed crisphead lettuce (Lactuca sativa L.) were studied. The processed lettuce tissue was kept in air or air plus ethylene at 2 or 5 μl·liter-1 at 2.5 or 5C for 1 to 4 days and then transferred to air at 2.5, 5, or 20C for 1 to several days. None of the above physiological attributes of the initial samples from eight lettuce cultivars (Calmar, El Toro, Sea Green, Pacific, Monterey, Salinas 88, 86-13, and Nerone) and three maturity stages (immature, mature, and overmature) correlated with their storage quality. However, ethylene-induced PPO and PAL activities and browning intensity measured 3 to 4 days after harvest consistently and significantly correlated with the final visual quality of the ethylene-treated, minimally processed lettuce after 6 to 10 days of storage. Among these three attributes, ethylene induced a 2.5- to 5.3-fold increase in PAL activity, while the relative changes in PPO activity and browning intensity were only 23% to 68%. Ethylene-induced PAL activity possibly may be used as an index to predict the storage life of minimally processed lettuce.
Abstract
Parthenocarpic cucumber fruit (Cucumis sativus L. cv. Deliva) were harvested from 3 to 30 days after an thesis. Fresh weight increase followed a single sigmoid curve. Commercial maturity was attained 10 to 11 days after anthesis, and these mature fruit had a 20- to 30-day shelf life and good color retention at 20°C. Chlorophyll content at harvest decreased with fruit age. Fruit harvested before commercial maturity showed declining rates of CO2 and C2H4 production at 20°, while commercially mature fruit maintained relatively constant rates throughout their holding period. Fruit harvested after commercial maturity showed increased respiration during holding; this increase was greatest for 30-day-old fruit. Fruit harvested 20, 25, and 30 days after anthesis showed peaks of C2H4 production during holding; this production was most pronounced for mature fruit.
Abstract
Mechanically bent petioles of potted poinsettia plants (Euphorbia pulcherrima Klotzsch ex. Willd., cvs. V-14, Eckespoint C-1 Red, Annette Hegg Diva, Annette Hegg White, and Annette Hegg Hot Pink) produced 3 to 70 times as much ethylene as petioles from unstressed plants. The Annette Hegg cultivars which were most susceptible to leaf epinasty after being sleeved for 24 hours showed the greatest enhancement of ethylene evolution after being mechanically stressed for 24 hours. Exposure to 10 ppm ethylene in air produced the same cultivar dependent pattern of epinasty in 4 hours as was produced by 24 hours of mechanical stress. Spraying with 250 ppm AgNO3, an antagonist of ethylene synthesis and action, reduced the severity of epinasty in ‘Annette Hegg Diva’ plants sleeved for 24 hours. The less susceptible ‘Eckespoint C-1 Red’ and ‘V-14’, produced less stress ethylene and were less susceptible to ethylene-induced epinasty.
Greenhouse-grown `Bison' and `Doria' peppers (Capsicum annuum L.) were harvested when mature green (MG) (>95% surface green) or ripe (>95% of surface red or yellow). Both cultivars responded similarly to temperature and neither exhibited chilling injury (CI), as indicated by surface pitting, after storage at 13C for 1 or 2 weeks. Ripe peppers showed no CI when held at 1C for 1 or 2 weeks, while MG peppers exhibited CI after these treatments. Exposing MG peppers to 1C for 3 days caused CI and stimulated C2H4 (12.3x) and CO2 production (2.5x). In contrast, a similar exposure of ripe peppers did not cause CI but stimulated C2H4 (6.5x) and CO2 production (1.4x). It seems that CO2 and C2H4 production was stimulated by exposure to 1C, not necessarily by CI development. Our data question the physiological significance of elevated CO2 and C2H4 production in CI development. The observed tolerance of ripe peppers to 1C suggests that ripe greenhouse-grown peppers can be stored at temperatures lower than those currently recommended for bell peppers.
The physiological responses associated with chilling of horticulturally mature cucumber (Cucumis sativus L.) fruit were examined using 13 lines that differ in chilling sensitivity. The low correlation coefficient between pitting and decay suggested that these two early manifestations of chilling injury are not significantly related. Likewise, fruit pitting and decay were not highly correlated with the tolerance of seedlings to chilling, suggesting that fruit and seedlings of the same line may have dissimilar sensitivity to chilling temperatures. Exudates from fruit cut in half transversely were collected on filter paper. The amount of exudate showed a significant correlation with pitting, decay, and percent ion leakage after 10 days of chilling. The fresh and dry weight of the exudates from fruit kept for 8 days at 12.5C ranged from 141- to 346-mg fresh weight and from 15 to 47-mg dry weight, respectively. Cucumber lines that were more sensitive to chilling had watery exudate, as indicated by their lower dry weight and percent solids. The conductivity of exudates from sensitive lines was higher (60 μsiemen/cm) than from chilling resistant lines (30 μsiemen/cm). Chilling-induced ethylene production was higher in sensitive than in resistant lines, and chilling caused a greater loss of ethylene forming enzyme activity in resistant lines than from chilling sensitive lines.