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- Author or Editor: Chien Yi Wang x
Temperature conditioning of zucchini squash (Cucurbita pepo L.) at 15°C for 2 days enhanced polyamine levels and delayed the development of chilling injury during storage at 5°C. Direct treatment of zucchini squash with polyamines increased the endogenous levels of polyamines and reduced chilling injury. However, treatment with polyamine inhibitors after harvest but before temperature conditioning suppressed the increase of endogenous polyamines and reduced the benefit obtained from temperature conditioning. These results suggest that the resistance of squash to chilling injury may be related to the endogenous levels of polyamines.
The endogenous levels of abscisic acid (ABA) in zucchini squash were increased by temperature conditioning at 10°C for 2 days. This temperature conditioning treatment reduced the severity of chilling injury in the squash during subsequent storage at 2.5°C. The ABA levels remained higher in treated squash than in untreated samples throughout storage. Direct treatments of squash with ABA at 0.5 mM and 1 mM before storage at 2.5°C increased ABA levels in the tissue and were also effective in reducing chilling injury. The involvement of ABA in reducing chilling injury will be discussed.
Various physiological and biochemical alterations occur in response to chilling stress in plants. The extent of these alterations and the ability of the plant to withstand these alterations determine whether the plant is sensitive or resistant to chilling at that temperature. Information concerning the physiological and biochemical responses of plants to chilling stress has been accumulating rapidly during recent years. However, when one looks into the literature, it does not take long to realize that there is no general consensus on a number of issues. Although some of the conflicting or contradicting points have been clarified by recent findings, there are still some ambiguous areas awaiting to be resolved. Some examples of these controversial issues are: a) the importance of bulk membrane lipid composition in determining the chilling sensitivity, b) the interference of energy production and utilization in tissues by chilling, c) the relationship of membrane permeability to chilling, and d) the capacity of water oxidation in photosystem II as affected by chilling.
Methyl jasmonate (MJ) was applied to zucchini squash (Cucurbita pepo L.) fruit be pressure-infiltration (82.7 kPa for 3 min). Control fruit were similarly treated with distilled water. All fruit were then stored at a chilling temperature of 5C. Chilling injury occurred in the control fruit within 4 days of storage. However, the onset of chilling injury was significantly delayed by the MJ treatment. MJ-treated fruit also maintained higher levels of carbohydrates, while malic acid was the major organic acid. These constituents deteriorated slower in the MJ-treated fruit than in the control fruit.
Chilling injury inhibits the growth and development of tropical plants and shortens the postharvest life of tropical horticultural commodities. This presentation will emphasize the postharvest aspects of chilling injury. While most tropical commodities are sensitive to temperatures below 10 to 15C, specific critical temperatures may vary with the species, stage of development, and type of tissue. Likewise, symptoms of chilling injury also vary with different commodities. Reduction of chilling injury can be achieved either by increasing the tolerance to chilling in sensitive tissues or by delaying the development of chilling injury symptoms. Some methods involve the manipulation and modification of the storage environment, whereas other techniques involve direct treatment to the commodities. Specific examples of the alleviation of chilling injury in various tropical commodities will be discussed.
Cucumbers (Cucumis sativus L.) and zucchini squash (Cucurbita pepo L.) were pressure-infiltrated (82.7 kPa for 3 min) with methyl jasmonate (MJ) in aqueous suspension and then stored at a chilling temperature of 5C. Control fruit were infiltrated with distilled water and handled in a similar manner. Treatment with MJ delayed the onset and reduced the severity of chilling injury symptoms in both cucumbers and zucchini squash. Analysis of polyamines in zucchini squash showed that putrescine increased with time in storage at 5C, while spermidine and spermine decreased during the same period. MJ treatment did not have an appreciable effect on putrescine, but the treated fruit maintained higher levels of spermidine and spermine than the control fruit throughout storage at 5C.
The activities of catalase and superoxide dismutase decreased while peroxidase activity increased in zucchini squash (Cucurbita pepo L., cv. `Elite') during storage at 5°C. Preconditioning of squash at 15°C for 2 days prior to the cold storage reduced the decline of catalase activity and suppressed the increase in peroxidase activity. The superoxide dismutase activity remained higher in temperature conditioned squash than in untreated squash. These results indicate that acclimation to chilling temperature in squash may also involve modifications in the activities of catalase, peroxidase, and superoxide dismutase.
The outer leaf laminae of Chinese cabbage (Brassica campestris L Pekinensis group) contain higher amounts of ascorbic acid than the outer midribs, inner leaf laminae, or inner midribs. However, the outer leaf laminae lost ascorbic acid at a faster rate than other parts of the Chinese cabbage during storage at 0°C. Quantitative differences in sugars were also found in different parts of the Chinese cabbage. The outer leaf laminae were low in total sugars and had higher amounts of fructose than glucose, whereas outer midribs contained much higher amounts of glucose than fructose. The inner leaf laminae were high in both fructose and glucose and had a higher ratio of glucose to fructose. A similar ratio was also found in inner midribs, but their total sugar content was lower than inner leaf laminae. Relatively low levels of sucrose were found in all parts of Chinese cabbage. Total sugars decreased, but the relative composition of individual sugars did not change during storage. Exposure of Chinese cabbage to 30 or 40% CO2 for 5 or 10 days was detrimental to quality. Short-term exposure to high but noninjurious concentrations of CO2 (10–20%) showed no beneficial effect on quality retention during subsequent storage in air at 0°. However, low O2 (1%) atmosphere was very effective in extending the storage life of Chinese cabbage at 0°. It slowed down the decline of ascorbic acid and sugar contents, delayed the loss of chlorophyll and yellowing of the leaves, and reduced the incidence of decay. The Chinese cabbage was not salable without extensive trimming after 3 months of storage at 0° in air, whereas those in 1% O2 at 0° were still in salable condition after 5 months of storage with only slight trimming. No off-odor, off-flavor, or other symptoms of suboxidation were found at the end of 5 months of storage in 1% O2 at 0°.