Effect of wash water temperature and chlorination on phenolic metabolism and browning of stored iceberg lettuce photosynthetic and vascular tissues

Cut tissues from distinct anatomical locations in iceberg lettuce (Lactuca sativa L.) were subjected to washing in cold (4 degrees C) and warm (47 degrees C) water with or without chlorine to assess their propensity to discoloration during storage. Total protein (Bradford method) and phenolic (TPH; Folin-Ciocalteu method) contents and polyphenol oxidase (PPO; spectrophotometric method using catechol as a substrate), peroxidase (POD; guaiacol substrate), and phenylalanine ammonia-lyase (PAL; phenylalanine substrate) activities were determined in photosynthetic and vascular tissue from outer and inner leaves. Unprocessed photosynthetic and inner leaf tissues had significantly higher (P < 0.05) levels of protein and TPH and PPO and POD activities than vascular and outer leaf tissues. PAL activities (on a fresh weight basis) were similar in all tissues. Changes in browning (light reflectance measurement) and phenolic metabolism in all four tissue types were observed during aerobic storage at 5 degrees C over 10 days. PAL activity increased in all tissues after 1-2 days of storage and then gradually decreased. POD activity also increased steadily for the storage duration. Protein content and PPO activity remained constant. Edge browning (measured with a Minolta Chroma Meter) and TPH increased in all tissues, especially in outer vascular tissue. Cut photosynthetic and vascular tissues washed at 4 and 47 degrees C with and without 100 microg mL(-1) chlorine for 3 min were analyzed during 7 days in storage at 5 degrees C. Enzyme activities and accumulation of phenolics in all tissues washed at 47 degrees C were significantly (P < 0.05) lower compared to controls or tissues washed at 4 degrees C. Chlorine had no additional effect at 47 degrees C but significantly (P < 0.05) reduced browning and accumulation of phenolics in lettuce washed at 4 degrees C. These results showed that inherent differences between tissues affect phenolic metabolism and browning in stored, fresh-cut lettuce.     

Effect of freezing and storage on the phenolics,ellagitannins, flavonoids,and antioxidant capacity of red raspberries

Scottish-grown red raspberries are a rich source of vitamin C and phenolics, most notably, the anthocyanins cyanidin-3-sophoroside, cyanidin-3-(2(G)-glucosylrutinoside), and cyanidin-3-glucoside, and two ellagitannins, sanguiin H-6 and lambertianin C, which are present together with trace levels of flavonols, ellagic acid, and hydroxycinnamates. The antioxidant capacity of the fresh fruit and the levels of vitamin C and phenolics were not affected by freezing. When fruit were stored at 4 degrees C for 3 days and then at 18 degrees C for 24 h, mimicking the route fresh fruit takes after harvest to the supermarket and onto the consumer's table, anthocyanin levels were unaffected while vitamin C levels declined and those of elligitannins increased, and overall, there was no effect on the antioxidant capacity of the fruit. It is concluded, therefore, that freshly picked, fresh commercial, and frozen raspberries all contain similar levels of phytochemicals and antioxidants per serving.     

Antioxidant systems and their relationship with the response of pepper fruits to storage at 20 degrees C

Fresh peppers (Capsicum annuum L., variety California) in their green and red ripe stages were stored at 20 degrees C for 7 and 19 days to determine the effects of storage on whole fruit antioxidant capacity (TAA) and ascorbate (ASC) content, as well as on some antioxidant enzyme activities, such as catalase (CAT), superoxide dismutase (SOD), and those of the ASC-glutathione cycle. At least one Mn-SOD, two Fe-SODs, and three CuZn-SODs were detected in the fruit extract after native polyacrylamide gel electrophoresis. All of the SOD isozymes and glutathione reductase had higher activity levels in the red control fruits than in the green fruits, whereas the activities of monodehydroascorbate and dehydroascorbate reductase were higher in green fruits. Ascorbate peroxidase (APX) was found to be similar in both fruits. SODs, CAT, and APX seem to be involved in pepper fruit ripening and senescence during storage at 20 degrees C, perhaps influencing the active oxygen species levels in the fruit. TAA, as well as the ASC content, was higher in red peppers than in green, and storage increased the ASC in both green and red fruits.     

Catalase in the heat-induced chilling tolerance of cold-stored hybrid Fortune mandarin fruits

Hybrid Fortune mandarins developed chilling injury (CI) upon cold storage, unless the fruits were conditioned at 37 degrees C for 3 days before they were held at low temperature. This heat treatment induced 2.5-, 1.2-, and 1.4-fold increases in the activities of catalase (CAT), ascorbate peroxidase (APX), and superoxide dismutase (SOD), respectively, and reduced the activity of glutathione reductase (GR). The differences in the activities afforded by the heat treatment were, in general, maintained during cold storage. However, SOD levels in nonconditioned Fortune fruits exhibiting CI were similar to those of conditioned fruits stored for 0 or 6 weeks at 2 degrees C. No difference between APX activity in the conditioned and nonconditioned fruits stored for 6 weeks at 2 degrees C was found. The data indicate that CAT may be a major antioxidant enzyme operating in the heat-induced chilling tolerance of cold-stored Fortune mandarin fruits.     

1-Methylcyclopropene interactions with diphenylamine on diphenylamine degradation, alpha-farnesene and conjugated trienol concentrations, and polyphenol oxidase and peroxidase activities in apple fruit

1-Methylcyclopropene (1-MCP) is a new technology that is applied commercially to inhibit ethylene action in apple fruit, but its interactions with existing technologies such as diphenylamine (DPA) for control of superficial scald development in fruit during and after storage is unknown. To investigate possible interactions between 1-MCP and DPA, Delicious apples were untreated or treated with 2 g L(-1) DPA, and then with or without 1 microL L(-1) 1-MCP. Ethylene production and respiration rates of fruit were measured immediately following treatment, and fruit was stored at 0.5 degrees C for 12 weeks. Internal ethylene concentrations (IEC), alpha-farnesene and conjugated trienol (CTol) concentrations, activities of peroxidase and polyphenol oxidase (PPO), and DPA levels in the skin of the fruit were measured at intervals during storage. 1-MCP reduced the rate of DPA loss from peel tissue so that by 12 weeks of storage concentrations of the chemical were 25% higher than in untreated fruit. 1-MCP, with and without DPA, markedly inhibited ethylene production and respiration rates, maintained low IEC and alpha-farnesene and CTol concentrations, while DPA had little effect on these factors except inhibition of CTol accumulation. Treatment effects on peroxidase and PPO activities were inconsistent.     

Carotenoid changes of intact watermelons after storage

Watermelon contains lycopene, a red carotenoid pigment that has strong antioxidant properties. The lycopene content of watermelon is substantial, contributing 8-20 mg per 180 g serving. There are no reports on carotenoid changes in whole watermelon during storage. Three types of watermelon, open-pollinated seeded, hybrid seeded, and seedless types, were stored at 5, 13, and 21 degrees C for 14 days and flesh color, composition, and carotenoid content were compared to those of fruit not stored. Watermelons stored at 21 degrees C had increased pH, chroma, and carotenoid content compared to fresh fruit. Compared to fresh fruit, watermelons stored at 21 degrees C gained 11-40% in lycopene and 50-139% in beta-carotene, whereas fruit held at 13 degrees C changed little in carotenoid content. These results indicate that carotenoid biosynthesis in watermelons can be affected by temperature and storage.     

Active oxygen detoxifying enzymes and phenylalanine ammonia-lyase in the ethylene-induced chilling tolerance in citrus fruit

The effects of applying ethylene (2 microL x L(-)(1)) during cold storage of Fortune mandarins on the development of chilling-induced peel damage and on changes in the activities of the enzymes of the antioxidant system, superoxide dismutase, catalase (CAT), ascorbate peroxidase, guaiacol peroxidase, and glutathione reductase, and on phenylalanine ammonia-lyase (PAL) have been investigated. Chilling damage was reduced by applying ethylene during fruit storage at 1.5 degrees C. PAL activity increased in response to cold stress and was higher in fruit held under ethylene than under air during the whole storage period, whereas CAT was temporarily higher in ethylene-treated fruit. In contrast, the activities of the other enzymes were not increased by ethylene. The global results suggest that the ethylene-induced chilling tolerance in Fortune mandarins might be due to increased PAL and CAT activities.     

Effect of freezing on the activity of catalase in apple flesh tissue

Catalase (CAT, EC 1.11.1.6) activity was measured in flesh tissue of six apple cultivars (Malus domestica Borkh. cvs. Braeburn, Gala, Jonagold, McIntosh, Red Delicious, and Spartan). Activity of CAT was determined for fresh and frozen tissue of the same fruit. Freezing resulted in reductions of 50 to 90% in CAT activity compared with the activity measured in crude extracts from fresh tissues. The rate of freezing had an impact on the level of reduction of CAT activity, with slower freezing procedures leading to greater losses in activity. Six additives to the extraction buffer were tested to evaluate their potential to reduce the inactivation of CAT from frozen tissue, but only EDTA and Tween 20 showed any benefit. However, EDTA and Tween 20 provided only partial recovery in CAT activity. In contrast, crude extracts prepared from fresh tissue showed no appreciable loss in CAT activity after frozen storage for two weeks at -80 degrees C. Gel electrophoresis and immunological analysis indicated that the loss in CAT activity from tissue freezing could be attributed to loss of both the tetrameric CAT enzyme structure and total CAT protein. The implications of using freezing to preserve apple tissue samples prior to catalase activity analysis is discussed.     

Evaluation of Saskatoon berry (Amelanchier alnifolia Nutt.) cultivars for their polyphenol content, antioxidant properties, and storage stability

The polyphenol contents and antioxidant activities were assessed for 17 Saskatoon berry cultivars grown in Canada in fresh and stored fruits at -20 degrees C for 9 months. The Nelson cultivar was the richest in total polyphenol, anthocyanin, and procyanidin contents (801, 382, and 278 mg/100 g fresh weight, respectively). This cultivar was characterized also by the highest antioxidant potential measured with DPPH and ABTS radicals (2.8 and 5.0 mM/100 g FW, respectively). Cultivar-dependent changes in polyphenol content after freezer storage were observed. In the Lee 2 cultivar, significant increases in anthocyanin and flavonol contents occurred, while in the Lee 3 and Martin cultivars considerable decreases were observed. During the freezer storage, the antioxidant activity remained unchanged except for the Smokey which showed to be the most sensitive cultivar during storage. The Nelson and Lee 2 were the most stable cultivars during storage. The high polyphenol content and antioxidant activity of the Nelson cultivar and its good storage stability would make this cultivar the optimal material for fruit growers and food producers.     

Apple peels as a value-added food ingredient

There is some evidence that chronic diseases, such as cancer and cardiovascular disease, may occur as a result of oxidative stress. Apple peels have high concentrations of phenolic compounds and may assist in the prevention of chronic diseases. Millions of pounds of waste apple peels are generated in the production of applesauce and canned apples in New York State each year. We proposed that a valuable food ingredient could be made using the peels of these apples if they could be dried and ground to a powder without large losses of phytochemicals. Rome Beauty apple peels were treated with citric acid dips, ascorbic acid dips, and blanches before being oven-dried at 60 degrees C. Only blanching treatments greatly preserved the phenolic compounds, and peels blanched for 10 s had the highest total phenolic content. Rome Beauty apple peels were then blanched for 10 s and dried under various conditions (oven-dried at 40, 60, or 80 degrees C, air-dried, or freeze-dried). The air-dried and freeze-dried apple peels had the highest total phenolic, flavonoid, and anthocyanin contents. On a fresh weight basis, the total phenolic and flavonoid contents of these samples were similar to those of the fresh apple peels. Freeze-dried peels had a lower water activity than air-dried peels on a fresh weight basis. The optimal processing conditions for the ingredient were blanching for 10s and freeze-drying. The process was scaled up, and the apple peel powder ingredient was characterized. The total phenolic content was 3342 +/- 12 mg gallic acid equivalents/100 g dried peels, the flavonoid content was 2299 +/- 52 mg catechin equivalents/100 g dried peels, and the anthocyanin content was 169.7 +/- 1.6 mg cyanidin 3-glucoside equivalents/100 g dried peels. These phytochemical contents were a significantly higher than those of the fresh apple peels if calculated on a fresh weight basis (p < 0.05). The apple peel powder had a total antioxidant activity of 1251 +/- 56 micromol vitamin C equivalents/g, similar to fresh Rome Beauty peels on a fresh weight basis (p > 0.05). One gram of powder had an antioxidant activity equivalent to 220 mg of vitamin C. The freeze-dried apple peels also had a strong antiproliferative effect on HepG(2) liver cancer cells with a median effective dose (EC(50)) of 1.88 +/- 0.01 mg/mL. This was lower than the EC(50) exhibited by the fresh apple peels (p < 0.05). Apple peel powder may be used in a various food products to add phytochemicals and promote good health.     

Processing and storage effects on monomeric anthocyanins, percent polymeric color, and antioxidant capacity of processed blackberry products

Blackberries are a rich source of polyphenolics, particularly anthocyanins, that may contribute to the reduced risk of chronic disease; however, as with most berries, the fresh fruit are only seasonally available. With most of the blackberries consumed as frozen or in thermally processed forms after long-term storage, the purpose of this study was to evaluate the effects of processing and 6 months of storage on the anthocyanins and antioxidant capacity of blackberries that were individually quick-frozen (IQF), canned-in-syrup, canned-in-water, pureed, and juiced (clarified and nonclarified). Monomeric anthocyanins, percent polymeric color, and antioxidant capacity by oxygen radical absorbance capacity (ORAC FL) and photochemiluminescence (PCL) were determined postprocessing (1 day) and after 1, 3, and 6 months of storage. Processing resulted in increases in polymeric color values (up to 7%) and losses in monomeric anthocyanins (up to 65%). For most products, processing also resulted in losses in antioxidant capacity (by ORAC FL and PCL). Storage at 25 degrees C of all processed products resulted in dramatic losses in monomeric anthocyanins with as much as 75% losses of anthocyanins throughout storage, which coincided with marked increases of percent polymeric color values of these products over 6 months of storage. There were no changes in ORAC FL or PCL for processed products throughout long-term storage. No significant changes in antioxidant capacity or anthocyanin content were observed in IQF fruit during long-term storage at -20 degrees C.     

The effects of frozen storage conditions on lycopene stability in watermelon tissue

The purpose of this investigation was to evaluate the rate of deterioration of lycopene in watermelon tissue during frozen storage, because little is known about the stability of watermelon tissue lycopene under cold storage conditions. Heart tissue from each of nine individual watermelons was stored at -20 or -80 degrees C as either small chunks or puree and periodically sampled over a year's time. Initial freeze-thaw experiments indicated that a small percentage of lycopene, approximately 4-6%, degraded during an initial freeze-thaw. Analyses of the samples showed a loss of approximately 30-40% lycopene over a year's storage at -20 degrees C and a loss of approximately 5-10% over the same period at -80 degrees C. Lycopene was slightly more stable in pureed compared with diced watermelon tissue at -20 degrees C, but not at -80 degrees C. The kinetic data were best fitted by application of two simultaneous, first-order decay processes. HPLC analysis of the samples after a year's storage suggested that beta-carotene was more stable during storage at -20 degrees C than was lycopene.     

Retention of phenylalanine ammonia-lyase activity in wheat seedlings during storage and in vitro digestion

The retention of phenylalanine ammonia-lyase (PAL) activity in Red Spring wheat seedlings during storage and in vitro protein digestion was evaluated toward assessing the efficacy of plant PAL as a dietary supplement for patients suffering from the metabolic disease, phenylketonuria. Retention of PAL activity in freeze-dried wheat seedling tissues following three months of storage at -20 degrees C ranged from 62% in the leaf to 89% in root/residual seed tissues. After a 3-h two-stage ("gastric-intestinal") in vitro digestion, 36% and 42% recovery of PAL activity was associated with chopped fresh leaf and root/residual seed tissues respectively; however, no activity was recovered from freeze-dried tissues. High performance liquid chromatographic analysis of the residual phenylalanine (Phe) after in vitro digestion confirmed that the fresh tissues effected a significantly higher conversion of exogenous Phe than freeze-dried tissues. These results demonstrate that the plant cell walls provide protection of PAL during in vitro digestion. In cases where exogenous Phe (100 mg; 24 mM) was supplied to the tissues, the product of the reaction, trans-cinnamic acid, may have exerted a significant inhibitory effect on PAL activity.     

Antioxidant capacity, vitamin C, phenolics, and anthocyanins after fresh storage of small fruits.

Fresh strawberries (Fragaria x ananassa Duch.), raspberries (Rubus idaeus Michx.), highbush blueberries (Vaccinium corymbosum L.), and lowbush blueberries (Vaccinium angustifolium Aiton) were stored at 0, 10, 20, and 30 degrees C for up to 8 days to determine the effects of storage temperature on whole fruit antioxidant capacity (as measured by the oxygen radical absorbing capacity assay, Cao et al., Clin. Chem. 1995, 41, 1738-1744) and total phenolic, anthocyanin, and ascorbate content. The four fruit varied markedly in their total antioxidant capacity, and antioxidant capacity was strongly correlated with the content of total phenolics (0.83) and anthocyanins (0.90). The antioxidant capacity of the two blueberry species was about 3-fold higher than either strawberries or raspberries. However, there was an increase in the antioxidant capacity of strawberries and raspberries during storage at temperatures >0 degrees C, which was accompanied by increases in anthocyanins in strawberries and increases in anthocyanins and total phenolics in raspberries. Ascorbate content differed more than 5-fold among the four fruit species; on average, strawberries and raspberries had almost 4-times more ascorbate than highbush and lowbush blueberries. There were no ascorbate losses in strawberries or highbush blueberries during 8 days of storage at the various temperatures, but there were losses in the other two fruit species. Ascorbate made only a small contribution (0.4-9.4%) to the total antioxidant capacity of the fruit. The increase observed in antioxidant capacity through postharvest phenolic synthesis and metabolism suggested that commercially feasible technologies may be developed to enhance the health functionality of small fruit crops.     

Effect of antioxidants, citrate, and cryoprotectants on protein denaturation and texture of frozen cod (Gadus morhua)

To investigate the role of antioxidants and cryoprotectants in minimizing protein denaturation in frozen lean fish, cod fillets were treated with either antioxidants (vitamin C (500 mg kg(-1)) or vitamin C (250 mg kg(-1)) + vitamin E (250 mg kg(-1))), antioxidants (vitamins C + E 250 mg kg(-1)each) with citrate (100 mg kg(-1)), cryoprotectants (4% (w/w) sucrose + 4% (w/w) sorbitol), or a mixture of antioxidants (vitamins C + E 250 mg kg(1)), citrate (100 mg kg(-1)), and cryoprotectants (sucrose 40 g kg(-1) + sorbitol 40 g kg(-1)). Untreated and treated fish samples were stored at -10 degrees C; cod fillets stored at -30 degrees C were used as a control. Stored frozen samples were analyzed at intervals for up to 210 days for changes in protein extractability, thermodynamic parameters (transition temperature T(m) and enthalpy DeltaH), structure by FT-Raman spectroscopy, and rheological properties by large and small deformation tests. Results indicated that protein denaturation and texture changes were minimized in the presence of cryoprotectants, as well as in the presence of antioxidants with citrate, antioxidants alone, or the mixture of antioxidants, citrate, and cryoprotectants. In the presence of increased formaldehyde levels in fish treated with vitamin C, toughening was still lower compared to that of the -10 degrees C control due to the antioxidant property of vitamin C. Thus, ice crystal formation and lipid oxidation products are the major factors that cause protein denaturation in lean frozen fish, and antioxidants in addition to cryoprotectants can be used to minimize toughness.     

Structural changes of hake (Merluccius merluccius L.) fillets: effects of freezing and frozen storage.

Structural changes in hake (Merluccius merluccius L.) fillets as affected by freezing method and frozen storage temperature have been studied through Raman spectroscopy and related to changes in texture and functionality. Changes in protein secondary structure were observed due to storage temperature, accompanied by changes in apparent viscosity and shear resistance. Samples at -10 degrees C showed greater structural alteration than at -30 degrees C in terms of increase of beta-sheets at the expense of alpha-helices. An increase of unordered protein structure was found only in samples stored at -10 degrees C. Exposure of buried tryptophan residues was observed at both storage temperatures. The decrease of the deltaCH(2) band upon storage suggested an increase of hydrophobic interactions of aliphatic residues. Except for liquid air frozen fillets, all samples showed a decrease of the nuO-H/nuC-H band ratio compared to the fresh ones, this decrease being higher the harsher the conditions.     

Combined salicyclic acid and ultrasound treatments for reducing the chilling injury on peach fruit

The effects of salicylic acid (SA; 1 mmol L(-1)) and ultrasound treatment (40 kHz, 10 min) either separately or combined on the chilling injury (CI) in cold-stored peach fruit ( Prunus persica Batsch cv. Baifeng) were investigated. The results showed that SA treatment alone alleviated CI during storage. Ultrasound alone had no influence, but when it was combined with SA, it resulted in greater inhibition of CI than SA alone. The activities of antioxidant enzymes, such as catalase, ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase, were induced by a combination of SA with ultrasound. In addition, the combined treatment also increased the endogenous SA concentrations in peaches. These results suggested that the induced tolerance against CI by the combination of ultrasound and SA treatment in cold-stored peach fruit was related to the induction of antioxidant enzymes and the increase in the SA concentration.     

Relationship between apple peel and the whole fruit antioxidant content: year and cultivar variation

Antioxidants are usually considered with regard to plant defense mechanisms due to the oxidative stress or their importance for human health or both. In the present research, a comprehensive study was made to test the relationship between the antioxidant content in apple peel and the whole fruit in two growing seasons. Antioxidants were mainly localized in the apple peel, but cultivars exhibited very high biodiversity in the distribution pattern. High or very high correlation coefficients between apple peel glutathione reductase and catalase activity as well as ascorbate, glutathione, and anthocyanins concentrations and the whole fruit were discovered on the basis of both fresh and dry weight basis in two growing seasons: 2004 and 2005. In the case of ascorbate peroxidase activity and phenolics or flavonol contents, it was proven only in 2005. It seems that apple peel could be a good marker of health values as well as antioxidant potential of apple fruit. Additional arguments, as compared to the previous study, were incorporated to support the suggestion of glutathione reductase as worth considering as an environmental stress marker and/or signalling molecule.     

Long-term preservation of egg and tissue homogenates for determination of organochlorine compounds: freezing versus freeze-drying

Storage of wet egg homogenates at temperatures from -18 degrees to -28 degrees C was more suitable for long-term preservation than freeze-drying. Changes in residue levels of heptachlor epoxide, oxychlordane, dieldrin, hexachlorobenzene,p,p'-DDE, mirex, and PCBs were not significant over a 3-year period in fresh herring gull egg homogenates stored at -18 degrees to -28 degrees C. Compounds with gas chromatographic retention times shorter than hexachlorobenzene vaporized during freeze-drying at a rate proportional to their volatility. Evaporative losses of components with vapor pressures less than hexachlorobenzene did not occur in naturally contaminated herring gull eggs after storage at room temperature for up to 1 year. Higher losses of all compounds, up to 25% for p,p'-DDE, occurred in freeze-dried whole-body herring gull homogenates. Easily dehydrochlorinated compounds were rapidly degraded in freeze-dried chicken egg homogenate at room temperature: The half-life of p,p'-DDT and p,p'-DDD was about 20 days, and that of alpha- and gamma-hexachlorocyclohexane was much less than 16 days. About one-third of oxychlordane in herring gull eggs was lost in 1 year under these conditions, but none was lost after freeze-drying when the homogenate was stored at -18 degrees to -28 degrees C.     

不同浓度镉胁迫对玉米幼苗光合作用、脂质过氧化和抗氧化酶活性的影响

以玉米为材料,通过营养液培养试验,研究浓度为5~100 μmol/L的镉胁迫后不同时间内,植株体内活性氧代谢及其抗氧化酶活性的变化特征,探讨镉胁迫导致植物体内活性氧自由基累积的原因及不同程度镉胁迫对植物体内活性氧代谢的影响。随着加镉量的增加,玉米地上部生物量明显降低,而根部生物量未表现出差异。镉处理降低了叶片光合作用速率,高镉处理的影响较早。镉处理4d后,5、20、和100 mol/L Cd2+浓度处理玉米叶片Fv/Fm减小,PSII系统的原初光能转换效率下降,但比光合作用速率下降的时间要晚;镉处理7d的叶片中丙二醛（MDA）含量还没有受到明显影响,但20和100 μmol/L Cd2+处理4d后,根系膜质过氧化增强,MDA含量升高。随着镉浓度升高,处理时间延长,活性氧酶清除系统包括超氧化物歧化酶（SOD）、过氧化物酶（POD）、过氧化氢酶（CAT）和谷胱甘肽还原酶（GR）等酶活性明显增加,受到镉胁迫诱导,高浓度镉处理该现象出现更早。本文试验结果表明,镉胁迫下植物体内活性氧形成增多,诱导活性氧酶清除系统活性升高,其中一个重要原因是与CO2同化受到限制有关。