MicroRNAs (miRNAs) are a class of regulatory RNAs of ∼21 nucleotides that posttranscriptionally regulate gene expression by directing mRNA cleavage or translational inhibition. Increasing evidence points to a potential role of miRNAs in diverse physiological processes. miR398 targets two closely related Cu/Zn superoxide dismutases (cytosolic CSD1 and chloroplastic CSD2) that can detoxify superoxide radicals. CSD1 and CSD2 transcripts are induced in response to oxidative stress, but the regulatory mechanism of the induction is unknown. Here, we show that miR398 expression is downregulated transcriptionally by oxidative stresses, and this downregulation is important for posttranscriptional CSD1 and CSD2 mRNA accumulation and oxidative stress tolerance. We also provide evidence for an important role of miR398 in specifying the spatial and temporal expression patterns of CSD1 and CSD2 mRNAs. Our results suggest that CSD1 and CSD2 expression is fine-tuned by miR398-directed mRNA cleavage. Additionally, we show that transgenic Arabidopsis thaliana plants overexpressing a miR398-resistant form of CSD2 accumulate more CSD2 mRNA than plants overexpressing a regular CSD2 and are consequently much more tolerant to high light, heavy metals, and other oxidative stresses. Thus, relieving miR398-guided suppression of CSD2 in transgenic plants is an effective new approach to improving plant productivity under oxidative stress conditions.

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Posttranscriptional Induction of Two Cu/Zn Superoxide Dismutase Genes in Arabidopsis Is Mediated by Downregulation of miR398 and Important for Oxidative Stress Tolerance

Fresh strawberries (Fragaria × 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 °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 °C, which was accompanied by increases in anthocyanins in strawberries and increases in anthocyanins and ...

Antioxidant Capacity, Vitamin C, Phenolics, and Anthocyanins after Fresh Storage of Small Fruits

Leaves of maize (Zea mays L.) seedlings were supplied with different concentrations of abscisic acid (ABA). Its effects on the levels of superoxide radical (O(2)(-)), hydrogen peroxide (H(2)O(2)) and the content of catalytic Fe, the activities of several antioxidative enzymes such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR), the contents of several non-enzymatic antioxidants such as ascorbate (ASC), reduced glutathione (GSH), alpha-tocopherol (alpha-TOC) and carotenoid (CAR), and the degrees of the oxidative damage to the membrane lipids and proteins were examined. Treatment with 10 and 100 microM ABA significantly increased the levels of O(2)(-) and H(2)O(2), followed by an increase in activities of SOD, CAT, APX and GR, and the contents of ASC, GSH, alpha-TOC and CAR in a dose- and time-dependent pattern in leaves of maize seedlings. An oxidative damage expressed as lipid peroxidation, protein oxidation, and plasma membrane leakage did not occur except for a slight increase with 100 microM ABA treatment for 24 h. Treatment with 1,000 microM ABA led to a more abundant generation of O(2)(-) and H(2)O(2) and a significant increase in the content of catalytic Fe, which is critical for H(2)O(2)-dependent hydroxyl radical production. The activities of these antioxidative enzymes and the contents of alpha-TOC and CAR were still maintained at a higher level, but no longer further enhanced when compared with the treatment of 100 microM ABA. The contents of ASC and GSH had no changes in leaves treated with 1,000 microM ABA. These results indicate that treatment with low concentrations of ABA (10 to 100 microM) induced an antioxidative defence response against oxidative damage, but a high concentration of ABA (1,000 microM) induced an excessive generation of AOS and led to an oxidative damage in plant cells.

Effect of abscisic acid on active oxygen species, antioxidative defence system and oxidative damage in leaves of maize seedlings.

Given the significant increase in consumer interest in organic food products, there is a need to determine to what extent there is a scientific basis for claims made for organic produce. Studies comparing foods derived from organic and conventional growing systems were assessed for three key areas: nutritional value, sensory quality, and food safety. It is evident from this assessment that there are few well-controlled studies that are capable of making a valid comparison. With the possible exception of nitrate content, there is no strong evidence that organic and conventional foods differ in concentrations of various nutrients. Considerations of the impact of organic growing systems on nutrient bioavailability and nonnutrient components have received little attention and are important directions for future research. While there are reports indicating that organic and conventional fruits and vegetables may differ on a variety of sensory qualities, the findings are inconsistent. In future studies, the possibility that typical organic distribution or harvesting systems may deliver products differing in freshness or maturity should be evaluated. There is no evidence that organic foods may be more susceptible to microbiological contamination than conventional foods. While it is likely that organically grown foods are lower in pesticide residues, there has been very little documentation of residue levels.

A comparison of the nutritional value, sensory qualities, and food safety of organically and conventionally produced foods

The use of 1-methylcyclopropene (1-MCP) on fruits and vegetables.

The occurrence of malondialdehyde (MDA), a secondary end product of the oxidation of polyunsatu- rated fatty acids, is considered a useful index of general lipid peroxidation A common method for measuring MDA, referred to as the thiobarbituric acid-reactive- substances (TBARS) assay, is to react it with thiobar- bituric acid (TBA) and record the absorbance at 532 nm However, many plants contain interfering compounds that also absorb at 532 nm, leading to overestimation of MDA values Extracts of plant tissues including purple eggplant (Solanum melongena L) fruit, carrot (Daucus carota L) roots, and spinach (Spinacia oleracea L) leaves were assessed for the presence of MDA and other non-MDA compounds absorbing at 532 nm A method described herein corrects for these interferences by subtracting the absorbance at 532 nm of a solution containing plant extract incubated without TBA from an identical solution containing TBA The reliability and eAciency of this spectrophotometric method was assessed by altering the relative ratios of exogenous MDA additions and/or extracts of red cabbage (Brassica oleracea L) leaves containing inter- fering compounds and then measuring MDA recovery Reliability was also validated through high-performance liquid chromatography and high-performance liquid chromatography-mass spectrometry techniques Results indicated that over 90% of exogenously added MDA could be recovered through the improved protocol If there were no corrections for interfering compounds, MDA equivalents were overestimated by up to 965% Interfering compounds were not detected in vegetables such as lettuce (Lactuca sativa L) and spinach which had low or negligible concentrations of anthocyanidin derivatives Comparisons between the TBARS method presented here and two currently accepted protocols indicated that the new modified method exhibits greater accuracy for quantifying TBA-MDA levels in tissues containing anthocyanins and/or other interfering com- pounds This modified protocol represents a facile and rapid method for assessment of lipid peroxidation in virtually all plant species that contain interfering com- pounds

Improving the thiobarbituric acid-reactive-substances assay for estimating lipid peroxidation in plant tissues containing anthocyanin and other interfering compounds

Effects of ozone and storage temperature on carrots and two postharvest pathogens— Botrytis cinerea Pers. and Sclerotinia sclerotiorum de Bary—were investigated. Pathogen-inoculated and uninoculated whole carrots were exposed to an ozone concentration of 0 (control), 7.5, 15, 30, or 60 μl·liter -1 . Treatment chambers were flushed with a total flow rate of 0.5 liters·min -1 (air and ozone) for 8 h daily for 28 days. The experiment was repeated twice at storage temperatures of 2, 8, and 16C. The residual ozone concentration (ozone supplied-exhausted and reacted ozone) increased with ozone supply concentration but was less at higher storage temperatures. A 50% reduction of daily growth rates of both fungi at the highest ozone concentration indicated that ozone was fungistatic. Carrot respiration rate, electrolyte leakage, and total color differences increased with ozone concentration. Ozone-treated carrots were lighter (higher L* values) and less intense (lower chroma values) in color than control carrots. Postharvest physiologist. Watery soft rot (Sclerotinia sclerotiorum) and gray mold (Bot- rytis cinerea) are common postharvest diseases of carrots. Until recently, growers used the fungicide benomyl to control these storage rots. The manufacturer's withdrawal of benomyl as a postharvest fungicidal dip on carrots has necessitated a search for alternatives; ozone is one potential candidate. Ozone is the tri-atomic form of oxygen that is unstable and decomposes either spontaneously or after it comes in contact with oxidizable surfaces. Ozone's high oxidation potential (Lide, 1991) makes it an effective disinfectant for poultry hatcheries, poultry chill water, water treatment plants, soft-drink bottling plants, and aquaria water (Guinvarch, 1959; Rosenthal and Wilson, 1987; Sheldon and Brown, 1986; Torricelli, 1959; Whistler and Sheldon, 1989; Yang and Chen, 1979). Since ozone can be easily and economically generated on site, transportation and storage costs are not incurred. Unlike CO 2 and N, which are two gases com- monly used in storage, ozone has a characteristic odor. For this reason, harmful levels of ozone can be instantly detected and avoided by workers. Ozone can be applied as a gas or as ozonated water. Reported differences on the effectiveness of ozone as a storage disinfectant may be due to differing application methods or measurements of ozone concentration, treatment period, and pathogen and product sensitivity to ozone. Gibson et al. (1960) and Rice et al. (1983) concluded that ozone is an effective agent for controlling microbial and fungal pathogens in stored produce such as cheese, strawber- ries, raspberries, currants, bananas, and potatoes. Continuous exposure to 0.05 ppm ozone (gas) effectively killed Escherichia

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Effect of ozone and storage temperature on postharvest diseases and physiology of carrots (Daucus carota L)

The ferrous oxidation−xylenol orange (FOX) assay was adapted for quantifying lipid hydroperoxides (LOOHs) in plant extracts. Excised pieces of several fruit and vegetable species were exposed to 83 kJ m-2 day-1 of biologically effective ultraviolet B irradiance (UV-BBE) for 10−12 days to induce cellular oxidation. The LOOH and thiobarbituric acid reactive substance (TBARS) concentrations of these plant tissues were assessed with the FOX and iodometric assays for the former and a modified TBARS assay for the latter. There was generally good agreement between the FOX and iodometric methods both prior to and following the UV exposure. However, the iodometric assay appeared to have some difficulty in consistently quantifying lower LOOH levels (<11 μM), whereas the FOX assay measured LOOH concentrations as low as 5 μM. All tissues exhibited UV-induced increases in TBARS, indicating a marked degree of cellular oxidation in the exposed tissue segments. Compared with the iodometric assay, the FOX method consisten...

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Using a modified ferrous oxidation-xylenol orange (FOX) assay for detection of lipid hydroperoxides in plant tissue.

Applications of chlorophyll fluorescence techniques in postharvest physiology

Kent' strawberries were harvested at red, pink, and white stages of development, and stored at 15C in the light. Fruit were sampled over a 10-day period and evaluated for volatile production and surface color. Volatile production by red and pink fruit peaked after 4 days of storage. Maximum volatile production by red fruit was 8- and 25-fold greater than maximum production by pink and white fruit, respectively. Aroma volatiles were not detected in the headspace over white berries until 4 days following harvest after which volatile production increased through the tenth day of storage. Changes in the surface color of white berries during postharvest ripening coincided with the production of volatiles. In another experiment, red, pink, and white 'Kent' strawberries were stored for 3 days at 10 or 20C in the dark or light. Fruit were then evaluated for volatile production, weight loss, anthocyanin content, and surface color changes. White berries produced volatile esters after 3 days of storage at 20C in the light. Both light and temperature influenced the relative production of the volatiles produced by pink fruit. Fresh weight loss, color change, and anthocyanin content were temperature and light dependent. The strawberry is a nonclimacteric fruit in which ripening is characterized by softening, anthocyanin synthesis, synthesis of flavor, a decrease in acidity, and an increase in sugar content (Abeles and Takeda, 1990; Hulme, 1971; Woodward, 1972). Fruit harvested slightly underripe will ship better and have a longer shelf-life than fully ripe fruit (Mitchell et al., 1964). These less mature berries are firmer, will maintain their shine longer, and decay less (Pritts et al., 1976; Skrede, 1984), but are usually poorer in overall flavor than fully ripe berries (Smith and Heinze, 1958). The flavor and aroma of strawberries are important quality attributes that influence consumer acceptability. The relative im- portance of aroma compounds to the flavor of fresh strawberries has been rated by many investigators (Dirinck et al., 1981; Hirvi, 1983; Larsen and Poll, 1992; Perez et al., 1992; Schreier, 1980). While the volatiles contributing to aroma vary among cultivars, some of the most important contributors to aroma include ethyl butanoate, 2, 5-dimethyl-4-hydroxy-3(2H)-furanone, ethyl hexanoate, methyl butanoate, linalool, and methyl hexanoate. Investigations of changes in the profile of volatile compounds during strawberry maturation are limited. Yamashita et al. (1977) monitored the conversion of added pentanal to pentanol, pentyl acetate, and pentyl butanoate during maturation of 'Hoko' straw- berries. Immature fruit, 5 days after flowering, converted added pentanal to 1-pentanol. But no ester formation was observed. However, the production of 1-pentyl acetate and 1-pentyl n- butanoate increased dramatically between 30 and 40 days after flowering. Ito et al. (1990) analyzed volatile components in headspace vapors of an unpicked strawberry fruit and reported an increase in the total amount of the volatile compounds produced during ripening of the berry. The volatiles produced were mainly esters, including large amounts of methyl acetate and methyl Received for publication 9 June 1994. Accepted for publication 22 Dec. 1994. Contribution no. 2136. We thank K.B. McRae for advice on experimental planning, statistical analysis, and presentation of results, W. Kalt for advice on anthocyanin determination method and manuscript review, and P. Harrison and M. Jordan for technical assistance. This work was conducted with the financial support of the Canada-Poland Agricultural agreement. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact. 1

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Robert K. Prange

Papers

Improving the thiobarbituric acid-reactive-substances assay for estimating lipid peroxidation in plant tissues containing anthocyanin and other interfering compounds

Effect of ozone and storage temperature on postharvest diseases and physiology of carrots (Daucus carota L)

Using a modified ferrous oxidation-xylenol orange (FOX) assay for detection of lipid hydroperoxides in plant tissue.

Applications of chlorophyll fluorescence techniques in postharvest physiology

Development of Aroma Volatiles and Color during Postharvest Ripening of `Kent' Strawberries