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prevent cross-contamination between light treatments across adjacent bench sections, ultraviolet-blocking plastic film (DuraGreen Marketing USA, Mount Dora, FL) was used to isolate treatment sections on each bench. The total amount of UVB radiation (W·m −2

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exposure to wavelengths in the ultraviolet (UV-A 400–320 nm/UV-B 320–290 nm/UV-C 290–100 nm) range ( Kerr and McElroy, 1993 ). The UV-B wavelengths that contact the earth’s surface are predicted to increase in springtime radiation by 50% to 60% from 2010 to

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, compared with the control ( Fig. 2B ). Stem length was also stimulated by supplemental UV-A radiation, although the tallest plants were seen in the UV-A8 treatment ( Fig. 2C ). Fig. 2. The effect of different ultraviolet (UV)-A treatments on ( A ) plant dry

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The ultraviolet radiation B region (UV-B, 280–315 nm) is critical for plant growth and development, morphogenesis, adaptive orientation, photosynthesis, and secondary metabolism ( Krizek, 2004 ; Rozema et al., 1997 ; Teramura, 1983 ). In recent

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Irradiation of fruit and vegetables can potentially be used by industry as a quarantine method to contain insect pests, microorganisms, and to extend shelf life. Gamma, electron beam, and ultraviolet radiation are the most frequently used radiation techniques. These radiation treatments have an effect on bioactive compounds. Grapefruit juice contains bioactive compounds such as limonoids, flavonoids, and furocoumarins. Bioactive furocoumarins in grapefruit juice have been found to increase the bioavailability of many drugs. Bergamottin, dihydroxybergamottin, and paradisin A are major furocoumarins that are shown to inhibit the activity of CYP P450 3A4 and P-gylcoprotein, which are involved in the first pass metabolism of drugs in the gut. This results in a dose-dependent increase of the drug beyond what is intended. Furocoumarins are photoreactive compounds and will readily react to ultraviolet radiation. The effect of various doses of ultraviolet radiation was investigated on `Rio Red' and `Marsh White' grapefruit. Grapefruit juice (50 mL) was irradiated with Ultraviolet A, B, and C radiation for either 5 or 10 min. Treated and control juice was extracted with 100, 50, and 50 mL of ethyl acetate. The extract was then dried and reconstituted with methanol and filtered through a 0.4-μm PTFE membrane filter. The methanol extracts were analyzed by HPLC and the concentrations of bergamottin, dihydroxybergamottin, and paradisin A were compared for UVA, UVB, UVC, and control. This project is based upon work supported by the USDA-CSREES under Agreement USDA IFAFS # 2001 52102 02294 and USDA # 2005-34402-14401 “Designing Foods for Health” through the Vegetable & Fruit Improvement Center.

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Plants possess various constitutive and inducible defense mechanisms such as pigment and antioxidant systems for protection against stresses such as ultraviolet-B (UV-B; 290 to 320 nm) radiation. Our previous research has indicated that higher chlorophyll, carotenoid, and anthocyanin concentrations were associated with greater tolerance of UV-B stress by `Georgetown' kentucky bluegrass (Poa pratensis L.). The objectives of this study were to determine if kentucky bluegrass cultivars with darker leaf color possessed greater pigment and antioxidant defense systems and if such increases were associated with greater resistance to UV-B. Eight cultivars exhibiting a range of green color intensity (`Apollo', `Brilliant', `Julius', Limerick', `Midnight', `Moonlight', `Nuglade', and `Total Eclipse') were selected and subjected to continuous, artificial UV-B radiation (70 μmol·m-2·s-1). UV-B irradiation reduced turf quality (55% to 62%) and photochemical efficiency (37% to 70%) when measured 5 days after initiation of UV-B exposure. Significant differences in turf color, photochemical efficiency, chlorophyll a, chlorophyll b, chlorophyll a+b, and carotenoids were found among the cultivars. `Moonlight' had greatest photochemical efficiency, chlorophyll, carotenoids, and turf quality. Positive correlations of pigment concentration with photochemical efficiency and turf color were observed under UV-B radiation stress, with correlation coefficients ranging from 0.49 to 0.62. The results of this study suggests that selecting cultivars with higher concentrations of chlorophyll and carotenoids and photochemical efficiency may be an effective way for turfgrass managers and sod producers to improve sod establishment and quality in environments with higher UV-B radiation.

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In order to determine whether the concentration of floral petal anthocyanin pigments could be increased, ultraviolet radiations in the UV-A and UV-B wavelength bands were presented to a variety of flowering plants to partly restore those wavelengths filtered out by greenhouse glass. In no tested plant did the supplementary ultraviolet radiation enhance floral anthocyanin content. Supplementary UV radiation has no economic value in greenhouse production of flowering plants.

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The change in the cold hardiness of Rhododendron (cv. `English Roseum' following chronic exposure to ultraviolet-B radiation (280-320 nm) was studied. Leaf disks removed from ultraviolet-B exposed plants exhibited a greater tolerance to freezing temperatures than plants which received no ultraviolet-B exposure. Visual browning and percent phenolic leakage indicated that UVB-exposed leaf disks were killed at -11 °C, while control disks were killed at -8°C. The increase in phenolics seen in UV-B exposed plants most likely contributed to their increased resistance to cold temperature through the synthesis of cell-wall associated components such as lignin and suberin.

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Abstract

Near ultraviolet radiation appears to be largely responsible for solar injury (SI) and vein tract browning (VTB) of cantaloupes (Cumis melo L., Reticulatus group, cv. PMR 45) grown under field conditions in the San Joaquin Valley of California. Incidence and severity of SI were substantially reduced when near UV flux impinging on the fruits at solar noon was reduced to 21 Wm-2 or less and especially when wavelengths below 320 nm were excluded by the use of plastic UV filters. VTB was reduced when UV flux was 12 Wm-2 or less or when wavelengths below 320 nm were excluded. In cantaloupes, near UV appears to directly induce SI but to indirectly induce VTB, a postharvest disorder, by accelerating aging of surface tissues.

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High ultraviolet-B (UV-B; 290-320 nm wavelength) radiation may significantly contribute to the quality decline and death of kentucky bluegrass (Poa pratensis L.) sod during summer transplanting. Antioxidants and protective pigments may be involved in plant defense against oxidative stress caused by UV-B. Selected exogenous hormones may alleviate UV-B damage by upregulating plant defense systems. The objectives of this study were to determine if exogenous hormone or hormone-like substances could alleviate UV-B damage to `Georgetown' kentucky bluegrass (Poa pratensis L.) under greenhouse conditions. The hormone salicylic acid at 150 mg·m-2 and the hormone-containing substances, humic acid (HA) at 150 mg·m-2 and seaweed extract (SWE) at 50 mg·m-2, were applied to plugs of kentucky bluegrass and then subjected to UV-B radiation (70 μmol·m-2·s-1). The UV-B irradiation stress reduced turf quality by 51% to 66% and photochemical efficiency by 63% to 68% when measured 10 or 12 days after initiation of UV-B. Endogenous alpha-tocopherol (AT) and antioxidant enzymes (superoxide dismutase (SOD) and catalase) were reduced by UV-B stress. Anthocyanin content was increased from day 1 to 5 and then decreased from day 5 to 10 of continuous UV-B irradiation. Application of SA and HA + SWE enhanced photochemical efficiency by 86% and 82%, respectively, when measured 10 or 12 days after UV-B initiation. In addition, application of the hormonal supplements increased AT concentration, SOD, catalase activity, and anthocyanin content when compared to the control at 10 days after UV-B initiation. Bluegrass with greater AT concentration and SOD and catalase activity exhibited better visual quality under UV-B stress. The results of this study suggest that foliar application of SA and HA + SWE may alleviate decline of photochemical efficiency and turf quality associated with increased UV-B light levels during summer.

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