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Xuetong Fan and James P. Mattheis

Enclosing `Fuji' apple (Malus ×domestica Borkh.) fruit in paper bags 2 months after full bloom delayed the increase in internal ethylene concentration at the onset of fruit ripening, and increased the respiration rate early in the bagging period. Bagging delayed and reduced red color development, especially on the blush side, but did not affect fruit resistance to gas diffusion. External surface color changed significantly within the first 4 days after bags were removed. Exclusion of UV-B from sunlight by Mylar film after paper bag removal impaired red color development. Bagging during fruit development increased superficial scald but eliminated stain during cold storage. Exposure to sunlight for 19 or 20 days before harvest reduced scald incidence in comparison with leaving bags on until harvest.

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Erik H. Ervin, Xunzhong Zhang, and John H. Fike

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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Donald T. Krizek, Steven J. Britz, and Roman M. Mirecki

The influence of ambient UV radiation on growth and flavonoid concentration of Lactuca sativa L. (`New Red Fire' lettuce) was examined. Plants were grown outdoors for 31 days from seed in window boxes covered with one of three different UV filters—UV transparent tefzel (10%T, 245 nm), UV-B-absorbing polyester (10%T, 319 nm), or UV-Aand UV-B-absorbing Llumar (10%T, 399 nm). Plants were grown in plastic pots filled with vermiculite and subirrigated with nutrient solution. Lettuce plants grown in the absence of solar UV-A and UV-B radiation showed a significant increase in leaf number and biomass of tops and roots as compared to those grown under ambient UV-A and UV-B. They also had a lower concentration of flavonoids and other UV-absorbing substances at 270, 300, and 330 nm (on both an area and on a dry-weight basis). These findings should be of interest to researchers involved in protected cultivation because the transmission of UV-B radiation is greatly attenuated by standard greenhouse glass. Our results also have implications for human nutrition, since bioflavonoids are important as antioxidants.

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Xunzhong Zhang, E.H. Ervin, and R.E. Schmidt

Ultraviolet-B [UV-B (280-320 nm)] radiation is one of the major factors causing quality decline of transplanted sod. Pigments and antioxidants are associated with plant stress resistance, but their roles in turfgrass tolerance to UV-B damage are not well understood. The objectives of this study were to determine if kentucky bluegrass (Poa pratensis L.) cultivars with darker green genetic leaf color possessed greater pigment and antioxidant defense capacities and if such characteristics were associated with greater resistance to UV-B. Two cultivars, `Moonlight' (dark green) and `Limerick' (light green), were selected and subjected to continuous, artificial UV-B radiation (70 μmol·m-2·s-1). UV-B irradiation reduced turf quality by 58% (`Moonlight') and 77% (`Limerick') relative to day 1 when measured 10 days after initiation of UV-B exposure. Higher canopy photochemical efficiency (PEc) was found in `Moonlight' relative to `Limerick' under UV-B stress and during recovery. `Moonlight' contained greater levels of chlorophyll (1.5 to1.6-fold), carotenoids (1.3-fold), superoxide dismutase [SOD (1.0-fold)] and catalase [CAT (1.5-fold)] than `Limerick' when measured at 10 days after UV-B initiation. Turfgrass quality and PEc were positively correlated with pigments (chlorophyll and carotenoids) and antioxidant enzymes (SOD and CAT), and negatively correlated with lipid peroxidation. The results suggest that selecting dark-green cultivars with greater pigment content and antioxidant activity may be an effective approach for turfgrass breeders and sod producers to improve tolerance of newly transplanted sod to environments with higher UV-B radiation.

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John J. Sheahan and Garry A. Rechnitz

Depietion of the ozone layer is increasing the amount of UV-B radiation reaching the earths surface. The enhanced aging and mutation associated with UV-B damage suggests that crop yields may be threatened. However, plants are protected by flavonols which absorb UV-B. Although a great deal of research has been done on the flavonols, progress has been hampered by their lack of color. To overcome this problem, a staining procedure that provided sensitive and specific fluorescence identification of flavonols in Arabidopsis thaliana was developed. Three T-DNA insertional mutants, which lacked flavonols were identified, and the heritability of each has been confirmed by its multiple occurance in the parental line. The Mutants are being outcrossed, and analysis of the F2 will test if any of the mutations are tagged by a T-DNA insert. If so, the tagged gene will then be cloned.

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Pinghai Ding* and Leslie H. Fuchigami

Sunburn can be caused either by heat stress or by UV-B radiation. Under natural conditions fruit sunburn is usually caused by the combination of both heat stress and UV-B radiation. To evaluate the use of reflectance spectroscopy in early detection of fruit sunburn, 5-year-old `Fuji' apple bearing trees growing in pot-in-pot system at the Lewis-Brown Horticulture Farm of Oregon State Univ. were used in the experiment. Fruit sunburn was monitored either under natural conditions or treated with UV-B, heat or both under controlled conditions after detached from the tree. Under natural conditions, the sun-exposed side of Fuji fruit has much higher anthocyanins than the shaded side. The increase in anthocyanins at the sun-exposed side is to protect the fruit from sunburn. When the temperature higher than 40 °C the sunburn symptom initiated first by change the color of the sun-exposed side from red to tan, then to yellow patches, and finally turn to brown and dark brown patches. The peel pigments analysis results indicated that anthocyanins decreased earlier than chlorophyll in the symptom development. The results of detached fruit exposure to 30,000μW/cm2 UV-B lights or to 40 °C at control conditions for 2, 4, 6, 8, 10, and 12 hours indicated that high intensity UV-B lights or high temperature alone can cause sunburn respectively. The UV-B and temperature combination treatment enhanced the sunburn processes. The apples with sunburn caused under natural conditions or under UV-B and temperature controlled conditions were scanned by using reflectance spectroscopy of FOSS NIR system at different stage of the sunburn. The results indicted that Fuji apple sunburn can be efficiently detected at the early stage of sunburn in both natural and controlled conditions.

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Donald T. Krizek, Roman M. Mirecki, and Steven J. Britz

The influence of ambient UV radiation on growth, chlorosis, and flavonoid content was examined in four cultivars of cucumber (`Ashley', `Poinsett', `Marketmore', and `Salad Bush'). Plants were grown from seed in UV exclusion chambers consisting of UV transmitting plexiglass (10% T, 285 nm), lined with 3- or 5-mil Llumar (10% T, 399 or 404 nm) to exclude UV-A and UV-B, 5-mil polyester (10%T, 319 nm) to exclude UVB, or cellulose acetate (10% T, 291 nm) to transmit UV-A and UV-B. Plants were grown in 15 cm plastic pots containing vermiculite and were fertilized daily with nutrient solution. Despite their differential sensitivity to supplemental UV-B radiation, all four cultivars responded similarly to the exclusion treatments. After 19 to 21 days, plants grown under ambient UV-A and UV-B generally had less stem, leaf, and root biomass and less total height and total leaf area than those grown under conditions in which UV-A and UV-B or only UV-B was excluded. Flavonoid content, leaf number, and floral development were unaffected by UV. These findings demonstrate the extreme sensitivity of cucumber to current levels of solar UV radiation.

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Erik H. Ervin, Xunzhong Zhang, and John H. Fike

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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Donald T. Krizek and Roman M. Mirecki

Cellulose diacetate has been widely used in UV-B enhancement studies under field and controlled-environment conditions since the early 1970s to remove wavelengths below ≈290 nm, without any evidence of toxicity effects. However, while conducting UV-B exclusion studies in window boxes covered with cellulose diacetate (CA) or in Plexiglas chambers lined with CA, there was marginal chlorosis and cotyledon epinasty in `Ashley' cucumber, which is normally resistant to elevated UV-B, while seedlings exposed to open sunlight and those grown under polyester (PE) film to exclude UV-B were free of visible injury. These findings suggested that the CA filter itself may be causing toxicity. To test this hypothesis, a UV exclusion study was conducted in which CA or Teflon (T), both UV-B and UV-A transmitting films, were used to cover window boxes in the following four combinations (top/bottom): CA/CA, CA/T,T/CA, and T/T. When CA was used as the bottom filter (CA/CA and T/CA), the plants showed significantly greater leaf injury and a 2- to 3-fold reduction in growth than when T was used as the bottom filter (CA/T and T/T). These findings suggest that toxicity is caused by CA itself rather than by solar UV-B radiation, possibly as a result of outgassing of phthalates known to be used as plasticizers in the manufacture of CA. Further evidence that CA was responsible for leaf injury was provided by a companion study in which T was replaced by PE and damage was still observed, although no significant growth effects of CA position were observed.

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Edward J. Nangle, David S. Gardner, James D. Metzger, Dominic P. Petrella, Tom K. Danneberger, Luis Rodriguez-Saona, and John L. Cisar

mathematically adjusted for biologically effective UV-B radiation ( Caldwell, 1971 ), taking into account the direct impact of UV-B on DNA and chromophores ( Table 1 ). The total biologically effective UV-B light turfgrasses were exposed to in this trial was then