Roman M. Mirecki

influence of UV-B radiation on polyamines, lipid peroxidation and membrane lipids in cucumber

Sensitive (Poinsett) and insensitive (Ashley) cultivars of cucumber (Cucumis sativus) were grown for four weeks from planting in unshaded greenhouses at 0 or 12.2 kJ m−2 day−1 of biologically effective ultraviolet-B (UY-BBE) radiation. The latter irradiance corresponded to a decrease in stratospheric ozone of ca 20% for clear sky conditions at Beitsville, MD on 21 June. The diamine putrescine and the polyamine spermidine accumulated in cotyledon and leaf tissues in response to UV-B radiation in both cultivars, but levels were not correlated with sensitivity to UV-B. Lipid peroxidation, as quantified by measurement of malondialdehyde (MDA), was increased by UV-B exposure. Significant cultivar differences were observed, with increases in lipid peroxidation in both cotyledons and leaves being correlated with UV-B sensitivity. Determination of membrane lipid composition indicated slight decreases in the unsaturated/saturated fatty acid ratios as a result of UV-B exposure. In general, Poinsett had a lower unsaturated/saturated ratio of fatty acids than did Ashley. These results indicate that membrane lipids may be a target of UV-B damage and that differences in the UV-B susceptibility of these two cultivars may involve differences in lipid metabolism. Polyamine accumulation in response to UV-B radiation stress is consistent with similar responses to other environmental stressors.

Influence of photosynthetically active radiation and spectral quality on UV-B-induced polyamine accumulation in soybean

Abstract UV-B-sensitive (Essex) and -insensitive (Williams) cultivars of soybean ( Glycine max ) were grown in growth chambers at photosynthetically active radiation (PAR) levels of 300 or 600 μmol m −2 sec −1 provided by either red- and far-red-deficient (MH) or blue-deficient (HPS/DX) lamps or a combination of both. The combined treatment provided a balanced output, similar to that provided by fluorescent plus incandescent lighting across the visible spectrum. Under the combined lamps, plants were exposed to 12 kJ m −2 day −1 of biologically effective UV-B (UV-B BE ) with 6-hr irradiance periods centred midway through the photoperiod. This irradiance corresponded to a decrease in stratospheric ozone of ca 20% for clear sky conditions at Beltsville, MD on 21 June. Plant growth was significantly inhibited by UV-B at 300 but not at 600 μmol m −2 sec −1 PAR. No cultivar differences were noted in the UV-B-induced inhibition of growth, although visible injury was less in Williams than in Essex. PAR had a large effect on polyamine levels in leaves, with higher levels of putrescine (Put) and spermidine observed at 600 than at 300 μmol m −2 sec −1 in both cultivars. UV-B-induced polyamine accumulation was observed primarily in Williams. Under MH or HPS/DX lamps alone, plants were exposed to two different UV-B levels, 9.9 and 12 kJ m −2 day −1 , corresponding to stratospheric ozone reductions of ca 9 and 20%. UV-B inhibited growth at both 300 and 600 μmol m −2 sec −1 PAR under either radiation source. There was no effect of PAR on the UV-B-induced growth inhibition with the HPS/DX lamps, but a partial amelioration of this inhibition occurred in Williams at 600 μmol m −2 sec −1 PAR under MH lamps. Dose-dependent UV-B-induced polyamine accumulation was also observed in both cultivars. PAR increased Put levels under MH but not HPS/DX lamps. These results indicate that the inhibition of UV-B stress by high PAR may require a balance of red and blue wavelengths and may involve polyamine accumulation.

Spectral Properties of Selected UV-blocking and UV-transmitting Covering Materials with Application for Production of High-value Crops in High Tunnels†

Abstract The spectral properties of selected UV-blocking and UV-transmitting covering materials were characterized by means of a UV–VIS spectroradiometer or a UV–VIS spectrometer to provide researchers and growers with guidelines for selecting suitable materials for use in studying the effects of ambient solar UV radiation on the production of tomatoes and other high-value crops in high tunnels. A survey was made of a wide range of plastic covering materials to identify commercially available products that had the desired characteristics of transmitting high levels of photosynthetically active radiation and of being stable under ambient solar UV radiation. The study was focused on evaluating films that either blocked or transmitted UV wavelengths below 380 nm to determine comparative growth, yield and market quality and to provide a tool for integrated pest management. Based on this survey, two contrasting covering materials of similar thickness (0.152 mm) and durability (4-year polyethylene), one a UV-blocking film and the other a UV-transmitting film, were selected and used to cover two high tunnels at Beltsville, MD. Spectroradiometric measurements were made to determine comparative spectral irradiance in these two high tunnels covered with these materials and under ambient solar UV radiation. Comparative measurements were also made of selected glass and plastic materials that have been used in UV exclusion studies.

Comparison of the Response of Soybean to Supplemental UV-B Radiation Supplied by Either Square-Wave or Modulated Irradiation Systems

Soybean [Glycine max (L.) Merr.] cv CNS was grown in a field study at the Beltsville Agricultural Research Center, USDA, Beltsville, MD. Supplemental UV-B radiation was provided by two contrasting UV-B delivery systems, both of which were intended to simulate a 25% depletion of stratospheric ozone as estimated by an empirical model. In the first system, a seasonally-based supplemental UV-B irradiance was provided in a square-wave fashion (SQ) and in the second, a state-of-the-art modulated (MOD) UV-B supplementation system was employed.

Evidence for phytotoxic effects of cellulose acetate in UV exclusion studies

Abstract Cellulose diacetate (CA) has been widely used in UV-B enhancement studies and has also been used along with Aclar and Teflon in UV-B exclusion studies. In recent UV exclusion studies conducted at Beltsville, MD under solar UV, cucumber plants were found to develop marginal chlorosis under CA filters. To test the hypothesis that CA was responsible for the phytotoxic effects observed, an experiment was conducted in which CA and/or Teflon (T), both UV-B and UV-A transmitting films, were used to cover ‘Ashley’ cucumber plants grown from seed in window boxes under the following four combinations (top layer/bottom layer): CA/CA; CA/T; T/CA; and T/T, one layer on top of the other. When CA was used as the bottom filter (CA/CA and T/CA), the plants were stunted and showed marginal chlorosis and epinasty of the cotyledons and first true leaf. However, when T was used as the bottom filter (CA/T and T/T), or the plants were grown in open air without any covering, the plants produced vigorous growth and were free of injury. These findings suggest that toxicity is caused by the CA itself rather than by solar UV radiation, possibly as a result of outgassing of a phthalate known to be used as a plasticizer in the manufacture of CA or some breakdown product. To avoid possible confounding effects from use of CA and to obtain maximum transmission of UV and visible radiation, we recommend that Teflon or Aclar be used in UV exclusion studies.

Influence of UV‐B radiation and putrescine on shoot and root growth of cucumber seedlings grown in nutrient solution

Abstract Poinsett cucumber (Cucumis sativus L.) seedlings were grown in growth chambers in nutrient solution containing 0 or 500 μM putrescine (Put) and were exposed to 0.2 or 15 kJ‐m‐2 day1 of biologically effective UV‐B radiation to determine the comparative sensitivity of shoots and roots to increased UV‐B and the possible protective effect of polyamines. Shoot growth in UV‐B‐treated plants was reduced 48%, root growth 63%, total leaf area 38%, and specific leaf weight (SLW) 22%. This was in contrast to previous reports of increased SLW in cucumber plants grown in vermiculite or in a peat‐vermiculite mix. Putrescine treatment increased leaf area in the second and third leaf and total leaf area and Put also increased dry weight of shoots, but had no effect on dry weight of roots or on SLW. The Put treatment was ineffective in ameliorating UV‐B induced leaf chlorosis. This is the first report of greater sensitivity of roots to UV‐B radiation than of shoots in plants grown in solution culture. This could ...

Effect of supplemental ultraviolet radiation on the concentration of phytonutrients in green and red leaf lettuce (Lactuca sativa) cultivars

Eight cultivars each of red and green leaf lettuce were raised in a greenhouse with supplemental UV radiation, either UV-A (wavelengths greater than ca. 315 nm) or UV-A+UV-B (wavelengths greater than ca. 290 nm; 6.4 kJ m-2 daily biologically effective UV-B), or no supplemental UV (controls). Several phytonutrients were analyzed in leaf flours to identify lines with large differences in composition and response to UV-B. Red leaf lettuce had higher levels of phenolic acid esters, flavonols and anthocyanins than green lines. Both green and red lines exposed to UV-B for 9 days showed 2-3-fold increases in flavonoids compared to controls, but only 45% increases in phenolic acid esters, suggesting these compounds may be regulated by different mechanisms. There were large differences between cultivars in levels of phenolic compounds under control conditions and also large differences in UV-B effects. Among red varieties, cv. Galactic was notable for high levels of phenolics and a large response to UV-B. Among green varieties, cvs. Black-Seeded Simpson and Simpson Elite had large increases in phenolics with UV-B exposure. Photosynthetic pigments were also analyzed. Green leaf lettuce had high levels of pheophytin, a chlorophyll degradation product. Total chlorophylls (including pheophytin) were much lower in green compared to red varieties. Lutein, a carotenoid, was similar for green and red lines. Total chlorophylls and lutein increased 2-fold under supplemental UV-B in green lines but decreased slightly under UV-B in red lines. Lettuce appears to be a valuable crop to use to study phytochemical-environment interactions.