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The influence of solar UV‐A and UV‐B radiation at Beltsville, MD, USA, on growth of Lactuca sativa L. (cv. New Red Fire lettuce) was examined during early summer of 1996 and 1997. Plants were grown from seed in plastic window boxes covered with Llumar to exclude UV‐A and UV‐B, polyester to exclude UV‐B, or tefzel (1996) or teflon (1997) to transmit UV‐A and UV‐B radiation. After 31–34 days, plants grown in the absence of solar UV‐B radiation (polyester) had 63 and 57% greater fresh weight and dry weight of tops, respectively, and 57, 72 and 47% greater dry weight of leaves, stems and roots, respectively, as compared to those grown under ambient UV‐B (tefzel or teflon). Plants protected from UV‐A radiation as well (Llumar) showed an additional 43 and 35% increase, respectively, in fresh and dry weight of tops and a 33 and 33% increase, respectively, in dry weight of leaves and stems, but no difference in root biomass over those grown under polyester. Excluding ambient UV‐B (polyester) significantly reduced the UV absorbance of leaf extracts at 270, 300 and 330 nm (presumptive flavonoids) and the concentration of anthocyanins at 550 nm as compared to those of leaf extracts from plants grown under ambient UV‐A and UV‐B. Additional removal of ambient UV‐A (Llumar) reduced the concentration of anthocyanins, but had no further effect on UV absorbance at 270, 300 or 330 nm. These findings provide evidence that UV‐B radiation is more important than UV‐A radiation for flavonoid induction in this red‐pigmented lettuce cultivar. Although previous workers have obtained decreases in lettuce yield under enhanced UV‐B, this is the first evidence for inhibitory effects of solar UV‐A and UV‐B radiation on lettuce growth.

The role of photosynthetically active radiation (400-700 nm) (PAR) in modifying plant sensitivity and photomorphogenic responses to ultraviolet-B (280-320 nm) (UV-B) radiation has been examined by a number of investigators, but few studies have been conducted on ultraviolet-A (320-400 nm) (UV-A), UV-B and PAR interactions. High ratios of PAR-UV-B and UV-A-UV-B have been found to be important in ameliorating UV-B damage in both terrestrial and aquatic plants. Growth chamber and greenhouse studies conducted at low PAR, low UV-A and high UV-B often show exaggerated UV-B damage. Spectral balance of PAR, UV-A and UV-B has also been shown to be important in determining plant sensitivity in field studies. In general, one observes a reduction in total biomass and plant height with decreasing PAR and increasing UV-B. The protective effects of high PAR against elevated UV-B may also be indirect, by increasing leaf thickness and the concentration of flavonoids and other phenolic compounds known to be important in UV screening. The quality of PAR is also important, with blue light, together with UV-A radiation, playing a key role in photorepair of DNA lesions. Further studies are needed to determine the interactions of UV-A, UV-B and PAR.

1997, Inhibitory effects of ambient levels of solar UV-A and UV-B radiation on growth of cucumber. -Physiol. Plant, 100: 886-893.The influence of solar UV-A and UV-B radiation at Beltsville, Maryland, on growth and flavonoid content in four cultivars of Cucumis sativus L. (Ashley, Poinsett, Marketmore, and Salad Bush cucumber) was examined during the summers of 1994 and 1995, Plants were grown from seed in UV exclusion chambers consisting of UV-transmitting Plexiglas, lined with Llumar to exclude UV-A and UV-B, polyester to exclude UV-B, or cellulose acetate to transmit UV-A and UV-B, Despite previously determined differences in sensitivity to supplemental UV-B radiation, all four cultivars responded similarly to UV-B exclusion treatment. After 19-21 days, the four cultivars grown in the absence of solar UV-B (polyester) had an average of 34, 55, and 40% greater biomass of leaves, stems, and roots, respectively, 27% greater stem height, and 35% greater leaf area than those grown under ambient UV-B (cellulose acetate). Plants protected from UV-A radiation as well (Llumar) showed an additional 14 and 22% average increase, respectively, in biomass of leaves and stems, and a 22 and 19% average increase, respectively, in stem elongation and leaf area over those grown under polyester. These findings demonstrate the extreme sensitivity of cucumber not only to present levels of UV-B but also to UV-A and suggest that even small changes in ozone depletion may have important biological consequences for certain plant species.

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Ripe mangoes`Tommy Atkins' were exposed to UV-C irradiation for 10 and 20 min, prior to storage for 14 days at 5 or 20°C and a shelf-life period of 7 days at 20°C. UV-C-treated fruit maintained better visual appearance than unirradiated controls. UV-C irradiation for 10 min was the most eective regime in suppressing decay symptoms and maintaining ®rmness during storage at 5 or 20°C. Such fruit (treated with UV-C for 10 min) showed greater levels of putrescine and spermidine after cold storage than controls and those treated with UV-C for 20 min. Higher levels of sugars and lower levels of organic acids were observed in mangoes treated with UV-C for 20 min. However, the most eective UV-C treatment (10 min) for reducing decay maintained sugar and organic acid levels similar to the controls. No UV-damage was observed on treated fruits after storage. These results indicate that UV-C irradiation could be used as an eective and rapid method to preserve the postharvest life of ripe mangoes without adversely aecting certain quality attributes.

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