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The effects of elevated temperature, carbon dioxide, and water stress on the isoflavone content of seed from a dwarf soybean line [Glycine max (L.) Merrill] were determined, using controlled environment chambers. Increasing the temperature from 18 degrees C during seed development to 23 degrees C decreased total isoflavone content by about 65%. A further 5 degrees C increase to 28 degrees C decreased the total isoflavone content by about 90%. Combining treatments at elevated temperature with elevated CO(2) (700 ppm) and water stress to determine the possible consequences of global climate change on soybean seed isoflavone content indicated that elevated CO(2) at elevated temperatures could partially reverse the effects of temperature on soybean seed isoflavone content. The addition of drought stress to plants grown at 23 degrees C and elevated CO(2) returned the total isoflavone levels to the control values obtained at 18 degrees C and 400 ppm CO(2). The promotive effects of drought and elevated CO(2) at 23 degrees C on the 6' '-O-malonygenistin and genistin levels were additive. The individual isoflavones often had different responses to the various growth conditions during seed maturation, modifying the proportions of the principal isoflavones. Therefore, subtle changes in certain environmental factors may change the isoflavone content of commercially grown soybean, altering the nutritional values of soy products.

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.

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.

ABSTRACISoybeans (Glycine max [L.] Merr. cv Essex) were grown in a greenhouse, and the first trifoliate leaf was either allowed to expand under a high photosynthetic photon flux density (PPFD) (1.4 millimoles per square meter per second) or a low PPFD (0.8 millimoles per square meter per second). After full leaf expansion, plants from each treatment were placed into a factorial design experiment with two levels of ultraviolet-B (UV-B) radiation (0 and 80 milliwatts per square meter biologically effective UV-B) effective UV-B radiation received at the earth's surface. Caldwell (7) estimated that a 1% decrease in stratospheric ozone concentration would result in an approximate 2% increase in UV-BBE2 radiation at temperate latitudes. Therefore, the recently projected 5 to 9% stratospheric ozone reduction (18) would result in up to a 19% increase in UV-BBE radiation.An increase in UV-B irradiance is of particular concern since energy in this waveband is readily absorbed by proteins and it has been demonstrated that plant processes such as photosynthesis (25), transpiration (7, 25), leaf expansion (10, 23, 26, 27), dark respiration (22,25), and biomass allocation (24) are affected. In the majority of UV-B studies, the UV-B dose utilized was 3-to 5-fold greater than the National Academy of Science's most recent estimates. Only a few studies have employed UV-B doses equivalent to less than a 20% reduction in the ozone layer. Nevertheless, these studies have also demonstrated the deleterious effects of UV-B irradiation upon plants (24)(25)(26)(27).In addition to unrealistically high UV-B irradiances, another criticism of many previous UV-B studies has been the low PPFD under which the plants were grown and irradiated. Only a few studies have examined the effects of UV-B radiation on plants grown under relatively high PPFDs, which more approximate natural conditions (24, 25). It was observed in a number of species that plants were less susceptible to UV-B-induced damage when grown under-high PPFDs-than under lower PPFDs, when all other conditions remained constant. This amelioration of UV-B-induced damage was attributed to photoprotection and photoreactivation.High PPFDs might also affect plant sensitivity to UV-B radiation by eliciting plant responses which provide absorbing screens from UV-B radiation. found that plants grown in the sun have greater concentrations offlavonoids in their leaves than shade plants. Several investigators (5,20,26,32) have shown that the flavonoid content of leaves increases after UV-B irradiation, providing a protective mechanism for the plant. Sun plants also have smaller, thicker leaves compared to shade-adapted plants (2, 9). Since UV-B radiation must penetrate the leaf to produce any damage, a thicker leaf might be more protected from damage by UV-B radiation. This suggests that plants grown in the sun could be more resistant to UV-Binduced damage than plants grown in the shade, simply due to anatomical/morphological differences in response to visible radiation.The purpose of this s...

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1993. UV-B response of cucumber seedlings grown under metal halide and high pressure sodium/ deluxe lamps. -Physiol. Plant. 88: 350-358.UV-B-sensitive (Poinsett) and -insensitive (Ashley) cuhivars of cucumber {Cucumts sativus L.) were grown in growth chambers al 600 nmol m -s ' of photosynthetically active radiation provided by metal halide (MH) or high pressure sodium/deluxe (HPS/DX) lamps. Plants were irradiated 15 days from seeding for 6 h per day under 18.2 kJ m -day"' of biologically effective UV-B (UV-Bj^) radiation. One of the most pronounced effects of UV-B was a 27 to 78% increase in phenylalanine ammonialyase (PAL) activity. UV-B also increased total polyamines. Catalase and superoxide dismutase varied greatly in their response to UV-B. There were no interactive effects on PAL or catalase activity, or total polyamines. There was a UV x PAR source interaction for superoxide dismutase activity. UV-B increased chlorosis and decreased height, dry weight and leaf area. Stem elongation, biomass production, leaf enlargement and chlorosis were greater under HPS/DX lamps than under MH lamps. Chlorosis was greater in Poinsett than in Ashley and in lower leaves than in upper ones. Aside from chlorosis, there were no interactive effects of UV-B, PAR source or cultivar on any of the growth parameters measured, suggesting that the growth response of cucumber seedlings to UV-B is unaffected by PAR source or cuitivar. Similarly, except for SOD activity, the biochemical response to UV-B was also nol influenced by PAR source or cultivar.

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