No abstract

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.