No abstract

1981, Effects of supplemental UV-B radiation on growth and leaf photosynthetic reactions of soyhean (Glycine max). -Physiol. Plant. 52: 353-362.Experiments were conducted under greenhonse conditions to investigate the effects of enhanced UV-B radiation (280 to 320 nm) OB height, fresh and dry weights, leaf chlorophyll and carotenoids, CO^ uptake rates, and Hill activity in soybean {Glycine max L. cv. Bragg). Plants were exposed for 6 h continuously from midmorning to midafternoon each day to UV-B radiation which was provided by Westinghouse FS-40 sun lamps filtered with 0.127-mm cellulose acetate film (UV-B enhanced) or 0.127-mni Mylar S film (UV-B Mylar control). Three different UV-B enhanced radiation levels were tested: 1.09 (treatment T,), 1,36 (treatment T^), and 1.83 (treatment T3) UV-B sun equivalent units (UV-BJ. where 1 UV-B5^" = 15.98 mW-m"^ of solar UV-B obtained by applying EXP -[(i-265)/21]^ a weighting function that simulates the DNA absorption spectrum, to the UV-B lamp systems. These UV-B levels correspond to a calculated decrease in stratospheric ozone content of 6%, 21%, and 36% for treatment T,, T^, and T3, respectively. Daily exposure of soybean plants to UV-B radiation significantly decre,ased height, fresh and dry weights, leaf chlorophyll and carotenoid contents, and CO3 uptake rates. Leaf pigment extracted in 80% acetone from UV-B-treated soybean plants showed considerable increase in absorption in the wavelength region of 330 to 400 nm with increased UV-B radiation levels. Chloroplast preparations from leaves of Tj and T3 plants showed significant reductions in Hill reaction measurements.

Effects of increased UV‐B radiation on activities of primary photosynthetic carboxylating enzymes and on contents of soluble proteins were studied in soybean (Glycine max [L.] Merr. cv. Bragg), pea (Pisum sativum L. cv. Little Marvel), tomato (Lycopersicon esculentum L. cv. Rutgers), and sweet corn (Zea mays L. cv. Golden Cross Bantam). The purpose was to evaluate the responses of agronomic crops to increases in solar UV‐B radiation. Plants were grown and exposed under greenhouse conditions for 6 h daily to supplemental UV‐B radiation which was provided by Westinghouse FS‐40 fluorescent sun lamps filtered with 0.127‐mm film of cellulose acetate (UV‐B treated) or Mylar S (Mylar control). Three UV‐B levels were tested: 1.09 (treatment T1), 1.36 (treatment T2), and 1.83 (treatment T3) UV‐Bseu where 1 UV‐Bseu equals 16.0 mW‐m2 weighted by EXP‐[(λ‐265)/21]2. These UV‐B levels corresponded to 6%,21%, and 36%, respectively, of decrease in stratospheric ozone content, based on the interpolations of UV‐B irradiances at a solar elevation angle of 60°. Leaves of plants of soybean, pea, and tomato exposed to UV‐B radiation were generally low in RuBP carboxylase activity. On a fresh weight basis, all three UV‐B radiation levels significantly reduced the enzyme activity in soybean and pea, whereas tomato plants showed significant reduction in RuBP carboxylase activity only when exposed to 1.83 and 1.36 UV‐Bseu. An apparent decrease in soluble proteins was observed in leaf extracts of soybean and pea plants exposed to 1.36 and 1.83 UV‐Bseu whereas higher amounts of proteins were detected in leaves of tomato plants grown under UV‐B radiation. Leaves of sweet corn plants grown under Mylar control were low in PEP carboxylase activity and proteins as compared with those of control plants receiving no supplemental UV and UV‐B treatment. Activities of PEP carboxylase in crode extracts from leaves of sweet corn were significantly suppressed under 1.36 and 1.83 UV‐Bseu as compared with the no UV control. Some stimulation of PEP carboxylase activity was observed in corn plants exposed to 1.09 UV‐Bseu.