Effects of enhanced uv b radiation 280 320 nanometers on ribulose 1 5 bis phosphate carboxylase in pea pisum sativum cultivar little marvel and soybean glycine max cultivar bragg

V.C.V.; Allen, L.H.Jr; Garrard, L.A.

Environmental and Experimental Botany 24(2): 131-144


ISSN/ISBN: 0098-8472
Accession: 005301914

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Pea and soybean were grown and exposed to UV-B radiation under greenhouse conditions. The effects of UV-B radiation on activities and kinetics of ribulose-1,5-biphosphate carboxylase (RuBPcase) in both pea and soybean and on growth, chlorophyll, carotenoids and soluble protein in pea were investigated. Plants were irradiated for 6 h daily from the day of planting with supplemental UV-B radiation which was provided by 2 Westinghouse FS-40 fluorescent sun lamps filtered with 0.127 mm film of cellulose acetate (UV-B treatment) or 0.127 mm film of Mylar S (Mylar control). Three UV-B radiation levels were used: 1.09 (treatment T1), 1.36 (treatment T2) and 1.83 (treatment T3) UV-Bseu equals 15.98 mW m-2 of weighted solar UV-B irradiance obtained by applying the weighting function, EXP-[(.lambda.-265)/21]2, which was designed to stimulate the DNA absorption spectrum. These UV-B levels correspond to 6, 21 and 36% calculated decreases in stratospheric ozone concentration for treatment T1, T2 and T3, respectively. In pea plants, stem lengths, plant weights, chlorophyll, carotenoids and soluble protein decreased with increased levels of UV-B radiation. Leaf pigment extracted with 80% acetone from UV-B-treated pea plants showed an increase in absorpton in the waveband from 330-440 nm. The Vmax (HCO3-) of RuBPcase from T3 pea plant leaves was 58% of that of the control. The Km (CO2) values were 22.4 and 33.9 .mu.M for Mylar control enzyme and T3 enzyme, respectively. The Vmax (RuBP) value of RuBPcase of T3 leaf samples was 42% of that of the control. The Km (RuBP) values were 0.36 and 0.14 mM for RuBPcase of the Mylar control and T3 treatment, respectively. In soybean, the Vmax (HCO3-) of T3 RuBPcase was 60% of that of the control. The Km (CO2) value was 19.9 .mu.M for the control vs. 26.8 .mu.M for the T3 enzyme. The Vmax (RuBP) of T3 enzyme was 40% of that of the Mylar control enzyme. The Km (RuBP) values were 0.44 and 0.18 mM for the Mylar control enzyme and T3 enzyme, respectively. Results from time-course studies in both pea and soybean showed that RuBPcase from Mylar control plants reached saturation rates faster than the enzyme extracted from T3 plants. When crude protein extracts from pea leaves were subjected to polyacrylamide gel electrophoresis, soluble protein contents in leaves of T3 plants were less than those of Mylar control plants. Electrophoretograms showed that the most prominent peak corresponding to a spinach RuBPcase marker was much smaller in area in the T3 sample than was observed in the Mylar control. An inhibitory effect of exercise UV-B radiation on the component reactions of photosynthesis in pea and soybean was shown. These inhibitions were manifested through reductions of photosynthetic pigments, protein and RuBPcase activity, which led to a reduction in photosynthesis and growth of these UV-B sensitive crop plants.