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The Response of Bean Plants to UV-B Radiation Under Different Irradiances of Background Visible Light
YAN-PING CEN and JANET F. BORNMAN
Journal of Experimental Botany
Vol. 41, No. 232 (November 1990), pp. 1489-1495
Published by: Oxford University Press
Stable URL: http://www.jstor.org/stable/23693334
Page Count: 7
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Plants of Phaseolus vulgaris L. (cv. Stella) were grown in controlled conditions under three different irradiances of visible light with or without UV-B (280—320 nm) radiation. The biologically effective UV-B radiation (UV-BBE) was 6.17 kJ m-2 d-1, and simulated a c. 5% decrease in stratospheric ozone at 55.7°N, 13.4°E. The photon flux densities of the photosynthetically active radiation (PAR, 400—700 nm) were either 700 μmol m-2 s-1 (HL), 500 μmol m-2 s-1 (ML) or 230 μmol m-2 s-1 PAR (LL). Under high light (HL) conditions plus UV-B radiation, bean plants appeared most resistant to the enhanced levels of UV-B radiation, and responded only by increasing leaf thickness by c. 18%. A small increase in UV screening pigments was also observed. Both the lower irradiances (ML and LL) increased the sensitivity of the plants to UV-B radiation. Changes in leaf structure were also observed. Photosystem II was inhibited under ML and LL together with UV-B radiation, as determined by Chl fluorescence induction and calculation of the fluorescence half-rise times. Leaf reflectivity measurements showed that the amount of PAR able to penetrate leaves of UV-B treated plants was reduced, and that a possible correlation may exist between the reduced PAR levels, loss of Chl and lowered photosynthetic activity, especially for LL + UV-B grown plants, where surface reflection from leaves was highest. Changes in leaf chlorophyll content were mostly confined to plants grown under LL + UV-B, where a decrease of c. 20% was found. With regard to protective pigments (the carotenoids and UV screening pigments) plants subjected to different visible light conditions responded differently. Among the growth parameters measured, there was a substantial decrease in leaf area, particularly under LL + UV-B (c. 47% relative to controls), where leaf dry weight was also reduced by c. 25%.
Journal of Experimental Botany © 1990 Oxford University Press