Journal of Experimental Botany, Vol. 54, No. 388, pp. 1771-1784,
July 1, 2003
© 2003 Oxford University Press
Response of purely symbiotic and NO3-fed nodulated plants of Lupinus luteus and Vicia atropurpurea to ultraviolet-B radiation
Received 23 October 2002; Accepted 11 April 2003
1 Botany Department, University of Cape Town, Private Bag Rhondebosch 7701, South Africa
2 National Botanical Institute, private bag X7, Claremont 7735, Cape Town, South Africa
3 Research Development, Cape Technikon, Room 2.800 Admin. Building Keizersgratch, PO Box 652, Cape Town 8000, South Africa
* To whom correspondence should be addressed. Fax: +27 21 460 3887. E-mail: dakora{at}ctech.ac.za
The effects of elevated UV-B radiation on growth, symbiotic function and concentration of metabolites were assessed in purely symbiotic and NO3-fed nodulated plants of Lupinus luteus and Vicia atropurpurea grown outdoors either on tables under supplemental UV-B radiation or in chambers covered with different types of plexi-glass to attenuate solar ultraviolet radiation. Moderately and highly elevated UV-B exposures simulating 15% and 25% ozone depletion as well as sub- ambient UV-B did not alter organ growth, plant total dry matter and N content per plant in both L. luteus and V. atropurpurea. In contrast, elevated UV-B increased (P <0.05) flavonoid and anthocyanin concentrations in roots and leaves of L. luteus, but not of V. atropurpurea. Feeding nodulated plants of L. luteus under elevated UV-B radiation with 2 mM NO3 increased (P <0.05) nodule, leaf and total dry matter, and whole plant N content. With V. atropurpurea, NO3 reduced (P <0.05) nodule activity, root %N and concentrations of flavonoids, anthocyanins in roots and leaves and soluble sugars in roots, in contrast to an observed increase (P <0.05) in nodule dry matter per plant. Similarly, supplying 2 mM NO3 to L. luteus plants exposed to sub-ambient UV-B radiation significantly reduced individual organ growth, plant total biomass, nodule dry matter, nodule %N, and whole plant N content, as well as root concentrations of flavonoids, anthocyanins, soluble sugars, and starch of L. luteus, but not V. atropurpurea plants. These results show no adverse effect of elevated UV-B radiation on growth and symbiotic function of L. luteus and V. atropurpurea plants. However, NO3 supply promoted growth in L. luteus plants exposed to the highly elevated UV-B radiation.
Key words: Anthocyanins, flavonoids, Lupinus luteus, NO3-feeding, nodulation and N2 fixation, soluble sugars, starch, ultraviolet radiation, Vicia atropurpurea.