THE PLANT CELL, Vol 5, Issue 2 171-179, Copyright © 1993 by American Society of Plant Biologists
Arabidopsis Flavonoid Mutants Are Hypersensitive to UV-B Irradiation
J. Li, T. M. Ou-Lee, R. Raba, R. G. Amundson and R. L. Last
Boyce Thompson Institute for Plant Research, Tower Road, Ithaca, New York 14853-1801
Increases in the terrestrial levels of ultraviolet-B (UV-B) radiation (280
to 320 nm) due to diminished stratospheric ozone have prompted an
investigation of the protective mechanisms that contribute to UV-B
tolerance in plants. In response to UV-B stress, flowering plants produce a
variety of UV-absorptive secondary products derived from phenylalanine.
Arabidopsis mutants with defects in the synthesis of these compounds were
tested for UV-B sensitivity. The transparent testa-4 (tt4) mutant, which
has reduced flavonoids and normal levels of sinapate esters, is more
sensitive to UV-B than the wild type when grown under high UV-B irradiance.
The tt5 and tt6 mutants, which have reduced levels of UV-absorptive leaf
flavonoids and the monocyclic sinapic acid ester phenolic compounds, are
highly sensitive to the damaging effects of UV-B radiation. These results
demonstrate that both flavonoids and other phenolic compounds play
important roles in vivo in plant UV-B protection.