GROWTH OF ARABIDOPSIS FLAVONOID MUTANT IS CHALLENGED BY RADIATION LONGER THAN THE UV-B BAND

Authors: Fiscus, Edwin; Booker, Fitzgerald

Submitted to: Environmental and Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/7/2002
Publication Date: 12/1/2002
Citation: Fiscus, E.L., Booker, F.L. 2002. Growth of Arabidopsis flavonoid mutant is challenged by radiation longer than the UV-B band. Environmental and Experimental Botany 48:213-224.

Interpretive Summary: Two genetic lines of the experimental plant Arabidopsis, which differ in their ability to produce UV-screening compounds, were grown in chambers that allow exposure to the full spectrum of visible and ultraviolet solar radiation. The purpose was primarily to determine the extent of the ultraviolet radiation band which may induce damage to plants and restrict their growth and productivity. It was previously thought that damaging radiation at ground level was restricted to the UV-B band (280-315nm wavelengths), the intensity of which is very sensitive to the concentration of ozone in the stratosphere. A series of filters was used to expose the plants to different portions of the UV spectrum during growth and then plant size, weight and seed production were measured at maturity along with estimates of production of UV-screening compounds. Data show that the wild type plants were able to produce sufficient UV-screening compounds to protect themselves from most damage effects. More importantly however, data from the mutant line showed that damaging radiation is found in the shorter wavelengths of the UV-A band, which is not affected by stratospheric ozone concentrations, as well as the UV-B band. The conclusion to be drawn from this work is that projections of plant damage from increased ultraviolet radiation as a result of stratospheric ozone depletion are likely to be over estimated.

Technical Abstract: Growth, seed yield and UV-absorbing compounds were studied in the chalcone isomerase defective tt-5 mutant of Arabidopsis thaliana and its Landsberg erecta (Ler) progenitor under full spectrum solar radiation and filters which attenuated progressively larger portions of the UV-B and UV-A radiation bands. We wanted to determine if: 1) the tt-5 mutant could grow normally if adequately protected from damaging UV; 2) the generalized plant action spectrum or a DNA damage action spectrum would best describe the observed responses; and 3) the traditional Mylar filter is an adequate control for UV damage studies. Plant growth seed yield, absorbance at 300 nm and total phenolic content before and after exposure to UV were measured. 3 types of UV filters were used: CD transmitting all the UV; Mylar cutting off below 320 nm; and PVC cutting off below 340 nm. Ler showed no growth effects under any of the treatments except for plant height which was reduced in the Mylar and CD. But, tt-5 exhibited progressive decreases in all the plant growth measures with the best growth under PVC, Mylar intermediate and CD worst. The disruption to secondary metabolism of the tt-5 mutation makes it unsuitable for mechanistic studies of high UV-B effects. The DNA action spectrum was best correlated with the effects suggesting part of the damaging radiation band is indifferent to stratospheric ozone, and the damaging radiation extends beyond the Mylar cut-in, so it is not an adequate control for UV damage studies.