An Arabidopsis mutant tolerant to lethal ultraviolet-B levels shows constitutively elevated accumulation of flavonoids and other phenolics - PubMed (original) (raw)
An Arabidopsis mutant tolerant to lethal ultraviolet-B levels shows constitutively elevated accumulation of flavonoids and other phenolics
K Bieza et al. Plant Physiol. 2001 Jul.
Abstract
The isolation and characterization of mutants hypersensitive to ultraviolet (UV) radiation has been a powerful tool to learn about the mechanisms that protect plants against UV-induced damage. To increase our understanding of the various mechanisms of defense against UVB radiation, we searched for mutations that would increase the level of tolerance of Arabidopsis plants to UV radiation. We describe a single gene dominant mutation (uvt1) that leads to a remarkable tolerance to UVB radiation conditions that would kill wild-type plants. Pigment analyses show a constitutive increase in accumulation of UV-absorbing compounds in uvt1 that increases the capacity of the leaves to block UVB radiation and therefore is likely to be responsible for the elevated resistance of this mutant to UVB radiation. These increases in absorption in the UV region are due, at least in part, to increases in flavonoid and sinapate accumulation. Expression of chalcone synthase (CHS) mRNA was shown to be constitutively elevated in uvt1 plants, suggesting that the increases in absorption may be a consequence of changes in gene expression. Expression of CHS in uvt1 was shown to be still inducible by UV, indicating that the uvt1 lesion may not affect the UV-mediated regulation of CHS gene expression. Our data support an important role for UV screens in the overall protection of plants to UVB radiation. The uvt1 mutant could prove to be an important tool to elucidate further the exact role of UV-absorbing pigments in UV protection as well as the relative contribution of other mechanisms to the overall tolerance of plants to UV radiation.
Figures
Figure 1
Effect of UVB-radiation on UV-sensitive and UV-tolerant seedlings of Arabidopsis (A) and on a segregating population of uvt1/uvs seedlings (B and C). A, Twelve-day old uvs and uvt1 plants were irradiated with 0.17 W m−2 UVB for 48 h and allowed to recover for 48 h under fluorescent lighting before being photographed. Representative individuals of UV-tolerant (uvt1) and UV-sensitive (uvs) plants are shown. B, Seventeen-day old seedlings from the F2 generation of a cross between wild-type and uvt1 plants were exposed to 0.17 W m−2 UVB for 37 h and allowed to recover for 27 h under fluorescent lighting before being photographed. Representative individuals of each of three distinct UV tolerance phenotypes observed, highly tolerant (uvt1), intermediate tolerance (WT) ,and low tolerance (uvs), are shown. C, Additional seedlings of the same experiment are shown to depict the segregation of the glabrous mutation (gl1) among uvt1 plants. All images were digitized before printing.
Figure 2
Effect of different regimes of UVB irradiation on mature wild-type and mutant Arabidopsis plants. One-month-old uvt1, wild-type (WT), and uvs plants were exposed to 0.10 W m−2 UVB (mid UV), 0.18 W m−2 UVB (high UV), or kept under fluorescent lighting (no UV) for 3 d and allowed to recover for 3 d under fluorescent lighting before being photographed. This image was digitized before printing.
Figure 3
Changes in the absorption spectra of pigment extracts from uvs, uvt1, and wild type after exposure to UVB. Thirteen-day-old wild type (WT), uvs, and uvt1 plants were exposed to fluorescent lighting with (+) or without (−) additional 0.15 W m−2 UVB-radiation for 21 h. Extracts were prepared from equal amounts of tissue in 80% (v/v) ethanol. This figure represents an extension of previously published work (Lois and Buchanan, 1994)
Figure 4
Level of UV-absorbing pigments in mutant and wild-type Arabidopsis plants. Pigments were extracted in 80% (v/v) ethanol from aerial tissues of 13-d-old plants before (−) and after (+) 21 h exposure to 0.15 W m−2 UVB -radiation. The height of the bars represents the mean value of A330 per milligrams tissue of three independent experiments. Error bars correspond to one
sd
. Lines below bars depict relevant cases of pairs of bars for which there is a statistically significant difference between their means (non-paired Student's t test, P < 0.05).
Figure 5
Anthocyanin levels in mutant and wild-type Arabidopsis plants. Anthocyanins were extracted in acidified methanol from leaves of 36-d-old wild-type control (WT) and uvs plants and from UV-tolerant individuals (uvt1). The height of the bars represents the mean value of A530 per milligrams tissue of three independent experiments. Error bars correspond to one
sd
. There is a statistically significant difference between the uvt1 value and each of the other two values (non-paired Student's t test, P < 0.05).
Figure 6
HPLC separation of UV-absorbing compounds from leaf tissues of uvt1 and wild-type plants. Pigments extracted from 16-d-old plants in 70% (v/v) methanol were separated by HPLC on a C18 column. The spectra represent the elution profiles between 9 and 19 min (the region where the most prominent peaks eluted) as monitored by spectrophotometry (A330, thick lines) and fluorescence (thin lines). The arrow indicates a peak corresponding to a highly fluorescent sinapate.
Figure 7
Spectra of UV light transmitted through leaves from wild-type and mutant Arabidopsis plants. Irradiance spectra were obtained from incident light (Lamp) and light transmitted through leaves from 7-week-old wild-type (WT), uvs, and uvt1 plants exposed to UVB radiation. The left ordinate corresponds to the spectra of UV transmitted through the leaves and the right ordinate to the incident light spectrum.
Figure 8
Relative transmission of UVB light through wild-type and mutant Arabidopsis plants. Irradiance spectra were obtained from incident light (Lamp) and light transmitted through leaves from 7-week-old wild-type (WT), uvs, and uvt1 plants exposed to UVB radiation. The height of the bars indicate the averages of percent transmission measurements for wavelengths between 290 and 320 nm taken in three or four places in each leaf lamina from at least three different leaves from uvs, wild-type, and uvt11 plants. Error bars correspond to one
sd
. The numbers above each bar represent the full range of percent transmittance values for each plant type.
Figure 9
Accumulation of CHS mRNA in mutant and wild-type Arabidopsis. Northern blot from total RNA samples isolated from aerial tissues of 13-d-old wild-type, uvt11, and uvs plants not exposed (−UV) and exposed (+UV) to 0.15 W m−2 UVB radiation for 21 h, hybridized with a CHS gene probe. The upper image shows the rRNA stained with methylene blue. This image was digitized before printing.
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