15th International Conference on Arabidopsis Research - TAIR

T04-067
The UV-B response in Arabidopsis involves the bZIP
transcription factor HY5
Roman Ulm(1), Alexander Baumann(1), Attila Oravecz(1), Zoltan Mate(2), Edward
Oakeley(3), Eberhard Schäfer(1), Ferenc Nagy(1, 2)
1-University of Freiburg, Institute of Biology II, Freiburg, Germany
2-Agricultural Biotechnological Center, Gödöllö, Hungary
3-Friedrich Miescher Institute, Basel, Switzerland
The light environment is a key factor that governs a multitude of developmental
processes during the entire life cycle of plants. Part of the incident
sunlight encompasses a segment of the UV-B region (280-320 nm) that, in
contrast to solar UV-C (24,000 genes) to compare responses of Arabidopsis
to different UV-B wavelength ranges. In all cases analysed, UV-B induction
was found to be independent of known photoreceptors. However, a subset
of genes required the bZIP transcription factor HY5, a main player of the
transition from dark- to light-growth. These results will be presented, together
with our recent progress in further elucidating the UV-B response.
T04 Interaction with the Environment 1 (Abiotic)
T04-068
VITAMIN C IS IMORTANT FOR ACCLIMATION TO AND
GROWTH IN HIGH LIGHT
Müller-Moule, Patricia(1), Golan, Talila(2), Niyogi, Krishna K.(2)
1-Institute for Plant Molecular and Developmental Biology, Heinrich-Heine University, D-40225
Düsseldorf, Germany
2-Department of Plant and Microbial Biology, University of California, Berkeley CA 94720-3102,
USA
To understand the importance of vitamin C and zeaxanthin as photoprotective
mechanisms, several ascorbate-deficient Arabidopsis mutants were subjected
to growth in high light (HL) or to a transfer from low light (LL) to HL. The
vtc2 mutant has only 10 ¯ 30% ascorbate compared to the wild type, while
the vtc2npq1 mutant in addition lacks zeaxanthin, which is necessary for
nonphotochemical quenching (NPQ), mechanisms that dissipate excess light
energy harmlessly as heat. Lastly, the vtc2npq4 mutant is also impaired in
nonphotochemical quenching, but has normal xanthophyll content.
All mutants were obviously impaired when grown in HL compared to the wild
type. They had lower electron transport, lower oxygen evolution rates and
lower quantum efficiency of PSII compared with the wild type, implying that
they experienced chronic photo-oxidative stress. The mutants lacking NPQ
in addition to ascorbate were only slightly more affected than vtc2. All three
mutants had higher glutathione levels than the wild type in HL, suggesting a
possible compensation for the lower ascorbate content.
In addition, when transferring vtc2 and vtc2npq1 plants from LL to HL, the
mature rosette leaves bleached partially or fully, respectively. The bleaching
in vtc2npq1 and vtc2 was paralleled by an increase in lipid peroxidation and
a drastic decrease in Fv/Fm, a fluorescence parameter used to estimate
photoinhibition. These results demonstrate the importance of ascorbate for
acclimation to HL and growth in HL. The more drastic phenotype of vtc2npq1
plants after transfer to HL also supports the proposed role of zeaxanthin as
an antioxidant.
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin