PARENT SESSION
Posters P6B Photosynthetic acclimation: Mechanisms and gene expression. Abstracts (531-578)

Characterization of Arabidopsis thaliana mutants with altered nonphotochemical quenching of chlorophyll fluorescence. Mieko Higuchi^*,1, Kintake Sonoike¹, ¹ Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwanoha 5-1-5, Kashiwa-shi, Chiba, Japan

ABSTRACT- Regulation of photosynthetic activity in response to high light is significant mechanism to avoid photoinhibition in plants. In order to investigate molecular mechanisms of this regulation, we employed imaging of chlorophyll fluorescence to screen Arabidopsis mutants with defects in high light response. To date, we screened 16,000 seedlings and isolated four candidates (36-2-20, 38-14-15, 22-18-21, 37-19-7) showing different chlorophyll fluorescence kinetics from that of WT. For further characterization of these mutants, chlorophyll fluorescence was investigated by pulse-amplified modulated (PAM) chlorophyll fluorometry. A 36-2-20 mutant showed lowered induction of nonphotochemical quenching (NPQ) and photochemical quenching (qP) although steady-state NPQ and qP was indistinguishable from WT. Sequencing of the genomic DNA flanking the T-DNA elements showed that a gene encoding a P-type ATPase was disrupted in 36-2-20. A 38-14-15 mutant showed rapid induction of high NPQ during excessive illumination. A rapid increase of NPQ was not detected after the treatment of DTT, an inhibitior of violaxanthin de-epoxidase, suggesting that xanthophyll cycle activity was enhanced in 38-14-15. Furthermore, electron transport rate (ETR) was decreased at light intensity more than 1,000 E. The NPQ of 22-18-21 was about 65% of WT under high light condition. The 22-18-21 mutant could not maintain high NPQ under high light although early stage of NPQ development was about the same as WT. A 37-19-7 mutant showed slightly reduced NPQ when exposed to high light. P700 oxidation ratio (A/Amax) in 37-19-7 was lowered with increasing light intensity, suggesting that electron transfer from PSI was limited under high light condition. The low level of NPQ in 37-19-7 might be caused by insufficient generation of pH due to limited electron transfer. We are now going to determine the position of the insertion of T-DNA elements in these mutants.

KEY WORDS: NPQ, chlorophyll fluorescence, high light, Arabidopsis