title: Chlorophyll b degradation by chlorophyll b reductase under high-light conditions.
abstract: The light-harvesting chlorophyll a/b binding protein complex of photosystem II (LHCII) is the main antenna complex of photosystem II (PSII). Plants change their LHCII content depending on the light environment. Under high-light conditions, the content of LHCII should decrease because over-excitation damages the photosystem. Chlorophyll b is indispensable for accumulating LHCII, and chlorophyll b degradation induces LHCII degradation. Chlorophyll b degradation is initiated by chlorophyll b reductase (CBR). In land plants, NON-YELLOW COLORING 1 (NYC1) and NYC1-Like (NOL) are isozymes of CBR. We analyzed these mutants to determine their functions under high-light conditions. During high-light treatment, the chlorophyll a/b ratio was stable in the wild-type (WT) and nol plants, and the LHCII content decreased in WT plants. The chlorophyll a/b ratio decreased in the nyc1 and nyc1/nol plants, and a substantial degree of LHCII was retained in nyc1/nol plants after the high-light treatment. These results demonstrate that NYC1 degrades the chlorophyll b on LHCII under high-light conditions, thus decreasing the LHCII content. After the high-light treatment, the maximum quantum efficiency of the PSII photochemistry was lower in nyc1 and nyc1/nol plants than in WT and nol plants. A larger light-harvesting system would damage PSII in nyc1 and nyc1/nol plants. The fluorescence spectroscopy of the leaves indicated that photosystem I was also damaged by the excess LHCII in nyc1/nol plants. These observations suggest that chlorophyll b degradation by NYC1 is the initial reaction for the optimization of the light-harvesting capacity under high-light conditions.
authors.affiliation: Institute of Low Temperature Science, Hokkaido University, N19 W8, Kita-ku, Sapporo, 060-0819, Japan.
authors.forename: Rei
authors.initials: R
authors.lastname: Sato
authors.affiliation: Institute of Low Temperature Science, Hokkaido University, N19 W8, Kita-ku, Sapporo, 060-0819, Japan. ito98@lowtem.hokudai.ac.jp.|CREST, Japan Science and Technology Agency, N19 W8, Kita-ku, Sapporo, 060-0819, Japan. ito98@lowtem.hokudai.ac.jp.
authors.forename: Hisashi
authors.initials: H
authors.lastname: Ito
authors.affiliation: Institute of Low Temperature Science, Hokkaido University, N19 W8, Kita-ku, Sapporo, 060-0819, Japan.|CREST, Japan Science and Technology Agency, N19 W8, Kita-ku, Sapporo, 060-0819, Japan.
authors.forename: Ayumi
authors.initials: A
authors.lastname: Tanaka
mesh_terms: D000429:Alcohol Oxidoreductases / Q000378:metabolism*; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002734:Chlorophyll / Q000737:chemistry / Q000378:metabolism*; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D045331:Photosystem I Protein Complex / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000378:metabolism; D018515:Plant Leaves / Q000378:metabolism / Q000528:radiation effects
chemical_list: D029681:Arabidopsis Proteins; D045342:Light-Harvesting Protein Complexes; D008565:Membrane Proteins; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D002734:Chlorophyll; C037184:chlorophyll b; C000604337:NON-YELLOW COLORING 1 protein, Arabidopsis; D010088:Oxidoreductases; D000429:Alcohol Oxidoreductases; C102575:chlorophyll b reductase
keywords: Arabidopsis; Chlorophyll b reductase; High-light conditions; Light-harvesting complex