RESUMO
STN8 kinase is involved in photosystem II (PSII) core protein phosphorylation (PCPP). To examine the role of PCPP in PSII repair during high light (HL) illumination, we characterized a T-DNA insertional knockout mutant of the rice (Oryza sativa) STN8 gene. In this osstn8 mutant, PCPP was significantly suppressed, and the grana were thin and elongated. Upon HL illumination, PSII was strongly inactivated in the mutants, but the D1 protein was degraded more slowly than in wild-type, and mobilization of the PSII supercomplexes from the grana to the stromal lamellae for repair was also suppressed. In addition, higher accumulation of reactive oxygen species and preferential oxidation of PSII reaction center core proteins in thylakoid membranes were observed in the mutants during HL illumination. Taken together, our current data show that the absence of STN8 is sufficient to abolish PCPP in osstn8 mutants and to produce all of the phenotypes observed in the double mutant of Arabidopsis, indicating the essential role of STN8-mediated PCPP in PSII repair.
Assuntos
Oryza/enzimologia , Complexo de Proteína do Fotossistema II/química , Complexo de Proteína do Fotossistema II/metabolismo , Proteínas de Plantas/metabolismo , Proteínas Quinases/deficiência , Proteínas Quinases/genética , Proteínas Serina-Treonina Quinases/deficiência , Proteínas Serina-Treonina Quinases/genética , Técnicas de Silenciamento de Genes , Luz , Mutagênese Insercional , Oryza/genética , Oryza/ultraestrutura , Fenótipo , Fosforilação/genética , Complexo de Proteína do Fotossistema I/metabolismo , Complexo de Proteína do Fotossistema II/antagonistas & inibidores , Folhas de Planta/metabolismo , Proteínas Serina-Treonina Quinases/metabolismo , Tilacoides/enzimologia , Tilacoides/metabolismo , Tilacoides/ultraestruturaRESUMO
The effects of photosystem II antenna size on reaction center-type energy-dependent quenching (qE) were examined in rice plants grown under two different light intensities using both wild type and qE-less (OsPsbS knockout) mutant plants. Reaction center-type qE was detected by measuring non-photochemical quenching at 50 micromol photons m(-2) s(-1) white light intensity. We observed that in low light-grown rice plants, reaction center-type qE was higher than in high light-grown plants, and the amount of reaction center-type qE did not depend on zeaxanthin accumulation. This was confirmed in Arabidopsis npq1-2 mutant plants that lack zeaxanthin due to a mutation in the violaxanthin de-epoxidase enzyme. Although the electron transport rate measured at a light intensity of 50 micromol photons m(-2) s(-1) was the same in high light- and low light-grown wild type and mutant plants lacking PsbS protein, the generation of energy-dependent quenching was completely impaired only in mutant plants. Analyses of the pigment content, Lhcb proteins and D1 protein of PSII showed that the antenna size was larger in low light-grown plants, and this correlated with the amount of reaction center-type qE. Our results mark the first time that the reaction center-type qE has been shown to depend on photosystem II antenna size and, although it depends on the existence of PsbS protein, the extent of reaction center-type qE does not correlate with the transcript levels of PsbS protein. The presence of reaction center-type energy-dependent quenching, in addition to antenna-type quenching, in higher plants for dissipation of excess light energy demonstrates the complexity and flexibility of the photosynthetic apparatus of higher plants to respond to different environmental conditions.