title: Acceleration of cyclic electron flow in rice plants (Oryza sativa L.) deficient in the PsbS protein of Photosystem II.
abstract: When compared with Photosystem I (PSI) in wild-type (WT) rice plants, PSI in PsbS-knockout (KO) plants that lack the energy-dependent component of nonphotochemical quenching (NPQ) was less sensitive to photoinhibition. Therefore, we investigated the relationship between NPQ and cyclic electron flow (CEF) around PSI as a photoprotective mechanism. Activities of two CEF routes (PGR5-dependent or NDH-dependent) were compared between those genotypes by using both dark-adapted plants and pre-illuminated plants, i.e., those in which the Calvin-Benson cycle is de-activated and activated, respectively. In dark-adapted leaves activity of the PGR5-dependent route was determined as the rate of P700 photooxidation. Activity was higher in the mutants than in the WT. However, no difference was noted when plants of either genotype were pre-illuminated. When the electron transport pathway was switched to the cyclic mode by infiltrating leaf segments with 150 mM sorbitol, 40 μM DCMU, and 2 mM hydroxylamine, the rate of P700 oxidation was faster in the mutant. That difference disappeared when leaves were infiltrated with antimycin A to inhibit the PGR5-dependent route. Chlorophyll fluorescence (Fo) was also evaluated. To achieve an Fo level comparable to that of the WT, activation of the NDH-dependent route in the mutant required pre-illumination at a certain dose. Therefore, we propose that, as an alternate pathway for the photoprotection of photosystems in the absence of energy-dependent quenching, this PGR5-dependent route is more highly activated in the PsbS-KO mutants than in the WT. Moreover, that stronger activity is probably responsible for slower activation of the NDH-dependent route in the mutant.
authors.affiliation: Department of Integrated Biological Science, Department of Molecular Biology, Pusan National University, Jangjeon-dong, Geumjeong-gu, Busan 609-735, Republic of Korea; Department of Biology, North-Eastern Federal University, 58 Belinsky Str., Yakutsk 677-027 Republic of Sakha (Yakutia), Russian Federation; Institute of Botany, Azerbaijan National Academy of Sciences, Patamdar Shosse 40, Baku, AZ 1073, Azerbaijan. Electronic address: iszulfugarov@pusan.ac.kr.
authors.forename: Ismayil S
authors.initials: IS
authors.lastname: Zulfugarov
authors.affiliation: Department of Integrated Biological Science, Department of Molecular Biology, Pusan National University, Jangjeon-dong, Geumjeong-gu, Busan 609-735, Republic of Korea; Department of Biology, Mongolian State University of Agriculture, Zaisan, 17024 Ulaanbaatar, Mongolia. Electronic address: zaya_erdem@yahoo.com.
authors.forename: Altanzaya
authors.initials: A
authors.lastname: Tovuu
authors.affiliation: Department of Integrated Biological Science, Department of Molecular Biology, Pusan National University, Jangjeon-dong, Geumjeong-gu, Busan 609-735, Republic of Korea. Electronic address: chlee@pusan.ac.kr.
authors.forename: Choon-Hwan
authors.initials: CH
authors.lastname: Lee
mesh_terms: D004583:Electrons; D012275:Oryza / Q000235:genetics / Q000378:metabolism*; D010788:Photosynthesis / Q000235:genetics / Q000502:physiology; D045331:Photosystem I Protein Complex / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism
chemical_list: D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D010940:Plant Proteins
keywords: Cyclic electron flow; Nonphotochemical quenching; Photosystem I; Photosystem II; PsbS; Rice