title: Cold stress effects on PSI photochemistry in Zea mays: differential increase of FQR-dependent cyclic electron flow and functional implications.
abstract: Cold-induced inhibition of CO(2) assimilation in maize (Zea mays L.) is associated with a persistent depression of the photochemical efficiency of PSII. However, very limited information is available on PSI photochemistry and PSI-dependent electron flow in cold-stressed maize. The extent of the absorbance change (ΔA(820)) used for in vivo quantitative estimation of photooxidizable P700(+) indicated a 32% lower steady-state oxidation level of the PSI reaction center P700 (P700(+)) in cold-stressed compared with control maize leaves. This was accompanied by a 2-fold faster re-reduction rate of P700(+) in the dark, indicating a higher capacity for cyclic electron flow (CEF) around PSI in cold-stressed maize leaves. Furthermore, the increased PSI-dependent CEF(s) was associated with a much higher stromal electron pool size and 56% lower capacity for state transitions compared with control plants. To examine NADP(H) dehydrogenase (NDH)- and ferredoxin:plastoquinone oxidoreductase (FQR)-dependent CEF in vivo, the post-illumination transient increase of F(o)' was measured in the presence of electron transport inhibitors. The results indicate that under optimal growth conditions the relatively low CEF in the maize mesophyll cells is mostly due to the NDH-dependent pathway. However, the increased CEF in cold-stressed plants appears to originate from the up-regulated FQR pathway. The physiological role of PSI down-regulation, the increased capacity for CEF and the shift of preferred CEF mode in modulating the photosynthetic electron fluxes and distribution of excitation light energy in maize plants under cold stress conditions are discussed.
authors.affiliation: Agriculture and Agri-Food Canada, Eastern Cereal and Oilseed Research Centre (ECORC), Central Experimental Farm, Ottawa, Ontario, Canada. leonid.savitch@agr.gc.ca
authors.forename: Leonid V
authors.initials: LV
authors.lastname: Savitch
authors.forename: Alexander G
authors.initials: AG
authors.lastname: Ivanov
authors.forename: Loreta
authors.initials: L
authors.lastname: Gudynaite-Savitch
authors.forename: Norman P A
authors.initials: NP
authors.lastname: Huner
authors.forename: John
authors.initials: J
authors.lastname: Simmonds
mesh_terms: D000968:Antimycin A / Q000494:pharmacology; D002245:Carbon Dioxide / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D003080:Cold Temperature; D003624:Darkness; D004579:Electron Transport; D005287:Ferredoxin-NADP Reductase / Q000187:drug effects / Q000378:metabolism; D005453:Fluorescence; D008627:Mercuric Chloride / Q000494:pharmacology; D058503:Mesophyll Cells / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D009252:NADPH Dehydrogenase / Q000187:drug effects / Q000378:metabolism*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D010788:Photosynthesis; D045331:Photosystem I Protein Complex / Q000187:drug effects / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000187:drug effects / Q000378:metabolism*; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D010940:Plant Proteins / Q000378:metabolism; D013312:Stress, Physiological; D020524:Thylakoids / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D003313:Zea mays / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*
chemical_list: D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D002734:Chlorophyll; D002245:Carbon Dioxide; C001785:chlorophyll P 700; D008627:Mercuric Chloride; D000968:Antimycin A; D005287:Ferredoxin-NADP Reductase; D009252:NADPH Dehydrogenase; D010100:Oxygen