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'Photosystem II' in keywords Facet   Publication Year 1998  [X]
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1Author    Krishna Bala, Swati Kolli, Prasanna Tiwari, MohantyRequires cookie*
 Title    Spirulina platensis  
 Abstract    When Spirulina platensis filaments were exposed to 0.75 mW.m_2.s_1 of ultraviolet-B radi­ ation (the ultraviolet-B radiation under clear sky condition is —1.0 mW.m_2.s_1), an inhibi­ tion in photosystem II activity was observed, the inhibition being 90% after 90 min exposure. Upon exposure to ultraviolet-B, the room temperature emission characteristics of Spirulina cells were altered when excited with light primarily absorbed by chlorophyll a or phycobili-somes. When the cells were exposed for 3 h the emission at 685 nm (F685), when excited at 440 nm (primarily chlorophyll a absorption), was enhanced compared to 715 nm (F 715) band of photosystem I suggesting a decrease in energy transfer from photosystem II to photosys­ tem I. Similarly, when the cells were excited at 580 nm (primarily the phycobilisomes), the ratio of emission intensity at 685 nm (F 685) to that of 655 nm (F655) was decreased in the exposed cells. This change in emission characteristics seems to be linked with the uncoupling of the energy transfer from allophycocyanin to chlorophyll a of photosystem II. A small shift in emission peak positions was also indicated when excited either at 440 nm or 580 nm. Analysis of the fast induction of chlorophyll a transients in the presence and absence of 10 jam 3-(3,4-dichlorophenyl)-l,l-dimethylurea (D CM U) indicated that ultraviolet-B expo­ sure initially affects Q A, the primary stable acceptor of photosystem II, and then the plas-toquinone (PQ) pool. Our results on the loss in photosystem Il-catalyzed Hill activity with p-benzoquinone or dichlorobenzoquinone as electron acceptors also supports the contention that ultraviolet-B, even at low dose, initially alters the Q A of photosystem II and subsequently PQ pool. The analysis of functional pool size of Spirulina suggests a substantial decrease in the functional pool size after 2 h UV-B exposure. These results indicate that in Spirulina low intensity of ultraviolet-B initially damages the reaction centre of photosystem II. 
  Reference    Z. Naturforsch. 53c, 369—3 (1998); received December 15 1997 
  Published    1998 
  Keywords    Fluorescence Transients, Photosystem II, Quinones, Spirulina, Ultraviolet-B 
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 TEI-XML for    default:Reihe_C/53/ZNC-1998-53c-0369.pdf 
 Identifier    ZNC-1998-53c-0369 
 Volume    53 
2Author    E.K N Én, N. Én, É. Th, M. F. RagataRequires cookie*
 Title    Effect of MgCl2 and Phosphatidylglycerol on CaCl2-Mediated Recovery of Oxygen Evolution in a Photosystem II Complex Depleted of the 17 and 24 kDa Extrinsic Proteins  
 Abstract    Phosphatidylglycerol (PG) is an anionic lipid of the thylakoid m em brane of higher plant chloroplasts. PG was shown previously to stimulate the evolution of oxygen in intact pho­ tosystem II (PSII) membranes [Fragata, M., Strzalka, K. and Nenonene, E. K. (1991) J. Pho-tochem. Photobiol. B: Biol 11, 329-342], In this work, a study was undertaken of the effect of MgCl2 and PG on the CaCl2-mediated recovery of oxygen evolution in a PSII complex depleted of the extrinsic proteins (EP) of molecular masses 17 kDa (EP17) and 24 kDa (EP24), hereunder designated d 1724PSII. This molecular system is structurally close to the PSII core complex of cyanobacteria and is therefore useful in the comparative analysis of PSII-PG relationships in cyanobacteria and the higher plants. This work reveals a new aspect of the thylakoid lipids role in the PSII function, namely the PG effect on intact PSII is observed as well in d 1724PSII. The results show that phosphatidylglycerol has the ability to compensate for the loss of EP17 and EP24 in the PSII complex. That is, PG restores the oxygen evolution in d 1724PSII incubated in the presence of MgCl2 and/or CaCl2 to the levels observed in native PSII. M oreover, the site of H 20 degradation in d 17 24PSII, including most probably the pool of calcium and chloride ions, would seem to be protected by phosphatidyl­ glycerol. This suggests that one of the docking sites of PG in the PSII complex is near EP24, inasmuch as this extrinsic protein participates in the regulation of the affinity of the calcium and chloride ions to the water oxidation site. Furtherm ore, taking into account that in d j7 24PSII the PSII core complex is directly exposed to PG, then the phospholipid effect reported here indicates that phosphatidylglycerol might be a functional effector and mem­ brane anchor of the D1 protein in the PSII core complex as was shown recently in the cyanobacterium Oscillatoria chalybea [Kruse, O. and Schmid, G. H. (1995) Z. Naturforsch. 50c, 380-390], 
  Reference    Z. Naturforsch. 53c, 39—4 (1998); received September 1/October 24 1997 
  Published    1998 
  Keywords    Extrinsic Proteins, Oxygen Evolution Recovery, Phosphatidylglycerol, Photosystem II, Salt-Mediated Effects 
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 TEI-XML for    default:Reihe_C/53/ZNC-1998-53c-0039.pdf 
 Identifier    ZNC-1998-53c-0039 
 Volume    53