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'Fluorescence Transients' 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