Responses of photosynthetic apparatus of the halotolerant microalga <Emphasis Type="Italic">Dunalliella maritima</Emphasis> to hyperosmotic salt shock |
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Authors: | I G Zakhozhii D A Matalin L G Popova Yu V Balnokin |
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Institution: | 1.Institute of Biology, Komi Research Center, Ural Branch,Russian Academy of Sciences,Syktyvkar,Russia;2.Timiryazev Institute of Plant Physiology,Russian Academy of Sciences,Moscow,Russia |
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Abstract: | Chlorophyll fluorescence induction curves were used as a means to assess the functional condition of the photosynthetic apparatus
in cells of the halotolerant green microalga Dunaliella maritima (Massjuk) (division Chlorophyta) exposed to hyperosmotic salt shock of various intensities. The shock was caused by the transfer
of algal cells grown in the medium with 0.5 M NaCl to the media with elevated NaCl concentrations (1.0, 1.5, and 2.0 M). Parameters
of chlorophyll fluorescence (F
0, F
m, F
0′, F
t′) were measured by means of a specialized pulse-amplitude-modulation fluorometer PAM 2100. In addition, the rate of photosynthetic
oxygen evolution as well as the intracellular Na+ and glycerol content (the main osmolyte in this microalga) were determined. The hyperosmotic salt shock was found to elevate
the intracellular Na+ content and reduce the functional activity of PSII in D. maritima. The suppression of PSII activity was evident from the decrease in the maximal quantum yield of photochemical energy conversion
in PSII, the decreased rate of linear electron transport, the increased reduction of the primary acceptor QA, and the suppression of photosynthetic O2 evolution. The functional activity of PSII recovered gradually along with restoration of osmotic and ionic balance in algal
cells. It is proposed that PSI ensures energy supply during cell responses of D. maritima to hyperosmotic salt shock. |
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Keywords: | |
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