Abstract
Summary Photosynthetic and respiratory intensity decrease in Microcystis and Synechocystis under the effects of a hyperosmotic shock. Such shocks affect primarily photosynthesis in Microcystis and respiration in Synechocystis. No adaptation to salt stress could be observed under dark conditions. Both algae with 0.12% NaCl in the medium (control) and NaCl-stressed algae reduced their respiration intensity substantially within 24 h. Photosynthetic intensity remained constant up to 48 h. The two algae species adapt differently to light conditions: In Microcystis a pronounced “salt respirationˮ can be observed, whereas photosynthesis is reduced in respect to dry weight or remains unaffected in respect to cell number. In Synechocystis typical “salt respirationˮ does not occur and photosynthesis is reduced in respect to dry weight or is increased if cell number is taken as the reference. Hypoosmotic NaCl shocks raise the level of photosynthetic intensity in Microcystis but have hardly any effect on the intensity of respiration. In Synechocystis, the intensity of photosynthesis is scarcely affected and the intensity of respiration is promoted only on dry weight basis. In case of Microcystis, the ratio photosynthesis: respiration indicates that the photosynthesis system I may be promoted by NaCl stressing. In Synechocystis, the protein metabolism is inhibited by NaCl stressing, possibly associated with a switch in the 14C-fixation path from the Calvin to the Hatch-Slack cycle.
Published Version
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