Department of Biochemistry, Weizmann Institute of Science, Rehovot, Israel.
Plant Physiol. 1972 Feb;49(2):240-3. doi: 10.1104/pp.49.2.240.
Dunaliella parva, a unicellular halophilic alga, was found to evolve oxygen photosynthetically only in the presence of a high osmolar concentration. Cell free preparations were obtained by placing the cells in a medium of low osmolarity. The fragments obtained showed a high photoreducing and photophosphorylating activity except for their inability to catalyze all ferredoxin dependent photoreactions. Placing the cells in a medium of intermediate osmolarity produced a "chloroplast" preparation which maintained some capacity for O(2) evolution and CO(2) fixation, while possessing the ability to catalyze the photoinduced reduction of ferricyanide. Enzymic and photosynthetic reactions of cell-free preparations from D. parva were inhibited, rather than stimulated, by the salt concentration optimal for growth. These results were interpreted as indicating the existence of a steep NaCl gradient in vivo between the medium and the cell compartments which are not permeable to salt.
小盐藻是一种单细胞嗜盐藻类，只有在高渗透压浓度存在的条件下才会进行氧气光合作用。通过将细胞置于低渗透压培养基中可以获得无细胞制剂。得到的片段显示出高的光还原和光磷酸化活性，只是不能催化所有铁氧还蛋白依赖的光反应。将细胞置于渗透压中等的培养基中会产生一种“叶绿体”制剂，它保持一定的 O(2) 释放和 CO(2) 固定能力，同时具有催化铁氰化物光诱导还原的能力。无细胞制剂的酶促和光合作用反应受到盐浓度的抑制，而不是刺激，这种盐浓度是最适合生长的。这些结果表明，在细胞内外的介质之间存在一个盐不可渗透的陡峭 NaCl 梯度。
