The effects of enriched CO₂ and enhanced UV-B radiation on ultra-structure of Dunaliella salina, singly and in combination

The effects of ambient CO₂/ambient UV-B,enriched CO₂/ambient UV-B,ambient CO₂/enhanced UV-B,and enriched CO₂/enhanced UV-B on the ultrastructure of Dunaliella salina were investigated.(1) The ultrastructure of D.salina cell in the control experiment showed that the arrangement of thylakoid lamellae was regular,and there were many large starch grains among the thylakoid lamellae.A prominent well-developed pyrenoid was found in the middle of the chloroplast.Nucleus envelope and nucleolus were clearly observed.The Golgi apparatus accompanied by numerous vesicles with a compact arrangement of cisternae and the peripheral tips of the cisternae were swollen to a size comparable to that of some of the associated vesicles.(2) The ultrastructure of D.salina cell in enriched CO₂ showed that the arrangement ofthylakoid was regular and the lamellae were vivid.Developed pyrenoids were found in the low-CO₂-grown cells,but not in the high-CO₂-grown cells.The mitochondria cristae were vivid.The arrangement of Golgi apparatus was compact.(3) The ultrastructure of D.salina cell in enhanced UV-B showed that the thylakoid was dissolved and the cells had a less developed pyrenoid or no detectable pyrenoid.Part of the nucleus envelope was dissolved.The number ofmitochondria was increased and some mitochondria cristae were disintegrated.The starch grains were broken apart into many small starch grains.The Golgi apparatus with a loose arrangement of cisternae and the peripheral tips of the Golgi cisternae were not especially swollen,with several large associated vesicles.(4) The ultrastructure of D.salina cell in the enriched CO₂/enhanced UV-B showed that part of the thylakoid and nucleus envelopes of some cells were dissolved.The pyrenoid was larger than that of the enhanced UV-B.There were many mitochondria between stroma and chloroplast membrane,but mitochondria cristae were partly dissolved.Many small starch grains were accumulated in cells.The starch sheath was broken into several discontinuous starch grains with different sizes.The arrangement of Golgi apparatus was loose.Above all,although the enriched CO₂ can alleviate the damage induced by the UV-B radiation,the effects of experimental UV-B radiation were larger than the effects of actual UV-B radiation,the damage induced by the UV-B radiation was so severe,therefore,CO₂ enrichment could not restore the ultrastructure to the control level.