UV radiation-stimulated activity of extraceUular carbonic anhydrase in the marine diatom Skeletonema costatum

【作者】 吴红艳； 高坤山；

【机构】 汕头大学海洋生物研究所；

【摘要】 <正>Previous studies showed that reduced levels of solar UV radiation（280-400 nm） could enhance photosynthetic carbon fixation of marine phytoplankton,but the mechanisms are not understood.CO₂ supply for photosynthesis is facilitated by extracellular（periplasmic）carbonic anhydrase（CAe）in marine phytoplankton species with it.The CAe activity may be influenced by UVR which drastically changes in marine environments.We have now shown that the CAe activity of Skeletonema costatum was stimulated when treated with UVA（320-400 nm）or UVA+UVB （280-320 nm）in addition to visible light.The presence of UVA and UVB, respectively,enhanced the activity by 28% and 24% at the low irradiance(PAR 175, UVA 40,UVB 1.3 W m^-2and by 21% and 19% at the high h’radiance(PAR 356, UVA 82,UVB 2.6 W m^-2)level for I h.Higher UV dose for 2 h exposure at the high irradiance level reversed the stimulation to inhibition of the CAe activity.The CAe protein increased in accord with the increased activity caused by UVR,which contributed up to 13% of the photosynthetic carbon fixation due to consequently enhanced supply of CO₂.As a result,there was less inhibition of photosynthetic carbon fixation compared with the apparent quantum yield.Both UVA and UVB enhanced the redox activity at the plasma membrane,which coincided with the stimulated CAe activity and synthesis.This strongly suggests that UVR can enhance the CAe activities,which then facilitate CO₂ supply by converting bicarbonate to CO₂ to sustain photosynthesis at reduced levels of sunlight.更多还原

【Abstract】 Previous studies showed that reduced levels of solar UV radiation（280-400 nm） could enhance photosynthetic carbon fixation of marine phytoplankton,but the mechanisms are not understood.CO₂ supply for photosynthesis is facilitated by extracellular（periplasmic）carbonic anhydrase（CAe）in marine phytoplankton species with it.The CAe activity may be influenced by UVR which drastically changes in marine environments.We have now shown that the CAe activity of Skeletonema costatum was stimulated when treated with UVA（320-400 nm）or UVA+UVB （280-320 nm）in addition to visible light.The presence of UVA and UVB, respectively,enhanced the activity by 28% and 24% at the low irradiance(PAR 175, UVA 40,UVB 1.3 W m^-2and by 21% and 19% at the high h’radiance(PAR 356, UVA 82,UVB 2.6 W m^-2)level for I h.Higher UV dose for 2 h exposure at the high irradiance level reversed the stimulation to inhibition of the CAe activity.The CAe protein increased in accord with the increased activity caused by UVR,which contributed up to 13% of the photosynthetic carbon fixation due to consequently enhanced supply of CO₂.As a result,there was less inhibition of photosynthetic carbon fixation compared with the apparent quantum yield.Both UVA and UVB enhanced the redox activity at the plasma membrane,which coincided with the stimulated CAe activity and synthesis.This strongly suggests that UVR can enhance the CAe activities,which then facilitate CO₂ supply by converting bicarbonate to CO₂ to sustain photosynthesis at reduced levels of sunlight.更多还原