不同混合速率下阳光UV辐射对假微型海链藻PSⅡ功能的影响

Effect of solar UV radiation on photosystem Ⅱ function in Thalassiosira pseudonana under different mixing rates

以浮游硅藻假微型海链藻(Thalassiosira pseudonana(Hustedt)Hasle et Heimdal CCMP 1335)为材料,研究不同混合速率下,随辐射水平增加,UV辐射和可见光PAR对其光系统Ⅱ功能的影响。结果显示,混合速率慢时,随着PAR及UV辐射水平的增加,假微型海链藻PSⅡ的光化学效率(F_v/F_m)持续受到抑制,光合效率α和相对最大电子传递速率rETR_(max)下降。尤其是UV辐射存在时,PSⅡ反应中心D1蛋白含量下降,有活性的PSⅡ反应中心数量减少,单位反应中心吸收(ABS/RC)和耗散(DI_0/RC)的能量增加。混合速率快时,PAR辐射下PSⅡ光化学活性相比混合速率慢时升高,D1蛋白含量增加;而UV辐射存在下各光合参数表现出与混合速率慢时类似的变化趋势。研究结果表明水体混合速率的加快可缓解高水平可见光导致的光抑制,而对UV辐射的抑制效应并未产生显著改变。

The marine diatom Thalassiosira pseudonana was selected as experimental material to investigate the impact of photosynthetically active radiation（ PAR） and PAR plus ultraviolet radiation（ UVR） on the function of photosystem Ⅱ（ PSⅡ） with increasing irradiance levels at two different mixing rates. Results showed that,at slow mixing speed,the maximum quantum yield of PS Ⅱ（ Fv/Fm）,photosynthetic efficiency parameter（ α）,and maximum relative electron transport rate（ rETR（max）） were progressively inhibited with increasing irradiance levels in both PAR and PAR ＋ UVR treatments. The decreased PS Ⅱ D1 protein content,which indicates less active PSⅡ reaction centers,led to the increase in energy fluxes for absorption（ ABS/RC） and dissipation（ DI0/RC） per reaction center. In contrast,at fast mixing speed,Fv/Fm increased under PAR compared with that at slow mixing and D1 protein content was also enhanced. However,similar changes were shown in various photosynthetic parameters under UVR. These results indicate that fast mixing could alleviate the photoinhibition caused by high PAR but could not modify the effects of UVR.