纳米二氧化钛(nTiO2)对三角褐指藻(Phaeodactylum tricornutum)光合系统的影响

Effects of Nano-titanium Dioxide on Photosystem of Phaeodactylum tricornutum

随着人工纳米材料(MNMs)的大规模使用,其环境暴露风险也随之升高。MNMs中纳米二氧化钛(nTiO2)产量最大,应用广泛,其环境与健康风险备受关注。已有大量研究关注短期暴露下nTiO2的毒性效应,但对暴露过程中浮游植物的应激机制仍缺乏认识;以往的研究发现nTiO2干扰浮游植物叶绿体的正常光合作用,但与浮游植物光合作用相关的基因表达在nTiO2胁迫下如何变化尚不清楚。该研究通过分析浮游植物光合系统相关指标如叶绿素a、Fv/Fm、光合作用基因的表达等,试图探究不同浓度nTiO2(0、5、10、20、50、100 mg·L-1)对三角褐指藻(Phaeodactylum tricornutum)的毒性效应及其潜在机制。叶绿素a的测定结果表明nTiO2对三角褐指藻的抑制效应较微弱,暴露于10 mg·L^-1 nTiO248 h后,三角褐指藻叶绿素a含量约为对照组的76.35%;暴露120 h后恢复至对照组的94%。此外,Fv/Fm在暴露48 h前后具有类似的趋势,暴露组在48 h前Fv/Fm显著低于对照(P<0.05),但48 h后并没有明显变化。这些结果表明nTiO2对三角褐指藻的毒性效应随时间逐渐减弱,推测三角褐指藻可能对nTiO2存在一定的抗性。进一步的研究发现,与光合作用相关基因rbcS和LcyB在三角褐指藻暴露48 h后显著下调,但处理120 h后,显著高于对照组。这一变化可能是叶绿素a含量先下降后恢复的分子机制。该研究结果为探讨nTiO2对海洋微藻的光合毒性效应以及海洋微藻在nTiO2暴露下的响应机制提供基础。

Along with the wide application of manufactured nanomaterials(MNMs),their environmental risk is increasing.Among MNMs,nano-titanium dioxide(nTiO2)shows the highest production and broadest application.Thus,its environmental and health risks have drawn great attention.Acute toxicity of nTiO2 has been well reported.However,the mechanisms underlying the stress response to nTiO2 in phytoplankton remain largely unknown.Moreover,although it has been demonstrated that exposure to nTiO2 disturbed the photosynthesis process in chloroplasts,the changes of photosynthesis-related genes in response to nTiO2 exposure have not been reported.In the present study,to investigate the toxic effects of nTiO2 on Phaeodactylum tricornutum and the underlying mechanisms,indices in relation to photosynthesis,including chlorophyll a content,Fv/Fm and transcription of key genes were measured in treatments with different concentration of nTiO2(0,5,10,20,50,and 100 mg·L^-1).The results showed that exposure to nTiO2 slightly inhibited the content of chlorophyll a in P.tricornutum.Compared with the control,content of chlorophyll a significantly decreased in the treatment with 10 mg·L^-1 nTiO2 after 48 h,corresponding to 76.35%of the value in the control.However,after 120 h,the chlorophyll a content in 10 mg·L^-1 treatment resumed to 94%of the value in the content.The changes of Fv/Fm showed the similar tendency to chlorophyll a content,which decreased significantly after exposure for 48 h and then resumed to the level in the control.These results indicated that toxicity of nTiO2 to P.tricornutum decreased along with exposure time and suggested that P.tricornutum might be able to resist nTiO2 contamination.Furthermore,real-time quantitative PCR results revealed that the mRNA levels of two photosynthesis-related genes(rbcS and LycB)were significantly lower in treatment with 10 mg·L^-1 nTiO2 after 48 h,but were significantly higher after 120 h,compared with those in the corresponding control.Transcriptional changes of these two genes might be the molecular mechanisms underlying the variation of chlorophyll a content in response to n TiO2 treatments.Overall,these data provided a theoretical basis for further understanding the toxicity of nTiO2 to photosynthesis and the mechanisms underlying responses to nTiO2 in marine algae.