Toxic Effect Of Nano-TiO₂ On The Marine Macroalgae Gracilaria Lemaneiformis

Gracilaria lemaneiformis is an important economic seaweeds,which not only can be used as repair materials to improve the ecological environment,but also has a high medicinal value.It plays an irreplaceable role in biological engineering,food and medicine.In recent years,with the continuous development of nanotechnology,nanoparticles have been widely applied in various fields,and its annual production is increasing.At the same time,nanoparticles discharged into the environment are also increasing year by year.Nanoparticles enter the aquatic environment extremely easily in the process of production and application and they will causing stress to the growth of aquatic organisms.Nano-TiO₂ has an adverse influence on aquatic organisms,which has attracted extensive attention from researchers.However,the current research on nanoparticles mainly focused on microalgae,while the toxicological effects of nanoparticles on marine macroalgae are rarely reported.In view of the important economic value of macroalgae and the widespread existence of nano-TiO₂,the study on the toxicity of nano-TiO₂ on macroalgae has also become a trend.In this paper,the effects of different concentrations of nano-TiO₂ on the physiological and biochemical characteristics,antioxidant defense system,antioxidant activity and antitumor activity of marine macroalgae G.lemaneiformis were studied.The main contents of this paper are as follows:Nano-TiO₂ has a significant inhibitory effect on the growth of macroalgae G.lemaneiformis.With the increase of the concentration of nano-TiO₂,the growth rate of G.lemaneiformis decreased gradually.It showed negative growth when G.lemaneiformis was exposed to 20 mg/L and 40 mg/L nano-TiO₂.The color of the algae became lighter,and even localized necrosis appeared.The photosynthetic pigments in the algae,such as chlorophyll a?Chla?,carotenoid?Car?and phycobiliprotein,were all significantly reduced.The contents of solution protein enhanced slightly after 3-day exposure but diminished thereafter gradually at the high concentrations in prolonged exposure.In addition,the activity of UV-absorbing compounds?UVACs?and nitrate reductase?NR?reduced linearly with the increase of nano-TiO₂ exposure concentration.Under the stress of nano-TiO₂,the antioxidant defense system of G.lemaneiformis was disturbed significantly.Compared with the control,the superoxide anion(O₂^·-)accumulated abundantly in the algae after being exposed to nano-TiO₂.The contents of O₂^·-reaches a maximum at the 15th day of culture in a concentration of 20 mg/L of nano-TiO₂ but diminished thereafter gradually at the high concentrations and prolonged exposure.Meanwhile,under the stress of nano-TiO₂,the level of malondialdehyde?MDA?in G.lemaneiformis increased significantly,whose maximum showed an increase of 3.26-fold.The activities of superoxide dismutase?SOD?and catalase?CAT?were also increased by 1.10-2.24 fold,and then decreased under long term and high concentration nano-TiO₂ exposure.Aqueous extracts of G.lemaneiformis?AEGL?has antioxidant capacity which can scavenge diphenyl picryl hydrazinyl radical?DPPH·?and hydroxyl radical?·OH?.However,as nano-TiO₂exposure concentration increased,the ability of scavenging free radicals of AEGL decreased slightly.AEGL showed anticancer activity against the proliferation of HepG-2 cells and the 48h-cell inhibition exceeds 35.47%.However,nano-TiO₂ showed inhibitory effect on the anticancer activity of AEGL.When G.lemaneiformiswas exposed to nano-TiO₂,the effect of the aqueous extract of G.lemaneiformis on the cell inhibition,reactive oxygen species production,apoptosis,cycle arrest of HepG-2 cells were significantly lessened,which were linearly associated with nano-TiO₂ exposure concentration.Those results further confirmed that nano-TiO₂ can inhibit the anticancer activity of G.lemaneiformis.The results in this work imply that macroalgae can be an effective biomarker of nano-TiO₂ contaminant,and can be useful indicator to evaluate ecological effects of increasing pollutants in marine ecosystem.