The Response Of Photosynthetic Process Of Platymonas Helgolandica To The Acute Stress Of Copper

Copper is a kind of essential nutrients for the growth of marine microalga,however, exposure to higher concentrations of copper may inhibit the growth. Thestability and sustainability of coastal waters of China are under threat of heavy copperpollution. Copper is toxic, hard to be biodegradable, and accumulating along the foodchain. Therefore, the impacts of copper on the marine environment are drawing bothinternational and local researchers’ wide attentions. Reports show that copper hasacute toxicity effects on marine organisms physiologically and biochemically.However, effects of copper on photosynthesis of marine microalgae have not beenfully reported yet. Marine microalgae are primary producers in marine ecosystem.Photosynthesis is the most important physiological process, driving energy flow andmaterial cycling in marine ecosystem. So photosynthesis of marine microalgae is thebest indicator to marine pollution.This study first applies chlorophyll fluorescence, flow cytometry （FCM）,traditional cell counting and transmission electronic microscope（TEM）to estimateacute toxic effects of Cu²⁺on Platymonas helgolandica, a common bait-algae inQingdao. Then absorption/fluorescence spectra analysis and PAM are applied to studythe response of photosynthesis of marine microalgae to copper stress. The mainresults are listed as follows:1. Acute toxicity effects of copper on P. helgolandica.（1）Copper stresssignificantly affects the growth of P. helgolandica. Within the stress scope, low Cu²⁺concentrations increase the microalgae’s growth, known as Hormesis, whereas thehigher treatments inhibit it. The estimated48h EC50and96h EC50are3.884mg.L-1and3.957mg.L-1respectively, indicating that P. helgolandica’s resistance to copper stress increases as time goes by.（2）Based on the microscopic and TEM observationresults, copper stress influences P. helgolandica’s activity level, cell shape and cellsize. Cell wall becomes thicker, cell membrane breaks and is separated away from thecell wall as copper concentration increases, showing that the biomembrane system isparticularly sensitive to Cu²⁺stress.（3）There is always a positive correlationrelationship between each pair of cell density, chlorophyll a content and chlorophyllfluorescence before and under Cu²⁺stress. The sensitiveness order to copper ischlorophyll fluorescence> chlorophyll a content> cell density, proving the validity ofchlorophyll fluorescence as a convenient way to determine cell density inecotoxicological study.2. Acute toxicity effects of copper on the photosynthetic pigments of P.helgolandica（1）Contents of Car，Chl a and Chl b decrease as copper concentrationincreases and the sensitiveness order to copper stress is Car> Chl a> Chl b.（2）Copper stress lowers the peaks of absorption, emission fluorescence and excitationfluorescence;（3）Copper doesn’t influence the energy flow between pigmentmolecules, light energy absorbed by Chl b and Car can be transported to PSII.However, the main excitation peak of Chl b moves towards the direction of blue light（em=650nm）.3. Acute toxicity effects of copper on chlorophyll fluorescence parameters of P.helgolandica（1）The optimal dark period under copper stress is15min. Cell densityinfluences the chlorophyll fluorescence, so all samples should be diluted to the sameconcentration before measurement.（2） As copper concentration goes up,photoinhibition increases, whereasFV/FM、PSII、FV/FOdecreases. Among all thechlorophyll fluorescence parameters measured, is most sensitive to copperstress, indicating that water-splitting apparatus is one of the major targets of coppertoxicity.All above results show that responses of photosynthesis of P. helgolandica tocopper stress are complicated. Biomemrane system、Chl fluorescence, Car content and the activity of water-splitting apparatus are the best biomarker to marineenvironmental copper pollution.