Physiological And Biochemical Responses Of Three Intertidal Macroalgae To Heavy Copper Stress

With the rapid development of modern industry and agriculture and the large-scale exploitation of mineral resources,the pollution of heavy metals to water has become one of the concerned problems in the word.Because of its special geographical location,heavy metal pollution in seawater is the unavoidable environmental pressure to be deal with in intertidal zone,which is located on intertidal rocks and marshes in the intertidal zone of large algae in intertidal zone.However,there are few systematic comparative studies on physiological and biochemical metabolic responses of intertidal macroalgae to heavy metal Cu²⁺stress.Therefore,three representative species of intertidal macroalgae along the coast of Yantai were selected as materials----Ulva pertusa?green algae?,Sargassum thunbergii?brown algae?and Gymnogongrus flabelliformis?red algae?.By measuring Photosynthetic parameters,the changes of photosynthetic physiological characteristics of three species of algae under copper stress were studied.At the same time,the changes of trehalose content,trehalase activity and gene expression related to metabolism were studied,and the responses and differences of three trehalose species to copper stress were understood.This study provided a theoretical basis for further exploring the relationship between physiological functions and metabolic processes of U.pertusa,S.thunbergii and G.flabelliformis and environmental conditions.The experimental results are as follows:?1?Response of Photosynthetic parameters of three seaweeds to Cu²⁺stressChlorophyll is the most basic substance for plant photosynthesis,and the determination of chlorophyll content is an important indicator of plant growth.In this study,the content of photosynthetic pigments of U.pertusa,S.thunbergii and G.flabelliformis decreased with the increase of stress.With the increase of Cu²⁺concentration,the content of photosynthetic pigments in U.pertusa decreased significantly.Significant analysis showed that compared with control group,the chlorophyll a?Chl.a?,chlorophyll b?Chl.b?and carotenoid?Car?were significantly different?P<0.05?or very significant?P<0.01?.Unlike U.pertusa,S.thunbergii and G.flabelliformis belong to brown algae and red algae,so there is no Chl.b in their cells.Chl.a and Car of S.thunbergii under copper stress were significantly different?P<0.05?or very significant?P<0.01?from the control.The content of car in G.flabelliformis was lower than that of U.pertusa and S.thunbergii,and Chl.a was significantly higher than that in CK?P<0.01?.Chlorophyll fluorescence parameters are a set of variables or constants describing the photosynthesis physiological state and mechanism of plants,and is an important index to study the relationship between plant photosynthesis and the environment of plants.In this study,the chlorophyll fluorescence parameters??light energy utilization efficiency?,rETRmax?the maximum relative electron transport rate?and I_K?semi-light saturated intensity?of three algae showed a downward trend in general,but the degree of reduction showed a fluctuating change.The Fv/Fm?PSII maximum energy conversion efficiency?value has the dual characteristics of sensitivity and stability,which can be used as the best detection and evaluation index for the adaptability of different algae growth and physiology to heavy metals.The results also showed that Fv/Fm of U.pertusa,S.thunbergii and G.flabelliformis were significant different from the control at the highest treatment concentration?P<0.01?,and the correlation coefficients between Fv/Fm of the three algae and the stress degree were-0.935,-0.973 and-0.823,respectively,showing a very significant negative correlation?P<0.01?.?2?Response of trehalose content and trehalase activity of three trehalose species to Cu²⁺stressIn this study,the trehalose content and TPS?trehalose-6-phosphate synthase?of U.pertusa,S.thunbergii and G.flabelliformis increased at first and then decreased with the increase of Cu²⁺concentration,reaching the maximum value at 0.5mg/L Cu²⁺concentration,which was significantly different from that of the control?P<0.01?.and the accumulation range of trehalose content in S.thunbergii was higher than that of U.pertusa and G.flabelliformis.The THase?trehalase?activity of three algae species was the highest at the concentration of Cu²⁺of 1.0mg/L,which was 4 significantly different from that of the control?P<0.01?.With the increase of stress,the THase activity of the three algae gradually decreased.Under copper stress,trehalose content,THase activity and TPS activity of U.pertusa,S.thunbergii and G.flabelliformis all changed to some extent,and the change of TPS activity was positively correlated with trehalose content.The trehalase activity of S.thunbergii decreased more than that of U.pertusa and G.flabelliformis under stress,so the accumulation of trehalose content was higher than that of U.pertusa and G.flabelliformis.In conclusion,chlorophyll content,fluorescence parameters and trehalose metabolism-related enzymes activities have certain stress and sensitivity differences in different species of macroalgae after copper stress,reflecting obvious interspecific differences.Among them,the basic expression activity?content?of the parameters of Sargassum Salvia was higher,and the decrease was smaller after copper treatment,so it showed strong resistance to stress.