Study On Ecophysiological Effects And Toxicant Mechanism Of Microcystin-LR On Oryza Sativa L.

In recent years cyanobacterial blooming has occurred frequently in lakes,which can bring about water pollution caused by its various derivatives and even lead to great ecological disasters in severe cases.Cyanobacterial bloom in lakes has certainly become challenge to the sustainable development of regional economy.Microcystins?MCs?have become common potential hazardous pollutant in aquatic environments for their great toxicity,widespread distribution and stable structures.Toxic effects of microcystin-LR on mammals,birds,and aquatic organisms have been widely investigated,but its phytotoxic effects and toxicity mechanisms under the conditions of low concentration and long-term exposure on terrestrial plants remain unclear.Mowever,there are few reports about the MCs-induced toxicological effects on terrestrial organism.Therefore the toxic mechanisms of MCs on terrestrial organism in practical environment cannot be cdearly explained based on existed studies,on top of this,the early warning system for cyanobacterial blooms cannot be developed.This article focuses on ecophysiological effects and toxic mechanisms of microcystin toxins on,one of the important terrestrial food crops,rice.In the present study,the indicators concerning growth,photosynthesis,physiological and biochemical,and gene expression of rice?Oryza sariva L.?were measured after exposed to 0,0.1,1,10,50 ?g/L of MC-LR for 7,15,20 and 34 days respectively.The main results were shown as follows:?1?The concentration of MC-LR in the environment impacts rice growth and photosynthesis.and the results showed:when the concentration of MC-LR is 0,1 ?g/L and 1 ?g/L,its effect to rice indicators in seeding stage is promoting,the higher concentration of MC-LR?10 ?g/L and 50?g/L?can inhibit the growth of rice,and the higher the concentration of MC-LR is,the more significant the of inhibition is?After 7 days in the early exposure period,its effect to rice growth is not significant?But as the exposure time continues,the promotion caused by MC-LR of lowe concentration and the inhibition caused byMC-LR of highe concentration become more significant.After 20-day exposure,the net photosynthetic rates of every concentration group increase significantly.During the whole exposure period,exposure makes transpiration rate of rice upgraded.Fv/Fm is the most yield of photo-chemical quantum of PS ?,and it's basically stable during the stress of every concentration.?2?The MC-LR accumulation in different parts of rice indicates that MC-LR can accumulate in leaves and roots of rice.The accumulation amount is largely related to the concentration of MC-LR,which in roots is generally more than that in leaves.As exposure time continues,accumulation showed a trend of increase after decreases,which may be caused by absorption of the plants or transformation of the poison.?3?The effects of MC-LR on antioxidant system of rice and activity of special enzymes showed that the content of superoxide anion O2·-dropped significantly first,then had a rising trend,and recovered near to the control level at 34 days exposure.,MC-LR influences the production of NO by affecting the enzyme activity of iNOS and TNOS.MDA content was strongly suppressed in the high concentration group?10,and 50 ?g/L?,and high concentration of MC-LR injured rice significantly.At the end of exposure period,the activity of SS declined in whole.During the middle and late period exposed to 50?g/L of MC-LR,GSH content in leaves and roots reduced more significantly than that in control group,which indicates that the conjugated reaction between GSH and toxins plays important role in the detoxification of plant,and corresponds to the result shown above that the toxin residue amount in roots and leaves decreased in the middle and late period of exposure.?4?The effects of MC-LR on gene expression of rice leaves showed that as exposure time changes,the expression of genes related to photosynthesis,carbon fixation and oxidative phosphorylation in rice leaves changes.Moreover,the changes become more significant as the concentration of MC-LR increases.Researchers found that MC-LR can significantly inhibit the expression of gene AK105925 which is one of the regulator genes of ATP enzyme,and can exert impact on PS? by stimulating the expression of gene COMBINER_EST.Furthermore,it can also inhibit the expression of gene NM₀01056199.1,by which influence the synthesis of sucrose.In addition of these above,there is no significant induction or inhibition effect shown on the other genes.