| Arsenic (As), which can be taken up and enriched by plants, is one of the mostcontaminated elements in the soil and produces poison effect on animals and humansthrough food chain. Arsenic pollution is very severe in many parts of the world includingsome regions of Southern China. Previous studies showed that supply of phosphate (Pi)tends to reduce uptake of arsenic because of the similarity of phosphorus (P) and As inphysical and chemical structure. It has been proposed that arsenic enters the plant rootsthrough high-affinity phosphate transporters in the cell membranes. The resistance of plantroots to arsenate (Asv) is likely due to their suppression of part of high affinity phosphateabsorption system. However, the biological mechanisms of the interaction between P andAS in plants, especially in molecular aspects, are not well understood yet. In addition,inoculation of mycorrhizal fungi can regulate expression of some Pi transporter genes andincrease uptake and utilization of P, alleviate the toxic effects of As in plants. However,there is no molecular evidence to demonstrate the direct relationship between the increaseof P uptake and decrease of As uptake in the mycorrhizal plants. Although five putative Pitransporter genes have been isolated in tomato, there was no any information on thepossible role of plant Pi transporters involved in enhancing the plant resistance to As stressby either mycorrhiza or P supply.In this thesis, we used the cultivar Micro-Tom, a model tomato with short life anddwarf size as plant material to investigate the influence of inoculation of Glomusintraradices and different Pi supply levels on the growth and nutrient uptake of the tomatowith and without As stresses under both solution and sand culture conditions. We also usedlept4 mutant, the knockdown of a mycorrhizal regulated Pi transporter gene LePT4 intomato to exam the contribution of LePT4 in acquiring P and As in tomato.The main findings are as following: 1. Provision of 0.05mM As~v in the sand culture medium resulted the significantdecrease of biomass yield and severe symptoms of As toxicity in the Micro Tom wild type.Higher external As above 0.05 mM very significantly decreased the inoculation rate by G.Intraradices in the roots. Inoculation of the mycorrhizal fungi significantly increased totalP uptake, biomass yield and decreased both the As concentration and total As uptake in theplant.2.Provision of 0.05 mM As~v decreased the uptake of P in the plant only whenconcentration of Pi in the culture solution was below 0.2 mM. Increase of P concentrationup to 0.4-0.6 mM significantly improve both P uptake and biomass yield and decrease ofboth concentration and total uptake of As in the roots and shoots. No visible effects of Asaddition on the expression patterns of all the Pi transporters in tomato when presences of Piin the solution was in the range between 0-0.4 mM.3. Mutation of LePT4 did not change the phenotype of the Micro Tom both of rootsand shoot and inoculation percentage by the AMF in the roots in the absence of arsenate.However, in comparison to the wild type, knockdown of LePT4 in the tomato verysignificantly decreased the acquisition of Pi from infected AMF. Existence of 0.05mMexternal As significantly decreased the AMF inoculation percentage in lept4 mutant, but notin the wild type. The expression of both LePT4 and LePT5 were specifically induced by theAMF inoculation in the roots. Such AMF regulated expression patterns were not affectedby exogenous addition of 0.05 mM As. Although the inoculation by G. Intraradicessignificantly decrease the concentration of As both in the roots and shoot and improved thegrowth and total P uptake, LePT4 mutation didn't significantly change the total As uptakeand distribution between the above and below ground parts. LePT4 mutation did not resultin visible phenotypc for increase of its resistance to 0.05mM As by the mycorrhiza and Pi.We conclude that there might be different pathways for the acquisition of As and Pi intomato.
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