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Nitrogen-related Research On Nitrate Assimilation Process Of Lettuce

Posted on:2016-04-26Degree:MasterType:Thesis
Country:ChinaCandidate:J F LinFull Text:PDF
GTID:2393330491458458Subject:Vegetable science
Abstract/Summary:PDF Full Text Request
In this study,Lactuca sativa L.was used as material,and hydroponic experiments conducted by five different nitrogen forms of nutrient solution(NO3--N:NH4+-N=100:0?70:30?50:50?30:70?0:100,namely P1?P2?P3?P4?P5).The experiment researched the effects of different nitrogen forms on the root growth,leaves quality and nitrate content of Lactuca sativa L.At the same time,the key enzymes of nitrate reductase(NR),nitrite reductase(NiR)gene were cloned by RT-PCR and RACE.The expression levels of NR,NiR were analyzed by qRT-PCR to analyze the coupling relationship of NR,NiR in the nitrate accumulation.These results would provide a reference for further understanding the regulation mechanism of nitrate accumulation.1.Effects of different nitrogen forms on the root growth of lettuceDifferent nitrogen forms affected the root morphological parameters and root activity.Full nitrate and suitable NO3--N/NH4+-N could promote root growth,improve the absorbing of NO3-and affect the accumulation of nitrate content in leaf.With the increasing of NH4+-N,biomass,length,surface area and volume of root decreased;average diameter of root increased;while tips number,forks number and activity of root increased firstly,then decreased with the further increase NH4+ amount.They were found to be the largest at P2,the least at P5.Root/shoot was the highest at P1,the lowest at P5.2.Effects of different nitrogen forms on growth of lettuceFull nitrate and suitable NO3--N/NH4+-N in solution could promote lettuce growth and increase yield.With the increasing of NH4+-N,yield,leaf width and plant height of lettuce decreased.The yield of lettuce at P1 and P2 had no significant difference.Leaf number and stem diameter increased with the increasing of NH4+-N,they were largest at P2,and then decreased quickly with increased NH4+-N,percentage from 50%to 100%.3.Effects of different nitrogen forms on quality of lettuceSuitable NO3--N/NH4+-N was good to improve quality of vegetable by increasing soluble protein and VC content,decreasing nitrate content,which helped to improve the nutritional quality and food safety quality of lettuce.Compared with single nitrate,suitable NO3--N/NH4+-N was more conductive to improving NR and NiR activity;while high level of NH4+-N seriously restrained their activity.With the increasing of NH4+-N,soluble sugar content of lettuce increased;soluble protein and VC content were highest at P2,and then decreased quickly with increased NH4+-N,they were lowest at P5.Nitrate content decreased with the increasing of NH4+-N.Nitrate content at P5 was significantly lower than other treatments.With the increasing of NH4+-N,NR and NiR activity of lettuce increased firstly,and then decreased quickly;they were the highest at P2.4.The application of fuzzy comprehensive evaluation on lettuce growth and quality analysis(1)The results of fuzzy comprehensive evaluation showed that under the five different nitrogen forms,root growth traits from good to bad in turn was:P1>P2>P3>P4>P5.The yield of lettuce from high to low in turn was:Pi>P2>P3>P4>P5.Therefore,root trait and aboveground yield had a close relationship.(2)Comprehensive evaluation of the quality of lettuce under five nitrogen forms by using fuzzy comprehensive evaluation.The sort was P2>P3>P1>P4>P5.The results showed that the best cultivation effect was nutrient solution of P2,which was a good way to hydroponic lettuce.5.Cloning and expression analysis of nitrate reductase gene in lettuceYmcNR gene was firstly cloned from Lactuca sativa L.by RT-PCR and RACE.The cDNA of NR was 3009bp containing a 2424bp opening-reading frame,encoding 807 amino acids.Phylogenetic analysis showed NR protein had a high identity to Cichorium intybusn.Protein structure analysis showed that the protein shared common structural features with NR from other higher plants and belonged to the style of NADH-NR.Real-time PCR analysis showed the expression of NR at P2 was the largest.It suggested compared with single nitrate,suitable NO3--N/NH4+-N was more conductive to promoting the expression of NR gene;high level of NH4+-N seriously restrained the expression of NR.6.Cloning and expression analysis of nitrite reductase gene in lettuceYmcNiR gene was cloned from Lactuca sativa L.by RT-PCR and RACE.The cDNA of NiR was 2047bp containing an 1824bp opening-reading frame,encoding 607 amino acids.Phylogenetic analysis showed high identity to tobacca NR protein.Protein structure analysis showed that the protein had a hemoprotein beta-component(ferredoxin-like),4Fe-4S region and a siroheme-binding site.Real-time PCR analysis showed the expression of NiR gene was the highest at P2.Suitable N03--N/NH4+-N can promote the expression of NiR gene;high level of NH4+-N seriously restrained the expression of NiR.7.The coupling relationship of NR and NiR in nitrate assimilation processNitrate absorption process has signal effects on metabolism on plant growth,and affects related enzyme activity and gene expression.In this experiment,the change trend of NR and NiR activity and gene expression were similar.7 d-28 d,nitrate content increased gradually,then quickly reduced on 35 d.NR activity and NR,NiR gene expression increased and then decreased,there was a small boom on 28 d.NiR activity change lagged the NR a period.The reason why there was not obvious nitrite accumulation in plants was the continuous action of NR and NiR.In short,in order to maintain metabolic balance in plants and reduce the damage to cells caused by toxicity of NO2-,when nitrate content was excessive in body,NR and NiR gene expression strengthened,their activity improved.By the continuous effects of the two enzymes,the nitrate accumulation in the body will reduce.
Keywords/Search Tags:Lactuca sativa L., Nitrate, Nitrate nitrogen, Ammonium nitrogen, Nitrate reductase, Nitrite reductase
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