Study On Interaction Of Molybdenum And Phosphorus And Its Mechanism Of Brassica Napus

Interaction of molybdenum(Mo) and phosphorus(P) is an important subject in plant nutrition sciences.However,studies on interaction of Mo and P in high plants are so conflict.Brassica napus,an important edible oil crop,and widely grown throughout the Yangtze River Basin,is highly sensitive to Mo or P deficiency,but both Mo and P deficiencies in the soils of Yangtze River Basin are in common.So far,little attention has been paid to the interaction of Mo and P with respect to Brassica napus.Based on the reviews of interaction of Mo and P in plants and Mo nutrition characteristic of Brassica napus,soil and solution culture experiments were conducted to investigate the interactive effects of Mo and P and its mechanism of Brassica napus.The main results as follows:1.Pot experiments were conducted to investigate the effects of Mo and P fertilizer application on dry matter yield(DM) at different stages,grain yield and yield components.The results indicated that both Mo and P fertilizer significantly increased DM at differant stages,and there was a synergistic effect on DM of seedlings between the two fertilizers,and Brassica napus was highly sensitive to Mo deficiency in soils at the seedling stage.P application increased grain yield in the absence or presence of Mo fertilizer,but Mo application increased grain yield only in the presence of P and there was also a synergistic effect between Mo and P.The highest values of DM at different stages,plant height and height increasing rate,grain yield,biomass yield and harvest indices all occurred in the combination treatments of Mo and P.Moreover,the impact of P fertilizer on grain yield of Brassica napus was mainly through increasing branches and pods of each plant while Mo fertilizer through increasing pods for each plant.2.Pot experiments were conducted to study the effects of Mo and P fertilizer application on grain quality of Brassica napus.The results indicated that Mo application increased oil content,oil yield and the contents of oleic and linoleic acids,decreased the contents of protein,glucosinolates,and linolenic and stearic acids,and improved the fatty acid components.P application resulted in the increases of oil yield and linoleic acid content and the decreases in the contents of erucic acid,glucosinolates and eicosenoic acid.And there were synergistic effects on oil yield and the contents of oleic and erucic acids.The co-application of Mo and P had remarkable influences on methionine,cystine, phenylalanine,aspartic acid,glutamic acid,lysine and tyrosine.Effects of Mo on the contents and proportions of each amino acid compositions were affected by different P levels:Mo application increased the content and proportion of essential amino acid compositions,and improved the nutrition values and quality of Brassica napus seed in the presence of 0.20 g P₂O₅ kg^-1 P fertilizer.3.A pot experiment was conducted to investigate the effects of Mo and P fertilizer application on photosynthetic characteristics and some N metabolism indices of seedlings of Brassica napus.The results indicated that both Mo and P fertilizers increased chlorophyll concentrations,net photosynthesis rate(P_n) and soluble sugar concentrations of seedling leaves,particularly with the combination of the two fertilizers, and P application enhanced the effects of Mo fertilizer.The Mo and P fertilizers increased photosynthetic rate through two different mechanisms,with Mo increasing photosynthetic activity of mesophyll cells,and P increasing stomatal conductance.Both Mo and P fertilizers decreased nitrate-N concentration of seedling leaves,and there was a synergistic effect between the two elements.Mo application increased free amino acid concentrations of seedling leaves,however,they were decreased by Mo application in the presence of higher P fertilizer.The effects of Mo fertilizer on the contents and proportions of each amino acid components were affected by different P levels.The co-application of Mo and P had remarkable effects on cystine,phenylalanine,glutamic acid,arginine,methionine,isoleucine,lysine and valine.Moreover,Mo application increased the contents and proportions of hydropphilic amino acids,decreased the proportions of hydrophobic amino acids,resulted in the increase of cell binding of water and was benefit to format cold and drought-resistance of plant cell.4.Soil and solution culture experiments were conducted to investigate the effects of Mo and P on uptake of Mo,P and other nutrient elements at different stages and distribution of Mo,P and other nutrient elements in different parts of Brassica napus. The results indicated that P application increased Mo concentrations at flowering stage, and there were synergistic effects on Mo concentrations at seedling and flowering stages between Mo and P fertilizer.P application increased Mo accumulations at seedling, flowering and maturity stages,and co-application of Mo and P fertilizer also had synergistic effects on Mo accumulations at seedling and maturity stages.P application decreased seed Mo concentrations and inhibited the translocation of Mo from stem to pod and from pod to seed.P application increased stem,pod and whole plant Mo accumulations,decreased seed Mo accumulations,and co-application of Mo and P fertilizer had synergistic effects on Mo accumulations of pod and whole plant while had an antagonistic effect on seed Mo accumulations.P application decreased Mo proportions of pod and seed and restrained Mo translocation from non-genital to genital organisms, especially in the absence of Mo fertilizer.Mo was mainly accumulated in the non-genital organisms of root and stem,and Mo application stimulated the Mo translocation from non-genital to genital organisms.Mo application increased P content at bud stage and P accumulations at seedlings,bud and maturity stages,and both Mo and P had synergistic effects on P content at bud stage and P accumulations at seedlings and bud stages.Mo application increased P accumulation of seed,and there was also a synergistic effect between the two elements.Mo application resulted in the increase of P proportion in seed and the decrease of P proportion in pod and increased the translocation of P from pod to seed.The results of solution culture experiment indicated that P increased Mo content and accumulation in shoots,decreased those in roots and improved the transport from root to shoot.Mo increased P content in roots and P accumulations in shoots and roots in the presence of solution P nutrition and resulted in the distribution of P in roots.Mo and P fertilizer had synergistic and antagonistic effects on contents,accumulations, translocations and distributions of N,K,Ca,Mg,B,Fe,Mn,Cu and Zn,but they were different at different stages and parts of Brassica napus.5.Stimulated soil and root-box culture experiments were conducted to investigate the interaction between Mo and P in the root - soil interface of Brassica napus.The results indicated that Mo application had increase trend on the content of available P in soil,and the effects of Mo were affected by P application and number of days training. Mo application had affected soil pH,and also affected by P application and number of days training.Mo application had a increase trend on soil APase activity in the time of 40 days.P application decreased the availability of soil Mo and increased the availability of fertilizer Mo.Both Mo and P increased DM and accumulations of Mo and P in shoots and roots,and there were synergistic effects between the two elements.P application increased the availability of Mo fertilizer,improved the Mo translocation from non-rhizosphere to rhizosphere,and increased Mo uptake by Brassica napus.Mo application increased the transformation from NaHCO₃-Po to NaHCO₃-Pi and the translocation of NaHCO₃-Pi from non- rhizosphere to rhizosphere,and decreased H₂O-Pi concentration.And H₂O-Pi and NaHCO₃-Pi were more available P fractions for the absorption of Brassica napus.The effects of Mo on NaOH-Po and HCl-Pi were different in the presence or absence of P fertilizer,and the decreasing effects of Mo on organic P contents in non- rhizosphere to rhizosphere soils might be related to the increasing effect of Mo on soil APase activity.6.A solution culture experiment was conducted to investigate the effects of Mo on the morphological and physiological characteristics of Brassica napus root under different P levels.The results indicated that application of 0.01 mg L^-1 Mo increased DM of roots and shoots and root volume,with solution Mo concentration further increased, they were decreased.Application of 0.01 mg L^-1 Mo also had an increase trend on root length,especially in the higher P levels.Moreover,Mo had an increase trend on ratio of root/shoot.Application of 0.01 mg L^-1 Mo increased total and active absorption areas of root,and the increasing effect of Mo on active absorption areas was greater in the presence of higher P levels.However,Mo had an increase trend on the proportion of active absorption areas but an decrease trend on specific surface areas,suggesting that the increase of P uptake due to Mo application was by means of increasing root P absorption capacity of unit area.Mo increased activity of ATPase in roots,improved the energy conditions of roots,decreased activity of APase secreted by roots and reflected indirectly the increase of P uptake and the improvement of P nutrition status in plants.7.A solution culture experiment was conducted to study the effects of Mo on the kinetic parameters of P absorption and the expression of P transporters in Brassica napus roots under different P levels.The results indicated that application of reasonable Mo concentration decreased Km and Cmin,improved the kinetic parameters of P absorption and enhanced the affinity between root and phosphate and and the tolerance of low-P stress.In the condition of low P,Mo significantly decreased the expression of Pht1;1 and Pht1;4,especially Pht1;1.Furthermore,Mo application remarkably decreased the expression of Pht2;1 and had a decreased trend on the expression of Pho1 in the absence or presence of P application.Combined with P fertilizer,Mo application also significantly decreased the expressions of Pht3 and Pht5.These suggested that the expressions of Pht1;1,Pht1;4,Pht2;1,Pht3 and Pht5 were intensively induced by Mo deficiency and molybdate could be absorbed by the site of phosphate absorption in root plasma membrane.In the conditions of normal P levels,Mo increased the expression of Pht1;1 but had no effect on the expression of Pht1;4.The results implied that Pht1;1 was the mainly expression form of P transporters and P uptake by Brassica napus roots was improved by the increase of the expression of Pht1;1.8.Nutrient solution culture experiments were conducted to study the effect of Mo on metabolism of inorganic and organic P fractions in Brassica napus under different P levels.The results indicated that Mo increased activity of APase in roots and shoots,and the effect of Mo was affected by P levels.Mo increased inorganic P contents in roots and shoots in the P levels of 1 and 30 mg L^-1,but Mo decreased those in the presence of 90 mg L^-1 P.Mo had a decrease trend on insoluble organic P content in roots in the presence of 30 and 90 mg L^-1 P.Moreover,Mo resulted in the increases of inorganic and soluble P proportions,and increased the P translocation and re-utilization capacity in Brassica napus. 9.Possible mechanisms of P uptake of Brassica napus enhanced by Mo application were summarized.Mo application affected soil pH and APase and the transformation of P fractions in rhizosphere and non-rhizosphere soils,and resulted in the increase of soil P availability;increased root length,volume,absorption areas and ratio of root/shoot and improved root morphology;increased the activity of ATPase,improved the kinetic parameters of P absorption and increased the expression of P transporter,and enhanced P absorption capacity;increased the activity of APase,inorganic P content and inorganic and soluble P proportions,decreased insoluble organic P content and enhanced P translocation and re-utilization capacity.