Characteristics Of Phosphate Solubilization Of Trichoderma Asperellum Q1and Their Effect On Salt-resistance Of Plants

Phosphorus is one of the essential nutrition elements for plant growth and development. Itplays a vital role in the metabolism of plants.Although the total content of phosphorus isabundance in the soil, majority phosphorus can’t be absorbed by plants directly.Phosphate fertilization is the main way of relieving plant phosphorus deficiency symptoms inagriculture production. The persistent and intensive applications of inorganic phosphaticfertilizers may result in large reservation of phosphorous in agricultural soils, which mostlyexists in insoluble (bound) forms such as tricalcium phosphate and dibasic calcium phosphate.Plants are able to utilize only small amount of phosphatic fertilizers that are applied, and themajority is rapidly converted into insoluble complexes in soil, which leads to salinization of soil.High-salt soils may reduce plant’s nutrient uptake and result in a vicious cycle of soil phosphorusdeficiency.In recent years, numerous studies have shown that the beneficial rhizospheremicroorganism of crops may promote insoluble phosphate dissolution and phosphate uptake ofplants. Trichoderma spp. are common inhabitants of rhizosphere and are well recognized asbiocontrol agents of soilborne plant pathogens. Moreover, some Trichoderma strains arerevealed that they can interact directly with roots, increase plant growth and tolerance to abioticstresses. So it is a highly desirable bioagent with dual potential for biocontrol and plant growthpromotion. Although some researches indicate that Trichoderma spp. could alleviate detrimentaleffects of abiotic stresses on plant, there are few reports on the role of phosphate solubilization inimproving salt tolerance of plants and the specific knowledge about the underlying mechanismsremain to be explored. To reveal the role of phosphate solubilization of Trichoderma in plantgrowth under salt stress and its possible mechanisms, some Trichoderma spp. which have beenreserved and identified in our lab were screened for high phosphate solubilizing ability andTrichoderma asperellum Q1was the selected strain. Applying strain Q1to sterile soil couldincrease the levels of available phosphorus in the soil due to phosphate solubilization. The abilityto dissolve insoluble phosphates of strain Q1under various stresses such as iron deficiency, acid stress, alkaline stress and salt stress which simulating the common soil conditions has beenevaluated and the potential of phosphate solubilization of the strain in alleviating negative effectsof salinity was revealed through water-cultivating method. In addition, acid phosphataseproduced by strain Q1was purified and was used in Petri-dish test for determine the effect oforganic phosphorus solubilization on salt resistance of arabidopsis. The specific results arepresented as follows:1. Trichoderma spp. which have been reserved and identified in our lab were screened bythe methods of solid agar and liquid cultivation, strain Q1was proved to have the highest abilityto dissolve insoluble inorganic and organic phosphates.2. The effect of T. asperellum strain Q1on available phosphorus and total phosphoruscontent in soil was assayed. The results showed that strain Q1could increase the content ofavailable phosphorus in the soil by dissolving insoluble phosphates.3. The abilities of strain Q1to dissolve insoluble phosphates under iron deficiency, acidstress, alkaline stress and salt stress were studied. The results showed that the solubilization ofTCP, DCP and phytin were significantly increased by T. asperellum Q1under salt stress.Furthermore, siderophores produced by Trichoderma asperellum Q1under iron-deficiency couldalleviate the adverse effect of salt stress on its growth.4. The role of solubilization of phosphates by the strain Q1on plant growth promotionunder salt stress was proved through water culture experiments. In the treatments with limitinginsoluble phosphates and60mmol/L NaCl stress, cucumber seedlings were cultivated with strainQ1culture filtrates or not. The result indicated that there was a particularly close connectionbetween phosphorus content and the growth rate of cucumber seedlings by comparing the size ofcucumber leaves, shoots and roots length under different conditions. Both inorganic and organicinsoluble phosphates could be transformed into available P by T. asperellum Q1culture filtrates,which can be easily absorbed by cucumber seedlings along with an increasing in their toleranceagainst salt stress.5. The mechanism of solubilization of organic phosphate was started from phytase andphosphatase which produced by the strain.Akind of acid phosphatase was purified by using(NH4)2SO4precipitation, DEAE-Sepharose Fast Flow and Sephadex G-100chromatography witha9.94purification fold, an overall yield of18.9%and an apparent molecular weight of55kDa. The purified acid phosphatase was used in determining the effect of organic phosphorussolubilization on salt resistance of Arabidopsis thaliana L. The result indicated that both plantheight and root length of Arabidopsis thaliana L. are maximum under the treatment of acidphosphatase with phytin in salt stress, compared to the other treatments. This clearlydemonstrated that the solubilization of insoluble organic phosphate by acid phosphataseproduced by strain Q1may play a vital role in promoting plant growth under salt stress andphosphorus deficient conditions.