Analysis Of The Growth-promoting Effects Of Two Plant Endophytes DLJ1 And SZ5

Endophytic bacteria are microorganisms which exist in various tissues and organs of healthy plants in a certain stage of its life cycle stage or the whole life.The infected host plants don't express any external disease symptom,but the endophytic bacteria can be isolated by the histological method or from the strictly surface-disinfected plant tissues.Bacillus cereus SZ5 and Pseudomonas fluorescensbiovax ? DLJ1 are isolated from the fruits of persimmon and pepper,respectively.Previous studies have showed that they can promote the growth and improve the resistance of the non-host plants tomatoes.Whether besides the promotion effect of growth and resistance on the Solanaceae plants,these two strains also have these promotion effects on other plants?In view of this,Brassica campestris L.,Triticum aestivum L.,Arabidopsis thalina and others plants are used as materials,and the effects of these two strains on the seed germination,seedling growth,resistant to mild stress,and the use of the bacteria agent,etc.were discussed in this paper.Results are as follows:When be treated before germination,these two bacteria suspensions showed no significant effect on the seed germinations of rape and wheat,while in both fermented liquids,especially in the SZ5 fermented liquid,there might be some kind of material which can slow down both seeds' germination.For seedling growth,the cole hypocotyl length,root surface area and leaf area were boosted 53.8%,39.4%and 77.3%respectively than control when rape were treated with DLJ1 fermented liquid before seed germination,its effect on the growth of wheat seedlings come the next,and the effect of SZ5 fermented liquid is relatively low.When treated after germination,the growth-promoting effect of DLJ1 mainly displayed in the elongation of rape hypocotyl,and to effect is reduced significantly when be compared with the treatment before germination,and the SZ5 treatment inhibits the growth of root system.The growth-promoting effect of these two strains on the rape and wheat seedlings might be related to their ACC deaminase activity.DLJ1 can produce siderophores which can provide Fe for seedling growth,and can prohibit Fe supply for pathogenic microorganisms which can promote plant growth indirectly.These results show that campared with the SZ5,DLJ1 might have more application prospects on the plant growth promotion and plant resistance to pathogenic mocroorganisms.Both SZ5 and DLJ1 can colonized in rape seedlings.Under normal conditions,with the time extension after the treatment,the growth-promoting effects of both strains on rape seedlings gradually disappear.But pretreatment with both strains,especially with DLJ1 still can improve the seedlings resistance to mild stresses as Cd stress and osmotic stress.Under mild Cd and PEG stress,fresh weight per plant decreased by 4.1%and 6.4%respectively in the DLJ1 treatment group but fresh weight per plant decreased by 17.4%and 15.9%respectively in the control.Treatments with two strains,especially with DLJ1,improve the contents of carotenoids and flavonoids,and promote the activities of PAL which is the key enzyme in the synthesis of flavonoids in rape seedlings.These results suggest that not only the ACC deaminase produced by these two strains might play a certain role in relieving stress through inhibiting ethylene generation,but also these two strains might improve the contents of flavonoids and carotenoids in plant through the ISR way to improve the comprehensive resistance of rape,and finally expressed as the fresh weight maintenance under mild Cd and PEG stress.The sclerotium is one of the important diseases in rape.Results from the table confrontation test showed that Sclerotinia sclerotiorum can inhibit the growth of SZ5;while DLJ1 can inhibit the growth of Sclerotinia sclerotiorum,and the inhibition is not from the direct contact inhibition.Further results prove that DLJ1 can absorb Fe competitively by siderophores under low Fe environment,which lead to the environment Fe content drop down further and finally inhibit the growth of Sclerotinia sclerotiorum.The results suggest that DLJ1 might have the potential to be applied in the control of Sclerotinia sclerotiorum.Although the suspensions of DLJ1 and SZ5 can improve the growth and mild stress resistance of rape and wheat seedlings,both bacteria powder prepared in this paper show little effects.The effects of both bacteria powder on different seeds such as Brassica campestris L.,Triticum aestivum L.,Capsella bursa-pastoris,Abelmoschus esculentus L.,Talinum paniculatum(Jacq.)Gaertn,and Malva crispa L.Different periods such as seed germination,seedling growth,and different stresses are different.Both bacteria powders show no growth-promoting effect on Arabidopsis thaliana and can't improve its resistance to natural drought stress.All the above results show that the effects of suspensions and powders of DLJ1 and SZ5 are different,and the preparation of of these two endophytic bacteria agent need futher study.Although the suspensions of these two endophytic bacteria show positive effects on rape seedling growth,the range of its application still need to be tested one by one.In conclusion,both fresh fermentation liquid of SZ5 and DLJ1,especially the DLJ1,can inhibit the seed germination and promote the seedling growth of rape and wheat when treated in the seed soaking period.Both can colonize in rape seedling and can alleviate the mild stress which caused by CdCl2 and PEG.These growth-promoting effect might be related to the ACC deaminase producing activity of the two bacteria;and the contents improvement of carotenoids and flavonoids by I SR which improve the seedling's comprehensive resistance further might also play some roles.DLJ1 can chelate Fe element through siderophores,the growth of Sclerotinia sclerotiorum need rich Fe,and DLJ1 can inhibit the growth of Sclerotinia sclerotiorum in Fe lackage enviroment.Thess suggest that DLJ1 might have the potential to be applied in the control of Sclerotinia sclerotiorum.The endophytic bacteria powder producted by milk powder has not been found the similar effect as fresh bacteria.The application scope and applicable formulation of these two endophytic bacteria still need to test one by one.