Symbiotic Enhancing Of Seed Germination Metabolism Analysis On Drought-stress By Endophytic Bacteria Of Ammodendron Bifolium

Due to damage of drought on desert ecosystem has been a worldwide problem,more and more scientists pay attention to special environment adaptability of desert plants.In recent years,symbiotic relationship between plants and microbes becomes the focus of research,which reveals stress-tolerant mechanism.Endangered desert plants Ammodendron bifolium(Pall.)is one of pioneer plants having good sand-fixation,and its seed hardly germination under arid environment is the main factor to endanger.The prophase research has got 37 endophytic bacteria isolates from roots,and most of them have effects that alleviate drought stress to promote seed germination.To further understanding the mechanism of Ammodendron bifolium(Pall.)endophytes alleviating drought stress,we studied the relationship between endophytic bacteria metabolites and promote seed germination rates,and symbiotic drought-resistant metabolic response surface from metabolites of in vitro cultural isolates and metabolites changes in seeds after inoculated isolates.The results as following:Test of indole acetic acids and proline were undertaken on endophytic bacteria from roots of Ammodendron bifolium(Pall.).It is showed that 37 endophytes can produce indole acetic acids and proline,in which indole acetic acids production of 26 endophytes is more than 1 ?g/m L,10 is more than 2 ?g/m L,and which of strains AER 311-8 is highest,up to 49.36 ?g/m L.Proline production of 26 endophytes is more than 1 ?g/m L,,and which of strains AER 110-11 is highest,up to 1.72 ?g/m L.But analysising relationship between production rates of indole acetic acid,proline and seed germination rate under 25 % PEG 6000 drought stress,we found that lower production rates had higher promoting rates such as AER 310-1,AER 317-1 and AER 11,in turn,higher production rates had lower promoting rates such as AER 311-8 and AER110-11,only 41% and 14% respectively.According to the results,we confirmed that the production rates of indole acetic acid,proline had no effects on seed germination rate of Ammodendron bifolium(Pall.)under drought stress,and speculated that promotion of seed germination rates is caused by other metabolites.AER 310-1,AER 119 and AER 317-1,which metabolites as roles,were in vitro cultured,after analyzed by gas chromatography-mass spectrometry(GC/MS),there were 14 kinds of metabolic components,10,8 and 6 from AER 310-1,AER 119 and AER 317-1 respectively.AER310-1 and AER 119 had 2 components intersection,AER 310-1,AER 119 and AER 317-1 had 4.By analysis of correlation coefficient of various metabolic components and the germination rates showed that metabolites of endophytic bacteria have different degrees of promoting effect on seed germination.To understand the effects degree of different growth periods of isolates,we inoculated different growth periods of isolates in seeds under drought conditions of 25 % PEG 6000.The results showed that 30 isolates of 37 endophytes effects degree was different with different growth periods,and 7 not.For the further understanding,we analyzed slurries of different period seeds inoculated AER 314-4,which starch content is 14.6 %,12.5 %,11 %,9.57 %,by GC/MS to detect the metabolic components.It showed that after absorbing water,the molecular weight of the main metabolites of control groups were between 200-300,and these metabolites shall be the normal metabolites of seed germination.Although some of them has nothing to do with the drought tolerance but they are closely related to the seed germination.Damage from drought stress of control groups and experiment groups were consistent at the beginning of germination group but after inoculating endophytes,molecular weight of less than 200 metabolites had a rapid increase,and produce special metabolites.These small-molecules metabolites can significantly reduce osmotic potential than macromolecular ones,which is the key to promote seed germination rates.Although small-molecules metabolites was decreasing in the middle of germination of experimental group,some hardly metabolic substances under drought stress was increasing,of them,D-Thermopsine,sparteine is closely related to seed germination.The results confirmed that endophytic bacteria of Ammodendron bifolium(Pall.)really involved in the metabolism of the seeds,by the way of producing small molecules or critical metabolites to alleviate the drought stress.In conclusion,the endophytic bacteria of Ammodendron bifolium(Pall.)can produce indole acetic acids and proline,but it is no use to seeds germination under drought stress;the main reason of seeds germination rates promoting was some special metabolites production of the endophytic bacteria of Ammodendron bifolium(Pall.);different growth periods of some endophytic bacteria had effects on seed germination,but some not;endophytic bacteria of Ammodendron bifolium(Pall.)regulated the metabolism of the seeds,by the way of producing small molecules or critical metabolites to alleviate the drought stress.The results had important theoretical value for understanding the symbiotic mechanism of drought tolerance of desert plant,and provided practical significance of species conservation and population restoration of rare and endangered plants.