The Effect Of UV-B Radiation On The Endophytic Bacteria In Plants Of Qinghai-Tibet Plateau

In most plant species,endophytic bacteria are ubiquitous,colonizing locally as well as systemically,and affecting plant health by suppression of disease,degradation of contaminants,and promotion of plant growth.Endophytic bacterial without doing any harm to the plant,and can be isolated from surface-disinfected or extracted from internal plant tissue.We make primary study and analyze on endophytic bacterial diversity in thirteen plants under ultraviolet irradiation and normal conditions,by disinfecting the plants surfaces to separete the endophytic bacterial to culture,and combining the traditional method(culture method) with molecule instrument(RFLP, 16S rRNA sequence analysis);And determined some physiological characteristics and functions of isolates.The major results are as follow:1.As the different morphologies of host plants,ultraviolet radiation will lead to different impact to endophytic bacteria.The colony density of endophytic bacteria that in the same kind plant is apparent differences under UV-B radiation and the normal growth conditions.Colony density of Endophytic bacteria in seven plants which under the treatment conditions,is significantly higher than normal conditions. The remaining six kinds of plants is just the opposite.It is different that species diversity of culturable endophytic bacteria isolated from these seven plants in the different treatment conditions.2.Based on the analysis of PCR-RFLP and 16S rRNA sequence analysis.A total 17 genus kinds of bacterial were isolated from thirteen plants after sequence analysis. The results showed that:A total of the formation of a-proteobacteria,γ-proteobacteria, high-G+C content Gram-positive bacteria(HGC),low G+C content Gram-positive bacteria(LGC),CFB.Of witch,HGC and LGC formed the largest cluster and possessed the highest taxonomic diversity.There are 5 genera in all isolates.3.The distribution of 22 kinds endophytic bacteria in thirteen plants are differences.Acinetobacter(Acinetobacter lwoffii) is broad distributed in 12 kinds of plants.It is Gram-negative bacteria,widely distributed in the external environment, mainly water and soil.It has a strong resistance to drought,H₂O₂,γ-ray and ultraviolet radiation.It also implied there is a mutual choice between endophytic bacteria and the host.4.The majority of cultivated endophytic bacteria,will be able to produce yellow, orange-red or pink pigment.Gram-positive bacterial(58.8%) were isolated more frequently than gram-negative bacteria.These characteristic of endophytes were closely related to their origin and growth environment of their host plants,i.e.,low temperature and UV radiation.The result is consistence with the characteristics of micro-organisms from other cold environment,such as permafrost and glaciers. However,it is different with the characteristics of endophytic bacteria in the plants from the mild environment.So environmental conditions have a strong selection on the population structure of bacteria,which is similar to the environmental selection of bacteria similar to those groups.It implied the the mechanisms and survival strategies of endophytic bacteria to adapt to the environment.