| Elephant grass and hybrid Pennisetum are excellent forage grass and energy plants,which give a good performance in stockbreeding,paper making industry and ecological field.While in marginal land,they have low biomass and poor salinity tolerance.Plant endophytic bacteria are important microbes,which are proved to possess the abilities of promoting plant growth,enhancing the stress tolerance of host plants.The endophytic bacterium,PP04,isolated from the root of elephant grass,was studied about its growth-promotion ability and rhizospheric colonization.It was found to own the abilities of nitrogen fixation,phosphate solubilization capacity and more importantly,high ACC deaminase activity.But the approaches to applications,related techniques and mechanisms in large-scale planting are uncertain.This study is aimed at a further investigation on the strain concerning the relief of salinity stress on the seed germination and plant growth of hybrid Pennisetum and laying a solid foundation on the development of biofertilizers for elephant grass and hybrid Pennisetum.The concrete results are as follows:1.The endophytic bacterium PP04 could mitigate the toxic effect of salt stress on the hybrid Pennisetum seeds under low(100 mmol·L-1),medium(200 mmol·L-1)salt concentration,enhancing and improving the seed germination rate,germination index and embryo length.Under low salinity stress,the plants inoculated endophyte(E+)had a higher amplification of 16.25%,19.59% and 20.98% in germination rate,germination index and embryo length than uninoculated plants(E-).Under medium salinity stress,the germination rate of E+ treated hybrid Pennisetums increased by 21.28%,germination index 35.75% and embryo length 3.36 times compared with Eplants.However,300 mmol·L-1 salt concentration was too high for PP04 to work.2.The endophytic bacterium relieved the effect of salinity stress on hybrid Pennisetum growth.The salinity stress could decrease the biomass of hybrid Pennisetum,but the inoculation of PP04 greatly enhanced the content of chlorophyll and root vigor,thus improving plants’ salt tolerance.The promotion effect reached the highest level at low and medium concentration when the height increased by 29.24%,18.33% and the weight increased by 59.44%,49.00%.3.Under salinity stress,PP04 could strengthen the enzymatic activity of CAT,APX,SOD and POD.When under 100 mmol·L-1 salt concentration,plants of E+ treated had an increase of 64.18%(CAT),73.14%(APX),32.34%(SOD)and 65.40%(POD)compared with E-group.This showed the adjustment of PP04 in antioxidant enzymes and erasing of malondialdehyde(MDA),a production of membrane lipid peroxidation leading to a relief in antioxidant stress and reinforced of salt tolerance.4.On the other hand,the infection of endophyte promoted the production of osmotic adjustment substances and stress tolerance of plants.Under medium and high salt stress,E+ treatment plants had higher content of proline,soluble protein and soluble sugar.Under low and medium stress,E+ plants had an accumulation of P content.Low and medium salt concentration decreased the plants’ K+/Na+ by 62.08%.However,inoculation of endophyte made an apparent increase of 47.14% in K+/Na+.This study explored the elementary mechanism of endophyte easing salinity stress on hybrid Pennisetum by improvement of antioxidant enzymes,osmotic adjustment substances and ion balance so as to guarantee the germination and growth of hybrid Pennisetum.The results better showed this strain is a fine plant endophyte for growth-promotion of hybrid Pennisetum.This paper explored the elementary mechanism of endophyte easing salinity stress on hybrid pennisetum while in reality,many factors should be taken into account to realize the commercialization of endophyte.Conducting wild field trial experiment is necessary for the strain to play a role in all kinds of ecological environment in the long run. |
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