Study Of Growth Promoting And Salt Tolerance Of Bacillus Spp. On Plant And The Resarch Of Underlying Mechanisms

The genus Bacillus spp. is an important type of plant growth-promoting rhizobacteria (PGPR), hermophilic, aerobic, and widely distributed, can produce a hardy spores, secreted antibiotic and antimicrobial metabolites, iron element, such as nitrogen, phosphate-solubilizing and induced systemic resistance (ISR) function, can promote the growth of plants, having the good biological control function. The study found that Bacillus spp. identificated by our laboratory have growth-promoting and induction of plant salt tolerance, so we carried out preliminary exploration its promoting and salt mechanism.First of all, the study tested the effect of plant growth-promoting of Bacillus spp. B3,86, NMSL88, CJLC2, GBSC56, RJGP41, and evaluated the synergy of these strains with sodium nitrophenolate (CSN) complex. Experimental results showed that these six strains of Bacillus spp. can promote plant growth. The efffect of plant growth-promoting was the best by B3treatment, improved cucumber root length, plant height and fresh weight10.43%,10.80%, and15.91%, as well as promotedthe growth of pepper, compared to its growth-promoting effect was much more significant than CSN alone treatment. Secondly,86treatment, improved cucumber root length, plant height and fresh weight6.36%,11.88%, and10.21%. NMSL88treatment, improved pepper root length, plant height and fresh weight10.12%,13.11%and12.26%. Six Bacillus spp. srains and CSN complex experimental results show that these six strains can significantly improve the promoting effect of cucumber and pepper compared with used alone. B3strains synergistic effect of the most significant, improved cucumber root length, plant height and fresh weight31.30%,28.17%and33.46%, then86treatment, improved cucumber root length, plant height and fresh weight22.52%,32.40%and26.82%. The same time, this study by detecting plant physiological indicators reveal the mechanism of these two types of substances promoting. Treated the seeds with compounded with Bacillus spp. and CSN can enhance the net photosynthetic rate, chlorophyll content and root activity, in order to improve Bacillus promoting ability. B3,86and NMSL88of three Bacillus spp. Strains with CSN mixture were the most significant effect. B3+CSN treatment on cucumber net photosynthetic rate, chlorophyll content and root activity increased by45.61%,26.99%and40.47%.This study investigated the salt stress on the effect of Bacillus growth curve of CJLC2(.Bacillus megatherium) and B3(Bacillus amyloliquefaciens), and determined of the physiological and biochemical indexes tomato seedling and content of mineral elements. The results showed that the salt had no effect on Bacillus growth at low concentration, along with the increase of salt concentration, Bacillus growth was inhibited, physiological indicators of tomato seedlings were worse. Under the same NaCl concentration, treatment added Bacillus than pure NaCl treatment more improved the physiological indices of tomato seedling, promoted the seedling growth. Phosphorus content of CJLC2treatment increased by190%than pure NaCl, the Sodium content was reduced by25.11%, proline content in leaves decreased in varying degrees from20.59%to33.33%. Compared with pure NaCl, B3treatment for plant height and fresh weight increased by38.05%and17.81%, water relative content increased by40.62%and soluble sugar content increased by55.69%, the water saturation deficit was reduced by28.57%, and ethylene releasing was reduced by18.46%. Under salt stress, Bacillus improved tomato plants to absorb moisture, had changed the content of osmotic regulation substances in order to reduce cell osmotic potential for osmotic balance. The Bacillus improved the absorption of mineral elements (P, K, Fe, Cu and Zn) and Na+/K+ratio, while reducing the absorption of sodium content, especially phosphorus content increased1.9times. Ability to regulate root absorption of mineral elements, enhance the uptake of K and transpirate Na, unavoidably reduce salt damage, and benefit for the normal growth of the plant.The study also reserach on improvement of the plant salt tolerance mechanism of Bacillus spp. The results showed that different culture time and temperature, as the culture time and temperature, higher ACC deaminase specific activity, with the culture of the time extension and temperature, the enzyme activity increased, after the decline in the highest specific activity under appropriate conditions, incubated at24℃for18h enzyme activity was the highest, reaching of1.134μmol·(mg·h)-1. Speculated CJLC2strains through the ACC deaminase and the decomposition of plant salt damage arising ethylene synthesis precursors1-amino-cyclopropane-l-carboxylic acid deamination, so that the ethylene concentration is reduced, thereby improving plant salt tolerance.The tomato salt stress-related gene expression by Real-time PCR, the results showed that under salt stress treatment, plus bacteria than the sterile processing significantly increased in tomato leaves salt stress related gene LeTRAMP, and the synthesis of aquaporins enhanced leaf cells the expression of LeAQP2, LePIPl, LePIP2and LeTIP water the ability to regulate and control, and reduce the expression of LeNHX1and tomPRO2leaf vacuole membrane Na+/H+antiporter activity and decreased synthesis of proline, add bacteria treatment makes the tomato leaves the absorption of moisture and proline synthesis ability to regulate enhanced to improve tomato ability to resist salt stress.