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Abstract

Coexisting microorganisms are abundant in nature. Plant growth promoting rhizobacteria (PGPR) is a group of beneficial microorganism living around the roots of plants which are able to confer beneficial effects on plant growth. Streptomyces sp. is a gram-positive bacteria as PGPR that can promote plant growth and enhance tolerance in adverse environment. This research was aimed to study the effects of plant growth promotion and stress tolerance of Streptomyces sp. in Arabidopsis and Brassica sp. The amount of indole-acetic acid (IAA) and phosphate solubility were assessed from isolated bacterial. Plant growth promotion was examined in 10-days old seedling with three independent experiments. Our results showed that Streptomyces sp. produced moderate levels of IAA and it was able to solubilize phosphate. Inoculation of Streptomyces sp. enhanced lateral root number, fresh weight and chlorophyll content in Arabidopsis thaliana. Moreover, the inoculation of Streptomyces sp. significantly increased vegetative growth on Arabidopsis and Brassica sp. by producing higher fresh weight and chlorophyll content. Streptomyces sp. also enhanced tolerance to abiotic stress in Arabidopsis and Brassica sp. by increasing fresh weight under condition of salt and heat stress. Under salt stress, inoculation of Streptomyces sp. in Arabidopsis induced activity of catalase enzyme and decreased hydrogen peroxide (H2O2) and malondialdehyde (MDA) production. In the molecular levels, Streptomyces sp. induced protein accumulations in Arabidopsis including nitrogen assimilation (GS1), carbohydrate metabolism (cFBPase), and the light-harvesting chlorophyll (Lhcb1) protein.

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Authors and Affiliations

Windy Manullang
Huey-wen Chuang
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Abstract

The effects of a microbial inoculant (Thervelics®: a mixture of cells of Bacillus subtilis C-3102 and carrier materials) on rice (Oryza sativa cv. Milkyprincess) and barley (Hordeum vulgare cv. Sachiho Golden) were evaluated in four pot experiments. In the first and second experiments, the dry matter production of rice and barley increased significantly by 10–20% with the inoculation of the mixture at a rate of 107 cfu ⋅ g–1 soil compared with the non-inoculated control. In the third experiment, the growth promoting effects of the mixture, the autoclaved mixture and the carrier materials were compared. The dry mater production of rice grains was the highest in the mixture, and it was significantly higher in the three treatments than in the control, suggesting that the carrier materials may also have a plant growth promoting effect and the living cells might have an additional stimulatory effect. To confirm the efficacy of the living cells in the mixture, only B. subtilis C-3102 cells were used in the fourth experiment. In addition, to estimate the mechanisms in growth promotion by B. subtilis C-3102, three B. subtilis strains with similar or different properties in the production of indole-3-acetic acid (IAA), protease and siderophore and phosphatesolubilizing ability were used as reference strains. Only B. subtilis C-3102 significantly increased the dry matter production of rice grains and the soil protease activity was consistently higher in the soil inoculated with B. subtilis C-3102 throughout the growing period. These results indicate that the microbial inoculant including live B. subtilis C-3102 may have growth promoting effects on rice and barley.

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Authors and Affiliations

Abdul Saleem Jamily
Yuki Koyama
Thida Aye Win
Koki Toyota
Seiya Chikamatsu
Takeshi Shirai
Taisuke Uesugi
Hiroaki Murakami
Tetsuya Ishida
Takaomi Yasuhara

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