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Growth Promotion of Salicornia bigelovii by Micromonospora chalcea UAE1, an Endophytic 1-Aminocyclopropane-1-Carboxylic Acid Deaminase-Producing Actinobacterial Isolate.

ABSTRACT: Salicornia bigelovii is a promising halophytic crop for saline soils in semi-arid regions. This study was designed to characterize isolates of endophytic actinobacteria from S. bigelovii roots and evaluate the effects associated with plant growth promotion. Twenty-eight endophytic isolates obtained from surface-sterilized roots of S. bigelovii were initially selected based on their production of 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase in vitro in a chemically defined medium. Application of Micromonospora chalcea UAE1, possessing the highest ACC deaminase activity, to S. bigelovii seedlings significantly enhanced the plant growth under gnotobiotic and greenhouse conditions. This was clear from the increases in the dry weight and length of both shoot and root, and seed yield compared to the non-ACC deaminase-producing isolate Streptomyces violaceorectus, or control treatment. The growth promotion was also supported by significant increases in the content of photosynthetic pigments and the levels of auxins, but significant decreases in the levels of ACC in planta. Under greenhouse conditions, M. chalcea recovered from inside the inoculated roots in all samplings (up to 12 weeks post inoculation), suggesting that the roots of healthy S. bigelovii are a suitable habitat for the endophytic actinobacterial isolates. Pure cultures of M. chalcea were not capable of producing auxins, gibberellic acid, cytokinins or polyamines in vitro. This indicates that the growth promotion is most likely to be due to the reduction of the endogenous levels of the stress hormone ethylene. Our findings suggest that growth and yields of S. bigelovii can be enhanced by the field application of the endophyte M. chalcea UAE1. This study is the first to report potential endophytic non-streptomycete actinobacteria to promote the growth of halophytic plants in semi-arid zones under greenhouse conditions.

SUBMITTER: El-Tarabily KA

PROVIDER: S-EPMC6668420 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Salicornia bigelovii is a promising halophytic cash crop that grows in seawater of the intertidal zone of the west-north coast of the UAE. This study assess plant growth promoting (PGP) capabilities of halotolerant actinobacteria isolated from rhizosphere of S. bigelovii to be used as biological inoculants on seawater-irrigated S. bigelovii plants. Under laboratory conditions, a total of 39 actinobacterial strains were isolated, of which 22 were tolerant to high salinity (up to 8% w/v NaCl). These strains were further screened for their abilities to colonize S. bigelovii roots in vitro; the most promising ones that produced indole-3-acetic acid, polyamines (PA) or 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase (ACCD) were selected for rhizosphere-competency under naturally competitive environment. Three outstanding rhizosphere-competent isolates, Streptomyces chartreusis (Sc), S. tritolerans (St), and S. rochei (Sr) producing auxins, PA and ACCD, respectively, were investigated individually and as consortium (Sc/St/Sr) to determine their effects on the performance of S. bigelovii in the greenhouse. Individual applications of strains on seawater-irrigated plants significantly enhanced shoot and root dry biomass by 32.3-56.5% and 42.3-71.9%, respectively, in comparison to non-inoculated plants (control). In addition, plants individually treated with Sc, St and Sr resulted in 46.1, 60.0, and 69.1% increase in seed yield, respectively, when compared to control plants. Thus, the synergetic combination of strains had greater effects on S. bigelovii biomass (62.2 and 77.9% increase in shoot and root dry biomass, respectively) and seed yield (79.7% increase), compared to the control treatment. Our results also showed significant (P < 0.05) increases in the levels of photosynthetic pigments, endogenous auxins and PA, but a reduction in the levels of ACC in tissues of plants inoculated with Sc/St/Sr. We conclude that the consortium of isolates was the most effective treatment on S. bigelovii growth; thus confirmed by principal component and correlation analyses. To this best of our knowledge, this is the first report about halotolerant rhizosphere-competent PGP actinobacteria thriving in saline soils that can potentially contribute to promoting growth and increasing yield of S. bigelovii. These halotolerant actinobacterial strains could potentially be exploited as biofertilizers to sustain crop production in arid coastal areas.

Dataset Information

Growth Promotion of Salicornia bigelovii by Micromonospora chalcea UAE1, an Endophytic 1-Aminocyclopropane-1-Carboxylic Acid Deaminase-Producing Actinobacterial Isolate.

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