Abstract
The aim of this study was to analyze possible positive effects of putatively endophytic PGPB (PGB_invit), which was isolated from long-term in vitro cultured fraser photinia microshoots, on seed and 7-day old seedling stages of Arabidopsis thaliana. Seeds and in vitro-germinated seedlings were inoculated with 107 CFU/mL and 108 CFU/mL active (A) and inactive (I) endophytic bacterial populations along with their mix compositions (A+I) and suspended in MPYE broth together with their controls (untreated ones). 14 days old seedlings were evaluated for various plant growth parameters [i.e., shoot and root fresh weight (FW), shoot length (SL), shoot and root dry weight (DW), root length (RL) and photosynthetic pigments including chlorophyll a, b and carotenoids of plantlets] as well as endophytic and rhizospheric trait of bacteria. Positive effects of inactive and active bacterium on FW, DW and photosynthetic pigments for 7-day inoculated seedlings were recorded whereas an increase in photosynthetic contents for seed stage inoculations was observed. Rhizospheric and endophytic colonization of the bacteria was confirmed by PCR with the presence of virD1 gene, which is previously recorded to be existed in the plasmid of bacterium after inoculation. Overall, these results demonstrated that this peculiar putative endophytic bacterium being beneficial in active and even more useful in inactive form for A. thaliana when optimum conditions and concentrations are used. Moreover, presence of virD1 gene suggested its potential possibility to be used in bioengineering along with various other beneficial PGPR features as biofertilizer.
Highlights
Plant growth promoting bacteria (PGPB) are among the beneficial interactions between plant and microorganisms which colonize the rhizosphere or internal tissues of many plant species and induce positive effects on physiology of plants such as increased plant growth and improved tolerance to biotic and abiotic stresses (Poupin et al, 2013)
For seed stage bacterial inoculations, both A 107 and 108 concentrations resulted in a decrease in fresh weight (FW) of seedlings while I inoculation at 107 concentration showed statistically insignificant result in comparison to control (Table 1)
When A and I form of bacterium were inoculated together, at both tested concentrations, the detrimental effect of the A form was not detected as the highest FW was obtained (47.08 mg) with along with their mix compositions (A+I) for 107
Summary
Plant growth promoting bacteria (PGPB) are among the beneficial interactions between plant and microorganisms which colonize the rhizosphere or internal tissues (endophytes) of many plant species and induce positive effects on physiology of plants such as increased plant growth and improved tolerance to biotic (caused by fungi, bacteria, viruses and nematodes) and abiotic stresses (Poupin et al, 2013). Many plant species are being monitored for the diversity of endophytic bacteria within their tissues and new endophytes are continuously being reported (Hallmann and Berg, 2006; Rosenblueth and MartinezRomero, 2006; Ryan et al, 2008) It is well-known that beneficial endophytic bacteria could promote plant growth and yield either directly by i.e., i) nitrogen fixation, ii) solubilization of phosphorus, iii) sequestering of iron by production of siderophores, iv) production of phytohormones such as auxins, cytokinins, gibberellins and v) lowering of ethylene concentration (Kloepper et al, 1989; Glick, 1995; Glick et al, 1999) or indirectly by i.e., i) antibiotic production, ii) synthesis of antifungal metabolites, iii) depletion of iron from the rhizosphere, iv) competition for colonization on roots, v) production of fungal cell wall lysing enzymes, and vi) induced systemic resistance (Weller and Cook, 1986; Dunne et al, 1993; Kloepper et al, 1988; Liu et al, 1995; Glick et al, 1999).
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