Indole acetic acid (IAA) producing endophytic bacteria on direct somatic embryogenesis and plant regeneration of Exacum
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RESEARCH ARTICLES
Indole acetic acid (IAA) producing endophytic bacteria on direct somatic embryogenesis and plant regeneration of Exacum travancoricum Bedd. Chellappan Soundar Raju1 · Abubakker Aslam2 · Devarajan Thangadurai3 · Jeyabalan Sangeetha4 · Krishnan Kathiravan5 · Appakan Shajahan2 Received: 7 March 2020 / Revised: 15 August 2020 / Accepted: 18 August 2020 © Society for Plant Research 2020
Abstract Endophytic bacteria were isolated from Withania somnifera (L.) Dunal and their potentials were explored through the in vitro plant regeneration techniques. Initially, indole acetic acid (IAA), phosphate solubilization and siderophore producing isolates were screened out. These isolates were identified using molecular tools like 16s rRNA gene sequences namely Bacillus pumilus AS02, Sphingobacterium thalpophilum AS34, Pseudomonas aeruginosa AS36, Agrobacterium tumefaciens AS38 and Enterobacter aerogenes AS75. Further, the regeneration efficacy of IAA producing endophytic bacteria has been analysed on an endangered plant—Exacum travancoricum Bedd. The leaf and inter-node explants of E. travancoricum with or without bacterial infection were tested on Murashige and Skoog’s (MS) medium encompassing 6-benzyladenine (BA; 2.0 mg L− 1) and l-tryptophan (0.2%; w/v). Somatic embryo induction was observed on both explants. The leaf explants infected with S. thalpophilum AS34, P. aeruginosa AS36 and E. aerogenes AS75 exhibited highest percentage of somatic embryo induction (93.3%) compared with the inter-node explants (86.6%). The explants without bacterial infection (control) and the presence of exogenous IAA exhibited lower level of response (88.8%, leaf and 75.5%, inter-node). Histological analysis revealed the appearance of globular embryogenic masses on epidermal, sub-epidermal regions of both explants. The development of torpedo, cotyledon stage and protoderm formation without the vascular connection from explants confirmed direct somatic embryogenesis. This was confirmed with scanning electron microscopy. Sub-culturing of cotyledon somatic embryos in MS liquid medium without growth regulators was performed to obtain well developed shoots with roots. Keywords Indole acetic acid · Endophytic bacteria · 16s rRNA gene sequence · Protoderm · Somatic embryos · Withania somnifera · Exacum travancoricum
Introduction
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s42535-020-00159-w) contains supplementary material, which is available to authorized users.
Recent advances in plant propagation include induction of beneficial microorganisms (Parray et al. 2015). Bacteria are found to be much helpful for plant growth and development due to the presence of plant growth regulators (PGR). A
* Chellappan Soundar Raju [email protected]
3
Department of Botany, Karnatak University, Dharwad 580003, Karnataka, India
Appakan Shajahan [email protected]
4
Department of Environmental Science, School of Earth Science Systems, Central University of Kerala, Kasaragod 6
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