Indole acetic acid (IAA) producing endophytic bacteria on direct somatic embryogenesis and plant regeneration of Exacum travancoricum Bedd.

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.

Isolation, Characterization, and Evaluation of Native Rhizobacterial Consortia Developed From the Rhizosphere of Rice Grown in Organic State Sikkim, India, and Their Effect on Plant Growth

“…Except for K. cowanii, which is considered to be from clinical origin, other species of the genus are nitrogen-fixing bacteria, which are commonly associated with plants (Li Y. et al, 2017). They are most frequently found in the nitrogen-fixing bacterial community of some non-leguminous plant, such as rice (Hardoim et al, 2013) and sugarcane (Raju et al, 2020). The Kosakonia species contains flagella, which enable them to swim and possibly help in the attachment to the plant surface.…”

Bacterial Bioprotectants: Biocontrol Traits and Induced Resistance to Phytopathogens

“…Rhizosphere bacteria have the ability to produce the phytohormones that play important roles in processes such as cell division in symbiotic as well as non-symbiotic plant roots [51]. Phytohormones are mainly classified as gibberellins, cytokinins, ethylene and auxins that affect plant-microbe associations [52,53].…”

“…The microbial phytohormones stimulate plant development and enhance plant tolerance to abiotic and biotic stresses [35,56]. Moreover, previous studies have reported that phytohormones stimulate the innate immunity of plants against pathogens such as bacteria and fungi [18,51,57]. Kapoor et al [58] reported the inhibition of Verticillium dahliae and Fusarium oxysporum growth and development by up to 70% by an IAA-producing endophytic fungi.…”

Phytoremediation and Microorganisms-Assisted Phytoremediation of Mercury-Contaminated Soils: Challenges and Perspectives

“…Bacterial synthesis of IAA is associated with root proliferation when the released IAA quantity is optimum for the associated plant species. However, the positive effects of bacteria-produced IAA on plant phenotype are seen only in conjunction with other PGP mechanisms [ 161 , 162 , 163 , 164 ], but bacteria-producing IAA might confer a significant advantage to plants in Hg phytoremediation field situations because it stimulates rooting. NH 3 production is often associated with N 2 -fixing bacteria.…”