title: Phytohormone production and colonization of canola (Brassica napus L.) roots by Pseudomonas fluorescens 6-8 under gnotobiotic conditions.
abstract: Pseudomonas fluorescens  6-8, a rhizosphere isolate previously shown to enhance root elongation of canola ( Brassica napus  L.), was characterized for its ability to produce indole-3-acetic acid and cytokinins in pure culture and in the rhizosphere of canola under gnotobiotic conditions in comparison with the cytokinin-producing strain P. fluorescens G20-18 and its mutant CNT2. Strain 6-8 produced isopentenyl adenosine, zeatin riboside, and dihydroxyzeatin riboside at levels similar to those of G20-18, but only very low concentrations of indole-3-acetic acid. In a gnotobiotic assay canola inoculated with 6-8 and G20-18 had higher concentrations of isopentenyl adenosine and zeatin riboside in the rhizosphere and greater root length than the noninoculated control. The ability of strain 6-8 to colonize canola roots was assessed following transformation with the green fluorescent protein and inoculation onto canola seed in a gnotobiotic assay. Higher populations of strain 6-8 were observed on the proximal region of the root closest to the seed than on the mid and distal portions 9 days after seed inoculation. The ability of P. fluorescens 6-8 to produce cytokinins, colonize the roots of canola seedlings, and enhance root elongation may contribute to its ability to survive in the rhizosphere and may benefit seedling growth.
authors.affiliation: Department of Food and Bioproduct Sciences, University of Saskatchewan, Saskatoon, SK, Canada.
authors.forename: Rajash
authors.initials: R
authors.lastname: Pallai
authors.forename: Russell K
authors.initials: RK
authors.lastname: Hynes
authors.forename: Brij
authors.initials: B
authors.lastname: Verma
authors.forename: Louise M
authors.initials: LM
authors.lastname: Nelson
mesh_terms: D000818:Animals; D029688:Brassica napus / Q000254:growth & development / Q000382:microbiology* / Q000502:physiology; D003583:Cytokinins / Q000378:metabolism; D005856:Germ-Free Life; D007210:Indoleacetic Acids / Q000378:metabolism; D007541:Isopentenyladenosine / Q000031:analogs & derivatives / Q000378:metabolism; D010937:Plant Growth Regulators / Q000378:metabolism*; D018517:Plant Roots / Q000254:growth & development / Q000382:microbiology / Q000502:physiology; D011551:Pseudomonas fluorescens / Q000502:physiology*; D058441:Rhizosphere; D036226:Seedlings / Q000382:microbiology; D012639:Seeds / Q000382:microbiology; D013559:Symbiosis
chemical_list: D003583:Cytokinins; D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; C030737:indoleacetic acid; D007541:Isopentenyladenosine; C009699:zeatin riboside