Aerobic Nitric Oxide Production by Azospirillum brasilense Sp245 and Its Influence on Root Architecture in Tomato

• Published in: Molecular plant-microbe interactions Vol. 21; no. 7; pp. 1001 - 1009
• Main Authors: Molina-Favero, Celeste, Creus, Cecilia Monica, Simontacchi, Marcela, Puntarulo, Susana, Lamattina, Lorenzo
• Format: Journal Article
• Language: English
• Published: St Paul, MN APS Press 01.07.2008; The American Phytopathological Society
• Subjects: adventitious roots; aerobic conditions; Aerobiosis; Azospirillum brasilense; Azospirillum brasilense - genetics; Azospirillum brasilense - physiology; Bacterial plant pathogens; biochemical pathways; Biological and medical sciences; Fundamental and applied biological sciences. Psychology; Genes, Bacterial; heterotrophic nitrification; indole acetic acid; Indoleacetic Acids - metabolism; lateral root; Lycopersicon esculentum; Lycopersicon esculentum - microbiology; Mutation; Nitrate Reductase - genetics; Nitrate Reductase - metabolism; nitric oxide; Nitric Oxide - biosynthesis; PGPB; Phytopathology. Animal pests. Plant and forest protection; plant architecture; plant growth-promoting rhizobacteria; Plant Roots - growth & development; Plant Roots - microbiology; root systems; Signal Transduction; Solanum lycopersicum var. lycopersicum; Symbiosis - genetics; Symbiosis - physiology; tomatoes; Auxin; Microbiology; Spirillaceae; Azospirillum brasilense; PGPB; lateral root; Dicotyledones; Indoleacetic acid; Angiospermae; Lycopersicon esculentum; Bacteria; Plant growth substance; Plant growth promoting rhizobacteria; Solanaceae; Spirillales; Root; Enzyme; Aerobe; heterotrophic nitrification; Seedlings; Strain; Vegetable crop; Nitrate reductase; Nitric oxide; Denitrification; Spermatophyta; Oxidoreductases; Mutation
• ISSN: 0894-0282; 1943-7706
• DOI: 10.1094/mpmi-21-7-1001

The major feature of the plant-growth-promoting bacteria Azospirillum brasilense is its ability to modify plant root architecture. In plants, nitric oxide (NO) mediates indole-3-acetic acid (IAA)-signaling pathways leading to both lateral (LR) and adventitious (AR) root formation. Here, we analyzed aerobic NO production by A. brasilense Sp245 wild type (wt) and its mutants Faj009 (IAA-attenuated) and Faj164 (periplasmic nitrate reductase negative), and its correlation with tomato root-growth-promoting effects. The wt and Faj009 strains produced 120 nmol NO per gram of bacteria in aerated nitrate-containing medium. In contrast, Faj164 produced 5.6 nmol NO per gram of bacteria, indicating that aerobic denitrification could be considered an important source of NO. Inoculation of tomato (Solanum lycopersicum Mill.) seedlings with both wt and Faj009 induced LR and AR development. In contrast, Faj164 mutant was not able to promote LR or AR when seedlings grew in nitrate. When NO was removed with the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5,-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), both LR and AR formation were inhibited, providing evidence that NO mediated Azospirillum-induced root branching. These results show that aerobic NO synthesis in A. brasilense could be achieved by different pathways and give evidence for an NO-dependent promoting activity on tomato root branching regardless of bacterial capacity for IAA synthesis.