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

MOLINA FAVERO C., CREUS C., SIMONTACCHI M., PUNTARULO S. Y LAMATTINA L.

MOLECULAR PLANT-MICROBE INTERACTIONS

AMER PHYTOPATHOLOGICAL SOC

Año: 2008 vol. 21 p. 1001 - 1009

0894-0282

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 root (AR) formation. Here, we analyzed aerobic NO production by A. brasilense Sp245 wt and its mutants Faj009 (IAA-deficient) and Faj164 (periplasmic nitrate reductase negative) and its correlation with 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 (Lycopersicon esculentum 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 cPTIO, both LR and AR formation were inhibited evidencing that NO mediates 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 root branching irrespective of bacterial capacity for IAA synthesis.