Inoculation with Azospirillum increased exudation of rhizobial nod- gene inducers by alfalfa roots

Azospirillum brasilense caused a significant increase in the nod-gene inducing activity of crude alfalfa root exudates when compared to exudates of the noninoculated controls. nod-gene inducing activity of exudates from yeast extract-elicited roots was also increased, but to a lesser extent. Fractions separated by HPLC from the exudates of roots treated with Azospirillum yeast extract, and a control showed different nod-gene inducing capacities. The profiles of flavonoids extracted from the Azospirillum - inoculated roots differed from those of controls, but the difference was less pronounced than was seen in the exudates. The profile of the flavonoids from elicited roots differed greatly from the former two. The data obtained from the flavonoid analyses were in accordance with enzyme activities taxi mRNA levels of the defense-related proteins phenylalanine ammonia-lyase (PAL), chalcone isomerase (CHI), and isoflavone reductase (IFR); CHI activity and its mRNA were induced in the roots elicited by yeast extract, whereas the activities of PAL and CHI, and mRNA levels of PAL, CHI, and IFR were not induced by Azospirillum .