Isoflavonoid induction and nitrogen assimilation in AM colonized red clover

Abstract

This study postulates that the symbiosis between red clover, Trifolium pratense L., and the arbuscular mycorrhizal (AM) fungus, Glomus intraradices Schenck & Smith, enhances secondary phenolic metabolism and nitrogen assimilation. To test this hypothesis, the four objectives set forth were to determine the impact of AM colonization and/or rhizobial inoculation in red clover on the: (1) growth parameters; (2) nitrogen assimilation, via the activity of glutamine synthetase (GS, E.C. 6.3.1.2), total N content and soluble protein concentration; (3) contents of isoflavonoids (e.g. genistein, daidzein, biochanin A, and formononetin); and (4) contents of these four isoflavonoids over time and with a hormonal factor, jasmonic acid (JA). To accomplish these objectives, four greenhouse experiments were performed. The overall results indicate that the colonized red clover plants, with 22% to 37% of AM root colonization, had enhanced shoot height as well as increased shoot and root dry masses. Co-inoculation with Rhizobium enhanced the growth parameters more than inoculation with either microsymbiont alone. The concentrations of micronutrients significantly increased in red clover with AM colonization and/or rhizobial inoculation, while the macronutrients did not vary to any great degree. (Abstract shortened by UMI.)