Nitrogenase activity and trehalose content of nodules of drought-stressed common beans infected with effective (Fix +) and ineffective (Fix −) rhizobia

Abstract

Nitrogenase activity and trehalose accumulation were measured in nodulated and non-nodulated common beans ( Phaseolus vulgaris) that were exposed to drought. Plants were infected with the Fix + Rhizobiumsp NGR234, or a Fix − derivative (NGRΩ fixF), or high trehalose-producing, native rhizobia. Trehalose content increased significantly while acetylene reduction activity (ARA) decreased in the nodules of plants exposed to drought. Nevertheless, ARA decreased at a slower rate in nodules with high trehalose levels. Under water stress, nodules infected with NGRΩ fixF tended to accumulate more trehalose than nodules infected with wild-type NGR234 (9±0.1 vs 8±0.1 mg g −1 dw, respectively). Highest trehalose accumulations were registered in nodules of plants infected with native rhizobia (average 16 mg g −1 dw), and these plants also exhibited the highest relative water content (65%), while in plants infected with the NGRΩ fixF RWC was significantly lower (56%). Our results suggest that nodule trehalose may protect bacterial nitrogenase activity under drought conditions, and that both trehalose and biological nitrogen fixation (BNF) contribute to drought tolerance.