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

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 (NGRΩfixF), 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 NGRΩfixF 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 NGRΩfixF 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.