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 (NGROmegafixF), 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 NGROmegafixF 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 NGROmegafixF 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. (C) 2004 Elsevier Ltd. All rights reserved.
