JXB Advance Access originally published online on January 16, 2006
Journal of Experimental Botany 2006 57(3):665-673; doi:10.1093/jxb/erj056
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RESEARCH PAPER |
Drought effects on carbon and nitrogen metabolism of pea nodules can be mimicked by paraquat: evidence for the occurrence of two regulation pathways under oxidative stresses
Departamento de Ciencias del Medio Natural, Universidad Pública de Navarra, Campus de Arrosadía, E-31006 Pamplona, Spain
* To whom correspondence should be addressed. E-mail: cesarai{at}unavarra.es
Biological nitrogen fixation (BNF) is dramatically affected by environmental constraints such as water stress or heavy metals. It has been reported that these stresses induce the over-production of reactive oxygen species (ROS) and, in turn, oxidative stress that may be responsible for the above-mentioned BNF decline at the molecular level. Oxidative stress, occurring under different environmental stresses, has been widely related to physiological damage. However, a direct relationship between oxidative stress and the decline of BNF, independently from any other cellular damage resulting from adverse environmental situations, has yet to be demonstrated. In order to study the likely in vivo relationship between ROS and BNF inhibition in the legume–Rhizobium symbiosis, two paraquat (PQ) doses, 1 (LPQ) and 10 (HPQ) mmol m–3, were applied to pea roots for 96 h in order to exacerbate ROS production. Whole-plant physiology and nodule metabolism parameters were determined every 24 h to monitor the evolution of plant responses to ROS. LPQ provoked BNF decline, which was preceded by a prior decrease in sucrose synthase (SS) activity. However, HPQ gave rise to a faster and more pronounced BNF inhibition, which coincided with a decline in SS and also with a reduction in leghaemoglobin (Lb) content. These results indicate a likely involvement of ROS in the effects of environmental stresses on BNF. Furthermore, these results support the occurrence of two regulation pathways for BNF under oxidative stress, one of these involving carbon shortage and the other involving Lb/oxygen flux.
Key words: Leghaemoglobin, nitrogen fixation, nodule metabolism, oxidative stress, paraquat, Pisum sativum L., ROS signalling, sucrose synthase
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