Reactive oxygen species and antioxidants in legume nodules

Abstract

Reactive oxygen species are a ubiquitous danger for aerobic organisms. This risk is especially elevated in legume root nodules due to the strongly reducing conditions, the high rates of respiration, the tendency of leghemoglobin to autoxidize, the abundance of nonprotein Fe and the presence of several redox proteins that leak electrons to O2. Consequently, nodules are particularly rich in both quantity and diversity of antioxidant defenses. These include enzymes such as superoxide dismutase (EC 1.15.1.1) and ascorbate peroxidase (EC 1.11.1.11) and metabolites such as ascorbate and thiol tripeptides. Nodule antioxidants have been the subject of intensive molecular, biochemical and functional studies that are reviewed here. The emerging theme is that antioxidants are especially critical for the protection and optimal functioning of N2 fixation. We hypothesize that this protection occurs at least at two levels: the O2 diffusion barrier in the nodule parenchyma (inner cortex) and the infected cells in the central zone.

Effects of double stress on antioxidant enzyme activity in Vigna radiata (L.)Wilczek

“…linity, drought, extremes of temperature and heavy metals. Physiologically these stresses cause oxidative damage to plants either directly or indirectly (COMBA et al 1998, BAISAK et al 1994, BECANA et al 2000, SHAH et al 2001, SIDDIQUI et al 2008. In fact, oxidative stress hazards are due to the production of reactive oxygen species which include superoxide radical (O 2 + ), hydroxyl radical (OH + ) and hydrogen peroxide (H 2 O 2 ).…”

Análise estrutural de folhas de Eugenia uniflora L. (Myrtaceae) coletadas em ambientes rural e urbano, SP, Brasil

“…Existem também os fotoxidantes, como o ozônio (O 3 ) e o nitrato de peroxiacetila (PAN), que são os poluentes secundários produzidos por meio de reações fotoquímicas, a partir de alguns poluentes primários (Freedman 1995). Tais substâncias podem provocar alterações fisiológicas, bioquímicas e estruturais nas plantas, uma vez que são muito reativas e atacam as membranas celulares (Becana et al 2000).…”

Nodules and oxygen

“…In spite of their relevance for O 2 transport, class II Hbs are generally believed to contribute to oxidative stress in nodules, i.e., to the production of reactive oxygen species (ROS) like superoxide anions (O 2 Ϫ ) and hydrogen peroxide (H 2 O 2 ; Becana et al 1998;2000). This has recently been confirmed by Ott et al (2005) who showed that RNAi inhibition of leghemoglobin (lb) gene transcription in nodules of L. japonicus led not only to an increase in free O 2 and the loss of nitrogenase and nitrogen fixation in nodules, but also to reduced H 2 O 2 contents (Günther et al 2007).…”

“…This has recently been confirmed by Ott et al (2005) who showed that RNAi inhibition of leghemoglobin (lb) gene transcription in nodules of L. japonicus led not only to an increase in free O 2 and the loss of nitrogenase and nitrogen fixation in nodules, but also to reduced H 2 O 2 contents (Günther et al 2007). The mechanism of ROS production by symbiotic hemoglobins is as follows: Lb (Fe 2ϩ ) that has bound O 2 can undergo spontaenous autooxidation to inactive Lb (Fe 3ϩ ) (Becana et al 2000), while the O 2 molecules are reduced and released as O 2 Ϫ . Lb (Fe 2ϩ ) is then regenerated by the action of ferric-Lb reductase (Ji et al 1992).…”