2 Pag., 1 Fig.Legume nodules have elevated respiratory rates in mitochondria and bacteroids to meet the energy requirements
for N2 fixation. However, respiration inevitably produces reactive oxygen species (ROS) such as superoxide
radicals and hydrogen peroxide (H2O2). We have studied the changes associated with natural senescence (aging)
in the antioxidant system of mitochondria purified from common bean (Phaseolus vulgaris) nodules. During
nodule aging, the concentrations of lipid peroxides and oxidized proteins increased in mitochondria, but not in
the cytosolic fraction. Also, the activities of three enzymes involved in ascorbate synthesis and regeneration were
down-regulated. By contrast, qRT-PCR analysis, immunoblots, and enzyme activity assays reveal a significant
up-regulation of manganese superoxide dismutase (MnSOD) activity during aging, whereas the protein level of
peroxiredoxin IIF (PrxIIF) remained unchanged. Overall, our results suggest that, in legume nodules, natural
senescence is associated with a decline in the capacity of mitochondria to synthesize and regenerate ascorbate,
and that this organelle is a preferential target of oxidative stress.This work was supported by the MICINN (AGL2008-01298) and Gobierno de Aragón (group A53).Peer reviewe