Involvement of Activated Oxygen in Nitrate-Induced Senescence of Pea Root Nodules

Stress-Induced Legume Root Nodule Senescence. Physiological, Biochemical, and Structural Alterations

“…The specific objective was to gain further information on the role of some important antioxidants (APX, thiols, and ferritin) in the protection of legume N 2 fixation against the noxious effects of peroxides, free radicals, and catalytic iron. Data presented in this paper are intended to complement two previous reports (Escuredo et al, 1996;Gogorcena et al, 1997) in providing an orthogonal comparison of nitrate-and dark-stress-induced senescence in determinate and indeterminate nodules.…”

“…Because this method could not distinguish between GSH and hGSH (Klapheck, 1988), and because it was uncertain whether hGSH was present in nodules, we estimated the concentration of total tripeptides in pea and bean nodules as 0.9 mm (Escuredo et al, 1996;Gogorcena et al, 1997). Using HPLC, we found in this work that hGSH is present in nodules at variable concentrations: 0.12 mm GSH and 0.31 mm hGSH for bean nodules, and 0.82 mm GSH and 0.11 mm hGSH for pea nodules.…”

“…Each increase in O 2 took 5 to 6 min and was followed by a 20-to 25-min equilibration period. These data were used to calculate the oxygen diffusion barrier (ODB) resistance and carbon costs of nitrogenase, as described in Escuredo et al (1996).…”

“…Prolongation of stress induces premature nodule senescence, which shares some features with natural senescence (nodule aging), such as the loss of N 2 fixation, the increase in lytic activities, and the formation of green pigments from leghemoglobin (Lb) (Pfeiffer et al, 1983;Sarath et al, 1986). This stress-induced senescence has been linked to the enhanced production of oxidants and the lowering of antioxidant defenses (Escuredo et al, 1996;Gogorcena et al, 1997). Oxidants include inorganic (H 2 O 2 ) and organic (lipid) peroxides as well as "catalytic iron," the fraction of iron in plant tissues capable of catalyzing the generation of hydroxyl radicals through Fenton reactions .…”

“…In most types of stress, the initial decrease of nitrogenase activity is associated with a decline in the O 2 concentration reaching the infected cells and bacteroids (Witty et al, 1986;Carroll et al, 1987;Layzell et al, 1990;Escuredo et al, 1996). Prolongation of stress induces premature nodule senescence, which shares some features with natural senescence (nodule aging), such as the loss of N 2 fixation, the increase in lytic activities, and the formation of green pigments from leghemoglobin (Lb) (Pfeiffer et al, 1983;Sarath et al, 1986).…”