The Response of Carbon Metabolism and Antioxidant Defenses of Alfalfa Nodules to Drought Stress and to the Subsequent Recovery of Plants

Abstract

Alfalfa (Medicago sativa) plants were exposed to drought to examine the involvement of carbon metabolism and oxidative stress in the decline of nitrogenase (N 2 ase) activity. Exposure of plants to a moderate drought (leaf water potential of 21.3 MPa) had no effect on sucrose (Suc) synthase (SS) activity, but caused inhibition of N 2 ase activity (243%), accumulation of succinate (136%) and Suc (158%), and up-regulation of genes encoding cytosolic CuZn-superoxide dismutase (SOD), plastid FeSOD, cytosolic glutathione reductase, and bacterial MnSOD and catalases B and C. Intensification of stress (22.1 MPa) decreased N 2 ase (282%) and SS (230%) activities and increased malate (140%), succinate (168%), and Suc (1435%). There was also up-regulation (mRNA) of cytosolic ascorbate peroxidase and down-regulation (mRNA) of SS, homoglutathione synthetase, and bacterial catalase A. Drought stress did not affect nifH mRNA level or leghemoglobin expression, but decreased MoFe-and Fe-proteins. Rewatering of plants led to a partial recovery of the activity (75%) and proteins (.64%) of N 2 ase, a complete recovery of Suc, and a decrease of malate (248%) relative to control. The increase in O 2 diffusion resistance, the decrease in N 2 ase-linked respiration and N 2 ase proteins, the accumulation of respiratory substrates and oxidized lipids and proteins, and the up-regulation of antioxidant genes reveal that bacteroids have their respiratory activity impaired and that oxidative stress occurs in nodules under drought conditions prior to any detectable effect on SS or leghemoglobin. We conclude that a limitation in metabolic capacity of bacteroids and oxidative damage of cellular components are contributing factors to the inhibition of N 2 ase activity in alfalfa nodules.

Photosynthetic carbon and nitrogen metabolism and the relationship between their metabolites and lipid peroxidation in dwarf bamboo (Fargesia rufa Yi) during drought and subsequent recovery

“…concentration (Table 3), which was similar to the result in leaves of Medicago sativa (Naya et al 2007). This indicates that dwarf bamboo may tolerate temporary NH 4 ?…”

Does a terminal drought tolerance QTL contribute to differences in ROS scavenging enzymes and photosynthetic pigments in pearl millet exposed to drought?

“…CAT was shown increased under drought treatment in e.g Prunus, tomato, sesame, alfalfa or wheat (Rubio et al, 2002;Luna et al, 2004;Sofo et al, 2005;Őnayayar, 2005;Naya et al, 2007;Fazeli et al, 2007), but decreased or unchanged in sunflower, pea and some grasses (Iturbe-Ormaetxe et al, 1998;Fu and Huang, 2001). In our piece, a new CAT isozyme was induced under drought conditions, but the total CAT activity did not increase significantly under drought stress.…”

“…maize, wheat, beans, rice, alfalfa (Pastori and Trippi, 1992;Kele and Oncel, 2002;Rubio et al, 2002;Sharma and Dubey, 2005;Naya et al, 2007;Torres-Franklin et al, 2008). APX is referred as an polygene family encoded enzyme with strong affinity to its substrate H 2 O 2 (e.g.…”

Will Elevated Carbon Dioxide Concentration Amplify the Benefits of Nitrogen Fixation in Legumes?

“…Despite considerable attention, the causes of drought-induced inhibition of N 2 fixation are still not well understood. There are a number of mechanisms proposed to account for the reduction in N 2 fixation under drought stress: (1) oxygen limitation, (2) C shortage, (3) regulation by N metabolism, and (4) oxidative damage of cellular components in the nodules (Serraj et al, 1999;Galvez et al, 2005;Ladrera et al, 2007;Marino et al, 2007;Naya et al, 2007). A detailed review of these mechanisms is beyond the scope of this Update.…”

“…Therefore, it is unlikely that additional Suc available to host cell in plants grown at elevated [CO 2 ] will be able to amielorate a drought-induced reduction in N 2 fixation. It is not clear if this mechanism is operating in all legume species and new evidence suggests that under moderate drought, impaired respiratory activity, and oxidative damage of nodule components precedes reductions in Suc synthase activity (Naya et al, 2007;Sassi et al, 2008).…”