Plant water status, ethylene evolution, N2-fixing efficiency, antioxidant activity and lipid peroxidation in Cicer arietinum L. nodules as affected by short-term salinization and desalinization

Salinity induced changes in ethylene evolution, antioxidant defense system, N2-fixing efficiency and membrane integrity in relation to water and mineral status in chickpea (Cicer arietinum L.) nodules were studied under screen house conditions. At vegetative stage (55-65 DAS) plants were exposed to single saline irrigation (Cl- dominated) of levels 0, 2.5, 5.0 and 10.0 dS m-1 and sampled after 3 d. The other set of treated plants was desalinized by flooding and the plants were sampled after further 3 d. Water potential (Ψw) of leaf and osmotic potential (Ψs) of leaf and nodules significantly decreased from -0.44 to -0.56 MPa and from -0.65 to -1.15 MPa and from -0.75 to -1.77 MPa, respectively upon salinization. RWC of leaf and nodules also reduced from 86.05% to 73.30% and 94.70% to 89.98%, respectively. The decline in Ψs of nodules was due to accumulation of proline and total soluble sugar. In comparison to control, the increase in ethylene (C2H4) production was 35-108% higher and correspondingly increase in 1-aminocycloprane-1-carboxylic acid (ACC) content (37-126%) and ACC oxidase activity (31-118%) was also noticed. Similarly, marked increase in H2O2 (25-139%) and thiobarbituric acid substances (TBRAS, 11-133%) contents was seen. N2-fixing efficiency i.e. N2-ase activity, leghemoglobin and N contents of nodules declined significantly after saline irrigation. The induction in specific activity of antioxidant enzymes was confirmed by the increase in activity of superoxide dismutase, peroxidase, ascorbate peroxidase, glutathione reductase and glutathione transferase, whereas reverse was true for catalase. These activated enzymes could not overcome the accumulation of H2O2 in nodules. Ascorbic acid content also declined from 20 to 38%, whereas Na+/K+ ratio and Cl- content were significantly enhanced. Upon desalinization, a partial recovery in all above metabolic processes and water relations parameters was noticed. It is suggested that ethylene in relation to water status and lipid peroxidation and along with other metabolic processes has an important role in induced nodules senescence under salinity.