Ethylene evoluation and modification of antioxidant defense mechanism as indices of salinity stress tolerance in Ciceer arietinum L. nodules

Salinity induced changes in the ethylene evolution, antioxidant activity, and membrane integrity in relation to water and mineral status in indeterminate type of chickpea (Cicer arietinum L.) nodules in cv. CSG-8962, (National check for salinity tolerance) were studied under natural conditions of screen house. At flowering stage (80-90 DAS) plants were exposed to single saline irrigation (CI--dominated) of levels 2.5, 5.0, and 10.0 dSm-1 and sampled after 3 d. The control plants were irrigated with canal water. The other set of treated plants were revived after desalinization and the plants were sampled after further 3 d. Water potential ('Pw) of leaf and osmotic potential ('Ps) of leaf and nodules significantly decreased from -0.77 to -0.93 MPa and from -0.86 to -1.35 MPa and from -0.94 to -1.75 MPa, respectively upon salinization. Relative water content (RWC %) of leaf and nodules also reduced from 82.55% to 75.60% and 95.75% to 85.35%, respectively. The decline in ('I's) of nodules was due to accumulation of proline and total soluble sugars. In comparison to control, the increase in ethylene (CzHJ production was 33% to 82% higher and correspondingly increases in 1-aminocyclopropane-1¬carboxylic acid (ACC) content (50-162%) and ACC oxidase activity (46-167%) was also noticed. Similarly, 1.42 to 3.08 fold and 1.08 to 1.61 fold increase in HzOz and thiobarbituric acid reactive substances (TBRAS) contents was also observed, respectively. N content of nodules declined after saline irrigation. The induction in specific activity of antioxidant enzymes was confirmed by the increase in specific activity of superoxide dismutase (11-133%), catalase (9-109%), peroxidase (50-227%), ascorbate peroxidase (17-87%), glutathione reductase (69-288%) and glutathione transferase (8-66%). The induced antioxidant enzymes activity was not sufficient to scavenge the oxidative damage of nodules as it is clear from the accumulation of H202 in nodules. Ascorbic acid (AA) content also declined from 13.24 to 54.50%, whereas Na+lK+ ratio and CI- content were significanty increased. All the metabolic changes were also correlated to the osmotic status of the nodules. Upon revival, a partial recovery in all above metabolic processes. a.nd water relation paramete\{s were noticed. It is concluded that under the cumulative effect of salinity and reduced water statusi ethylene, lipid peroxidation and H20Z are playing a key role in the functioning of chickpea nodules.