Ethylene evolution and antioxidant defence mechanism in Cicer arietinum roots in the presence of nitrate and aminoethexyvinylglycine

The plants of chickpea (Cicer arietinum L.) cv. HC-1 were raised in earthen pots filled with 5 kg washed river sand under naturel conditions of the screen house. Forty to forty-five days after sowing, the roots were exposed to 10, 20 and 40 mM NO3- through rooting medium with the aim for studying NO3- induced changes in ethylene production and root functioning. Aminoethoxyvinylglycine (AVG, 5 mu-M), an ethylene biosynthesis inhibitor, was added after 24 h of NO3- treatments. Three days after the treatments, NO3- applied at 10 mM induced a significant increase in 1-amino cyclopropane-1-carboxylic acid (ACC) content (49 %) and in vivo ACC oxidase activity (100 %) which were associated with an increase in ethylene production (25 %) and with an important increase in both H2O2 (60 %) and malondialdehyde (MDA, 1270 %). In contrast, supply of NO3- at 40 mM resulted in an important increase in ethylene production (400 %) by inducing significant enhancement of ACC content (123 %), ACC oxidase activity (128 %) and with simultaneous increase of H2O2 (160 %) and MDA (1 900 %). The reversible membrane alteration showed a linear correlation with ethylene production. This was confirmed by a sharp decline in NO3- induced ethylene evolution by AVG. An oxidative damage by NO3- to the defence mechanism was evident from the increase in H202 content which is apparent from the decrease in activities of superoxide dismutase (EC 1.15.1.1), catalase (EC 1.11.1.6), ascorbate peroxidase (EC 1.11.1.11 ) and glutathione reductase (EC 1.11.1.9) to 23-67, 39-43, 33-55 and 26-45 %, respectively. The AVG treatment showed partial recovery in the activities of these enzymes and decrease in H2O2 content (17-32 %). It is inferred that ethylene evolution due to NO3-is the key marker interfering with the functioning of roots along with the weakening of antioxidant defence mechanism