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Waterlogging usually results from overuse and/or poor management of irrigation water and is a serious constraint with damaging effects. The rapidly depleting oxygen from submerged root zone is sensed and plant adjusts expressing anaerobic proteins. Plant cells shift their metabolism towards low energy yielding anaerobic fermentation pathways in the absence of oxygen. Structural modifications are also induced as aerenchyma formation and adventitious rootings, etc. Studies at molecular and biochemical levels to facilitate early perception and subsequent responses have also been worked out to produce resistant transgenic plants. This review explores the sequential changes of plant responses at different levels regarding their defense strategies and efforts made to enhance them, tailoring crucial regulators so that they can withstand waterlogging stress.

417Salicylic acid (SA) is considered to be a potent plant hormone because of its diverse regulatory roles in plant metabolism (Hayat et al. 2010). SA is an endogenous plant growth regulator of phenolic nature that possesses an aromatic ring with a hydroxyl group or its functional derivative. SA is known to affect growth and bioproductivity in the crops (Hayat et al. 2010). It is also recognized that SA potentially generates a wide array of metabolic responses in plants and also affects photosynthetic parameters and plant water relations (Fariduddin et al. 2003, Hayat et al. 2005. The oxidative damage caused to the plants due to the increased generation of reactive oxygen species under stressful environment could be mitigated by the external application of SA (Hayat et al. 2010). A large body of literature demonstrates the effect of SA seed soaking on plant growth and development. However, very little is known about the effect of SA applied to foliage on plant growth and development. Keeping in view the diverse physiological roles played by SA, the present research was undertaken to improve our understanding of the effect of the various concentrations of SA applied as foliar spray on the growth, photosynthesis, nitrogen fixation and its assimilation in chickpea and to screen for the most effective concentration of SA. MATERIAL AND METHODSPlant material and growth condition. The certified seeds of chickpea (Cicer arietinum L.) cv. Avarodhi were purchased from the National Seed Corporation Ltd., New Delhi, India. The seeds were surface sterilized with 0.01% mercuric chloride solution followed by inoculation with Rhizobium and were sown in earthen pots (0.254 m in diameter) filled with sandy loam soil and farmyard manure (6:1) arranged under a simple randomized block design in the net house of the Botany Department of Aligarh Muslim University, India during the winter season (November-February). The temperature was 15-25°C and irrigation was done on alternate days during the experiment. At the stage of 30 days after sowing (DAS), the foliage of the plants was sprayed uniformly either with double distilled water (control), ethanol (5%), Tween-20 (0.5%) or with different concentrations (10 -4 , 10 -5 or 10 -6 mol/L) of SA dissolved in ethanol to elucidate the effect of exogenous SA on plants. The plants were sampled at 90 DAS to assess various growth and physiological parameters. Tween-20 was used as a surfactant. Both ethanol and Tween 20 were sprayed separately to see whether the effects are solely by SA or by the combination of these.Salicylic acid mediated changes in growth, photosynthesis, nitrogen metabolism and antioxidant defense system in Cicer arietinum L. ABSTRACTThe present study reveals that the foliar application of salicylic acid (SA), irrespective of the concentration used, generated an increase of dry mass per plant, nodule dry mass and leghemoglobin content in chickpea plants. The activity of nitrogenase (E.C 1.18.6.1), nitrate reductase (NR) (E.C. 1.6.6.1), glutamine synthetase (GS) (E.C 6.3.1.2), ...

Surface-sterilized seeds of two tomato cultivars (cv. K-25 and Sarvodya) were soaked in 100 microM CdCl(2) for 8 h (shotgun approach). The resulting 59-day-old seedlings were sprayed with 10(-8) M of 28-homobrassinolide (HBL) or 24-epibrassinolide (EBL) to their foliage. Both cultivars showed significantly different response to Cd stress. Cadmium severely restricted the growth, photosynthetic efficiency, and activity of nitrate reductase (E.C. 1.6.6.1) and carbonic anhydrase (E.C. 4.2.1.1) in Sarvodya as compared to K-25. However, the activities of antioxidative enzymes were significantly higher in K-25. This result may be considered an indication of better tolerance of the K-25 cultivars to Cd stress. Moreover, the spray of both the brassinosteroids (HBL/EBL) were found very effective in neutralizing the adverse effects generated by metals that reflect in better photosynthetic performance by the cultivars. An interesting aspect of this study is that HBL or EBL spray caused a further increase in proline content and antioxidative enzyme activities, which were already enhanced by Cd stress. This effect of brassinosteroids (HBL/EBL) was more pronounced in K-25 than in Sarvodya, representing the tolerance and adoptable behavior of K-25.

-Seeds of chickpea inoculated with Rhizobium were sown in pots supplemented with different doses of cadmium (0, 25, 50 or 100 mg per kg of soil). At the stage of 30 days after sowing (DAS), the plants were sprayed with 20 mM solution of proline and were sampled at 90 DAS to assess the various parameters. The foliar treatment of proline resulted in the alleviation of the adverse effects generated by metal exposure, which was expressed in terms of the increase in plant growth. The activity of carbonic anhydrase in the cadmium-fed plants sprayed with proline was higher than that of control. The proline applied as foliar spray increased the photosynthetic attributes and yield characteristics in the cadmium-stressed plants. The activity of antioxidative enzymes increased with increasing concentration of cadmium. Maximum values were recorded in the plants exposed to 100 mg cadmium per kg of soil.