Abstract

Abiotic stress factors like cold, heat, drought, flood, salinity, or oxidizing agents are the major threats to agricultural system in any country that affect the economic yield of crops. Phytohormones, the chemical messengers, play a vital role in resistance of plants to the changing environments by regulating physiological and molecular processes.

Salinity

Salinity is one of the major stresses in aridand semi arid regions causing adverse effectsat like physiological, biochemical, and molecular levels,limiting crop productivity.Salt stress can disturb growth and photosynthetic processes by causing changes in the accumulation of Na+, Cl–, and nutrients.

Antioxidant Enzyme

Leaves used for photosynthesis measurement were selected for the assay of antioxidant enzymes. Leaf tissue (200 mg) was homogenized with an extraction buffer containing 0.05% (v/v) Triton X-100 and 1% (w/v) poly vinyl pyrrolidone in 100 mM potassium-phosphate buffer (pH 7.0) using a chilled mortar and pestle. The homogenate was centrifuged at 15000 × g for 20 min at 4ºC. The supernatant obtained after centrifugation was used for the assay of SOD and GR enzymes.For the assay of APX, extraction buffer was supplemented with 2 mM ascorbate, SOD activity was assayed by monitoring the inhibition of photochemical reduction of nitro blue tetrazolium (NBT), according to the methods of Beyer and Fridovich.

The antioxidant enzyme system constitutes super oxide dismutase (SOD) as the primary step of cellular defense. It dis mutates superoxide ions (O2–) to H2O2 and O2.Further, the accumulation of H2O2 is restricted by theaction of the ascorbate glutathione cycle, whereas corbate peroxidase (APX, EC)reduces it to H2O. The final step is catalyzed by glutathione reductase (GR), which catalyzes the NADPH dependent reaction of oxidized glutathione (GSSG) to reduced gluco tathione (GSH).

Natural Enzyme

Salicylic acid (SA),a naturally occurring plant hormone, acts as an important signaling molecule in plants, and has diverse effects on tolerance to abiotic stress. Exogenous application of SA may participate in the regulation of physiological processes in plants, such as stomatal closure, ion uptake and transport,membrane permeability, and photosynthesis and growth. Its role in abiotic stress tolerancebsuch as ozone, UV-B, heat, heavy metal, andosmotic stress has been reported.

Studies on barley (Hordeum vulgare), maize (Zeamays), wheat (Triticum aestivum), bean(Phaseolus vulgaris), lentil (Lens culinaris),and sunflower (Helianthus annuus) suggested that SA may be used to alleviate salt stress.

Photosynthetic Trait

The activity CA in leaf was estimated in the leaves used for photosynthesis measurements according to method describe by makino dependant reduction on pH 7.25-8.45 .

Yield Trait

All harvest pods were collected and counted. Pods were counted on meter scale.Yield traits Plants grown with 50 mM NaCl exhibited decrease of 13.3% in pod length,19.1% in podnumber,21.8% in seed number, and 20.1% inseed yield in comparison to the control. The application of 0.5 mM SA grown under mM NaCl (control) increased pod length by 19.9%, pod number by 19.9%, seed number by 20.2%,and seed yield by 20.1% in comparison to the control. SA at 0.5 mM concentration was found to alleviate the salt stress effects maximally, and nullified the effect of NaCl when compared with the control. SA at 1.0 mM was found to be inhibitory and increased the decrease in yield traits caused by 50 mM NaCl alone.