ALLEVIATION OF SALINITY STRESS ON Vicia faba L. PLANTS VIA SEED PRIMING WITH MELATONIN

Melatonin is an environmentally friendly-molecule with a potent free radical scavenger and antioxidant capacity. Two pot experiments were conducted during two successive winter seasons (2011/2012 and 2012/2013) at the wire-house of the National Research Centre, Dokki, Cairo, Egypt to study the potentiality of melatonin (100 mM and 500 mM) in alleviating the harmful effect of diluted seawater at a relatively low and high concentrations (3.85 dS/m and 7.69 dS/m, respectively) on the performance of faba bean plants. The results revealed that irrigation of faba bean plants with diluted seawater reduced growth parameters (plant height, leaves number/plant, fresh and dry weights of plant), relative water content (RWC), photosynthetic pigments (chlorophylls a, b and carotenoids), indole acetic acid, total carbohydrate, K+, Ca+2, as well as the ratios of K+/Na+ and Ca+2/Na+. This was accompanied by significant increases in phenolic content, compatible solutes (total soluble carbohydrate, free amino acids, proline), Na+ and Cl- relative to the control plants (untreated plants). On the other hand, melatonin treatments improved growth parameters, RWC, photosynthetic pigments, total carbohydrate, total phenolic content, indole acetic acid, K+, Ca+2 as well as K+/Na+ and Ca+2/ Na+ ratios, either in the plants irrigated with tap water or with diluted seawater, as compared with corresponding controls. Meanwhile, melatonin treatments reduced the levels of compatible solutes, as well as Na+ and Cl- contents, relative to those of corresponding controls. Salinity stress and/or melatonin treatments induced the production of new protein bands that did not occur in the control plants. Melatonin at 500 mM had a more pronounced effect in alleviating the adverse effects of the two salinity levels under study on the performance of faba bean plants than 100 mM melatonin.