Foliar application of 28-homobrassinolide mitigates salinity stress by increasing the efficiency of photosynthesis in Brassica juncea

Prior to sowing, seeds of Brassica juncea Czern and Coss cv. Varuna were soaked in water (controls) or in 50, 100 or 150 mM of sodium chloride (NaCl) for 6 h. The resulting plants, at 15, 30 and 45 days after sowing (DAS) were either not treated (controls) or were treated with aqueous solutions of the hormone 28-homobrassinolide (HBL), which was applied to their foliage in concentrations of 10(-10), 10(-8) or 10(-6) M. The concentration of NaCl showed an inverse correlation with the activity of nitrate reductase (EC 1.6.6.1), the activity of carbonic anhydrase (EC 4.2.1.1), chlorophyll content at 60 DAS, the rate of photosynthesis at 60 DAS, and seed yield at 140 DAS (at harvest), all of which decreased in parallel with increases in NaCl concentration. However, treatment with HBL attenuated those decreases and neutralized the ill effects of salinity stress, completely at the lowest NaCl concentration and partially at the higher NaCl concentrations. The seed yield of the crop can be increased by the foliar application of HBL, even under conditions of salinity stress.