The effect of spraying of methyl jasmonate and 24-epi-brassinolide on photosynthesis, chlorophyll fluorescence and leaf stomatal traits in black mustard (Brassica nigra L.) under salinity stress

Methyl jasmonate and Epi-brassinolide as plant growth regulators have significant biological effects on plant growth, including increased tolerance to salt stress in plants. In this study, the effects of salinity stress and its interaction with methyl jasmonate and Epi-brassinolide on chlorophyll concentration, rate of photosynthesis, transpiration, stomatal conductance and resistance and chlorophyll fluorescence in medical plant of black mustard (Brassica nigra L.) in hydroponic conditions, were evaluated based on a factorial design in completely randomized design with four replications. So that four weeks after germination plants were treated with various concentrations of sodium chloride (80, 40, 0 mM), methyl jasmonate (0 and 75 mM) and Epi-brassinolide (0, 5.1, 3 mM). The plants treated with salinity, with increasing concentration of sodium chloride, their chlorophyll concentrations, Hill reaction rate, transpiration and stomatal conductance decreased but the stomatal resistance, the initial fluorescence (F0) and maximum fluorescence (Fm) increased. At the same amounts of NaCl, with increasing concentrations of methyl jasmonate and Epi-brassinolide all tested traits were improved, such that by spraying 75 mM of methyl jasmonate, stomatal conductance (90.23 m2s mol-1) reached its highest level. With increasing levels of Epi-brassinolide in the same condition, the salinity of maximum fluorescence (Fm) reached to (559.21). The results of this experiment showed that the application of methyl jasmonate and Epi-brassinolide can improve the efficiency of photosynthesis and thereby improves the growth of black mustard (Brassica nigra L.) under salinity stress.