Effects of Methyl Jasmonate on some photosynthetic parameters of peppermint (Mentha piperita) in saline conditions

The present study was aimed to evaluate a biological solution to improve peppermint plant growth and production in the salt-affected soil. The experiment was arranged in a factorial experiment based on completely randomized design with three replications in the greenhouse under controlled conditions (28/15 oC in day/night). Three levels of methyl jasmonate (0, 75 and 150 µM) and four levels of sea water (0, 3, 6, 9 dS/m) were the treatments. After nine weeks, ETR, Fv/ Fm, Fm, transpiration, RWC, chlorophyll a, chlorophyll b, stomatal conductance and leaf dry weight were measured. The results showed that salinity decreased ETR, Fv/ Fm, Fm, transpiration, RWC, chlorophyll a, chlorophyll b, stomatal conductance and leaf dry weight while increased anthocyanins, Fo and NPQ. The measured traits were influenced by the different levels of methyl jasmonate. Where plants grown at salinity of 9 dS/m and sprayed with 75 µM of methyl jasmonate, anthocyanin increased up to 8% while the membrane electrolyte leakage decreased by 35%. Methyl jasmonate also ameliorate the negative effects of salinity on stomatal conductance (54%), ETR (10%) and leaf relative water content (6%). Higher levels of methyl jasmonate (150 µM), however, had an inhibitory effect on stomatal conductance, chlorophyll a and ETR. Overall, it seems that methyl jasmonat had a positive role under salt conditions due in particular to improving plant water relations, stomatal conductance and therfore, increasing electron transfer rate and the photosystem II efficiency. In conclusion, spraying of methyl jasmonate at the rate of 75 µM improved growth parameters of peppermint medicinal plant under salt cnditions.