Methyl jasmonate induces oxidative/nitrosative stress and the accumulation of antioxidant metabolites in Phoenix dactylifera L.

Objectives: The present study aimed to explore the eliciting effects of increasing concentrations (50, 100, and 200 µM) of methyl jasmonate (MeJA). We cultivated actively proliferating buds of Phoenix dactylifera L. cv. Barhee in a temporary immersion system and we monitored the bioactive compound accumulation after 7 days of culture.

Methods: Total phenolic (TPC) and flavonoid (TFC) contents were determined by high-performance liquid chromatography (HPLC), Fourier-transform infrared (FTIR), and radical scavenging activity using DPPH and ABTS assays. We also explored the activity of phenylpropanoid pathway enzymes, namely phenylalanine ammonia-lyase (PAL), tyrosine ammonia-lyase (TAL) and polyphenol oxidase (PPO).

Results: Our results revealed that MeJA treatment induced oxidative stress, and at the same time increased the activity of related defense enzymes in a dose-dependent manner. Exogenous application of MeJA at 200 µM increased ROS (two fold), hydrogen peroxide (3.7 fold), nitric oxide (14 fold), MDA (6.3 fold), superoxide dismutase (5.9 fold), catalase (4.4 fold) and guaiacol peroxidase (3.87 fold). Furthermore, the results demonstrated that 200 µM MeJA treatment enhanced the activities of PAL (3.65 fold), TAL (4.35 fold), PPO (threefold) and increased TPC (twofold) and TFC (1.75 fold) contents in buds cultures higher than the control. HPLC analysis showed that buds cultures exposed to 200 µM MeJA accumulated maximum amount of catechin (11 fold), 4-hydroxybenzoic acid (1.48 fold), caffeic acid (2.5 fold) and p-coumaric acid (1.76 fold) and demonstrate antioxidant capacity with the lowest DPPH (114.5 µg ml) and ABTS (90.2 µg ml) IC50 values on day 7 of culture as compared to the control. The MeJA in the culture medium directly reduced cell viability in a dose dependent manner up to 35% with the highest concentration.

Conclusion: The results of this study has revealed, for the first time, that MeJA offers a promising potential for the production of phenolic compound in Phoenix dactylifera L. buds.