Enhancement of freezing tolerance of olive leaves by foliar application of methyl jasmonate and 24-epibrassinolide through changes in some metabolites and antioxidant activity

The olive production is limited by the important factor of winter freezing damage. The purpose of this research was to investigate the probable role of exogenously applied methyl jasmonate (MeJA; 0.02, 0.1, and 0.2 mM) and 24-epibrassinolide (EBR; 0.2, 0.4, and 0.6 mu M) to alleviate the adverse effect of freezing stress in olive (Olea europaea L. cv. Koronieki) leaves, which was conducted in a research orchard. Furthermore, some physiological and biochemical changes were studied in olive leaves at six sampling dates, and their relationship with freezing tolerance (expressed as LT50) were investigated. The results indicated that the olives freezing tolerance, soluble carbohydrates, proline, total soluble proteins, antioxidant enzymes, DPPH radical scavenging capacity, as well as total phenolic content were significantly increased using the foliar application of MeJA and EBR. The highest and lowest freezing tolerance in EBR 0.6 mu M and control olives was as much as -8.22 degrees C and -6.87 degrees C, respectively. The LT50 profile had a significant negative correlation with accumulation of some compounds such as leaf soluble carbohydrates, total soluble protein, total phenolic content, DPPH scavenging capacity, as well as activating the catalase enzyme. Moreover, EBR 0.6 mu M and control treatments respectively had the highest and lowest ratio between unsaturated fatty acids and saturated fatty acids (UFA/SFA ratio), especially in January. It can be concluded that the freezing tolerance of olive leaves can be increasing by the foliar application of MeJA and EBR treatments, which can be utilized as a preventive instrument to decrease freezing damage.

Automated summary

This study found that foliar application of MeJA and EBR can significantly increase freezing tolerance in olive leaves, with improvements in soluble carbohydrates, proline, total soluble proteins, antioxidant enzymes, DPPH radical scavenging capacity, and total phenolic content. Notably, the highest freezing tolerance was observed in EBR 0.6 mu M treatment and the lowest in the control group.