Salt stress in apple seedlings was mitigated by n-propyl dihydrojasmonate, a synthetic analog of jasmonic acid

The effects of n-propyl dihydrojasmonate (PDJ) application, which is a synthetic analog of jasmonic acid (JA) against sodium chloride (NaCl) stress in apple seedlings, were examined. The malondialdehyde (MDA) and proline concentrations, endogenous JA and abscisic acid (ABA) concentrations, antioxidant activities, Na+ and K+ concentrations, along with 9-cis-epoxycarotenoid deoxygenase 1 (MdNCED1), ABA 8'-hydroxylase 1 (MdCYP707A1), allene oxide synthase 1 (MdAOS1), jasmonate resistant (MdJAR), jasmonate ZIM-domain 2 (MdJAZ2), Delta 1-pyrroline-5-carboxylate synthetase (MdP5CS), ornithine aminotransferase 1 (Md0AT1), proline dehydrogenase (MdPDH), salt overly sensitive 1 (MdS0S1) and Na+/H+ exchanger 1 (MdNHX1) gene expressions in the leaves were analyzed. NaCl treatment without PDJ application (PDJ NaCl+) significantly decreased chlorophyll concentrations and superoxide (SOD), peroxidase (POD) and catalase (CAT) activities, but increased the ion leakage, MDA, proline, and Na+ concentrations, as well as the hydrogen peroxide (H2O2) and endogenous JA and ABA concentrations in the leaves. Foliar application of PDJ before NaCl treatment (PDJ(+)NaCl(+)) decreased Na+ concentrations, ion leakage, MDA, proline accumulation and H2O2 generation, but increased K+ concentrations, antioxidant capacity, and chlorophyll concentrations in the leaves. In the PDJ(+)NaCl(-). group, although the JA and ABA concentrations and MdAOS1, MdJAR, and MdNCED1 gene expressions were increased, the MdJAZ2 and MdCYP707A1 gene expressions were decreased. In addition, the PDJ(+)NaCl(+) group showed higher MdPDH, MdSOS1, and MdNHX1 gene expressions and lower MdP5CS gene expressions than the PDJ(-)NaCl(+) group at 7 and 10 days after treatment. The present data suggested that PDJ application could induce rapidly endogenous JA and ABA, enhance SOD, POD, and CAT activities, decrease the Na+ uptake, and mitigate NaCl stress.