Jasmonic acid regulates the ascorbate-glutathione cycle in Malus baccata Borkh. roots under low root-zone temperature

Jasmonic acid (JA), which is an important phytohormone, plays a key role in plant growth, development and stress responses. Here, Malus baccata Borkh. seedlings were used to study the mechanism by which JA alleviates the oxidative damage induced by low root-zone temperature (5 degrees C) through regulating the ascorbate-glutathione (AsA-GSH) cycle. The roots of M. baccata Borkh. were subjected to three treatments [5 degrees C, 5 degrees C + JA, and 5 degrees C + ibuprofen (IBU)] for 0, 12, 24, and 48 h. The results showed that treatment with low root-zone temperature could modulate the non-enzymatic and enzymatic components of the AsA-GSH cycle, significantly inducing the accumulation of MDA and H2O2. Additionally, the endogenous JA content changed dramatically, and the expression levels of the related genes [lipoxygenase (LOX), allene oxide synthase (AOS), and allene oxide cyclase (AOC)] showed different trends. In plants pretreated with JA, the endogenous JA content increased at 24 h, and the gene expression levels of LOX, AOS, and AOC were upregulated. We also found a marked increase in the activities of antioxidant enzymes [ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), and glutathione reductase (GR)], a decrease in oxidized glutathione (GSSG) and an increased GSH/GSSG ratio, which resulted in lower MDA and H2O2 contents. Thus, the oxidative stress was alleviated. Plants pretreated with IBU experienced an opposite effect on the function of the AsA-GSH cycle and the gene expression in the JA synthesis route relative to those subjected to exogenous JA treatment, indicating that endogenous JA can alleviate oxidative damage by regulating the function of the AsA-GSH cycle under low root-zone temperature.