NO is involved in JA- and H2O2-mediated ALA-induced oxidative stress tolerance at low temperatures in tomato

Low temperature is a limiting factor in tomato production during early spring and winter in North China. Plants perceive low temperature through activation of cold-sensitive signaling pathways, which up-regulate cold-responsive gene expression and increase plant cold tolerance. Many studies reported that 5-aminolevulinic acid (ALA) protect plants against environmental stresses. We showed that ALA pretreatment enhanced cold-triggered oxidative stress tolerance in tomato via hydrogen peroxide (H2O2) signaling and subsequent cross-talk with redox signals. Here, we investigated whether ALA induced the jasmonic acid (JA) and nitric oxide (NO) signaling in response to cold stress in tomato, and evaluated the relationships between JA, NO, and H2O2. Tomato plants were pretreated with inhibitors of JA synthesis [salicylhydroxamic acid (SHAM) and diethyldithiocarbamic acid (DIECA)] or NO synthesis [tungstate and NG-nitro-L-arginine methyl ester (L-NAME)] as well as scavengers of NO [2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO)] or H2O2 [dimethylthiourea (DMTU)]. Then, these plants were treated with exogenous ALA, JA, or H2O2. Finally, plants were grown under normal or low temperature conditions, The results showed that ALA dramatically elevated JA levels under normal-and low-temperature conditions. Exogenous JA and H2O2 dramatically increased superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) activities and reduced membrane lipid peroxidation. The JA synthesis inhibitors SHAM and DIECA did not significantly affect membrane lipid damage and SOD, CAT, and GR activities, compared with cold-treated plants alone. Whereas ALA significantly attenuated the inhibition effects of SHAM and DIECA. In contrast, JA and H2O2 mitigated the DMTU-, SHAM-, and DIECA-mediated reduction in antioxidation. ALA, JA, and H2O2 up-regulated nitrate reductase (NR) and nitric oxide synthase (NOS) transcript levels and NR and NOS activities, thereby triggering the NO bust. cPTIO, tungstate and L-NAME weakened JA-mediated, and essentially abolished H2O2-mediated antioxidase activity and mitigated membrane lipid damage. These results indicate that ALA induced H2O2 and JA displayed independent but synergistic roles in regulating tomato antioxidation. NO may act downstream of H2O2 along with JA to regulate antioxidant enzyme gene expression and increase tomato cold tolerance. In conclusion, NO is a downstream signal of H2O2 which cooperated with JA, mediated ALA-regulated oxidative stress tolerance under low temperatures in tomato.