Objectives This study examined the physiological and biological mechanisms of ammonium molybdate on alleviating the frost damage of peach leaves, in order to provide a theoretical reference for alleviating low temperature stress through nutrient management in peach production.

Methods Peach seedlings with 20 open leaves were used as test materials in pot experiments. In optimum spraying concentration experiment, ammonium molybdate solutions of 0.01%, 0.04%, 0.08% and 0.12% were sprayed three times, each spraying consumed 50 mL of Mo-containing solution and in 5 days’ interval, and water was sprayed at the same way in control (M0). When the spraying was completed, the seedlings were cultivated at 0℃. At 0 h, 12 h, 24 h and 48 h of treatment, samples of seedling functional leaves were collected, and the frost index, relative electrical conductivity, proline and soluble sugar contents were determined. In biological response pot experiment, seedlings were sprayed with 0.04% ammonium molybdate solution in the same way as above. When spraying was completed, the seedlings were cultivated under normal (20℃) and low temperature (0℃) condition. At the 0, 24 and 48 h of treatment, samples of seedling functional leaves were collected, and oxidative damage to cell membranes, osmosis regulating substance contents and the gene expression levels for molybdenum cofactor sulfurase (LOS5/ABA3), proline synthase (P5CS1) and peroxidase (RCI3) under normal temperature conditions were determined.

Results 1) Optimum spraying concentration experiment showed that under low temperature stress, compared with M0, the frost index was significantly decreased by 23.8%, 38.4%, 29.6%, 24.0% in treatments of 0.01%, 0.04%, 0.08% and 0.12% of ammonium molybdate, respectively. The relative conductivity was significantly decreased by 5.10%, 7.19%, 3.77%, 5.03%, respectively. The SPAD values and net photosynthetic rates decreased slowly, the proline contents were significantly increased by 0.89%, 11.67%, 8.54%, 5.06%, respectively, and the soluble sugar contents were significantly increased by 1.95%, 9.64%, 6.73%, 4.50%, respectively. The optimum sparying concentration appeared to be 0.04% of molydbate. 2) Biological response experiment showed that as compared with M0 at 0℃, the gene expression levels for LOS5/ABA3, P5CS1 and RCI3 were all significantly increased, the increment were 2.76 times, 2.64 times and 1.50 times respectively at 24 h, and 2.54 times, 2.29 times and 1.66 times respectively at 48 h. With 48 h of treatment, the proline and soluble sugar contents were increased by 8.27% and 8.69% respectively, the activities of CAT (catalase), POD (peroxidase), SOD (superoxide dismutase) were increased by 1.98%, 11.79% and 9.15% respectively, and the MDA (malondia ldehydes) content was decreased by 10.8%.

Conclusions Spraying of ammonium molybdate could regulate the gene expression of LOS5/ABA3, P5CS1, and RCI3 in functional leaves of peach seedlings, increase the contents of soluble sugar, proline and the activity of antioxidant enzyme, relieve cell membrane oxidation damage, and alleviate the damage of low temperature stress to peach seedling.