Abstract: Three-year-old ‘Zaozhong No. 6’ loquat (Eriobotrya japonica Lindl.) seed lings were foliar-sprayed with 02, 05, 10 and 15 mmol·L-1 o f sodium nitroprusside (SNP), subjected to low temperature (-3 ℃) stress for 6 hours, and then cultured at 25 ℃ for four days. The antioxidant metabolites and enzymes in the seedling leaves were determined 0, 1, and 4 days after recovery. Comparing with the control (water spraying), all SNP treatments had a decreased H2O2 content but an increased content of glutathione (GSH) and ascorbic aci d (AsA) and increased activity of ascorbate peroxidase (APX), glutathione reduct ase (GR), dehydroascorbate reductase (DHAR) and monodehydroascorbate reductase ( MDAR) in the seedling leaves. Four days after recovery, the H2O2 content in the seedling leaves treated with 05 mmol·L-1 of SNP decreased by 7553 %, while the GSH and AsA contents and the APX, GR, DHAR and MDAR activities were increased by 2912%, 2340%, 500%, 444%, 4953%, and 6268%, respectivel y. All of these suggested that appropriate dosage of exogenous NO could enhance the activity of antioxidant system in loquat leaves and alleviated the cell inju ry of loquat leaves under low temperature stress. In this study, the appropriate dosage of NO was 05 mmol·L-1 of SNP.

Key words: nitrogen fertilizer, rice straw, biological activity, soil function, heat stress.