Abstract: In a solution culture experiment, the effects of exogenous sodium nitroprusside (SNP) as nitric oxide (NO) donor on ryegrass(Lolium perenne L.) seedlings in growth, active oxygen metabolism, polyamine content and photosynthesis under the stress resulting from 100 mmol·L^-1 NaCl were studied, and the results showed that 50 μmol·L^-1 SNP significantly increased the activities of superoxide dismutase(SOD), peroxidase (POD) and ascorbate peroxidase (APX) and the contents of glutathione(GSH), spermine (Spm) and spermidine (Spd), and (Spm+Spd)/Put ratio, decreased the contents of putrescence(Put), O^—·₂, H₂O₂ and malondiadehyde (MDA) in ryegrass seedling leaves under NaCl stress, SNP also increased the contents of chlorophyll and carotene, net photosynthetic rate (P_n), stomatal conductance(G_s), reduced intercellular carbon dioxide concentration (C_i) and increased relative dry weight of seedlings. The kinetic data of chlorophyll fluorescence revealed that SNP reduced the minimal fluorescence (F₀) of ryegrass seedling leaves under NaCl stress, which indicated that SNP has certain protecting effect on photosynthetic membrane system. SNP could not only significantly raised the maximum fluorescence (F_m), PSⅡ potential fluorescence efficiency (F_v/F₀) and PSⅡ maximum fluorescence efficiency (F_v/F_m) of ryegrass seedling leaves under NaCl stress but also increased the actual photochemical efficiency of PSⅡ (Φ_PSⅡ), photochemical quenching (q_P), electron transport rate (ETR) and photochemical rate (PCR), reduced nonphotochemical quenching (NPQ) and antennae heat dissipation (D), but were ineffective treated with 1 mmol·L^-1 PTIO(2-phenel-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, a NO scavenger) and 0.5 μmol·L^-1 NaNO₂ (as control). These results suggested that the alleviation of salt damage by exogenous NO may be because of increasing the capacity of antioxidation and the capture and conversion of solar energy help enhance the photosynthetic capacities of ryegrass suffering salt stress.

Key words: nitric oxide, salt stress, ryegrass, active oxygen metabolism, polyamine, photosynthesis