Involvement of nitric oxide in 5-aminolevulinic acid-induced antioxidant defense in roots of Elymus nutans exposed to cold stress

Nitric oxide (NO) and 5-aminolevulinic acid (5ALA) play fundamental roles in plant responses to environmental stresses, but their cross-talk in antioxidant defense in cold-stressed Elymus nutans Griseb. have not been investigated. We herein report that 5ALA and NO donor, sodium nitroprusside (SNP), alleviated cold stress-induced plant growth inhibition and lipid peroxidation in roots of two E. nutans ecotypes (Damxung, DX and Zhengdao, ZD). However, application of an NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt (PTIO) differentially blocked these protective effects indicating that an inhibition of NO accumulation reduced 5ALA-enhanced cold resistance. Application of exogenous 5ALA or NO markedly up-regulated activities of superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase, enhanced reduced glutathione accumulation and reduced glutathione to oxidized glutathione ratio, activated plasma membrane (PM) H + -ATPase, and reduced Na + /K + ratio in roots of the two E. nutans ecotypes. Moreover, in the presence of 5ALA, nitric oxide synthase (NOS) activity and NO release in cold-resistant DX were higher than those in cold-sensitive ZD. Conversely, both NO treatment and inhibition of endogenous NO accumulation by PTIO or NOS inhibitor N ω -nitro-L-arginine did not induce 5ALA production. These results suggest that NO might be acting as a downstream signal to mediate 5ALA-induced cold resistance by activating antioxidant defense and PM H + -ATPase and maintaining Na + and K + homeostasis.