NOS-like-mediated nitric oxide is involved in Pinus thunbergii response to the invasion of Bursaphelenchus xylophilus

The content of NO and H2O2 as well as the activities of nitric oxide synthase (NOS)-like and nitrate reductase (NR) were monitored in the needles of Pinus thunbergii infected by Bursaphelenchus xylophilus. The results showed that the content of NO increased significantly only 8 h after the invasion of B. xylophilus, while H2O2 increased 12 h after invasion. NO donor SNP could promote and NO scavenger cPTIO could prevent the production of NO and H2O2. The content of NO changed earlier than that of H2O2. In addition, the symptoms appeared 9, 5 and 12 days, respectively, after the inoculation with B. xylophilus, SNP pre-treatment and cPTIO pre-treatment followed by B. xylophilus infection. After B. xylophilus infection, the content of NO in P. thunbergii changed fiercely more earlier than the appearance of external symptoms, which indicated that the content of NO was related with the appearance and the development of the symptoms. The treatment with l-NNA (NOS inhibitor) inhibited the content of NO significantly, whereas, Na2WO4 (NR inhibitor) had no effect. The further analysis of NOS revealed that NO changed in consistent with cNOS activity. To sum up, NO, as the upstream signal molecule of H2O2, was involved in the pine early response to the invasion of B. xylophilus and influenced the accumulation of the content of H2O2. Moreover, NOS-like rather than NR was responsible for the endogenous NO generation, which was modulated by cNOS during the interaction between P.thunbergii and B. xylophilus.