Gene Expression of Lupeol Synthase and Biosynthesis of Nitric Oxide in Cell Suspension Cultures of Betula platyphylla in Response to a Phomopsis Elicitor

Abstract

The current work aimed to characterize the generation of nitric oxide (NO) and gene expression of lupeol synthase (LUS) in Betula platyphylla cells exposed to a Phomopsis elicitor. The effects of nitrate reductase (NR) and NO synthase (NOS), the two key enzymes responsible for endogenous NO biosynthesis in plants, were also investigated. NO production in B. platyphylla cell cultures exhibited a biphasic pattern, reaching the Wrst plateau within 1.0–10 h of exposure to the Phomopsis elicitor. LUS gene expression was found to increase abruptly 10 h after Phomopsis induction, reaching its highest level (18.08) at 24 h. The maximum levels of NOS and NR activities in elicitor-treated cells were found to be 1.7-fold and 6.9-fold those of untreated cells, respectively. Pharmacological experiments showed that Phomopsis elicitor-induced NO production and LUS gene expression level were significantly suppressed by the NOS inhibitor NG-nitro-l-Arg methyl ester (l-NAME), the NR inhibitor sodium azide (NaN3), and the NO-specific scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO). NaNO2 and l-arginine (the substrates that produce NO via NR and NOS) and NO donor sodium nitroprusside (SNP) were found to increase both NO production and LUS gene expression. These results suggest that the increase in LUS gene expression due to fungal elicitor-induced NO may involve the NR and NOS biosynthetic pathways.