Nitric Oxide Functions as a Signal in Ultraviolet-B-Induced Baicalin Accumulation in Scutellaria baicalensis Suspension Cultures

Jin-Jie Zhang,Xue-Qin Li,Song-Heng Jin,Jun-Wei Sun

doi:10.3390/ijms15034733

Abstract

Stress induced by ultraviolet-B (UV-B) irradiation stimulates the accumulation of various secondary metabolites in plants. Nitric oxide (NO) serves as an important secondary messenger in UV-B stress-induced signal transduction pathways. NO can be synthesized in plants by either enzymatic catalysis or an inorganic nitrogen pathway. The effects of UV-B irradiation on the production of baicalin and the associated molecular pathways in plant cells are poorly understood. In this study, nitric oxide synthase (NOS) activity, NO release and the generation of baicalin were investigated in cell suspension cultures of Scutellaria baicalensis exposed to UV-B irradiation. UV-B irradiation significantly increased NOS activity, NO release and baicalin biosynthesis in S. baicalensis cells. Additionally, exogenous NO supplied by the NO donor, sodium nitroprusside (SNP), led to a similar increase in the baicalin content as the UV-B treatment. The NOS inhibitor, Nω-nitro-l-arginine (LNNA), and NO scavenger, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) partially inhibited UV-B-induced NO release and baicalin accumulation. These results suggest that NO is generated by NOS or NOS-like enzymes and plays an important role in baicalin biosynthesis as part of the defense response of S. baicalensis cells to UV-B irradiation.

Highlights

Ultraviolet-B (UV-B) irradiation can negatively affect plant growth, photosynthesis and pigmentation [1,2]
The induction of intracellular nitric oxide (NO) production by UV-B irradiation in S. baicalensis cells could be directly observed by detecting the green fluorescence of
The present study demonstrates that UV-B irradiation increases nitric oxide synthase (NOS) activity and induces NO and baicalin generation in S. baicalensis cells

Summary

Introduction

Ultraviolet-B (UV-B) irradiation can negatively affect plant growth, photosynthesis and pigmentation [1,2]. Plants have developed a variety of defense strategies in response to UV-B irradiation. Plant cells synthesize a number of secondary metabolites, including flavonoids, to mitigate UV-B damage [3,4,5]. UV-B irradiation can be used as an effective method to increase the yield of useful secondary metabolites in plant cell cultures. Nitrogen monoxide or nitric oxide (NO) is a free radical gas formed endogenously in many biological systems, including animals, plants and microbes. The physiological functions of NO in plants remain to be fully characterized, evidence is emerging that NO plays a regulatory role in plant growth, development, defense responses and seed dormancy [6,7,8,9,10]. As the production of NO in plant tissues and cells usually occurs in response to pathogen invasion [11], fungal elicitors [12] and abiotic stresses [13,14,15], it is possible that

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