title: Nitric oxide is associated with long-term zinc tolerance in Solanum nigrum.
abstract: Nitric oxide (NO) has been identified as a signal molecule that interplays with reactive oxygen species in response to heavy metal stresses. Roles of NO in regulating cadmium toxicity and iron deficiency have been proposed; however, the function of NO in zinc (Zn) tolerance in plants remains unclear. Here, we investigated NO accumulation and its role in plant Zn tolerance. Zn-induced NO production promoted an increase in reactive oxygen species accumulation in Solanum nigrum roots by modulating the expression and activity of antioxidative enzymes. Subsequently, programmed cell death (PCD) was observed in primary root tips. Inhibiting NO accumulation by 2-phenyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide (a specific NO scavenger) or N(G)-nitro-l-arginine-methyl ester (a NO synthase inhibitor) prevented the increase of superoxide radical and hydrogen peroxide as well as the subsequent cell death in the root tips, supporting the role of NO in Zn-induced PCD in the root tips. Zn-induced NO production affected the length of primary roots, the number of lateral roots, and root hair growth and thereby modulated root system architecture and activity. Investigation of metal contents in Zn-treated roots suggests that NO is required for metal (especially iron) uptake and homeostasis in plants exposed to excess Zn. Taken together, our results indicate that NO production and the subsequent PCD in root tips exposed to excess Zn are favorable for the S. nigrum seedling response to long-term Zn toxicity by modulating root system architecture and subsequent adaptation to Zn stress.
authors.affiliation: Key Laboratory of Agricultural Water Resources, Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Shijiazhuang, China.
authors.forename: Jin
authors.initials: J
authors.lastname: Xu
authors.forename: Hengxia
authors.initials: H
authors.lastname: Yin
authors.forename: Yulong
authors.initials: Y
authors.lastname: Li
authors.forename: Xiaojing
authors.initials: X
authors.lastname: Liu
mesh_terms: D000975:Antioxidants / Q000378:metabolism; D017209:Apoptosis; D008969:Molecular Sequence Data; D009569:Nitric Oxide / Q000378:metabolism*; D018384:Oxidative Stress; D018517:Plant Roots / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism; D032324:Solanum nigrum / Q000201:enzymology / Q000378:metabolism*; D015032:Zinc / Q000378:metabolism*
chemical_list: D000975:Antioxidants; D017382:Reactive Oxygen Species; D009569:Nitric Oxide; D015032:Zinc