Comparative Physiological Analysis Reveals the Role of NR-Derived Nitric Oxide in the Cold Tolerance of Forage Legumes.

Peipei Zhang,Zhenfei Guo,Pengcheng Zhao,Shaoyun Lu,Shuangshuang Li

doi:10.3390/ijms20061368

Abstract

The role of nitric oxide (NO) signaling in the cold acclimation of forage legumes was investigated in this study. Medicago sativa subsp. falcata (L.) Arcang. (hereafter M. falcata) is a forage legume with a higher cold tolerance than Medicago truncatula, a model legume. Cold acclimation treatment resulted in increased cold tolerance in both M. falcata and M. truncatula, which was suppressed by pretreatment with tungstate, an inhibitor of nitrate reductase (NR), and 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO), a scavenger of NO. Likely, NITRATE REDUCTASE 1 (NIA1), but not NIA2 transcript, NR activity, and NO production were increased after cold treatment. Treatments with exogenous NO donors resulted in increased cold tolerance in both species. Superoxide dismutase (SOD), catalase (CAT), and ascorbate-peroxidase (APX) activities and Cu,Zn-SOD2, Cu,Zn-SOD3, cytosolic APX1 (cAPX1), cAPX3 and chloroplastic APX1 (cpAPX1) transcript levels were induced in both species after cold treatment, which was suppressed by tungstate and 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO). Treatment with exogenous NO resulted in enhanced activities of SOD, CAT, and APX. Moreover, higher levels of NIA1 transcript, NR activity, NO production, and antioxidant enzyme activities and transcripts were observed in M. falcata as compared with M. truncatula after cold treatment. The results suggest that NR-derived NO production and upregulated antioxidant defense are involved in cold acclimation in both species, while the higher levels of NO production and its derived antioxidant enzymes are associated with the higher cold tolerance in M. falcata as compared with M. truncatula.

Highlights

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Summary

Introduction

Low temperature is one of the major abiotic stresses limiting plant growth and development. Temperate plants have evolved a mechanism known as cold acclimation, by which they respond to low, but non-freezing temperatures to increase their freezing tolerance [1,2]. Some of the COR genes encode key enzymes for osmolyte biosynthesis and the antioxidant defense system that lead to an accumulation of cryoprotective proteins and soluble sugars for the stabilization of the cellular osmotic potential under low temperature [3,4] and activation of antioxidant defense for scavenging of reactive oxygen species (ROS) [5]. The antioxidant defense system includes superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), and non-enzyme antioxidants, such as ascorbate (AsA) and glutathione (GSH). Numerous investigations reveal that the antioxidant defense system protects plants against oxidative damages induced by cold stress [5]

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