Abstract
Nitric oxide (NO) and 5-aminolevulinic acid (ALA) are both extremely important signalling molecules employed by plants to control many aspects of physiology. In the present study, the role of NO in ALA-induced antioxidant defense in leaves of two sources of Elymus nutans Griseb. (Damxung, DX and Zhengdao, ZD) was investigated. Chilling stress enhanced electrolyte leakage, accumulation of malondialdehyde (MDA), hydrogen peroxide (H2O2) and superoxide radical in two E. nutans, which were substantially alleviated by exogenous ALA and NO application. Pretreatment with NO scavenger PTIO or NOS inhibitor L-NNA alone and in combination with ALA induced enhancements in electrolyte leakage and the accumulation of MDA, H2O2 and superoxide radical in leaves of DX and ZD exposed to chilling stress, indicating that the inhibition of NO biosynthesis reduced the chilling resistance of E. nutans and the ALA-enhanced chilling resistance. Further analyses showed that ALA and NO enhanced antioxidant defense and activated plasma membrane (PM) H+-ATPase and decreased the accumulation of ROS induced by chilling stress. A pronounced increase in nitric oxide synthase (NOS) activity and NO release by exogenous ALA treatment was found in chilling-resistant DX plants exposed to chilling stress, while only a little increase was observed in chilling-sensitive ZD. Furthermore, inhibition of NO accumulation by PTIO or L-NNA blocked the protective effect of exogenous ALA, while both exogenous NO treatment and inhibition of endogenous NO accumulation did not induce ALA production. These results suggested that NO might be a downstream signal mediating ALA-induced chilling resistance in E. nutans.
Highlights
Low temperature is one of severe environmental stress that limits plant growth, development, survival and crop productivity [1]
Chilling stress resulted in significant growth suppression in two E. nutans seedlings, with dry weight decreasing by 22% and 11% of the control in ZD and DX, respectively (Fig 1)
A biphasic response in the changes of dry weight was observed in both E. nutans plants exposed to 0.5–25 mg l-1 aminolevulinic acid (ALA) treatment and cold stress, with the first increase occurring after 0.5 mg l-1 ALA treatment and a maximum being reached after 1 mg l-1 ALA treatment, but higher concentration of ALA (!5 mg l-1) reduced the dry weight
Summary
Low temperature is one of severe environmental stress that limits plant growth, development, survival and crop productivity [1]. The generation of ROS is increased with the enhancement in antioxidant enzyme activities and antioxidant concentrations, indicating that the antioxidant defense system may play a pivotal role in the improvement of resistance in plants under stress conditions such as chilling stress [6]. Plant growth regulators (PGRs) play an important role in the physiology of plants which include the uptake of nutrients, stomatal movement, photosynthesis and activities of different enzymes under the different stress conditions [7, 8] One of these PGRs is 5-aminolevulinic acid (ALA), which is believed to be an essential biosynthetic precursor for the biosynthesis of tetrapyrrols such as heme and chlorophyll [9]. Our results showed that NOS-dependent NO generation acts downstream of ALA mediating chilling stress induced oxidative damage by the up-regulation of antioxidant enzyme activities and the activation of PM H+-ATPase
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