Salicylic Acid Alleviates the Adverse Effects of Salt Stress on Dianthus superbus (Caryophyllaceae) by Activating Photosynthesis, Protecting Morphological Structure, and Enhancing the Antioxidant System.

Renjuan Qian,Xiaohua Ma,Jian Zheng,Qingdi Hu,Xule Zhang

doi:10.3389/fpls.2017.00600

Abstract

Salt stress critically affects the physiological processes and morphological structure of plants, resulting in reduced plant growth. Salicylic acid (SA) is an important signal molecule that mitigates the adverse effects of salt stress on plants. Large pink Dianthus superbus L. (Caryophyllaceae) usually exhibit salt-tolerant traits under natural conditions. To further clarify the salt-tolerance level of D. superbus and the regulating mechanism of exogenous SA on the growth of D. superbus under different salt stresses, we conducted a pot experiment to examine the biomass, photosynthetic parameters, stomatal structure, chloroplast ultrastructure, reactive oxygen species (ROS) concentrations, and antioxidant activities of D. superbus young shoots under 0.3, 0.6, and 0.9% NaCl conditions, with and without 0.5 mM SA. D. superbus exhibited reduced growth rate, decreased net photosynthetic rate (Pn), increased relative electric conductivity (REC) and malondialdehyde (MDA) contents, and poorly developed stomata and chloroplasts under 0.6 and 0.9% salt stress. However, exogenously SA effectively improved the growth, photosynthesis, antioxidant enzyme activity, and stoma and chloroplast development of D. superbus. However, when the plants were grown under severe salt stress (0.9% NaCl condition), there was no significant difference in the plant growth and physiological responses between SA-treated and non-SA-treated plants. Therefore, our research suggests that exogenous SA can effectively counteract the adverse effect of moderate salt stress on D. superbus growth and development.

Highlights

IntroductionAbiotic stresses, especially salt stress, has a triple effect on plant growth
Under natural conditions, abiotic stresses, especially salt stress, has a triple effect on plant growth
Our results clearly suggested that D. superbus is a salt-tolerant plant, and exogenous supply of Salicylic acid (SA) could alleviate the deleterious effects of moderate salinity on the growth of D. superbus, through enhanced activation of the photosynthetic process and the relief of membrane injury

Summary

Introduction

Abiotic stresses, especially salt stress, has a triple effect on plant growth It leads to ion imbalance or turbulence in ion homeostasis and third, it results in plant toxicity (ionic effects; Roussos et al, 2007). Plants exhibit a high degree of variability response to salt stress according to the species and the developmental stage Such as the salt-tolerant species, mangrove, could increase the chlorophyll content, enhance the activities of the antioxidant enzymes (CAT and SOD), and decrease the steady-state rates of transpiration and light-saturated rates of photosynthesis to adapt to the increase of salt concentration (Takemura et al, 2000). Exogenously applied compounds can dramatically increase plant growth and development and promote the salt tolerance of plants by enhancing enzymatic antioxidants (Gossett et al, 1994)

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