Abstract
Salicylic acid (SA), as an enigmatic signalling molecule in plants, has been intensively studied to elucidate its role in defence against biotic and abiotic stresses. This review focuses on recent research on the role of the SA signalling pathway in regulating cadmium (Cd) tolerance in plants under various SA exposure methods, including pre-soaking, hydroponic exposure, and spraying. Pretreatment with appropriate levels of SA showed a mitigating effect on Cd damage, whereas an excessive dose of exogenous SA aggravated the toxic effects of Cd. SA signalling mechanisms are mainly associated with modification of reactive oxygen species (ROS) levels in plant tissues. Then, ROS, as second messengers, regulate a series of physiological and genetic adaptive responses, including remodelling cell wall construction, balancing the uptake of Cd and other ions, refining the antioxidant defence system, and regulating photosynthesis, glutathione synthesis and senescence. These findings together elucidate the expanding role of SA in phytotoxicology.
Highlights
Cadmium (Cd) is one of the most toxic pollutants for all living organisms with a long biological half-life [1,2]
The following information can be inferred: (1) Concentrations used in Cd treatments range from 0.56 to 300 mg L−1 with a mean of 31.6 mg L−1 and a variable coefficient of 160%; (2) concentrations of Salicylic acid (SA) spray treatments range from 10 to 2170 μM with a mean of 585 μM and a variable coefficient of 104%; (3) concentrations of SA used in seed presoaking treatments range from 100 to 1000 μM with a mean of 464 μM and a variable coefficient of 70%; and (4) concentrations of SA used in hydroponic exposure treatments range from 1 to 500 μM with a mean of 148 μM and a variable coefficient of 117%
Taking a comprehensive view of SA roles in response to Cd toxicity, this review focuses on the recent advances in the physiological and molecular mechanisms of the following aspects: plant growth, Cd immobilization and distribution, element assimilation, photosynthesis, reactive oxygen species (ROS) and the antioxidant defence system, glutathione, and senescence
Summary
Cadmium (Cd) is one of the most toxic pollutants for all living organisms with a long biological half-life [1,2]. The following information can be inferred: (1) Concentrations used in Cd treatments range from 0.56 to 300 mg L−1 (mg kg−1) with a mean of 31.6 mg L−1 (mg kg−1) and a variable coefficient of 160%; (2) concentrations of SA spray treatments range from 10 to 2170 μM with a mean of 585 μM and a variable coefficient of 104%; (3) concentrations of SA used in seed presoaking treatments range from 100 to 1000 μM with a mean of 464 μM and a variable coefficient of 70%; and (4) concentrations of SA used in hydroponic exposure treatments range from 1 to 500 μM with a mean of 148 μM and a variable coefficient of 117% From these studies, it was determined that the levels of SA in spray or pre-soaking treatments are generally higher than those in hydroponic treatments, suggesting that the regulation of SA levels in plants through root uptake is more efficient than that in the other two modes of application. Ja. nMtoiol.xSicdi.a2n0t1s9y, 2st0e, m29,60III photosynthesis, IV Cd uptake, V Ion uptake, VI phytochelatins, VII SA or C5do-fin19duced genes
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