Stress-protective and regulatory properties of salicylic acid and prospects of its use in plant production

Abstract

Salicylic acid (SA), as a secondary phenolic metabolite with phytohormonal activity, is an important component of the plant defense system against biotic and abiotic stresses. The scale of industrial synthesis of SA in the world is constantly growing, it is used as an intermediate for the synthesis of drugs and dyes, it is also used in cosmetology, food industry, plant biotechnology, etc. Recently, it has been considered as a promising growth-regulating agent in crop production for decreasing harmful effects of biotic and abiotic stresses in plants. Over the past two decades, numerous data have been published concerning the metabolic pathways of SA synthesis and its signaling in plant immunity. It regulates and affects various stages of plant ontogenesis and metabolism: seed germination, flowering, stomatal movements, pigment synthesis, photosynthesis and respiration, ethylene biosynthesis, thermoregulation, the activity of antioxidant enzymes, nutrient absorption, membrane integrity and functioning, nodulation in legumes, synthesis of secondary metabolites, general growth and development of plants. Numerous studies have confirmed that endogenous SA and/or its derivatives are involved in stress responses to heavy metals (HMs), hyper- and hypothermia, salinity, water deficiency, and, primarily, pathogenic infections. In parallel with fundamental studies of regulatory functions of SA and/or its derivatives, new ways of their exogenous application are constantly discovered. The use of low concentrations of exogenous SA (0.1–0.5 mM) for seed priming or foliar treatment is reported as an economically viable alternative approach for increasing plant tolerance from both economic and environmental points of view. Exogenous SA leads to an increase in endogenous SA levels that induces plant adaptive responses by changing phytohormonal status, increased synthesis of a number of secondary metabolites (alkaloids, cyanogenic glycosides, phenolics, terpenes), by increasing activity of antioxidant enzymes. One of the main advantages of using SA in crop production is the ability to reduce the dosage of pesticides and fertilizers that are potentially harmful to the environment and human health. It is also reported that the use of SA in some cases may lead to negative results – growth retardation, sterility, and yield decrease; the causes of this phenomenon are actively investigated. Further studies are necessary to clarify the mechanisms of exogenic SA action and its use on various crops in different growing conditions. This review aims to analyze the recent data on SA, crop production, and biotechnology areas where it is possible to effectively apply the SA and/or its derivatives.