Abstract
Salicylic acid (SA) is a very simple phenolic compound (a C7H6O3 compound composed of an aromatic ring, one carboxylic and a hydroxyl group) and this simplicity contrasts with its high versatility and the involvement of SA in several plant processes either in optimal conditions or in plants facing environmental cues, including heavy metal (HM) stress. Nowadays, a huge body of evidence has unveiled that SA plays a pivotal role as plant growth regulator and influences intra- and inter-plant communication attributable to its methyl ester form, methyl salicylate, which is highly volatile. Under stress, including HM stress, SA interacts with other plant hormones (e.g., auxins, abscisic acid, gibberellin) and promotes the stimulation of antioxidant compounds and enzymes thereby alerting HM-treated plants and helping in counteracting HM stress. The present literature survey reviews recent literature concerning the roles of SA in plants suffering from HM stress with the aim of providing a comprehensive picture about SA and HM, in order to orientate the direction of future research on this topic.
Highlights
Salicylic acid (SA), known as ortho-hydroxybenzoic acid, is a phenolic derivative widely distributed in the plant kingdom and is known as a regulator of severalMolecules 2020, 25, 540; doi:10.3390/molecules25030540 www.mdpi.com/journal/moleculesMolecules 2020, 25, 540 physiological and biochemical processes such as thermogenesis, plant signaling or plant defense, and response to biotic and abiotic stress [1,2].From a chemical point of view, SA belongs to a large group of plant phenolics, and SA can be isolated in plants in both free and conjugated form
It was discovered that almost all the willow trees including Salix alba, S. purpurea, S. fragilis, and S. daphnoides were rich in this natural compound, in which the concentration in plants significantly fluctuates during the different seasons reaching values of 3 mg/g of fresh biomass in plants of S. laponum [8]
Many reports have demonstrated that enhanced production of phenolic compounds under heavy metal (HM) stress can protect from oxidative damage [163,164]
Summary
Salicylic acid (SA) (from Latin Salix, willow tree), known as ortho-hydroxybenzoic acid, is a phenolic derivative widely distributed in the plant kingdom and is known as a regulator of several. Several recent manuscripts reported that SA can alleviate HM toxicity influencing both their uptake and/or accumulation in plant organs [32,33,34,35,36,37,38], as well as scavenging of reactive oxygen species (ROS) and/or decreasing their accumulation and/or enhancing the antioxidant defense system [39,40,41,42], protecting membrane stability and integrity [43], interacting with plant hormones [44], upregulating heme oxygenase [45], and improving the performance of the photosynthetic machinery [42,46,47] Focusing on these aspects, the present review provides a comprehensive assemblage concerning. SA roles in plant defense from HM stress, with the aim to provide a clear view of SA and HM to orientate the direction of future research on this topic
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