Although the role of salicylic acid (SA) in plant physiological processes has been widely studied for a long time, many open questions remain several fields. The importance of SA synthesis is illustrated by the four review papers published in this Special Issue that represent a wide range of approaches, indicating that a growing body of evidence needs to be summarized in a thought-provoking manner. The investigations presented in the six original studies extend upon the understanding of the involvement of SA in anthracnose infection and light-dependent cold acclimation, highlighting the use of SA mutant Arabidopsis plants. The studies also focused on the application of novel SA analogs or SA in combination with Rhizobacteria inoculation. We hope that the four reviews and six studies provide a deeper understanding of the role of SA and its complex tasks, as well as a new direction for research to address gaps and open questions, including both at the metabolite and gene expression levels, in the use of agriculturally important crop or mutant model plants, and in both basic research and practical applications.

The small phenolic compound salicylic acid (SA) is critical for plant defense against a broad spectrum of pathogens. SA is also involved in multi-layered defense responses, from pathogen-associated molecular pattern triggered basal defense, resistance gene-mediated defense, to systemic acquired resistance. Recent decades have witnessed tremendous progress towards our understanding of SA-mediated signaling networks. Many genes have been identified to have direct or indirect effect on SA biosynthesis or to regulate SA accumulation. Several SA receptors have been identified and characterization of these receptors has shed light on the mechanisms of SA-mediated defense signaling, which encompass chromosomal remodeling, DNA repair, epigenetics, to transcriptional reprogramming. Molecules from plant-associated microbes have been identified, which manipulate SA levels signaling. SA does not act alone. It engages in crosstalk with other signaling pathways, such as those mediated by other phytohormones, in an agonistic or antagonistic manner, depending on hormones and pathosystems. Besides affecting plant innate immunity, SA has also been implicated in other cellular processes, such as flowering time determination, lipid metabolism, circadian clock control, and abiotic stress responses, possibly contributing to the regulation of plant development. The multifaceted function of SA makes it critically important to further identify genes involved in SA signaling networks, understand their modes of action, and delineate interactions among the components of SA signaling networks. In addition, genetic manipulation of genes involved in SA signaling networks has also provided a promising approach to enhance disease resistance in economically important plants. This ebook collects articles in the research topic “Salicylic Acid Signaling Networks.” For this collection we solicited reviews, perspectives, and original research articles that highlight recent exciting progress on the understanding of molecular mechanisms underlying SA-mediated defense, SA-crosstalk with other pathways and how microbes impact these events.

Phytohormones are known to affect the growth and development of plant directly as well as indirectly. Salicylic acid (SA) is a phenolic phytohormone which induces systemic resistance in plants and also regulates defence responses. The derivatives of SA also play an important role in the regulation of various physiological and developmental processes in plants under normal and stressful environmental conditions. SA regulates seed germination, photosynthesis, ethylene biosynthesis, enzyme activities, nutrition, flowering, legume nodulation and overall growth and development of plant. Recently, advancement in elucidating the specific pathways of SA signal transduction has been noticed which helps in understanding the expression of specific genes associated with different developmental programs. The horizon of SA-mediated regulation of various physiological processes has also expanded, and various studies enumerating the efficacy of exogenously applied SA in practical agriculture have also been documented. Therefore, information regarding such recent developments needs to be compiled in the form of a book. This book aims to provide a collective information regarding SA which makes it a versatile plant growth regulator. The chapters included both theoretical and practical aspects that could be of immense use for researches and possible significant developments in future. It is intended that this book will be a help for students, teachers, and researchers, in understanding the relation between the phytohormone and agricultural sciences.

The book “Salicylic acid: A Plant Hormone” was first published in 1997 and was praised for its excellent balance of traditional and modern topics. This time, we're building on the success of the prior edition to provide an even more effective second edition. The present book is comprised of 16 chapters highlighting the updated mechanisms of its biosynthesis, physiological role, its action in response to water deficit, relationship of SA with signal transduction, transport of SA and related compounds. Further, the interplay between environmental signals and SA, its impact on transport and distribution of sugars, salicylic acid mediated stress-induced flowering and some aspects of interplay of SA with JA during the establishment of plant resistance to pathogens with different types of nutrition and participation of peroxidases have also been discussed at length. Potential use of SA in food production and its efficiency on post-harvest of perishable crops as well as practical use of SA are also covered. ​ ​

Demand for agricultural crops and nutritional requirement continues to escalate in response to increasing population. Also, climate change exerts adverse effects on agriculture crop productivity. Plant researchers have, therefore, focused to identify the scientific approaches that minimize the negative impacts of climate change on agricultural crops. Thus, it is the need of the hour to expedite the process for improving stress tolerance mechanisms in agricultural crops against various environmental factors, in order to fulfil the world’s food demand. Among the various applied approaches, the application of phytohormones has gained significant attention in inducing stress tolerance mechanisms. Jasmonates are phytohormones with ubiquitous distribution among plants and generally considered to modulate many physiological events in higher plants such as defence responses, flowering and senescence. Also, jasmonates mediate plant responses to many biotic and abiotic stresses by triggering a transcriptional reprogramming that allows cells to cope with pathogens and stresses. Likewise, salicylates are important signal molecules for modulating plant responses to environmental stresses. Salicylic acid influences a range of diverse processes in plants, including seed germination, stomatal closure, ion uptake and transport, membrane permeability and photosynthetic and growth rate. Understanding the significant roles of these phytohormones in plant biology and from agriculture point of view, the current subject has recently attracted the attention of scientists from across the globe. Therefore, we bring forth a comprehensive book “Jasmonates and Salicylates Signalling in Plants” highlighting the various prospects involved in the current scenario. The book comprises chapters from diverse areas dealing with biotechnology, molecular biology, proteomics, genomics, metabolomics, etc. We are hopeful that this comprehensive book furnishes the requisite of all those who are working or have interest in this topic.

Salicylic acid (SA) and methyl jasmonate (MJ) signaling is associated with phospholipids and the enzymes that metabolize them. However, despite the many studies conducted, the role of SA or MJ signalling via phospholipids in plant responses is not yet fully understood. The signaling pathways of SA and MJ have been evaluated in plant cell suspensions, and it was observed that these compounds regulate enzymatic activities to generate a rapid cellular response. This book discusses the immune responses induced by salicylic acid and jasmonic acids against plant parasites; the induction by SA of in vitro thermotolerance during thermotherapy; aalicylic acid, methyl jasmonate and phospholipid signaling in suspension cells; the self-association of salicylic acid derivatives in aqueous solutions studied by methods of absorption and fluorescence; and the role of exogenous salicylic acid applications for salt tolerance in tomato plants.

Agriculture faces many challenges to fulfil the growing demand for sustainable food production and ensure high-quality nutrition for a rapidly growing population. To guarantee adequate food production, it is necessary to increase the yield per area of arable land. A method for achieving this goal has been the application of growth regulators to modulate plant growth. Plant growth regulators (PGRs) are substances in specific formulations which, when applied to plants or seeds, have the capacity to promote, inhibit, or modify physiological traits, development and/or stress responses. They maintain proper balance between source and sink for enhancing crop yield. PGRs are used to maximize productivity and quality, improve consistency in production, and overcome genetic and abiotic limitations to plant productivity. Suitable PGRs include hormones such as cytokinins and auxins, and hormone-like compounds such as mepiquat chloride and paclobutrazol. The use of PGRs in mainstream agriculture has steadily increased within the last 20 years as their benefits have become better understood by growers. Unfortunately, the growth of the PGR market may be constrained by a lack of innovation at a time when an increase in demand for new products will require steady innovation and discovery of novel, cost-competitive, specific, and effective PGRs. A plant bio-stimulant is any substance or microorganism applied to plants with the aim to enhance nutrition efficiency, abiotic stress tolerance and/or crop quality traits, regardless of its nutrients content. Apart from traditional PGRs, which are mostly plant hormones, there are a number of substances/molecules such as nitric oxide, methyl jasmonate, brassinosteroids, seaweed extracts, strigolactones, plant growth promoting rhizobacteria etc. which act as PGRs. These novel PGRs or bio-stimulants have been reported to play important roles in stress responses and adaptation. They can protect plants against various stresses, including water deficit, chilling and high temperatures, salinity and flooding. This book includes chapters ranging from sensing and signalling in plants to translational research. In addition, the cross-talk operative in plants in response to varied signals of biotic and abiotic nature is also presented. Ultimately the objective of this book is to present the current scenario and the future plan of action for the management of stresses through traditional as well as novel PGRs. We believe that this book will initiate and introduce readers to state-of-the-art developments and trends in this field of study.