Long Distance Systemic Signaling And Communication In Plants

Our view of plants is changing dramatically. Rather than being only slowly responding organisms, their signaling is often very fast and signals, both of endogenous and exogenous origin, spread throughout plant bodies rapidly. Higher plants coordinate and integrate their tissues and organs via sophisticated sensory systems, which sensitively screen both internal and external factors, feeding them information through both chemical and electrical systemic long-distance communication channels. This revolution in our understanding of higher plants started some twenty years ago with the discovery of systemin and rapid advances continue to be made. This volume captures the current ‘state of the art’ of this exciting topic in plant sciences.

Plant neurobiology is a newly emerging field of plant sciences. It covers signalling and communication at all levels of biological organization – from molecules up to ecological communities. In this book, plants are presented as intelligent and social organisms with complex forms of communication and information processing. Authors from diverse backgrounds such as molecular and cellular biology, electrophysiology, as well as ecology treat the most important aspects of plant communication, including the plant immune system, abilities of plants to recognize self, signal transduction, receptors, plant neurotransmitters and plant neurophysiology. Further, plants are able to recognize the identity of herbivores and organize the defence responses accordingly. The similarities in animal and plant neuronal/immune systems are discussed too. All these hidden aspects of plant life and behaviour will stimulate further intense investigations in order to understand the communicative plants in their whole complexity.

The ability of plants to exchange RNA molecules and transcription factors between cells and tissues is a relatively recent discovery. However, all areas of research such as plant development, metabolism, and plant pathogen interactions now realize the importance of this phenomenon. In this book, experts from the field of intercellular transport deal with various aspects on intercellular transport of viruses and plant endogenous macromolecules such as transcription factors, small silencing-induced and micro RNAs, and other RNAs and their function as signals. The aim of the book is to provide the basic information on the cell-to-cell transport mechanism and to give an overview of the current knowledge of this relatively new field of research. To quote the words of W.J. Lucas “...pioneering discoveries in this field of cell-to-cell and long-distance signaling should certainly entice talented young scholars to join this frontier area of plant biology” . He is certainly right as we got only a first glimpse on the cellular factors regulating intercellular transport and the functional diversity of the ever-increasing number of proteins and RNA molecules found to move between cells.

This is the first comprehensive monograph on all emerging topics in plant signaling. The book addresses diverse aspects of signaling at all levels of plant organization. Emphasis is placed on the integrative aspects of signaling.

Oxygen (O ) appeared in significant amounts in the Earth’s atmosphere over 2. 2 2 billion years ago, largely due to the evolution of photosynthesis by cyanobacteria (Halliwell 2006). The O molecule is a free radical, as it has two impaired electrons 2 that have the same spin quantum number. This spin restriction makes O prefer to 2 accept its electrons one at a time, leading to the generation of the so-called reactive oxygen species (ROS). The chemical nature of these species dictates that they can create damage in cells. This has contributed to the creation of the “oxidative stress” concept; in this view, ROS are unavoidable toxic products of O metabolism and 2 aerobic organisms have evolved antioxidant defences to protect against this tox- ity (Halliwell 1981; Fridovich 1998). Indeed, even in present-day plants, which are full of antioxidants, much of the protein synthetic activity of chloroplasts is used to replace oxidatively damaged D1 and other proteins (Halliwell 2006). Yet, the use of the “oxidative stress” term implies that ROS exert their effects through indiscriminate widespread inactivation of cellular functions. In this context, ROS must not be able to react with lipids, proteins or nucleic acids in order to avoid any damage to vital cellular components. However, genetic evidence has suggested that, in planta, purely physicoche- cal damage may be more limited than previously thought (Foyer and Noctor 2005).

Since the concept of allelopathy was introduced almost 100 years ago, research has led to an understanding that plants are involved in complex communicative interactions. They use a battery of different signals that convey plant-relevant information within plant individuals as well as between plants of the same species or different species. The 13 chapters of this volume discuss all these topics from an ecological perspective. Communication between plants allows them to share physiological and ecological information relevant for their survival and ?tness. It is obvious that in these very early days of ecological plant communication research we are illuminating only the ‘tip of iceberg’ of the communicative nature of higher plants. Nevertheless, knowledge on the identity and informative value of volatiles used by plants for communication is increasing with breath-taking speed. Among the most spectacular examples are sit- tions where plant emitters warn neighbours about a danger, increasing their innate immunity, or when herbivore-attacked plants attract the enemies of the herbivores (‘cry for help’ and ‘plant bodyguards’ concepts). It is becoming obvious that plants use not only volatile signals but also diverse water soluble molecules, in the case of plant roots, to safeguard their evolutionary success and accomplish self/non-self kin rec- nition. Importantly, as with all the examples of biocommunication, irrespective of whether signals and signs are transmitted via physical or chemical pathways, plant communication is a rule-governed and sign-mediated process.

This book provides a comprehensive update on the recent developments concerning the role of plant neurotransmitters in signaling and communication. Physiological investigations over the past few decades have demonstrated that plants employ neurotransmitters in various signaling pathways. Plant-based neurotransmitters (serotonin, melatonin, dopamine, acetylcholine, and GABA) share biochemical similarities with those in animal systems in terms of their chemical nature and biochemical pathways. Plant–environment interaction associated with abiotic stress management, growth modulation, flowering, circadian rhythm, fruit ripening, and allelopathic interactions are a major focus of research in the field, and recent advances in genomic, trascriptomic, and metabolomic approaches have resulted in the deciphering of the molecular mechanisms associated with various neurotransmitters in plants. Other current and potential areas of investigation include the putative phytohormone phytomelatonin, and receptor-mediated signaling in plant neurotransmitters. Providing an up-to-date overview of molecular crosstalk mechanisms between various neurotransmitters, the book offers essential insights to help readers gain a better understanding of the physiology of plant signaling and communication with the environment.

Plants face a daunting array of creatures that eat them, bore into them, and otherwise use virtually every plant part for food, shelter, or both. But although plants cannot flee from their attackers, they are far from defenseless. In addition to adaptations like thorns, which may be produced in response to attack, plants actively alter their chemistry and physiology in response to damage. For instance, young potato plant leaves being eaten by potato beetles respond by producing chemicals that inhibit beetle digestive enzymes. Over the past fifteen years, research on these induced responses to herbivory has flourished, and here Richard Karban and Ian T. Baldwin present the first comprehensive evaluation and synthesis of this rapidly developing field. They provide state-of-the-discipline reviews and highlight areas where new research will be most productive. Their comprehensive overview will be welcomed by a wide variety of theoretical and applied researchers in ecology, evolutionary biology, plant biology, entomology, and agriculture.