With Communication, Plants Coordinate Complex Interactions
Plants have long been considered metabolic growth automatons with very simple stimuli-response reactions based on input-output mechanics. Research in last decades completely changed this picture. We now know plants as highly sensitive organisms which actively sense their environment on different levels within their plant body (intraorganismic) and interact with same, related, and nonrelated plants (interorganismic); with nonplant organisms such as fungi, bacteria, and animals (transorganismic); and—additionally—with abiotic influences from the environment such as nutrient and water availability, light, gravity, wind, and temperature. All these sensory data have to be processed, memorized, and compared with memorized information to generate appropriate response behavior. Information processing occurs in parallel as well as the response behavior is of tremendous complexity and involves decision, organization of appropriate signaling molecules for a variety of different signaling patterns, and a highly sophisticated coordination of all steps and substeps especially in the root zone and in root-stem communication. Biocommunication means there will be no coordination and organization of plant organisms without signaling processes.
Plants assess their surroundings, estimate how much energy they need for particular goals, and then realize the optimum variant. Plants constantly take measures to control certain environmental resources. They perceive themselves and can distinguish between self and nonself. This capability allows them to protect their territory and promote kinship. They process and evaluate information and then modify their behavior accordingly. Successful communication processes allow the plants to prosper; unsuccessful ones have negative, potentially lethal repercussions. Intraorganismic communication involves sign-mediated interactions in cells (intracellular) and between cells (intercellular). Intercellular communication processes are crucial in coordinating growth and development, shape, and dynamics. Such communication must function on both the local level as well as between widely separated plant parts. This allows plants to react in a differentiated manner to its current developmental status and physiological influences.
The communication processes between tissues and cells in plants are incredibly complex and encompass nucleic acids, oligonucleotides, proteins and peptides, minerals, oxidative signals, gases, mechanical signals, electrical signals, fatty acids, and oligosaccharides, growth factors, several amino acids, various secondary metabolite products, and simple sugars.
Semiochemical Vocabulary: Transmitters, Hormones, RNAs, Reusable Elements
The chemical communication in and between plants is so complex that more than 20 different groups of molecules with communicatory function have currently been identified. Up to 100,000 different substances, known as secondary metabolites, are active in the root zone. For synaptic neuronal-like cell-cell communication, plants use neurotransmitter-like auxin and presumably also neurotransmitters such as glutamate, glycine, histamine, acetylcholine, and dopamine. Alongside the classical phytohormones auxin, cytokinin, gibberellin, ethylene, and abscisic acid, the plant peptide hormone systemin has been noticed to be important; plants use this to systematically react to local injuries. In activating an effective defense response, a combination of systemin, jasmonate, and ethylene serves as signal molecules. The production (biosynthesis) of brassinolide hormones is important for cellular processes and development steps . Plant hormones control not only plant growth and development but also serve in communication within the same species, with related or unrelated plant species, and with insects. Beyond phytohormones, the chemical messenger substances include peptides such as phytosulphokine growth factors and RNAs.
MicroRNAs play an important role in intracellular communication during plant development, either in cleavage during translation/transcription or in preventing translation. MicroRNAs are apparently necessary for meristem function, organ polarity, vascular development, floral patterning, and hormone response. Many of them are developmentally or environmentally regulated. Small interfering RNA probably serves as a signal during early development. In later developmental phases, the RNAi-dependent epigenetic processes are reminded of this early development phase, for example the heterochromatin configuration. At any rate, these RNAs play important roles in chromatin regulation and therefore in epigenetic silencing. Small molecules and proteins that normally support important functions in plant immunity, such as nitric oxide and reactive oxygen species (ROS), have been identified as multiply reusable components of other biological processes. Nitric oxide (NO) is a substance that has a regulatory function in numerous signal processes such as germination, growth, reproduction, and disease resistance. The same is true for diverse species of ROS.
Signaling Molecules Serve in More than One Communication Process
Auxin is used in hormonal, morphogenic, and transmitter pathways. As an extracellular signal at the plant synapse, auxin serves to react to light and gravity. It also serves as an extracellular messenger substance to send electrical signals and functions as a synchronization signal for cell division. At the intercellular, whole plant level, it supports cell division in the cambium, and at the tissue level, it promotes the maturation of vascular tissue during embryonic development, organ growth as well as tropic responses and apical dominance. In intracellular signaling, auxin serves in organogenesis, cell development, and differentiation. Especially in the organogenesis of roots, for example, auxin enables cells to determine their position and their identity. These multiple functions of auxin demonstrate that identifying the momentary usage is extremely difficult because the context (investigation object of pragmatics) of use can be very complex and highly diverse.
Interpretation and Response Behavior to Sensory Data of Inanimated Nature
The entire configuration of a plant (morphogenesis) is partially determined by mechanical inputs, for example, wind and gravity. Responses to contact involve signal molecules and hormones along with intracellular calcium, reactive oxygen species, octadecanoids, and ethylene. Another common feature is contact-related gene expression. Many of these genes code for calcium-binding proteins, cell wall changes, defense, transcription factors, and kinase proteins. The detection of resources and their periodic, cyclic availability plays a key role in plant memory, planning, growth, and development. Interpretation processes in the plant body are highly sensitive. In taller growing plants, for example, the water balance places enormous demands on cell wall development and cell wall structures, which must adapt to the (often extreme) pressures involved in storage and pressure distribution. A sophisticated and multileveled feedback and feedforward system guarantees a plant-compatible water balance even under extreme environmental conditions. Plants are especially sensitive to light and have various receptors for UV, blue, green, red, and far red light. The angle of the light, combined with sensation of the growth of adjoining plants, is decisive in enabling plants to coordinate their growth with respect to the optimal light angle and shade avoidance. The roots receive constant signals from the aboveground parts of the plant for specific growth orientations .
Sign-mediated interactions with organisms belonging to other species, genera, families, and organismic kingdoms are vital for plants and are coordinated and organized in parallel. They are almost always symbiotic or parasitic and range from mutually beneficial via neutral, up to damaging behaviors. The different forms of symbiotic communication require very different behaviors from the participating partners. This involves large numbers of complementary direct and indirect defense behaviors. A limited number of chemical messenger substances are available to maintain and simultaneously conduct the communication between
(a) root cells (of three different types),
(b) root cells and microorganisms,
(c) root cells and fungi, and
(d) root cells and insects.
The communication process in the root zone is generally trans-, inter-, and intraorganismic and requires a high communicative competence in order to be successfully interactive on all three levels and to distinguish messenger molecules from (similar) molecules not being part of messages. A special type of plant synapse resembles the immunological synapse of animal cells and allows plants to respond to pathogen and parasite attacks as well as to establish stable symbiotic interactions with rhizobia bacteria and fungal mycorrhiza. Electrical signals can reinforce chemical signals or overcome short-distance responses of fungal mycelia that can be present on root surfaces. Some rhizobia bacteria are taken up in plant cells via phagocytosis during symbiotic interactions with roots of leguminous plants. The symbiotic relationship between legumes and rhizobial bacteria leads to the formation of nitrogen-binding nodules in the root zone.
Nod factor signaling and thigmotropic responses of root hairs overlap here as well. Today, several hundred species of fungi colonize more than 100,000 different plant species. This type of cohabitation requires symbiotic signaling. Roots develop from rhizomes in order to provide better conditions for mycorrhizal fungi, which in turn supply plants with better nutrients. For the fungus, the relationship is either balanced or predatory. Endophytic fungi, however, live in plants without triggering disease symptoms. Similar to the symbiosis between plants and mycorrhizal fungi, the symbiosis between asexual endophytes and grasses also represents a type of complementary parasitism .
Plants, insects, and microbes share a particular repertoire of signals. Some are therefore also employed strategically. Thus, plants also use insect hormones (prostaglandins) for specific defense behavior. Signal theft is common. Because plants can detect their own signals, they can presumably also detect similar signals that are used in communication between insects.
Interorganismic Communication in Plants
Plants can distinguish between self and nonself. Thus, defense activities are initiated against foreign roots in order to protect the plant’s own root zone against intruders. The individual sphere of a root, along with its symbiotic partners, requires certain fundamental conditions in order to survive and thrive. When these prerequisites are threatened by the roots of other plants, substances are produced and released in the root zone that hinder this advance. Such defense activities are also deployed as antimicrobial substances against the microflora in the root zone. Plant roots produce a wide range of chemical substances:
(a) some enable species-specific interactions;
(b) many of these substances are released tens of centimeters into the surroundings;
(c) these substances have strong but not necessarily negative effects on animals, bacteria, viruses, and fungi;
(d) released substances have a defensive function against other plants; and
(e) many substances have absorptive characteristics that reduce the negative effects of substances.
Plants use biotic signals to inform each other about the presence, absence, and identity of neighboring plants, growth space, growth disturbances, and competition
Short-distance communication differs considerably from long-distance communication. As a rule, both complement each other. Intercellular communication in the root zone (in the soil) differs from that in the stem region aboveground. Both are necessarily coordinated with one another in order to enable life in these different habitats. Intercellular communication informs other plant parts about events in specific organs or regions of the plant (especially in large plants), for example, sugar production in leaves, the reproduction in flowers, and resource utilization by the roots. Plant cells are connected by plasmodesmata. These connecting channels enable the flow of small molecules as well as ions, metabolites, and hormones, and allow the selective exchange (size exclusion limit) of macromolecules such as proteins, RNAs, and even cell bodies. The plasmodesmata impart plants with a cytoplasmic continuum known as the symplasm. But plasmodesmata are more than mere transport channels; they also regulate and control the exchange of messenger substances in a very complex manner. In symplastic signaling, the intercellular communication of plants differs fundamentally from that in other organismic kingdoms.
It integrates various communication types such as local and long-distance communication. Beyond symplastic communication (especially in the meristem, where new tissues are produced), plants also exhibit the receptor-ligand communication typical of animals. While receptor-ligand communication determines stomatal patterning in the epidermis of mature leaves, trichome patterning is mediated by symplastic signaling. For long-distance signaling movement, proteins play an important role. Movement proteins convey information bearing RNA from the stem and leaves to the remote roots and flowers. The movement protein allows the mRNA to enter the plasmodesmata tunnel, into the phloem flow. Once it has entered this transport system, it can relatively rapidly reach all parts of the plant. These RNAs can control the levels of other proteins. The level contains information for local tissues, for example, about the general physical condition of the plant, the season, or the presence of dangerous enemies.
Plasmodesmata are prerequisites for intercellular communication in higher plants. In embryogenesis, they are an important information channel between fetal and maternal tissue. The further the development of the embryo, the more reduced the cell-cell communication between embryo and maternal tissue. Cell-cell communication via direct transmission of transcription factors plays a central role in root radial and epidermal cell patterning as well as in shoot organogenesis. The cellular organization of the roots is determined during the plant’s embryonic development and is controlled by intercellular communication.
There are about 1,000 known protein kinases/phosphatases, numerous secondary messengers, and many thousands of other proteins. Through their life cycles and their growth zones, plants develop a life history of environmental experience that they can pass on to later generations and, should they themselves grow to be several hundred years old, utilize themselves. Even small plants store stress experiences in their memories and then use these memories to coordinate future activities
Intracellular communication in plants takes place between the symbiogenetically assimilated unicellular ancestors of the eukaryotic cell, mainly between the cell body and cell periphery. It transforms and transmits external messages into internal messages that exert a direct (epigenetic) influence on the DNA storage medium and trigger genetic processes; this leads to the production of signal molecules that generate a response behavior. Reports on the transfer of mitochondrial genes between unrelated plant species caused some surprise. While gene transfer is an extremely rare event in animals and fungi, it is common between plant mitochondria. Variations in repetitive DNA that manifest themselves as variation in the nuclear DNA complex have far-reaching ecological and life history consequences for plants.
The function of a eukaryotic cell depends on successful communication between its various parts. Plastids send signals to regulate nuclear gene expression and thus to reorganize macromolecules in response to environmental influences. It has been shown that microRNAs regulate certain developmental processes such as organ separation, polarity, and identity, and that they define their own biogenesis and function. Eukaryotic genomes are regionally divided into transcriptionally active euchromatin and transcriptionally inactive heterochromatin. Epigenetic changes can take place without changes in genomes, for example, through various inactivations and activations of genetic datasets via chromatin remodeling, transposon/retrotransposon release, DNA methylation, novel transcription, histone modification, and transcription factor interactions. Various stress situations in plants are known to cause transposon movements, and bacterial infections or UV stress can cause chromosomal rearrangements, that is, changes in higher-order regulation levels that control the transcription processes of the protein-coding DNA. Repetitive
DNA is present in two syntactic combinations: tandem repeats and dispersed repeats. Tandem repeats consist of sequences that can contain several thousand copies of elements that are dispersed throughout the genome. Pericentromeric sequences consist of a central repetitive nucleus flanked by moderately repetitive DNA. Telomeric and subtelomeric sequences consist of tandem repeats at the physical end of the chromosomes. Retroelements and transposable elements are involved in replication and reinsertion at various sites in complex processes: These include activation of excision, DNA-dependent RNA transcription, translation of RNA into functioning proteins, RNA-dependent DNA synthesis (reverse transcription), and reintegration of newly produced retroelement copies into the genome.
Scientists Discover Plants Have "Brains" That Determine When They Grow 2
Plants have some incredible traits, and as a new study led by the University of Birmingham reveals, a “brain” may also be one of them. Not one in the same sense that animals have, mind you, but a series of cells acting as a command center of sorts.
Found within plant embryos, these cells have been found to make key decisions in terms of the plant’s life cycle. Most significantly, they trigger germination, something that needs to be timed perfectly in order to avoid appearing too early in a frigid winter or too late in a warm summer populated by too much competing flora.
Writing in the Proceedings of the National Academy of Sciences, researchers first located these all-important cells within a plant called Arabidopsis, commonly known as thale cress. The command center is split between two types of cell – one that encourages seeds to remain dormant and one that initiates germination.
Using hormones to communicate, much in the way that nerve cells within brains do, the cells assess the environmental conditions around them and decide when it’s best to begin the birthing process, so to speak.
Coming to the conclusion that this hormonal exchange was controlling the germination process, the team then used a genetically modified version of the thale cress plant to make sure the cells were more prominently interconnected. This way, the movement of hormones between the cells showed up more – and ultimately, the team spotted the command center cells talking to each other in this way.
“Our work reveals a crucial separation between the components within a plant decision-making center,” lead author Professor George Bassel said in a statement.
So why have two types of cell rather than one? Well according to the team, this means that they can have a different “opinion” of the environmental conditions around them – and germination only occurs when a consensus has been arrived at.
“It's like the difference between reading one critic's review of a film four times over, or amalgamating four different critics’ views before deciding to go to the cinema,” Dr Iain Johnston, a bio-mathematician involved in the study, added. Together, they form the “Rotten Tomatoes” average score. So plants may not technically have brains, but they sure act like they do.
Plant Seeds Use Mini 'Brains' to Decide When to Sprout 3
Plant seeds may use miniature "brains" to help them decide whether to sprout or stay dormant, new research suggests.
These seed "brains" don't have traditional gray matter, but they do use the same architecture for information-processing as our brains do, interpreting a cascade of hormone signals to decide when to germinate, the study found.
"Plants are just like humans in the sense that they have to think and make decisions the same way we do," said study co-author George Bassel, a plant biologist at the University of Birmingham in England.
Instead of centralized brain tissue, a newly emerging field of plant science, dubbed “plant neurobiology,” is suggesting that plants may actually have thousands of brain-like entities that are involved in the emergence of intelligent behavior. These entities are a type of tissue known as meristems. Current theories suggest that the meristematic tissue, located at the tips of roots and shoots, combined with the vascular strands capable of complex molecular and electrical signalling, may well comprise the plant equivalent of the nervous/neuronal system. 4
Each root apex is proposed to harbor brain-like units of the nervous system of plants. The number of root apices in the plant body is high, and all “brain units” are interconnected via vascular strands (plant neurons) with their polarly-transported auxin (plant neurotransmitter), to form a serial (parallel) neuronal system of plants. Plant neurobiology researchers regard this decentralized assessment and response system to be the most effective for maximizing plant fitness.56 Such a system is thought to enable decentralized behavior (i.e.,growth), which allows plants to thrive in complex and everchanging rhizospheric environments.
At so-called “plant synapses,” vesicular transport of auxin moves this signaling molecule from cell to cell. Although the exact processes have yet to be uncovered, it has been proposed that this extracellular transport of auxin “exerts rapid electrical responses” across the plant synapse and “initiates the electrical responses of plant cells. As well as auxin and electrical signals, plants produce and use a variety of neurotransmitter molecules to communicate from cell to cell. Dopamine, acetylcholine, glutamate, histamine, and glycine are all touted as potential signaling chemicals between cells.59 Other complex communication molecules include protein kinases, minerals, lipids, sugars, gases, and nucleic acids. Trewavas has drawn attention to this complexity and notes that from the current rate of progress, it looks as though communication is likely to be as complex as that within a [animal] brain.
How plants see, hear, smell, and respond without animal sense organs 5
Plants fight for territory, seek out food, evade predators and trap prey. They are as alive as any animal, and – like animals – they exhibit behavior.
"To see this, you just need to make a fast movie of a growing plant – then it will behave like an animal," enthuses Olivier Hamant, a plant scientist at the University of Lyon, France. Indeed, a time-lapse camera reveals the alien world of plant behaviour in all its glory.
For example, despite lacking eyes, plants such as Arabidopsis possess at least 11 types of photoreceptor, compared to our measly four. This means that, in a way, their vision is more complex than ours. Plants have different priorities, and their sensory systems reflect this. As Chamovitz points out in his book: "light for a plant is much more than a signal; light is food." Genetics, electrophysiology and the discovery of transposons are just a few examples of fields that began with research in plants, and they have all proved revolutionary for biology as a whole.
The remarkable Dodder plant might be the most intelligent plant 6
- Mathematical ability – Plants can calculate the exact amount of sugar to last the night, even if light and sugar amounts are experimentally altered.
- Memory – Plants dmonstrate short-term memory, immune memory and long term memory across generations.
- Engineering – Plants can engineer their environment to increase survival – putting more soil in places and changing elevations.
- Elaborate Vision – Microscopic plants can see four different colors and send information about the four colors simultaneously giving them advantages in placing themselves at the right level for photosynthesis.
- Altruism – Sagebrush, when eaten by deer, grasshoppers and other predators signal other comrades with chemicals in the air to start defenses.
- Electric communication with bees– When bees land on flowers they change electrical potential. Flowers use bright color, smells and electricity to attract bees. Bees learn about the flower best from the electric signal.
Research shows that Dodder is able to sense other plants, even feet away, and won’t grow towards a fake plant. It grows towards the plant using its sense of smell for navigation. When near, it touches the plant with a feeler and can detect whether it is a high quality plant with the necessary nutrients. If the plant is not to it’s liking with little nutrient stores, such as a wheat plant, it pulls away and grows towards another plant.
Matanya WIK Cuscuta_racemosaWhen it finds a plant with many nutrients, such as a tomato plant, it winds itself around the victim multiple times and, then, produces a device called a haustoria, which inserts itself into the vascular system of the victim to extract nutrients.
Recently, it was found that it extracts a lot more than nutrients. The Dodder plant, as well as moving, sensing, analyzing, and extracting nutrients has, now, been shown to take up the RNA information of its Arabidopsis and tomato victims. Remarkably, it passes this genetic information on to other plants. The RNAs move both to and from the Dodder plant. These RNA pieces included the full information of thousands of genes, including half of the victim plant’s genes.
Plant Intelligence Primer and Update 2015 7
Current research has uncovered many specific signals that produce decision-making in plants:
Plants respond to light changes during different times of day including shade, length of day, seasons and daily circadian rhythms. Plants respond individually to the wavelengths of ultraviolet, green, far red, blue and red.
Plants respond to temperatures in a variety of ways including the ability to calculate the number of days at specific temperature ranges. Plants respond to freezing with many defensive mechanisms.
Plants respond to many mechanical factors including sound, wind, touch, being moved and shaken and other vibrations.
Plants have elaborate mechanisms to respond to all aspects of water including too little, too much, and salt in water.
Plants respond to gravity in a variety of ways including sending roots down and shoot up, as well as bending, and weight of branches.
Plants can determine many qualities of soil including obstacles for roots, surface structures, and the elements in the soil such as clay, sand and stones.
Plants respond to electricity and send electrical signals.
Plants sense and distinguish differences between airborne chemicals including oxygen, CO2, mist, C2H4, NO. They help respond to nearby plants and roots, as well as predators.
Plants sense and distinguish many chemicals and qualities including acidity and alkalinity, insecticides, calcium, heavy metals, potassium, boron, nitrates, and phosphates.
Plants respond to their environment and space available. At times, they participate in re engineering of the environment, such as building up banks of soil. They are aware of and respond to plants that are nearby.
1. Biocommunication of Plants, page 2
4. PLANTS AS PERSONS A Philosophical Botany, Page 147