Plant communication

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Plant communication encompasses communication using volatile organic compounds, electrical signaling, and common mycorrhizal networks between plants and a host of other organisms such as soil microbes,[1] other plants[2] (of the same or other species), animals,[3] insects,[4] and fungi.[5] Plants communicate through a host of volatile organic compounds (VOCs) that can be separated into four broad categories, each the product of distinct chemical pathways: fatty acid derivatives, phenylpropanoids/benzenoids, amino acid derivatives, and terpenoids.[6] Due to the physical/chemical constraints most VOCs are of low molecular mass (< 300 Da), are hydrophobic, and have high vapor pressures.[7] The responses of organisms to plant emitted VOCs varies from attracting the predator of a specific herbivore to reduce mechanical damage inflicted on the plant [4] to the induction of chemical defenses of a neighboring plant before it is being attacked.[8] In addition, the host of VOCs emitted varies from plant to plant, where for example, the Venus Fly Trap can emit VOCs to specifically target and attract starved prey.[9] While these VOCs typically lead to an increase in herbivory resistance in neighboring plants, there is no clear benefit to the emitting plant in helping nearby plants. As such, whether neighboring plants have evolved the capability to "eavesdrop" or whether there is an unknown tradeoff occurring is subject to much scientific debate.[10]

Communication between mycorrhizae and plants:

The host legume roots leaches out a specific kind of proteins called lectins, which diffuse in soil and interact with the glycoproteins of the capsule of rhizobium bacteria. This serves as a measure of communication and directing the growth of bacterial colonies towards host root.

Volatile Organic Compounds[edit]

In Runyon et al 2006, the researchers demonstrate how the parasitic plant Cuscuta pentagona (dodder weed) uses VOCs to interact with various hosts and determine locations. Dodder seedlings show direct growth toward tomato plants (Lycopersicon esculentum) and specifically elicited tomato plant volatiles. This was tested by growing a dodder weed seedling in a contained environment, connected to two different chambers. One chamber contained tomato VOC’s while the other had artificial tomato plants. After 4 days of growth, the dodder weed seedling showed a significant growth towards the direction of the chamber with tomato VOC’s. Their experiments also showed that the dodder weed seedlings could distinguish between wheat (Triticum aestivum) VOCs and tomato plant volatiles. As when one chamber was filled with each of the two different VOCs, dodder weeds grew towards tomato plants as one of the wheat VOC’s is repellent. These findings show evidence that volatile organic compounds determine ecological interactions between plant species and show statistical significance that the dodder weed can distinguish between different plant species by sensing elicited volatile organic compounds (Runyon et al. 2006).

Tomato plant to plant communication is further examined in Zebelo et al 2012, which studies tomato plant response to herbivory. Upon herbivory by Spodoptera littoralis, tomato plants emit VOCs that are released into the atmosphere and induce responses in neighboring tomato plants. When the herbivory-induced VOCs bind to receptors on other nearby tomato plants, responses occur within seconds. The neighboring plants experience a rapid depolarization in cell potential and increase in cytosolic calcium. These emitted volatiles were measured by GC-MS and the most notable were 2-hexenal and 3-hexenal acetate. It was found that depolarization increased with increasing green leaf volatile concentrations. These results indicate that tomato plants communicate with one another via airborne volatile cues, and when these VOC’s are perceived by receptor plants, responses such as depolarization and calcium influx occur within seconds (Zebelo 2012).

Terpenoids[edit]

The terpenoid verbenone is a plant pheromone, signalling to insects that a tree is already infested by beetles.[11]

Terpenoids facilitate communication between plants and insects, mammals, fungi, microorganisms, and other plants.[12] Terpenoids may act as both attractants and repellants for various insects. For example, pine shoot beetles (Tomicus piniperda) are attracted to certain monoterpenes ( (+/-)-a-pinene, (+)-3-carene and terpinolene) produced by Scots pines (Pinus sylvestris), while being repelled by others (such as verbenone).[13]

Terpenoids are a large family of biological molecules with over 22,000 compounds.[14] Terpenoids are similar to terpenes in their carbon skeleton but unlike terpenes contain functional groups. The structure of terpenoids is described by the biogenetic isoprene rule which states that terpenoids can be thought of being made of isoprenoid subunits, arranged either regularly or irregularly.[15] The biosynthesis of terpenoids occurs via the methylerythritol phosphate (MEP) and mevalonic acid(MVA) pathways[6] both of which include isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) as key components.[16] The MEP pathway produces hemiterpenes, monoterpenes, diterpenes, and volatile carotenoid derivatives while the MVA pathway produces sesquiterpenes.[6]

Electrical Signaling[edit]

Plants also communicate via electrical signals, which is explored in Calvo et al. 2017. These electrical signals are mediated by cytosolic Ca2+ ions. Cytosolic calcium signals are mediated by hundreds of protein and protein kinases, and many of the signals also induce action potentials in plants. The phloem of the plant serves as the pathway for electrical communication, and as the plant grows and learns from its past, the phloem becomes increasingly cross linked. Plants respond to various environmental cues and elicit electrical responses internally to alter the function of the plant body. This can range from avoiding predation, releasing defense mechanisms, responding to changing temperature, changing growth direction, and sharing nutrients in the soil. This form of memory stored in the plant’s phloem allows it to better respond to similar stimuli in the future and shows how electrical signaling allows a plant to communicate with itself and alter its’ own physiology to better suit certain environmental cues (Calvo et al. 2017).

Common Mycorrhizal Networks[edit]

Another form of plant communication occurs through their complex root networks. Through roots, plants can share many different resources including nitrogen, fungi, nutrients, microbes, and carbon. This transfer of below ground carbon is examined in Philip et al. 2011. The goals of this paper were to test if carbon transfer was bi-directional, if one species had a net gain in Carbon, and if more Carbon was transferred through the soil pathway or common mycorrhizal network (CMN). CMNs occur when fungal mycelia link roots of plants together (Philip et al. 2011). To test this, the researchers followed seedlings of paper birch and Douglas-fir in a greenhouse for 8 months, where hyphal linkages that crossed their roots were either severed or left intact. The experiment measured amounts of CO2 in both seedlings. It was discovered that there was indeed a bi-directional sharing of CO2 between the two trees, with the Douglas-fir receiving a slight net gain in CO2. Also, the Carbon was transferred through both soil and the CMN pathways, as transfer occurred when the CMN linkages were interrupted, but much more transfer occurred when the CMN’s were left unbroken. This experiment showed that through fungal mycelia linkage of the roots of two plants, plants are able to communicate with one another and transfer nutrients as well as other resources through below ground root networks (Philip et al. 2011). Further studies go on to argue that this underground “tree talk” is crucial in the adaptation of forest ecosystems. Plant genotypes have shown that mycorrhizal fungal traits are heritable and play a role in plant behavior. These relationships with fungal networks can be mutualistic, commensal, or even parasitic. It has been shown that plants can rapidly change behavior such as root growth, shoot growth, photosynthetic rate, and defense mechanisms in response to mycorrhizal colonization (Gorzelak et al. 2015). Through root systems and common mycorrhizal networks, plants are able to communicate with one another below ground and alter behaviors or even share nutrients depending on different environmental cues.

References[edit]

  1. ^ Wenke, Katrin; Kai, Marco; Piechulla, Birgit (2010-02-01). "Belowground volatiles facilitate interactions between plant roots and soil organisms". Planta. 231 (3): 499–506. doi:10.1007/s00425-009-1076-2. PMID 20012987.
  2. ^ Yoneya, Kinuyo; Takabayashi, Junji (2014-01-01). "Plant–plant communication mediated by airborne signals: ecological and plant physiological perspectives". Plant Biotechnology. 31 (5): 409–416. doi:10.5511/plantbiotechnology.14.0827a.
  3. ^ Leonard, Anne S.; Francis, Jacob S. (2017-04-01). "Plant–animal communication: past, present and future". Evolutionary Ecology. 31 (2): 143–151. doi:10.1007/s10682-017-9884-5.
  4. ^ a b De Moraes, C. M.; Lewis, W. J.; Paré, P. W.; Alborn, H. T.; Tumlinson, J. H. (1998). "Herbivore-infested plants selectively attract parasitoids". Nature. 393 (6685): 570–573. doi:10.1038/31219.
  5. ^ Bonfante, Paola; Genre, Andrea (2015). "Arbuscular mycorrhizal dialogues: do you speak 'plantish' or 'fungish'?". Trends in Plant Science. 20 (3): 150–154. doi:10.1016/j.tplants.2014.12.002. hdl:2318/158569. PMID 25583176.
  6. ^ a b c Dudareva, Natalia (April 2013). "Biosynthesis, function and metabolic engineering of plant volatile organic compounds". New Phytologist. 198 (1): 16–32. doi:10.1111/nph.12145. JSTOR newphytologist.198.1.16. PMID 23383981.
  7. ^ Rohrbeck, D.; Buss, D.; Effmert, U.; Piechulla, B. (2006-09-01). "Localization of Methyl Benzoate Synthesis and Emission in Stephanotis floribunda and Nicotiana suaveolens Flowers". Plant Biology. 8 (5): 615–626. doi:10.1055/s-2006-924076. PMID 16755462.
  8. ^ Baldwin, Jan T., and Jack C. Schultz. “Rapid Changes in Tree Leaf Chemistry Induced by Damage: Evidence for Communication between Plants.” Science, vol. 221, no. 4607, 1983, pp. 277–279., www.jstor.org/stable/1691120.
  9. ^ Hedrich, Rainer; Neher, Erwin (March 2018). "Venus Flytrap: How an Excitable, Carnivorous Plant Works" (PDF). Trends in Plant Science. 23 (3): 220–234. doi:10.1016/j.tplants.2017.12.004. ISSN 1360-1385. PMID 29336976.
  10. ^ Heil, Martin; Karban, Richard (2010-03-01). "Explaining evolution of plant communication by airborne signals". Trends in Ecology & Evolution. 25 (3): 137–144. doi:10.1016/j.tree.2009.09.010. ISSN 0169-5347. PMID 19837476.
  11. ^ Mafra-Neto, Agenor; de Lame, Frédérique M.; Fettig, Christopher J.; Perring, Thomas M.; Stelinski, Lukasz L.; Stoltman, Lyndsie L.; Mafra, Leandro E. J.; Borges, Rafael; Vargas, Roger I. (2013). "Manipulation of Insect Behavior with Specialized Pheromone and Lure Application Technology (SPLAT®)". In John Beck; Joel Coats; Stephen Duke; Marja Koivunen (eds.). Natural Products for Pest Management. 1141. American Chemical Society. pp. 31–58.
  12. ^ Llusià, Joan; Estiarte, Marc; Peñuelas, Josep (1996). "Terpenoids and plant communication". Bull. Inst. Cat. Hist. Nat. 64: 125–133.
  13. ^ Byers, J. A.; Lanne, B. S.; Löfqvist, J. (1989-05-01). "Host tree unsuitability recognized by pine shoot beetles in flight". Experientia. 45 (5): 489–492. doi:10.1007/BF01952042. ISSN 0014-4754.
  14. ^ Hill, Ruaraidh; Connolly, J.D. (1991). Dictionary of terpenoids. Chapman & Hall. ISBN 978-0412257704. OCLC 497430488. Check date values in: |year= / |date= mismatch (help)
  15. ^ Ružička, Leopold (1953). "The isoprene rule and the biogenesis of terpenic compounds". Cellular and Molecular Life Sciences. 9 (10): 357–367. doi:10.1007/BF02167631. PMID 13116962.
  16. ^ McGarvey, Douglas J.; Croteau, Rodney (July 1995). "Terpenoid Metabolism". The Plant Cell. 7 (7): 1015–1026. doi:10.1105/tpc.7.7.1015. JSTOR 3870054. PMC 160903. PMID 7640522.

Calvo et al. 2017. “Plant, Cell, & Environment. Are Plants Sentient?”

Gorzelak et al. 2015. “Inter-plant communication through mycorrhizal networks mediates complex adaptive behaviour in plant communities.”

Martin Heli and Richard Karban. 2010. “Explaining evolution of plant communication by airborne signals.”

Phillip et al. 2011 “Pathways for below ground carbon transfer between paper birch and Douglas-fir seedlings”

Runyon et al. 2006 “Volatile Chemical Cues Guide Host Location and Host Selection by Parasitic Plants.”

Zebelo et al. 2012. “Plasma membrane potential depolarization and cytosolic calcium flux are early events involved in tomato (Solanum lycopersicon) plant-to-plant communication”.