How plants communicate - Essay Example

? How Plants Communicate Introduction Plants are highly sensitive but sessile organisms that compete for resources that occur both below and above the ground. Just as with all organisms, the growth, development and evolution of plants depends on the success of the communication process. Plants would assess their environment, estimate the energy they would require to meet particular goals and realize the optimum option. They adopt measures that control the resources in the environment, perceive themselves and distinguish between non-self and self thus enabling them to protect their territory. They would process the information and evaluate it and consequently modify their behaviour appropriately. These competencies indicate parallel communication processes in the body of plants, referred to as intraorganismic; between different and same species, referred to as interorganismic; and between plants and their non-plant counterparts, referred to as transorganismic (Witzany, 2010). Intraorganismic communication entails sign-mediated interactions between cells and within cells, referred to as intercellular and intracellular respectively. Intercellular communication processes particularly coordinate growth and development, dynamics and shape, allowing plants to differentially react to physiological influences and developmental status. Witzany and Baluska (2012) observe that finding meaning functions of signalling molecules would be pegged on coherently investigating interactional patterns where signalling occurs. In these interactions, there would be active coordination and organization of various ordered steps conveyed by signs. These signs encompass a wide array of physical influences and chemical substances. According to Witzany (2010), these chemical molecules used as signs function as memory media, information carriers, messenger substances and signals. With different biotic and abiotic influences, there would be need for different behaviours which determine the set of signs in a given genera, family or species of plants and their production, combination and transportation. Therefore, different communicative processes would be executed with same chemical molecules thus optimizing energy cost. Foraging and Movement in Plants Plants are known to move in response to physical stimuli. Sensitive legumes would fold their leaflets when disturbed by insects with neighbouring leaves folding up upon being wounded. Adler (2011) cites some tropical legumes which lower leaves during heavy but not light rains or alighting insects, a response that accelerates the drying up of the leaf surface. Carnivorous plants would rapidly catch insects and trigger hairs that would take up the meal. These responses in plants could be attributed to osmotic changes in the concentration of ions, action potentials, electrical signals and turgor, compared to actinmyosin system in animals. Through circumnutation, plant organs would undergo subtle movements at their elongation axes, explaining directed and conspicuous movement of plants in response to gravity, light and similar stimuli, thus capturing the required resources (Witzany 2006). Through morphological plasticity, plants efficiently forage for light. Karban (2008) observes that vertical shoots would branch more and elongate less in adequate lighting as opposed to those in limited light. Witzany (2010) further indicates that light transmitted through leaves would have a lower red: far red than unfiltered illumination ratio. Roots would be more abundant in soils with higher nutrients in an attempt to increase the acquisition of resources. Bais, Park, Weir, Callaway, and Vivanco (2004) refer to the underground with densely populated roots which face competition for water, mineral nutrients and space from invading neighbouring root systems as the rhizosphere. Mating and Germination Other than acquisition for resources, plants’ reproductive behaviours show how they respond to environmental cues. Plants that do not get pollinated respond by increasing their reproduction abilities under suboptimal conditions such that they increase their attractiveness to insects (Witzany & Baluska, 2012). Others in pollination unfavourable conditions would produce cleistogamous flowers that self-pollinate and do not open. Ipomopsis aggregate species that flower once and die would shift from being semelparous to being iteroparous, thus flower again Karban (2008). Additionally, depending on the environmental conditions, plants adjust their functional gender, investing more in male flowers when exposed to environmental stresses and more in female reproduction when water and nutrients are accessible. Herbivory on reproductive tissues could cause plants to selectively abort or re-grow these tissues (Witzany, 2006). In a majority of plants, germination would be determined by environmental conditions. Therefore, germination should be appreciated as a conditional response as contrasted to the other developmental processes during germination. Among these conditions include the spectral light quality, carbon dioxide, fire, temperature, exposure to water and oxygen and other chemicals. This response allows seeds to germinate into growth favourable environments and remain dormant in unfavourable conditions. Response to Herbivory and Pathogens In response to herbivores and pathogens, plants change their phenotypic traits including physiological, morphological and chemical responses. These responses make plants less preferred by attackers or less susceptible thus increasing their fitness. When attacked by microbes, plants undergo chemical and physical changes to prevent infection, curtail pathogen growth and survive an attack. Karban (2008) also points out the induction of secondary compounds synthesis by herbivores such as nicotine accumulation as observed in tobacco plants that have been damaged. This alkaloid would be produced in the roots and transported through the xylem to the leaves. Being deadly to most herbivorous, nicotine protects plants from being fed on. Injured plants would then secrete aromatic substances that warn the others which in turn secrete enzymes that render the leaves unpalatable to the herbivores. Roots exudates varied compounds that regulate the microbial community in immediate soil environment, encourage symbioses, withstand herbivory and change the chemical and physical composition of the soil so as to inhibit growth of rival plants. Allelopathy describes the regulation of the rhizosphere by plants through secondary metabolites secreted by roots (Bais et al., 2004). Roots also produce front line detached living cells, referred to as border cells which have varied biological chemicals that protect vulnerable tips from infection by pathogens. Plants also respond indirectly by causing a shift on behaviour on a third trophic level. Here, plants would release volatile blends which attract predators and parasitoids thus increase predation and parasitism and reduce the damage that herbivores inflict on the plants. According to Witzany (2010), leaves always emit these volatiles in minimal doses and only increase the quantities of emission when infested. While Adler (2011) indicates that these volatiles could be used for private communication within the plant, they could also be perceived by neighbouring plants causing an initiation of pre-emptive defensive response. Plants have the ability to differentiate between the damage by mechanical injuries and by insects such that while mechanical injuries would result to emission of volatiles ignored by the other plants, pest infestation would cause a release of volatiles that would cause reaction in all the neighbouring plants. Gagliano (2012) adopts a different approach in his study, indicating that plants would produce sound waves in the range of audio acoustic emissions between 10 and 240 Hz and the ultrasonic acoustic emissions, UAE between 20 and 300 kHz. These emissions would be released when there is tension in the plant’s water transport system due to cavitations as water gets pulled through the xylem to the leaves from the roots. This would be used when instantaneous response is required such as calling for help from carnivorous attackers of the invading herbivores. Conditional Mutualism A situation where parasites and predators increase plant fitness benefit both the plants and the predators. When the risk of herbivory increases, these plants would increase rewards to these mutualists such as increasing the production of extrafloral nectar. During low herbivory risks, this would be reduced. While reviewing some experiments, Karban (2008) observed that when the benefits provided by bacteria in leguminous plants were reduced, the plants responded by reducing the supply of oxygen to the bacteria thus reducing bacteria reproduction by up to 50%. In considering how plants communicate within themselves and between each other, auxin, a growth hormone, would be used in morphogenic, hormonal and transmitter pathways. For cell-to-cell communication within plants, neurotransmitter-like auxin, histamine and glutamate would be used. Plants react to auxin as an extracellular signal so as to cause the plant to react to gravity and light stimuli. In intracellular signalling, it functions in cell differentiation and development and organogenesis. Important to note here as documented by Witzany (2010) is the fact that signal theft exists in plants just as in organisms where plants could use insect hormones for defence. Since plants can detect their signals, they could also presumably detect similar signals used in insect communication. But in the same way, Adler (2011) indicates that private signals by plants aimed at coordinating actors with common interests could be interfered with by pathogens such as Pseudomonas syringea. Conclusion Plants have evolved to become intelligent and possess complex hormonal systems, whose communication involving nucleic acids, turgor communication, electrical communication and proteins protects it from herbivory. Due to their sessile nature, the reaction of plants to attack communication aims at defending themselves against pest infestation and mechanical damage. In these sign-mediated interactions, these chemicals functioning as signs are referred to as sociochemicals. Plants coordinate their defence mechanisms depending on the density of pest infestation and severity of injury and in a stepwise approach. Just as in other organisms, communication could be misinterpreted or rules of communication broken in such cases breaking the organisation of life processes. References Adler, F. R. (2011). Plant signalling: The opportunities and dangers of chemical communication. Biology Letters, 7(2), 161 – 162. Bais, H. P., Park, S., Weir, T. L., Callaway, R. M. & Vivanco, J. M. (2004). How plants communicate using the underground information. Trends in Plant Science, 9(1), 26 – 32. Gagliano, M. (2012). Green symphonies: A call for studies on acoustic communication in plants. Behavioural Ecology. Retrieved 2 May 2013 from http://beheco.oxfordjournals.org/content/early/2012/11/24/beheco.ars206.full.pdf+html Karban, R. (2008). Plant behaviour and communication. Ecology Letters, 11, 727 – 739. Witzany, G. & Baluska, F. (2012). Biocommunication of plants. London: Springer. Witzany, G. (2006). Plant communication from biosemiotic perspective. Plant Signalling & Behaviour, 1(4), 169 – 178. Witzany, G. (2010). Biocommunication and natural genome editing. London: Springer. Read More