Green symphonies: a call for studies on acoustic communication in plants

Plant ultrasound detection: a cost-effective method for identifying plant ultrasonic emissions

Plants have been observed to produce short ultrasonic emissions (UEs), and current research is focusing on developing noninvasive techniques for recording and analyzing these emissions. A standardized methodology has not been established yet; in this paper we suggest a cost-effective procedure for recording, extracting, and identifying plant UEs using only a single ultrasound microphone, a laptop computer, and open-source software.

How (not) to Talk to a Plant: An Application of Automata Theory to Plant Communication

Plants are capable of a range of complex interactions with the environment. Over the last decade, some authors have used this as evidence to argue that plants are cognitive agents. While there is no consensus on this view, it is certainly interesting to approach the debate from a comparative perspective, trying to understand whether different lineages of plants show different degrees of responsiveness to environmental cues, and how their responses compare with those of animals or humans. In this paper, I suggest that a potentially fruitful approach to these comparative studies is provided by automata theory. Accordingly, I shall present a possible application of this theory to plant communication. Two tentative results will emerge. First, that different lineages may exhibit different levels of complexity in response to similar stimuli. Second, that current evidence does not allow to infer great cognitive sophistication in plants.

Symphonies of Growth: Unveiling the Impact of Sound Waves on Plant Physiology and Productivity

The application of sound wave technology to different plant species has revealed that variations in the Hz, sound pressure intensity, treatment duration, and type of setup of the sound source significantly impact the plant performance. A study conducted on cotton plants treated with Plant Acoustic Frequency Technology (PAFT) highlighted improvements across various growth metrics. In particular, the treated samples showed increases in the height, size of the fourth expanded leaf from the final one, count of branches carrying bolls, quantity of bolls, and weight of individual bolls. Another study showed how the impact of a 4 kHz sound stimulus positively promoted plant drought tolerance. In other cases, such as in transgenic rice plants, GUS expression was upregulated at 250 Hz but downregulated at 50 Hz. In the same way, sound frequencies have been found to enhance the osmotic potential, with the highest observed in samples treated with frequencies of 0.5 and 0.8 kHz compared to the control. Furthermore, a sound treatment with a frequency of 0.4 kHz and a sound pressure level (SPL) of 106 dB significantly increased the paddy rice germination index, as evidenced by an increase in the stem height and relative fresh weight. This paper presents a complete, rationalized and updated review of the literature on the effects of sound waves on the physiology and growth parameters of sound-treated plants.

Developmental programming by prenatal sounds: insights into possible mechanisms

In recent years, the impact of prenatal sound on development, notably for programming individual phenotypes for postnatal conditions, has increasingly been revealed. However, the mechanisms through which sound affects physiology and development remain mostly unexplored. Here, I gather evidence from neurobiology, developmental biology, cellular biology and bioacoustics to identify the most plausible modes of action of sound on developing embryos. First, revealing often-unsuspected plasticity, I discuss how prenatal sound may shape auditory system development and determine individuals' later capacity to receive acoustic information. I also consider the impact of hormones, including thyroid hormones, glucocorticoids and androgen, on auditory plasticity. Second, I review what is known about sound transduction to other - non-auditory - brain regions, and its potential to input on classical developmental programming pathways. Namely, the auditory pathway has direct anatomical and functional connectivity to the hippocampus, amygdala and/or hypothalamus, in mammals, birds and anurans. Sound can thus trigger both immediate and delayed responses in these limbic regions, which are specific to the acoustic stimulus and its biological relevance. Third, beyond the brain, I briefly consider the possibility for sound to directly affect cellular functioning, based on evidence in earless organisms (e.g. plants) and cell cultures. Together, the multi-disciplinary evidence gathered here shows that the brain is wired to allow multiple physiological and developmental effects of sound. Overall, there are many unexplored, but possible, pathways for sound to impact even primitive or immature organisms. Throughout, I identify the most promising research avenues for unravelling the processes of acoustic developmental programming.

Evidence for the role of sound on the growth and signal response in duckweed

Sound vibration, an external mechanical force, has been proven to modulate plant growth and development like rain, wind, and vibration. However, the role of sound on plants, especially on signal response, has been usually neglected in research. Herein, we investigated the growth state, gene expression, and signal response in duckweed treated with soft music. The protein content in duckweed after music treatment for 7 days was about 1.6 times that in duckweed without music treatment. Additionally, the potential maximum photochemical efficiency of photosystem II (Fv/Fm) ratio in duckweed treated with music was 0.78, which was significantly higher in comparison with the control group (P < .01). Interestingly, music promoted the Glu and Ca signaling response. To further explore the global molecular mechanism, we performed transcriptome analysis and the library preparations were sequenced on an Illumina Hiseq platform. A total of 1296 differentially expressed genes (DEGs) were found for all these investigated genes in duckweed treated with music compared to the control group. Among these, up-regulation of the expression of metabolism-related genes related to glycolysis, cell wall biosynthesis, oxidative phosphorylation, and pentose phosphate pathways were found. Overall, these results provided a molecular basis to music-triggered signal response, transcriptomic, and growth changes in duckweed, which also highlighted the potential of music as an environmentally friendly stimulus to promote improved protein production in duckweed.

Understanding the mechanobiology of phytoacoustics through molecular Lens: Mechanisms and future perspectives

BACKGROUND

How plants emit, perceive, and respond to sound vibrations (SVs) is a long-standing question in the field of plant sensory biology. In recent years, there have been numerous studies on how SVs affect plant morphological, physiological, and biochemical traits related to growth and adaptive responses. For instance, under drought SVs navigate plant roots towards water, activate their defence responses against stressors, and increase nectar sugar in response to pollinator SVs. Also, plants emit SVs during stresses which are informative in terms of ecological and adaptive perspective. However, the molecular mechanisms underlying the SV perception and emission in plants remain largely unknown. Therefore, deciphering the complexity of plant-SV interactions and identifying bonafide receptors and signaling players will be game changers overcoming the roadblocks in phytoacoustics.

AIM OF REVIEW

The aim of this review is to provide an overview of recent developments in phytoacoustics. We primarily focuss on SV signal perception and transduction with current challenges and future perspectives.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Timeline breakthroughs in phytoacoustics have constantly shaped our understanding and belief that plants may emit and respond to SVs like other species. However, unlike other plant mechanostimuli, little is known about SV perception and signal transduction. Here, we provide an update on phytoacoustics and its ecological importance. Next, we discuss the role of cell wall receptor-like kinases, mechanosensitive channels, intracellular organelle signaling, and other key players involved in plant-SV receptive pathways that connect them. We also highlight the role of calcium (Ca2+), reactive oxygen species (ROS), hormones, and other emerging signaling molecules in SV signal transduction. Further, we discuss the importance of molecular, biophysical, computational, and live cell imaging tools for decoding the molecular complexity of acoustic signaling in plants. Finally, we summarised the role of SV priming in plants and discuss how SVs could modulate plant defense and growth trade-offs during other stresses.

No ultrasounds detected from fungi when dehydrated

Many organisms (including certain plant species) can be observed to emit sounds, potentially signifying threat alerts. Sensitivity to such sounds and vibrations may also play an important role in the lives of fungi. In this work, we explore the potential of ultrasound activity in dehydrating fungi, and discover that several species of fungi do not emit sounds (detectable with conventional instrumentation) in the frequency range of 10kHz to 210kHz upon dehydration. Over 5 terabytes of ultrasound recordings were collected and analysed. We conjecture that fungi interact via non-sound means, such as electrical or chemical.

The Electrome of a Parasitic Plant in a Putative State of Attention Increases the Energy of Low Band Frequency Waves: A Comparative Study with Neural Systems

Selective attention is an important cognitive phenomenon that allows organisms to flexibly engage with certain environmental cues or activities while ignoring others, permitting optimal behaviour. It has been proposed that selective attention can be present in many different animal species and, more recently, in plants. The phenomenon of attention in plants would be reflected in its electrophysiological activity, possibly being observable through electrophytographic (EPG) techniques. Former EPG time series obtained from the parasitic plant Cuscuta racemosa in a putative state of attention towards two different potential hosts, the suitable bean (Phaseolus vulgaris) and the unsuitable wheat (Triticum aestivum), were revisited. Here, we investigated the potential existence of different band frequencies (including low, delta, theta, mu, alpha, beta, and gamma waves) using a protocol adapted from neuroscientific research. Average band power (ABP) was used to analyse the energy distribution of each band frequency in the EPG signals, and time dispersion analysis of features (TDAF) was used to explore the variations in the energy of each band. Our findings indicated that most band waves were centred in the lower frequencies. We also observed that C. racemosa invested more energy in these low-frequency waves when suitable hosts were present. However, we also noted peaks of energy investment in all the band frequencies, which may be linked to extremely low oscillatory electrical signals in the entire tissue. Overall, the presence of suitable hosts induced a higher energy power, which supports the hypothesis of attention in plants. We further discuss and compare our results with generic neural systems.

Sounds emitted by plants under stress are airborne and informative

Stressed plants show altered phenotypes, including changes in color, smell, and shape. Yet, airborne sounds emitted by stressed plants have not been investigated before. Here we show that stressed plants emit airborne sounds that can be recorded from a distance and classified. We recorded ultrasonic sounds emitted by tomato and tobacco plants inside an acoustic chamber, and in a greenhouse, while monitoring the plant's physiological parameters. We developed machine learning models that succeeded in identifying the condition of the plants, including dehydration level and injury, based solely on the emitted sounds. These informative sounds may also be detectable by other organisms. This work opens avenues for understanding plants and their interactions with the environment and may have significant impact on agriculture.

Ariadne’s thread and the extension of cognition: A common but overlooked phenomenon in nature?

Over recent decades, our philosophical and scientific understanding of cognition has changed dramatically. We went from conceiving humans as the sole truly cognitive species on the planet to endowing several organisms with cognitive capacities, from considering brains as the exclusive seat of cognition to extending cognitive faculties to the entire physical body and beyond. That cognition could extend beyond the organism’s body is no doubt one of the most controversial of the recent hypotheses. Extended cognition (ExC) has been discussed not only to explain aspects of the human cognitive process, but also of other species such as spiders and more recently, plants. It has been suggested that ExC could offer insights for the grounding of environmentally extended cognitive traits in evolved ecological functions. Here, we reviewed the ecological literature for possible ExC examples that satisfy the mutual manipulability criterion, which can be used to establish experimentally the boundaries of cognitive systems. Our conclusion is that ExC might be far more common than previously thought, and present in organisms as diverse as plants, fungi, termites, spiders, mammals, and slime moulds. Experimental investigation is needed to clarify this idea which, if proven correct, could illuminate a new path into understanding the origins and evolution of cognition.

Stress-Induced Volatile Emissions and Signalling in Inter-Plant Communication

The sessile plant has developed mechanisms to survive the "rough and tumble" of its natural surroundings, aided by its evolved innate immune system. Precise perception and rapid response to stress stimuli confer a fitness edge to the plant against its competitors, guaranteeing greater chances of survival and productivity. Plants can "eavesdrop" on volatile chemical cues from their stressed neighbours and have adapted to use these airborne signals to prepare for impending danger without having to experience the actual stress themselves. The role of volatile organic compounds (VOCs) in plant-plant communication has gained significant attention over the past decade, particularly with regard to the potential of VOCs to prime non-stressed plants for more robust defence responses to future stress challenges. The ecological relevance of such interactions under various environmental stresses has been much debated, and there is a nascent understanding of the mechanisms involved. This review discusses the significance of VOC-mediated inter-plant interactions under both biotic and abiotic stresses and highlights the potential to manipulate outcomes in agricultural systems for sustainable crop protection via enhanced defence. The need to integrate physiological, biochemical, and molecular approaches in understanding the underlying mechanisms and signalling pathways involved in volatile signalling is emphasised.

Recent developments in physical invigoration techniques to develop sprouts of edible seeds as functional foods

For nutritional security, the availability of nutrients from food sources is a crucial factor. Global consumption of edible seeds including cereals, pulses, and legumes makes it a valuable source of nutrients particularly vitamins, minerals, and fiber. The presence of anti-nutritional factors forms complexes with nutrients, this complexity of the nutritional profile and the presence of anti-nutritional factors in edible seeds lead to reduced bioavailability of nutrients. By overcoming these issues, the germination process may help improve the nutrient profile and make them more bioavailable. Physical, physiological, and biological methods of seed invigoration can be used to reduce germination restraints, promote germination, enhance early crop development, to increase yields and nutrient levels through sprouting. During sprouting early start of metabolic activities through hydrolytic enzymes and resource mobilization causes a reduction in emergence time which leads to a better nutritional profile. The use of physical stimulating methods to increase the sprouting rate gives several advantages compared to conventional chemical-based methods. The advantages of physical seed treatments include environment-friendly, high germination rate, early seedling emergence, uniform seedling vigor, protection from chemical hazards, and improved yield. Different physical methods are available for seed invigoration viz. gamma irradiation, laser irradiation, microwaves, magnetic field, plasma, sound waves, and ultrasonic waves. Still, further research is needed to apply each technique to different seeds to identify the best physical method and factors for seed species along with different environmental parameters. The present review will describe the use and effects of physical processing techniques for seed invigoration.

Ultrasound Pulse Emission Spectroscopy Method to Characterize Xylem Conduits in Plant Stems

Although it is well known that plants emit acoustic pulses under drought stress, the exact origin of the waveform of these ultrasound pulses has remained elusive. Here, we present evidence for a correlation between the characteristics of the waveform of these pulses and the dimensions of xylem conduits in plants. Using a model that relates the resonant vibrations of a vessel to its dimension and viscoelasticity, we extract the xylem radii from the waveforms of ultrasound pulses and show that these are correlated and in good agreement with optical microscopy. We demonstrate the versatility of the method by applying it to shoots of ten different vascular plant species. In particular, for Hydrangea quercifolia, we further extract vessel element lengths with our model and compare them with scanning electron cryomicroscopy. The ultrasonic, noninvasive characterization of internal conduit dimensions enables a breakthrough in speed and accuracy in plant phenotyping and stress detection.

Is There a Role for Sound in Plants?

Plants have long been considered passive, static, and unchanging organisms, but this view is finally changing. More and more knowledge is showing that plants are aware of their surroundings, and they respond to a surprising variety of stimuli by modifying their growth and development. Plants extensively communicate with the world around them, above and below ground. Although communication through mycorrhizal networks and Volatile Organic Compounds has been known for a long time, acoustic perception and communication are somehow a final frontier of research. Perhaps surprisingly, plants not only respond to sound, they actually seem to emit sound as well. Roots emit audible clicks during growth, and sounds are emitted from xylem vessels, although the nature of these acoustic emissions still needs to be clarified. Even more interesting, there is the possibility that these sounds carry information with ecological implications, such as alerting insects of the hydration state of a possible host plant, and technological implications as well. Monitoring sound emissions could possibly allow careful monitoring of the hydration state of crops, which could mean significantly less water used during irrigation. This review summarizes the current knowledge on sound perception communication in plants and illustrates possible implications and technological applications.

Demonstration of laser biospeckle method for speedy in vivo evaluation of plant-sound interactions with arugula

In recent years, it is becoming clearer that plant growth and its yield are affected by sound with certain sounds, such as seedling of corn directing itself toward the sound source and its ability to distinguish stuttering of larvae from other sounds. However, methods investigating the effects of sound on plants either take a long time or are destructive. Here, we propose using laser biospeckle, a non-destructive and non-contact technique, to investigate the activities of an arugula plant for sounds of different frequencies, namely, 0 Hz or control, 100 Hz, 1 kHz, 10 kHz, including rock and classical music. Laser biospeckles are generated when scattered light from biological tissues interfere, and the intensities of such speckles change in time, and these changes reflect changes in the scattering structures within the biological tissue. A leaf was illuminated by light from a laser light of wavelength 635 nm, and the biospeckles were recorded as a movie by a CMOS camera for 20 sec at 15 frames per second (fps). The temporal correlation between the frames was characterized by a parameter called biospeckle activity (BA)under the exposure to different sound stimuli of classical and rock music and single-frequency sound stimuli for 1min. There was a clear difference in BA between the control and other frequencies with BA for 100 Hz being closer to control, while at higher frequencies, BA was much lower, indicating a dependence of the activity on the frequency. As BA is related to changes from both the surface as well as from the internal structures of the leaf, LSM (laser scanning microscope) observations conducted to confirm the change in the internal structure revealed more than 5% transient change in stomatal size following exposure to one minute to high frequency sound of 10kHz that reverted within ten minutes. Our results demonstrate the potential of laser biospeckle to speedily monitor in vivo response of plants to sound stimuli and thus could be a possible screening tool for selecting appropriate frequency sounds to enhance or delay the activity of plants. (337 words).

Leaking elastic capacitor as model for active matter

We introduce the "leaking elastic capacitor" (LEC) model, a nonconservative dynamical system that combines simple electrical and mechanical degrees of freedom. We show that an LEC connected to an external voltage source can be destabilized (Hopf bifurcation) due to positive feedback between the mechanical separation of the plates and their electrical charging. Numerical simulation finds regimes in which the LEC exhibits a limit cycle (regular self-oscillation) or strange attractors (chaos). The LEC acts as an autonomous engine, cyclically performing work at the expense of the constant voltage source. We show that this mechanical work can be used to pump current, generating an electromotive force without any time-varying magnetic flux and in a thermodynamically irreversible way. We consider how this mechanism can sustain electromechanical waves propagating along flexible plates. We argue that the LEC model can offer a qualitatively new and more realistic description of important properties of active systems with electrical double layers in condensed-matter physics, chemistry, and biology.

Application of naturally occurring mechanical forces in in vitro plant tissue culture and biotechnology

Cues and signals of the environment in nature can be either beneficial or detrimental from the growth and developmental perspectives. Plants, despite their limited spatial mobility, have developed advanced strategies to overcome the various and changing environmental impacts including stresses. In vitro plantlets, tissues and cells are constantly exposed to the influence of their environment that is well controlled. Light has a widely known morphogenetic effect on plants; however, other physical cues and signals are at least as important but were often neglected. In this review, I summarize our knowledge about the role of the mechanical stimuli, like sound, ultrasound, touch, or wounding in in vitro plant cultures. I summarize the molecular, biochemical, physiological, growth, and developmental changes they cause and how these processes are controlled; moreover, how their regulating or stimulating roles are applied in various plant biotechnological applications. Recent studies revealed that mechanical forces can be used for affecting the plant development and growth in plant tissue culture efficiently, and for increasing the efficacy of other plant biotechnological methods, like genetic transformation and secondary metabolite production.

Mining sequences with similarity to XTH genes in the Solanum tuberosum L. transcriptome: introductory step for identifying homologous XTH genes

The xyloglucan endotransglucosylase/hydrolase (XTH) genes in Arabidopsis thaliana (L.) Heynh. form part of a group of mechano-stimulated genes and play an important role in abiotic stress tolerance. Mining the RNAseq transcriptomic database of 40,430 potato (Solanum tuberosum L.) genes based on functional annotation and homology search, our objective was to discover potentially homologous XTH genes. A Gene Ontology-based XTH homology search and functional annotation discovered, from among the 33 A. thaliana (AtXTH) and 25 tomato (Solanum lycopersicum L.) (SlXTH) XTH genes, 35 gene sequences corresponding to 20 AtXTH genes and 40 gene sequences corresponding to 21 SlXTH genes, respectively. Thirteen sequences corresponding to 11 putative XTH genes in potato, named as StXTH after SlXTH genes, were significantly up- or down-regulated in response to ultrasound. These putative StXTH genes in potato can serve for future functional genetic analyses.

Abiotic stress elements in in vitro potato (Solanum tuberosum L.) exposed to air-based and liquid-based ultrasound: A comparative transcriptomic assessment

Ultrasound (US) can modify the plant growth and development. Previous assessments of the transcriptome of in vitro potato (Solanum tuberosum L.) exposed to US transmitted through air (AB-US) or liquid (PE-US) revealed the up- or down-regulation of several stress-related differentially expressed genes (DEGs) related to abiotic stress. In a bid to better characterize stress-related elements over a four-week period, the transcriptome of AB-US was compared to that of PE-US. When comparing the controls of both treatments, DEGs related to hypoxia were not detected. Nevertheless, hypoxia-related DEGs were detected in the combination of liquid medium and ultrasonication. DEGs coding for chitinase, peroxidase, glutathione-S-transferase, transcription factors of ERF (ethylene responsive factor), DREB (dehydration-responsive element-binding), WRKY and MYB were also significantly highly expressed in PE-US, relative to AB-US. Up- and down-regulation of DEGs related to metabolic processes, and enzymes of the antioxidant system also confirm that PE-US is a more acute abiotic stress than AB-US. KEY MESSAGE: A transcriptomic analysis revealed that liquid-based ultrasonication was a stronger abiotic stressor than air-based ultrasonication. Of particular interest were the heat shock proteins and transcription factors in this comparison. Despite the ultrasound stress, explants survived and plantlets developed.

Effects of hydric stress on vibrational frequency patterns of Capsicum annuum plants

Plants that experience a lack of sufficient irrigation undergo hydric stress, which causes the modification of their mechanical properties. These changes include a complex network of chemical and physical signals that interact between plant-plant and plant-environment systems in a mechanism that is still not well understood, and that differs among species. This mechanical response implies different levels of vibration when the plant experiences structural modifications from self-hydraulic adjustments of flux exchange at specific frequencies, with these carrying behavioral information. To measure these signals, highly sensitive instrumentation that allows the decoding of displacement velocity and displacement of plants, which is possible through calibrated equipment such as 3D scanning laser vibrometers, is necessary. Laser vibrometry technology allows for noninvasive measurements in real-time. Physiological changes could reasonably affect the biomechanical condition of plants in terms of the frequency (hertz) and intensity of the plant's vibration. In this research, it is proposed that the frequency changes of a plant's vibration are related to the plant's hydric condition and that these frequency vibrations have the ecological potential to communicate water changes and levels of hydric stress. The peak of the velocity of plant displacements was found to vary from 0.079 to 1.74 mm/s, and natural frequencies (hertz) range is between 1.8 and 2.6 Hz for plants with low hydric stress (LHS), between 1.3 and 1.6 Hz for plants with medium hydric stress (MHS), and between 6.7 and 7.8 Hz for plants with high hydric stress. These values could act as preliminary references for water management using noninvasive techniques and, knowledge of the range of natural frequencies of hydric stress risk in chili pepper crops can be applied in precision agriculture practices.

Chemical Responses of Nicotiana tabacum (Solanaceae) Induced by Vibrational Signals of a Generalist Herbivore

Plants are able to sense their environment and respond appropriately to different stimuli. Vibrational signals (VS) are one of the most widespread yet understudied ways of communication between organisms. Recent research into the perception of VS by plants showed that they are ecologically meaningful signals involved in different interactions of plants with biotic and abiotic agents. We studied changes in the concentration of alkaloids in tobacco plants induced by VS produced by Phthorimaea operculella (Lepidoptera: Gelechiidae), a generalist caterpillar that naturally feeds on the plant. We measured the concentration of nicotine, nornicotine, anabasine and anatabine in four treatments applied to 11-weeks old tobacco plant: a) Co = undamaged plants, b) Eq = Playback equipment attached to the plant without VS, c) Ca = Plants attacked by P. operculella herbivory and d) Pl = playback of VS of P. operculella feeding on tobacco. We found that nicotine, the most abundant alkaloid, increased more than 2.6 times in the Ca and Pl treatments as compared with the Co and Eq treatments, which were similar between them. Nornicotine, anabasine and anatabine were mutually correlated and showed similar concentration patterns, being higher in the Eq treatment. Results are discussed in terms of the adaptive significance of plant responses to ecologically important VS stimuli.

mRNA transcription profile of potato (Solanum tuberosum L.) exposed to ultrasound during different stages of in vitro plantlet development

KEY MESSAGE

In response to an ultrasound pulse, several hundred DEGs, including in response to stress, were up- or down-regulated in in vitro potato plantlets. Despite this abiotic stress, plantlets survived. Ultrasound (US) can influence plant growth and development. To better understand the genetic mechanism underlying the physiological response of potato to US, single-node segments of four-week-old in vitro plantlets were subjected to US at 35 kHz for 20 min. Following mRNA purification, 10 cDNA libraries were assessed by RNA-seq. Significantly differentially expressed genes (DEGs) were categorized by gene ontology or Kyoto Encyclopedia of Genes and Genomes identifiers. The expression intensity of 40,430 genes was studied. Several hundred DEGs associated with biosynthesis, carbohydrate metabolism and catabolism, cellular protein modification, and response to stress, and which were expressed mainly in the extracellular region, nucleus, and plasma membrane, were either up- or down-regulated in response to US. RT-qPCR was used to validate RNA-seq data of 10 highly up- or down-regulated DEGs, and both Spearman and Pearson correlations between SeqMonk LFC and RT-qPCR LFC were highly positive (0.97). This study examines how some processes evolved over time (0 h, 24 h, 48 h, 1 week and 4 weeks) after an abiotic stress (US) was imposed on in vitro potato explants, and provides clues to the temporal dynamics in DEG-based enzyme functions in response to this stress. Despite this abiotic stress, plantlets survived.

An Organisational Approach to Biological Communication

This paper aims to provide a philosophical and theoretical account of biological communication grounded in the notion of organisation. The organisational approach characterises living systems as organised in such a way that they are capable to self-produce and self-maintain while in constant interaction with the environment. To apply this theoretical framework to the study of biological communication, we focus on a specific approach, based on the notion of influence, according to which communication takes place when a signal emitted by a sender triggers a change in the behaviour of the receiver that is functional for the sender itself. We critically analyse the current formulations of this account, that interpret what is functional for the sender in terms of evolutionary adaptations. Specifically, the adoption of this etiological functional framework may lead to the exclusion of several phenomena usually studied as instances of communication, and possibly even of entire fields of investigation such as synthetic biology. As an alternative, we reframe the influence approach in organisational terms, characterising functions in terms of contributions to the current organisation of a biological system. We develop a theoretical account of biological communication in which communicative functions are distinguished from other types of biological functions described by the organisational account (e.g. metabolic, ecological, etc.). The resulting organisational-influence approach allows to carry out causal analyses of current instances of phenomena of communication, without the need to provide etiological explanations. In such a way it makes it possible to understand in terms of communication those phenomena which realise interactive patterns typical of signalling interactions-and are usually studied as such in scientific practice-despite not being the result of evolutionary adaptations. Moreover, this approach provides operational tools to design and study communicative interactions in experimental fields such as synthetic biology.

Root Tropisms: Investigations on Earth and in Space to Unravel Plant Growth Direction

Root tropisms are important responses of plants, allowing them to adapt their growth direction. Research on plant tropisms is indispensable for future space programs that envisage plant-based life support systems for long-term missions and planet colonization. Root tropisms encompass responses toward or away from different environmental stimuli, with an underexplored level of mechanistic divergence. Research into signaling events that coordinate tropistic responses is complicated by the consistent coincidence of various environmental stimuli, often interacting via shared signaling mechanisms. On Earth the major determinant of root growth direction is the gravitational vector, acting through gravitropism and overruling most other tropistic responses to environmental stimuli. Critical advancements in the understanding of root tropisms have been achieved nullifying the gravitropic dominance with experiments performed in the microgravity environment. In this review, we summarize current knowledge on root tropisms to different environmental stimuli. We highlight that the term tropism must be used with care, because it can be easily confused with a change in root growth direction due to asymmetrical damage to the root, as can occur in apparent chemotropism, electrotropism, and magnetotropism. Clearly, the use of Arabidopsis thaliana as a model for tropism research contributed much to our understanding of the underlying regulatory processes and signaling events. However, pronounced differences in tropisms exist among species, and we argue that these should be further investigated to get a more comprehensive view of the signaling pathways and sensors. Finally, we point out that the Cholodny-Went theory of asymmetric auxin distribution remains to be the central and unifying tropistic mechanism after 100 years. Nevertheless, it becomes increasingly clear that the theory is not applicable to all root tropistic responses, and we propose further research to unravel commonalities and differences in the molecular and physiological processes orchestrating root tropisms.

Exploring the sound-modulated delay in tomato ripening through expression analysis of coding and non-coding RNAs

Background and Aims

Sound is omnipresent in nature. Recent evidence supports the notion that naturally occurring and artificially generated sound waves induce inter- and intracellular changes in plants. These changes, in turn, lead to diverse physiological changes, such as enhanced biotic and abiotic stress responses, in both crops and model plants.

Methods

We previously observed delayed ripening in tomato fruits exposed to 1 kHz sound vibrations for 6 h. Here, we evaluated the molecular mechanism underlying this delaying fruit ripening by performing RNA-sequencing analysis of tomato fruits at 6 h, 2 d, 5 d and 7 d after 1 kHz sound vibration treatment.

Key Results

Bioinformatic analysis of differentially expressed genes and non-coding small RNAs revealed that some of these genes are involved in plant hormone and cell wall modification processes. Ethylene and cytokinin biosynthesis and signalling-related genes were downregulated by sound vibration treatment, whereas genes involved in flavonoid, phenylpropanoid and glucan biosynthesis were upregulated. Furthermore, we identified two sound-specific microRNAs and validated the expression of the pre-microRNAs and the mRNAs of their target genes.

Conclusions

Our results indicate that sound vibration helps to delay fruit ripening through the sophisticated regulation of coding and non-coding RNAs and transcription factor genes.

The basic roles of indoor plants in human health and comfort

Humans have a close relationship with nature, and so integrating the nature world into indoor space could effectively increase people's engagement with nature, and this in turn may benefit their health and comfort. Since people spend 80-90% of their time indoors, the indoor environment is very important for their health. Indoor plants are part of natural indoor environment, but their effect on the indoor environment and on humans has not been quantified. This review provides a comprehensive summary of the role and importance of indoor plants in human health and comfort according to the following four criteria: photosynthesis; transpiration; psychological effects; and purification. Photosynthesis and transpiration are important mechanisms for plants, and the basic functions maintaining the carbon and oxygen cycles in nature. Above all have potential inspiration to human's activities that people often ignored, for example, the application of solar panel, artificial photosynthesis, and green roof/facades were motivated by those functions. Indoor plants have also been shown to have indirect unconscious psychological effect on task performance, health, and levels of stress. Indoor plants can act as indoor air purifiers, they are an effective way to reduce pollutants indoor to reduce human exposure, and have been widely studied in this regard. Indoor plants have potential applications in other fields, including sensing, solar energy, acoustic, and people's health and comfort. Making full use of various effects in plants benefit human health and comfort.

Ultrasonication of in vitro potato single node explants: Activation and recovery of antioxidant defence system and growth responses

The ability to use sound or ultrasound (US) to modify plant growth in vitro, and if possible, to improve yield or productivity, would benefit horticultural scientists. In this study, potato (Solanum tuberosum L. cv. Desirée) in vitro node segments with a single leaf were exposed to US (35 kHz, 70 W, for 20 min). Morphological, physiological and biochemical parameters were measured. Treatment with US 24 h after ultrasonication temporarily accelerated shoot growth but inhibited the development and growth of roots due to a decrease in the level of AA directly after ultrasonication. At the end of the subculture period, i.e., 4 weeks after US treatment, shoot length increased 20% more than control shoots after 4 weeks, while shoot fresh weight was 24% higher than that of control shoots, representing the long-term after-effect of the US treatment. The antioxidant defence system was induced, partly by intensive plantlet growth and development from node segments, and partly by abiotic stress caused by the US treatment. Immediately (0 h) or 24 h after ultrasonication, superoxide dismutase, ascorbate peroxidase, and glutathione reductase activity increased significantly, as did the concentration of low molecular weight antioxidants (GSSG, GSH, AA, TCPa). However, there was no glutathione peroxidase activity, most likely due to the lack of selenium in the basal in vitro growth medium. Therefore, the glutathione-S-transferase path of the ascorbate-glutathione pathway was induced both by metabolic processes and by abiotic stresses and took part in the reduction of organic peroxides using glutathione. US treatment ameliorated the ratios of ascorbic acid/glutathione and reduced/oxidized glutathione, ensuring the development of plantlets with significantly improved shoot parameters, such as higher shoot length and fresh weight, by the end of the subculture period.

Drought tolerance induced by sound in Arabidopsis plants

We examined the responses of sound-treated arabidopsis adult plants to water deprivation and the associated changes on gene expression. The survival of drought-induced plants was significantly higher in the sound treated plants (24,8%) compared with plants kept in silence (13,3%). RNA-seq revealed significant upregulation of 87 genes including 32 genes involved in abiotic stress responses, 31 involved in pathogen responses, 11 involved in oxidation-reduction processes, 5 involved in the regulation of transcription, 2 genes involved in protein phosphorylation/dephosphorylation and 13 involved in jasmonic acid or ethylene synthesis or responses. In addition, 2 genes involved in the responses to mechanical stimulus were also induced by sound, suggesting that touch and sound have at least partially common perception and signaling events.

Exhibiting Music in a Sound Community

Exhibiting music in a sound community announces the presence and potential of an ecological rationality. Two or more beings co-present to each other in sound resonate at the same frequency with one another and comprise a sound community. Co-presence in sound is intersubjective and relational, a subject-to-subject resonant and reciprocal way of knowing, rather than a subject-to-object, asymmetrical and manipulative knowledge. In a sound community music is communicative, as natural as breathing, participatory and exchanged freely, strengthening and sustaining individuals and communities. A sound community exhibits a sound economy, just, participatory and egalitarian. Wealth and power are widely distributed and shared, and maintained through the visible hand of democratic management. A sound economy is based in a sound ecology where exchanges are based in honest signals that invite reciprocity and trust. In a sound ecology, sound being and sound knowing lead to sound action, which is cooperative, mutually beneficial, and just.

Tuned in: plant roots use sound to locate water

Because water is essential to life, organisms have evolved a wide range of strategies to cope with water limitations, including actively searching for their preferred moisture levels to avoid dehydration. Plants use moisture gradients to direct their roots through the soil once a water source is detected, but how they first detect the source is unknown. We used the model plant Pisum sativum to investigate the mechanism by which roots sense and locate water. We found that roots were able to locate a water source by sensing the vibrations generated by water moving inside pipes, even in the absence of substrate moisture. When both moisture and acoustic cues were available, roots preferentially used moisture in the soil over acoustic vibrations, suggesting that acoustic gradients enable roots to broadly detect a water source at a distance, while moisture gradients help them to reach their target more accurately. Our results also showed that the presence of noise affected the abilities of roots to perceive and respond correctly to the surrounding soundscape. These findings highlight the urgent need to better understand the ecological role of sound and the consequences of acoustic pollution for plant as well as animal populations.

Plant blindness and the implications for plant conservation

Plant conservation initiatives lag behind and receive considerably less funding than animal conservation projects. We explored a potential reason for this bias: a tendency among humans to neither notice nor value plants in the environment. Experimental research and surveys have demonstrated higher preference for, superior recall of, and better visual detection of animals compared with plants. This bias has been attributed to perceptual factors such as lack of motion by plants and the tendency of plants to visually blend together but also to cultural factors such as a greater focus on animals in formal biological education. In contrast, ethnographic research reveals that many social groups have strong bonds with plants, including nonhierarchical kinship relationships. We argue that plant blindness is common, but not inevitable. If immersed in a plant-affiliated culture, the individual will experience language and practices that enhance capacity to detect, recall, and value plants, something less likely to occur in zoocentric societies. Therefore, conservation programs can contribute to reducing this bias. We considered strategies that might reduce this bias and encourage plant conservation behavior. Psychological research demonstrates that people are more likely to support conservation of species that have human-like characteristics and that support for conservation can be increased by encouraging people to practice empathy and anthropomorphism of nonhuman species. We argue that support for plant conservation may be garnered through strategies that promote identification and empathy with plants.

Does the whistling thorn acacia (Acacia drepanolobium) use auditory aposematism to deter mammalian herbivores?

Auditory signaling including aposematism characterizes many terrestrial animals. Auditory aposematism by which certain animals use auditory aposematic signals to fend off enemies is well known for instance in rattlesnakes. Auditory signaling by plants toward animals and other plants is an emerging area of plant biology that still suffers from limited amount of solid data. Here I propose that auditory aposematism operates in the African whistling thorn acacia (Acacia drepanolobium = Vachellia drepanolobium). In this tree, the large and hollow thorn bases whistle when wind blows. This type of aposematism compliments the well-known conspicuous thorn and mutualistic ant based aposematism during day and may operate during night when the conspicuous thorns are invisible.

Plant acoustics: in the search of a sound mechanism for sound signaling in plants

Being sessile, plants continuously deal with their dynamic and complex surroundings, identifying important cues and reacting with appropriate responses. Consequently, the sensitivity of plants has evolved to perceive a myriad of external stimuli, which ultimately ensures their successful survival. Research over past centuries has established that plants respond to environmental factors such as light, temperature, moisture, and mechanical perturbations (e.g. wind, rain, touch, etc.) by suitably modulating their growth and development. However, sound vibrations (SVs) as a stimulus have only started receiving attention relatively recently. SVs have been shown to increase the yields of several crops and strengthen plant immunity against pathogens. These vibrations can also prime the plants so as to make them more tolerant to impending drought. Plants can recognize the chewing sounds of insect larvae and the buzz of a pollinating bee, and respond accordingly. It is thus plausible that SVs may serve as a long-range stimulus that evokes ecologically relevant signaling mechanisms in plants. Studies have suggested that SVs increase the transcription of certain genes, soluble protein content, and support enhanced growth and development in plants. At the cellular level, SVs can change the secondary structure of plasma membrane proteins, affect microfilament rearrangements, produce Ca(2+) signatures, cause increases in protein kinases, protective enzymes, peroxidases, antioxidant enzymes, amylase, H(+)-ATPase / K(+) channel activities, and enhance levels of polyamines, soluble sugars and auxin. In this paper, we propose a signaling model to account for the molecular episodes that SVs induce within the cell, and in so doing we uncover a number of interesting questions that need to be addressed by future research in plant acoustics.

Acoustic communication in plant-animal interactions

Acoustic communication is widespread and well-studied in animals but has been neglected in other organisms such as plants. However, there is growing evidence for acoustic communication in plant-animal interactions. While knowledge about active acoustic signalling in plants (i.e. active sound production) is still in its infancy, research on passive acoustic signalling (i.e. reflection of animal sounds) revealed that bat-dependent plants have adapted to the bats' echolocation systems by providing acoustic reflectors to attract their animal partners. Understanding the proximate mechanisms and ultimate causes of acoustic communication will shed light on an underestimated dimension of information transfer between plants and animals.

Stridulatory sound-production and its function in females of the cicada Subpsaltria yangi

Acoustic behavior plays a crucial role in many aspects of cicada biology, such as reproduction and intrasexual competition. Although female sound production has been reported in some cicada species, acoustic behavior of female cicadas has received little attention. In cicada Subpsaltria yangi, the females possess a pair of unusually well-developed stridulatory organs. Here, sound production and its function in females of this remarkable cicada species were investigated. We revealed that the females could produce sounds by stridulatory mechanism during pair formation, and the sounds were able to elicit both acoustic and phonotactic responses from males. In addition, the forewings would strike the body during performing stridulatory sound-producing movements, which generated impact sounds. Acoustic playback experiments indicated that the impact sounds played no role in the behavioral context of pair formation. This study provides the first experimental evidence that females of a cicada species can generate sounds by stridulatory mechanism. We anticipate that our results will promote acoustic studies on females of other cicada species which also possess stridulatory system.

How do "mute" cicadas produce their calling songs?

Insects have evolved a variety of structures and mechanisms to produce sounds, which are used for communication both within and between species. Among acoustic insects, cicada males are particularly known for their loud and diverse sounds which function importantly in communication. The main method of sound production in cicadas is the tymbal mechanism, and a relative small number of cicada species possess both tymbal and stridulatory organs. However, cicadas of the genus Karenia do not have any specialized sound-producing structures, so they are referred to as "mute". This denomination is quite misleading, as they indeed produce sounds. Here, we investigate the sound-producing mechanism and acoustic communication of the "mute" cicada, Karenia caelatata, and discover a new sound-production mechanism for cicadas: i.e., K. caelatata produces impact sounds by banging the forewing costa against the operculum. The temporal, frequency and amplitude characteristics of the impact sounds are described. Morphological studies and reflectance-based analyses reveal that the structures involved in sound production of K. caelatata (i.e., forewing, operculum, cruciform elevation, and wing-holding groove on scutellum) are all morphologically modified. Acoustic playback experiments and behavioral observations suggest that the impact sounds of K. caelatata are used in intraspecific communication and function as calling songs. The new sound-production mechanism expands our knowledge on the diversity of acoustic signaling behavior in cicadas and further underscores the need for more bioacoustic studies on cicadas which lack tymbal mechanism.

Biological effect of audible sound control on mung bean (Vigna radiate) sprout

Audible sound (20-20000 Hz) widely exists in natural world. However, the interaction between audible sound and the growth of plants is usually neglected in biophysics research. Not much effort has been put forth in studying the relation of plant and audible sound. In this work, the effect of audible sound on germination and growth of mung bean (Vigna radiate) was studied under laboratory condition. Audible sound ranging 1000-1500 Hz, 1500-2000 Hz, and 2000-2500 Hz and intensities [80 dB (A), 90 dB (A), 100 dB (A)] were used to stimulate mung bean for 72 hours. The growth of mung bean was evaluated in terms of mean germination time, total length, and total fresh weight. Experimental results indicated that the sound wave can reduce the germination period of mung bean and the mung bean under treatments of sound with intensity around 90 dB and frequency around 2000 Hz and significant increase in growth. Audible sound treatment can promote the growth of mung bean differently for distinct frequency and intensity. The study provides us with a way to understand the effects and rules of sound field on plant growth and a new way to improve the production of mung bean.

Love thy neighbour: facilitation through an alternative signalling modality in plants

Background

Both competitive and facilitative interactions between species play a fundamental role in shaping natural communities. A recent study showed that competitive interactions between plants can be mediated by some alternative signalling channel, extending beyond those channels studied so far (i.e. chemicals, contact and light). Here, we tested whether such alternative pathway also enables facilitative interactions between neighbouring plant species. Specifically, we examined whether the presence of a ‘good’ neighbouring plant like basil positively influenced the germination of chilli seeds when all known signals were blocked. For this purpose, we used a custom-designed experimental set-up that prevented above- and below-ground contact and blocked chemical and light-mediated signals normally exchange by plants.

Results

We found that seed germination was positively enhanced by the presence of a ‘good’ neighbour, even when the known signalling modalities were blocked, indicating that light, touch or chemical signals may not be indispensible for different plant species to sense each other’s presence.

Conclusions

We propose that this alternative signalling modality operates as a general indicator of the presence of heterospecifics, enabling seeds to detect and identify a neighbour prior to engaging in a more finely-tuned, but potentially more costly, response.

Acoustic and magnetic communication in plants: Is it possible?

Over the last two decades, important insights into our understanding of plant ecology and the communicative nature of plants have not only confirmed the existence of a wide range of communication means used by plants, but most excitingly have indicated that more modalities remain to be discovered. In fact, we have recently found that seeds and seedlings of the chili plant, Capsicum annuum, are able to sense neighbors and identify relatives using alternative mechanisms beyond previously studied channels of plant communication. In this addendum, we offer a hypothetical mechanistic explanation as to how plants may do this by quantum-assisted magnetic and/or acoustic sensing and signaling. If proven correct, this hypothesis prompts for a re-interpretation of our current understanding of plasticity in germination and growth of plants and more generally, calls for developing a new perspective of these biological phenomena.

Out of sight but not out of mind: alternative means of communication in plants

Current knowledge suggests that the mechanisms by which plants communicate information take numerous forms. Previous studies have focussed their attention on communication via chemicals, contact and light; other methods of interaction between plants have remained speculative. In this study we tested the ability of young chilli plants to sense their neighbours and identify their relatives using alternative mechanism(s) to recognised plant communication pathways. We found that the presence of a neighbouring plant had a significant influence on seed germination even when all known sources of communication signals were blocked. Furthermore, despite the signalling restriction, seedlings allocated energy to their stem and root systems differently depending on the identity of the neighbour. These results provide clear experimental evidence for the existence of communication channels between plants beyond those that have been recognized and studied thus far.