Sexual behaviour in Euplotes raikovi is accompanied by pheromone-induced modifications of ionic currents

Bioelectric control of locomotor gaits in the walking ciliate Euplotes

Diverse animal species exhibit highly stereotyped behavioral actions and locomotor sequences as they explore their natural environments. In many such cases, the neural basis of behavior is well established, where dedicated neural circuitry contributes to the initiation and regulation of certain response sequences. At the microscopic scale, single-celled eukaryotes (protists) also exhibit remarkably complex behaviors and yet are completely devoid of nervous systems. Here, to address the question of how single cells control behavior, we study locomotor patterning in the exemplary hypotrich ciliate Euplotes, a highly polarized cell, which actuates a large number of leg-like appendages called cirri (each a bundle of ∼25-50 cilia) to swim in fluids or walk on surfaces. As it navigates its surroundings, a walking Euplotes cell is routinely observed to perform side-stepping reactions, one of the most sophisticated maneuvers ever observed in a single-celled organism. These are spontaneous and stereotyped reorientation events involving a transient and fast backward motion followed by a turn. Combining high-speed imaging with simultaneous time-resolved electrophysiological recordings, we show that this complex coordinated motion sequence is tightly regulated by rapid membrane depolarization events, which orchestrate the activity of different cirri on the cell. Using machine learning and computer vision methods, we map detailed measurements of cirri dynamics to the cell's membrane bioelectrical activity, revealing a differential response in the front and back cirri. We integrate these measurements with a minimal model to understand how Euplotes-a unicellular organism-manipulates its membrane potential to achieve real-time control over its motor apparatus.

Cell motility: Bioelectrical control of behavior without neurons

Single cells are capable of remarkably sophisticated, sometimes animal-like, behaviors. New work demonstrates bioelectric control of motility through the differential regulation of appendage movements in a unicellular organism that walks across surfaces using leg-like bundles of cilia.

Integrated information as a possible basis for plant consciousness

It is commonly assumed that plants do not possess consciousness. Since the criterion for this assumption is usually human consciousness this assumption represents a top down attitude. It is obvious that plants are not animals and using animal criteria of consciousness will lead to its rejection in plants. However using a bottom up evolutionary approach and a leading theory of consciousness, Integrated Information Theory, we report that we find evidence that indicates that plant meristems act in a conscious fashion although probably at the level of minimal consciousness. Since many plants contain multiple meristems these observations highlight a very different evolutionary approach to consciousness in biological organisms.

Signalling in ciliates: long- and short-range signals and molecular determinants for cellular dynamics

In ciliates, unicellular representatives of the bikont branch of evolution, inter- and intracellular signalling pathways have been analysed mainly in Paramecium tetraurelia, Paramecium multimicronucleatum and Tetrahymena thermophila and in part also in Euplotes raikovi. Electrophysiology of ciliary activity in Paramecium spp. is a most successful example. Established signalling mechanisms include plasmalemmal ion channels, recently established intracellular Ca²⁺ -release channels, as well as signalling by cyclic nucleotides and Ca²⁺ . Ca²⁺ -binding proteins (calmodulin, centrin) and Ca²⁺ -activated enzymes (kinases, phosphatases) are involved. Many organelles are endowed with specific molecules cooperating in signalling for intracellular transport and targeted delivery. Among them are recently specified soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs), monomeric GTPases, H⁺ -ATPase/pump, actin, etc. Little specification is available for some key signal transducers including mechanosensitive Ca²⁺ -channels, exocyst complexes and Ca²⁺ -sensor proteins for vesicle-vesicle/membrane interactions. The existence of heterotrimeric G-proteins and of G-protein-coupled receptors is still under considerable debate. Serine/threonine kinases dominate by far over tyrosine kinases (some predicted by phosphoproteomic analyses). Besides short-range signalling, long-range signalling also exists, e.g. as firmly installed microtubular transport rails within epigenetically determined patterns, thus facilitating targeted vesicle delivery. By envisaging widely different phenomena of signalling and subcellular dynamics, it will be shown (i) that important pathways of signalling and cellular dynamics are established already in ciliates, (ii) that some mechanisms diverge from higher eukaryotes and (iii) that considerable uncertainties still exist about some essential aspects of signalling.

Roles of ion transport in control of cell motility

Cell motility is an essential feature of life. It is essential for reproduction, propagation, embryonic development, and healing processes such as wound closure and a successful immune defense. If out of control, cell motility can become life-threatening as, for example, in metastasis or autoimmune diseases. Regardless of whether ciliary/flagellar or amoeboid movement, controlled motility always requires a concerted action of ion channels and transporters, cytoskeletal elements, and signaling cascades. Ion transport across the plasma membrane contributes to cell motility by affecting the membrane potential and voltage-sensitive ion channels, by inducing local volume changes with the help of aquaporins and by modulating cytosolic Ca(2+) and H(+) concentrations. Voltage-sensitive ion channels serve as voltage detectors in electric fields thus enabling galvanotaxis; local swelling facilitates the outgrowth of protrusions at the leading edge while local shrinkage accompanies the retraction of the cell rear; the cytosolic Ca(2+) concentration exerts its main effect on cytoskeletal dynamics via motor proteins such as myosin or dynein; and both, the intracellular and the extracellular H(+) concentration modulate cell migration and adhesion by tuning the activity of enzymes and signaling molecules in the cytosol as well as the activation state of adhesion molecules at the cell surface. In addition to the actual process of ion transport, both, channels and transporters contribute to cell migration by being part of focal adhesion complexes and/or physically interacting with components of the cytoskeleton. The present article provides an overview of how the numerous ion-transport mechanisms contribute to the various modes of cell motility.

On classical and quantum error-correction in ciliate mate selection

Ciliated protozoa sensing pheromones secreted from nonself mating types engage in preconjugal "courtship" dances and contacts. Using simulated "social" trials, I recently showed the heterotrich ciliate, Spirostomum ambiguum, can learn to advertise degrees of mating fitness to "suitors" and "rivals" when serially contracting or (ciliary) reversing at variable rates. Conspicuous consumers signal higher quality reproductive status by playing "harder-to-get" via metabolically wasteful avoidance displays that hinder the exchange of preconjugal touches between "courting" couples. Conversely, prudent savers conserve energy pending situations more favorable for conjugating a partner. These ciliates reply with lower avoidance frequencies, guaranteeing nearby conspecifics of being "easier-to-get". By deciding to switch from behavioral strategies signaling conspicuous consumption to those signaling prudent savings, fitter ciliates learn to altruistically sacrifice net payoffs and persuade suitors to participate in paired reproduction. Less fit ciliates, unable to sustain long periods of high response rates, switch their behavioral strategies of prudent savings to briefly emit conspicuous consumption and thus learn to opportunistically cheat superior rivals. Mating competency depends, in part, on the efficiency of heuristics formed from recursive strategy searches and use. Heuristics represent stored patterns of action which evolve into ordered computational networks supporting entire courting repertoires. As ciliates expand signaling skills over many trials, the connectivity between strategies strengthens from Hebbian-like learning, leading to faster decisions about the appropriateness of courting messages and replies. The best experts master signaling decisions at efficiencies comparable to finding target solutions from superposed states with Grover's quantum search algorithm. I here append these findings with a critique on the feasibility of serial behavioral strategies to perfect ciliate mate selection via classical repetition and quantum bit-flip error-correction codes that safeguard transmitted social information from noise and might be exploited for signal encryption.

Potassium Channels Keep Mobile Cells on the Go

Cell motility is a prerequisite for the creation of new life, and it is required for maintaining the integrity of an organism. Under pathological conditions, “too much” motility may cause premature death. Studies over the past few years have revealed that ion channels are essential for cell motility. This review highlights the importance of K+ channels in regulating cell motility.

Wound-induced green leaf volatiles cause the release of acetylated derivatives and a terpenoid in maize

Green leaf volatiles (GLVs), generally occurring C6 alcohols, aldehydes and acetates from plants, play an important role in plant-plant communication. These compounds induce intact plants to produce jasmonic acid, and induce defense-related gene expression and the release of volatile compounds. Here, we address wound-induced GLVs cause the release of acetylated derivatives and a terpenoid, (E)-4,8-dimethylnona-1,3,7-triene (DMNT) in intact maize, which may be a type of plant-plant interaction mediated by airborne GLVs. Upon exposure of intact maize seedlings to wound-induced GLVs, (Z)-3-hexenyl acetate was consistently the most abundant compound released. Exogenous application of individual alcohols and aldehydes mostly resulted in the release of corresponding acetate esters. C6-alcohols with a double bond between the second and third, or the third and fourth carbon atoms, C5- or C6-aldehydes, and (Z)-3-hexenyl acetate triggered the release of DMNT. When (Z)-3-hexenyl acetate and hexyl acetate were used to treat maize seedlings, they were recovered from the plants. These data demonstrated that: (1) apart from direct adsorption and re-release of acetate esters, absorption and conversion of exogenous alcohols and aldehydes into acetate esters occurred, and (2) DMNT was induced by a range of aldehydes and unsaturated alcohols.