Cytotoxic activity of naphthoquinones with special emphasis on juglone and its 5-O-methyl derivative

The cytotoxicity of nine naphthoquinones (NQ) was assayed against HL-60 (leukaemia), MDA-MB-435 (melanoma), SF-295 (brain) and HCT-8 (colon), all human cancer cell lines, and peripheral blood mononuclear cells (PBMC), as representatives of normal cells, after 72 h of incubation. 5-Methoxy-1,4-naphthoquinone was the most active compound, showing IC₅₀ values in the range of 0.31 (1.7 μM) in HL-60 to 0.88 μg/mL (4.7 μM) in SF-295 and IC₅₀ of 0.69 μg/mL (3.7 μM) against PBMC. With the introduction of a bromo-substituent in position 2 or 3 of juglone, the IC₅₀ significantly decreased, regardless of the position on the NQ moiety. However, compared with juglone methyl ether, the halogen substitution decreased the activity. To further understand the mechanism underlying the cytotoxicity of 5-methoxy-1,4-naphthoquinone, studies involving DNA fragmentation, cell cycle analysis, phosphatidyl serine externalization, mitochondrial depolarization and activation of caspases 8 and 3/7 were performed in HL-60 cell line, using doxorubicin as a positive control. The results indicate that the cytotoxic 5-methoxy-1,4-naphthoquinone activates caspases 8 and 3/7 and thus induces apoptosis independent of mitochondria.     

The use of light in prey capture by the tropical pitcher plant Nepenthes aristolochioides

Nepenthes pitcher plants deploy tube-shaped pitchers to catch invertebrate prey; those of Nepenthes aristolochioides possess an unusual translucent dome. The hypothesis was tested that N. aristolochioides pitchers operate as light traps, by quantifying prey capture under three shade treatments. Flies are red-blind, with visual sensitivity maxima in the UV, blue, and green wavebands. Red celluloid filters were used to reduce the transmission of these wavebands into the interior of the pitchers. Those that were shaded at the rear showed a 3-fold reduction in Drosophila caught, relative to either unshaded control pitchers, or pitchers that were shaded at the front. Thus, light transmitted through the translucent dome is a fundamental component of N. aristolochioides' trapping mechanism.     

Effect of pitcher age on trapping efficiency and natural prey capture in carnivorous Nepenthes rafflesiana plants

Background and Aims

Nepenthes pitchers are sophisticated traps that employ a variety of mechanisms to attract, capture and retain prey. The underlying morphological structures and physiological processes are subject to change over the lifetime of a pitcher. Here an investigation was carried out on how pitcher properties and capture efficiency change over the first 2 weeks after pitcher opening.

Methods

Prey capture, trapping efficiency, extrafloral nectar secretion, pitcher odour, as well as pH and viscoelasticity of the digestive fluid in N. rafflesiana pitchers were monitored in the natural habitat from pitcher opening up to an age of 2 weeks.

Key Results

Pitchers not only increased their attractiveness over this period by becoming more fragrant and secreting more nectar, but also gained mechanical trapping efficiency via an enhanced wettability of the upper pitcher rim (peristome). Consistently, natural prey capture was initially low and increased 3–6 d after opening. It was, however, highly variable within and among pitchers. At the same time, the pH and viscoelasticity of the digestive fluid decreased, suggesting that the latter is not essential for effective prey capture.

Conclusions

Prey capture and attraction by Nepenthes are dynamic processes strongly influenced by the changing properties of the pitcher. The results confirm insect aquaplaning on the peristome as the main capture mechanism in N. rafflesiana.Key words: Carnivorous plants, pitcher development, prey attraction, prey capture, insect aquaplaning, extrafloral nectar, Nepenthes rafflesiana     

In vitro propagation and assessment of clonal fidelity of Nepenthes khasiana Hook. f.: a medicinal insectivorous plant of India

An efficient in vitro protocol for large-scale multiplication of Nepenthes khasiana, a threatened insectivorous plant of India, has been developed from nodal stem segments. The highest shoot proliferation of 19.16 ± 0.23 shoots/explant was recorded in half-strength Murashige and Skoog (MS) medium supplemented with 2.5 mg/l kinetin, 2.0 mg/l 6-benzyl aminopurine, 3 % sucrose and 0.8 % agar. The best rooting was achieved in half-strength MS medium supplemented with 2.0 mg/l α-naphthalene acetic acid with an average of 9.04 ± 0.46 roots/shoot. The plantlets were successfully transferred to the greenhouse with survival rate of 92 %, exhibiting normal development. Cytological and random amplified polymorphic DNA (RAPD) analyses were carried out to assess the genetic integrity of the regenerated plantlets. Cytological analysis revealed no change in chromosome number with cells studied showing 2n = 80. Of the 80 primers screened for RAPD analysis, 14 primers resulted in clear and scorable bands. A total of 72 amplification products were obtained out of which only 4.1 % bands were polymorphic. Cluster analysis of the RAPD profile revealed an average similarity coefficient ranging from 0.98 to 1.0, thus suggesting genetic stability in the micropropagated plants of N. khasiana.     

The integration of locomotion and prey capture in vertebrates: Morphology, behavior, and performance

For most vertebrates, locomotion is a fundamental componentof prey capture. Despite this ubiquitous link, few studies havequantified the integration of these complex systems. Severalvariables related to locomotor performance, including maximumspeed, acceleration, deceleration, maneuverability, accuracy,and approach stability, likely influence feeding performancein vertebrates. The relative importance of these measures ofperformance, however, depends on the ecology of the predator.While factors such as morphology and physiology likely definethe limits of these variables, other factors such as motivationof the predator, prey type, and habitat structure can also influenceperformance. Understanding how these variables relate to feedingunder a given suite of ecological conditions is central to understandingpredator–prey interactions, and ultimately how locomotionand feeding have co-evolved. The goals of this article are todiscuss several variables of locomotor performance related toprey capture, present new data on the relationship between locomotorand feeding morphology in fishes, discuss the evolution of preycapture in cichlid fishes, and outline some future directionsfor research. While suction feeding is a primary mechanism ofprey capture in fishes, swimming is vital for accurately positioningthe mouth relative to the prey item. Many fishes decelerateduring prey capture using their body and fins, but the pectoralfins have a dominant role in maintaining approach stability.This suggests that fishes employing high-performance suctionfeeding (relatively small mouth) will have larger pectoral finsto facilitate accurate and stable feeding. I provide new dataon the relationship between pectoral fin morphology and maximumgape in centrarchid fishes. For seven species, pectoral finarea was significantly, and negatively, correlated with maximumgape. This example illustrates that the demands from one complexsystem (feeding) can influence another complex system (locomotion).Future studies that examine the morphological, physiological,and functional evolution of locomotion involved in prey captureby aquatic and terrestrial vertebrates will provide insightinto the origin and consequences of diversity.     

Temperature and prey capture: opposite relationships in two predator taxa

Abstract 1. All other things equal, predator capture rates are expected to depend on encounter rate with prey, prey escape capability (including prey defences), and on predator agility. Ectotherm predators and their prey both respond to increasing temperature by increased activity, i.e. predators increase their search area and prey may enhance their escape capability. This means that, as temperature changes, the ability of a predator to catch prey will decrease, increase, or remain unchanged depending on the relative effect of temperature on predator and prey. Their responses may further be differentially moulded by light conditions depending on whether the predator is diurnally or nocturnally active. It was hypothesised that flying Diptera are vulnerable to carabid beetles only at low temperatures and over the full temperature range for spiders because carabids, in contrast to spiders, are not built to catch swiftly moving prey. 2. The first experiment examined the spontaneous locomotor activity of the predators and of fruit flies at different temperatures (5, 10, 15, 20, 25, and 30 °C) and light conditions (light, dark). A second experiment examined the effect of temperature and light on the predation rate of two carabid beetles (Pterostichus versicolor and Calathus fuscipes) and two spiders (Clubiona phragmitis and Pardosa prativaga) using fruit flies (Drosophila melanogaster) as prey. 3. All four predators and the fruit fly increased their locomotory activity at higher temperatures. Activity of the carabid beetles peaked at intermediate temperatures; spiders and fruit flies were most active at the highest temperatures. Predation rate of the spiders increased with temperature whereas the beetles caught flies only at low temperatures (5 and 10 °C). 4. Diurnal variation in temperature may bring different prey groups within the set of potential prey at different times of the day or at different seasons. The ability of many carabid beetles to forage at low temperatures may have nutritional benefits and increases the diversity of interactions in terrestrial food webs.     

Functional morphology of prey capture in the sturgeon,Scaphirhynchus albus

Acipenseriformes (sturgeon and paddlefish) are basal actinopterygians with a highly derived cranial morphology that is characterized by an anatomical independence of the jaws from the neurocranium. We examined the morphological and kinematic basis of prey capture in the Acipenseriform fish Scaphirhynchus albus, the pallid sturgeon. Feeding pallid sturgeon were filmed in lateral and ventral views and movement of cranial elements was measured from video sequences. Sturgeon feed by creating an anterior to posterior wave of cranial expansion resulting in prey movement through the mouth. The kinematics of S. albus resemble those of other aquatic vertebrates: maximum hyoid depression follows maximum gape by an average of 15 ms and maximum opercular abduction follows maximum hyoid depression by an average of 57 ms. Neurocranial rotation was not a part of prey capture kinematics in S. albus, but was observed in another sturgeon species, Acipenser medirostris. Acipenseriformes have a novel jaw protrusion mechanism, which converts rostral rotation of the hyomandibula into ventral protrusion of the jaw joint. The relationship between jaw protrusion and jaw opening in sturgeon typically resembles that of elasmobranchs, with peak upper jaw protrusion occurring after peak gape.     

Speciation through the lens of biomechanics: locomotion,prey capture and reproductive isolation

Speciation is a multifaceted process that involves numerous aspects of the biological sciences and occurs for multiple reasons. Ecology plays a major role, including both abiotic and biotic factors. Whether populations experience similar or divergent ecological environments, they often adapt to local conditions through divergence in biomechanical traits. We investigate the role of biomechanics in speciation using fish predator–prey interactions, a primary driver of fitness for both predators and prey. We highlight specific groups of fishes, or specific species, that have been particularly valuable for understanding these dynamic interactions and offer the best opportunities for future studies that link genetic architecture to biomechanics and reproductive isolation (RI). In addition to emphasizing the key biomechanical techniques that will be instrumental, we also propose that the movement towards linking biomechanics and speciation will include (i) establishing the genetic basis of biomechanical traits, (ii) testing whether similar and divergent selection lead to biomechanical divergence, and (iii) testing whether/how biomechanical traits affect RI. Future investigations that examine speciation through the lens of biomechanics will propel our understanding of this key process.     

Modulation in the feeding prey capture of the ant-lion, Myrmeleon crudelis

Ant-lions are pit-building larvae (Neuroptera: Myrmeleontidae), which possess relatively large mandibles used for catching and consuming prey. Few studies involving terrestrial arthropod larva have investigated prey capture behavior and kinematics and no study has shown modulation of strike kinematics. We examined feeding kinematics of the ant-lion, Myrmeleon crudelis, using high-speed video to investigate whether larvae modulate strike behavior based on prey location relative to the mandible. Based on seven capture events from five M. crudelis, the strike took 17.60 ± 2.92?msec and was characterized by near-simultaneous contact of both mandibles with the prey. Modulation of the angular velocity of the mandibles based on prey location was clearly demonstrated. M. crudelis larvae attempted to simultaneously contact prey with both mandibles by increasing mean angular velocity of the far mandible (65 ± 21?rad?sec(-1) ) compared with the near mandible (35 ± 14?rad?sec(-1) ). Furthermore, kinematic results showed a significant difference for mean angular velocity between the two mandibles (P<0.005). Given the lengthy strike duration compared with other fast-striking arthropods, these data suggest that there is a tradeoff between the ability to modulate strike behavior for accurate simultaneous mandible contact and the overall velocity of the strike. The ability to modulate prey capture behavior may increase dietary breadth and capture success rate in these predatory larvae by allowing responsive adjustment to small-scale variations in prey size, presentation, and escape response.     

Modulation and variability of prey capture kinematics in clariid catfishes

Species with narrow or limited diets (trophic specialists) are expected to be less flexible in their feeding repertoire compared to species feeding on a wide range of different prey (trophic generalists). The ability to modulate prey capture kinematics in response to different prey types and prey position, as well as the overall variability in prey capture kinematics, is evaluated in four clariid species ranging from trophic generalist (Clarias gariepinus) to species with morphological specializations and a narrow diet (Channallabes apus and Gymnallabes typus). High-speed video recordings were made of prey captures on two prey that differ in shape, attachment strength and hardness. While the observed amount of strike-to-strike variability in prey capture kinematics is similar for all species and not influenced by prey type, only the two less specialized species showed the ability to modulate their prey capture kinematics in function of the presented prey types. All species did, however, show positional modulation during the strike by adjusting the magnitude of neurocranial elevation. These results indicate that the narrow dietary breadth of trophic specialists is indeed indicative of functional stereotypy in this group of fishes. Although most studies focussing on prey processing found a similar result, the present study is one of the few that was able to demonstrate this relationship when focussing on prey capture mechanics. Possibly, this relationship is less frequently observed for prey capture compared to prey processing because, regardless of prey type, the initial capture of prey requires a higher amount of variability.     

Cost of prey capture, growth rate and ration size in pike, Esox lucius L., as functions of prey wheight

Prey intake, amount of time feeding, pursuit and manipulation times and growth rate were studied in the pike, Esox lucius , in relation to prey weight. Predator and prey were observed in tanks at 15°C and with a 14:10 h LD photoperiod. A total of 444 captures were recorded from five 1 g prey weight groups varying from 0 to 4.9 g. Ten pike were used weighing between 50 and 149 g.
As prey weight increased, the number and weight of prey consumed decreased as did the time spent feeding, which became concentrated into the first trial of the day. Pursuit time did not vary with prey weight, but manipulation time and the weight of prey gained per unit pursuit plus manipulation time increased with prey weight.
The growth rate of pike was a positive function of ration size and a negative function of the amount of time spent capturing each gramme of prey (capture cost). Growth rate was also correlated with the mean length and weight of prey eaten.
The most profitable prey, as estimated from optimal foraging theory, need only be available once every 84 min for pike to maximize their net energy gain. The data show that feeding behaviour can have a direct influence on the reproductive success of pike through its effect on growth rate.     

Aquatic prey capture in ambystomatid salamanders: patterns of variation in muscle activity

Functional morphologists commonly study feeding behavior in vertebrates by recording electrical activity from head muscles during unrestrained prey capture. Rarely are experiments designed to permit a partitioning variation in muscle electrical activity patterns. Analysis of muscle activity during aquatic prey capture in two morphologically distinct species of salamanders, Ambystoma dumerilii and A. mexicanum, is conducted to assess variation at four levels: between species, among individuals within species, among experiments conducted on different days, and among feedings. The results show that 1) mean correlations among the 11 electromyographic variables measured for each feeding are low and vary considerably among individuals, 2) many of the variables show significant differences among experimental days, 3) only one variable, the difference in timing between the depressor mandibulae and sternohyoideus muscles, showed significant variation between species, and 4) seven of the 11 variables showed significant variation among individuals within species. Overall, the variation between feedings (trials) was high, and there was some variation between days on which the experiments were conducted. Neither electrode position within the muscle nor satiation contributed to the high trial variance. The results suggest that functional analyses of feeding behavior should include an assessment of variation due to individuals, days, and trials, because the amount of variation at these levels may render differences between species nonsignificant.     

Aquatic prey capture in ray-finned fishes: a century of progress and new directions

The head of ray-finned fishes is structurally complex and is composed of numerous bony, muscular, and ligamentous elements capable of intricate movement. Nearly two centuries of research have been devoted to understanding the function of this cranial musculoskeletal system during prey capture in the dense and viscous aquatic medium. Most fishes generate some amount of inertial suction to capture prey in water. In this overview we trace the history of functional morphological analyses of suction feeding in ray-finned fishes, with a particular focus on the mechanisms by which suction is generated, and present new data using a novel flow imaging technique that enables quantification of the water flow field into the mouth. We begin with a brief overview of studies of cranial anatomy and then summarize progress on understanding function as new information was brought to light by the application of various forms of technology, including high-speed cinematography and video, pressure, impedance, and bone strain measurement. We also provide data from a new technique, digital particle image velocimetry (DPIV) that allows us to quantify patterns of flow into the mouth. We believe that there are three general areas in which future progress needs to occur. First, quantitative three-dimensional studies of buccal and opercular cavity dimensions during prey capture are needed; sonomicrometry and endoscopy are techniques likely to yield these data. Second, a thorough quantitative analysis of the flow field into the mouth during prey capture is necessary to understand the effect of head movement on water in the vicinity of the prey; three-dimensional DPIV analyses will help to provide these data. Third, a more precise understanding of the fitness effects of structural and functional variables in the head coupled with rigorous statistical analyses will allow us to better understand the evolutionary consequences of intra- and interspecific variation in cranial morphology and function.     

The role of adhesion in prey capture and predator defence in arthropods

Adhesive devices are used by arthropods not only in terrestrial locomotion but also in prey capture and predator defence. We argue that the physical mechanisms involved in both these contexts must mainly be capillarity and the viscosity of an adhesive secretion, whereas other mechanisms, such as friction or intermolecular forces, are of minor importance. Adhesive prey-capture devices might function as passive devices or might be actively extended toward the prey, sometimes in a very rapid manner. Adhesive mechanisms used for predator defence might involve firm adhesion to the substratum or the discharge of a sticky secretion to immobilize the appendages of the opponent. We review the occurrence of adhesive devices as employed in both functional contexts across the Arthropoda and argue that these mechanisms are of particular importance for slow-moving and relatively clumsy life forms. We discuss three case studies in more detail. (1) Loricera larvae (Carabidae) use galeae with an extremely flexible cuticle in combination with an adhesive secretion. (2) Adult Stenus species (Staphylinidae) employ two highly flexible paraglossae that are covered by an adhesive emulsion of lipid droplets dispersed in an aqueous proteinaceous liquid. (3) Springtails often adhere to the mouthparts, the antennae, the legs, or other parts of the integument of Stenus larvae before being captured with the mandibles.     

Contribution of pitcher fragrance and fluid viscosity to high prey diversity in a Nepenthes carnivorous plant from borneo

Mechanisms that improve prey richness in carnivorous plants may involve three crucial phases of trapping:attraction, capture and retention.Nepenthes rafflesiana var. typica is an insectivorous pitcher plant that is widespread in northern Borneo.It exhibits ontogenetic pitcher dimorphism with the upper pitchers trapping more flying prey than the lower pitchers.While this difference in prey composition has been ascribed to differences in attraction,the contribution of capture and retention has been overlooked.This study focused on distinguishing between the prey trapping mechanisms, and assessing their relative contribution to prey diversity.Arthropod richness and diversity of both visitors and prey in the two types of pitchers were analysed to quantify the relative contribution of attraction to prey trapping.Rate of insect visits to the different pitcher parts and the presence or absence of a sweet fragrance was recorded to clarify the origin and mechanism of attraction.The mechanism of retention was studied by insect bioassays and measurements of fluid viscosity. Nepenthes rafflesiana was found to trap a broader prey spectrum than that previously described for any Nepenthes species,with the upper pitchers attracting and trapping a greater quantity and diversity of prey items than the lower pitchers.Capture efficiency was low compared with attraction or retention efficiency.Fragrance of the peristome,or nectar rim,accounted mainly for the observed non-specific, better prey attraction by the upper pitchers, while the retentive properties of the viscous fluid in these upper pitchers arguably explains the species richness of their flying prey.The pitchers of N. rafflesiana are therefore more than simple pitfall traps and the digestive fluid plays an important yet unsuspected role in the ecological success of the species.     

Spatio-temporal changes of photosynthesis in carnivorous plants in response to prey capture,retention and digestion

Carnivorous plants have evolved modified leaves into the traps that assist in nutrient uptake from captured prey. It is known that the traps of carnivorous plants usually have lower photosynthetic rates than assimilation leaves as a result of adaptation to carnivory. However, a few recent studies have indicated that photosynthesis and respiration undergo spatio-temporal changes during prey capture and retention, especially in the genera with active trapping mechanisms. This study describes the spatio-temporal changes of effective quantum yield of photochemical energy conversion in photosystem II (Φ_PSII) in response to ant-derived formic acid during its capture and digestion.Key words: action potential, carnivorous plants, formic acid, photosynthesis, respiration, animal-plant interactionCarnivorous plants have evolved their leaves into the modified structures called traps, which assist in nutrient uptake from prey bodies.¹ The traps attract, catch and digest the animal prey; however, some species obtain substantial amount of nutrients from leaf litter (Nepenthes ampullaria), algae (Utricularia) or from faeces of tree shrew Tupaia montana (Nepenthes lowii, N. rajah, N. macrophylla) as a result of adaptive radiation with regard to nitrogen sequestration.^2–5 Carnivorous plants are mainly restricted to sunny, moist and nutrient-poor environment, because only in this environment would the cost of producing traps be lower than the benefits gained from prey.⁶ From carbon metabolism point of view, the benefit is in term of increased rate of photosynthesis per unit leaf mass as a result of increased nitrogen concentration in the leaf or an increase in the total leaf mass that can be supported.^6–8 The costs of carnivory include reduced rate of net photosynthesis (A_N) in traps as a result of leaf adaptation to carnivory or increased rate of respiration (R_D) as a result of extra energy requirements for attracting, capturing and digesting the prey.⁹ Whereas the reduced A_N in the traps has been confirmed several times, the higher R_D in traps is still ambiguous.^9–12Until now studies assessing the cost of carnivory have usually been confined to measurements of A_N and R_D in carnivorous traps vs. non-carnivorous leaves, to the construction costs and payback times for carnivorous organs or to the carbon costs of sticky mucilage secretion by glands.^9–16 There is a growing body of evidences that prey-catching is active process involving spatio-temporal changes in A_N and R_D in traps, at least in carnivorous plants with active trapping mechanisms.¹⁷ First evidence, however not convincing, came from the work of Knight.⁹ She found that bladders of aquatic bladderwort Utricularia macrorhiza had a slightly greater R_D (10%) than assimilation leaves, but these differences were not significant. Later Adamec found that R_D of bladders in six Utricularia species was 75–200% greater than that in the leaves.¹⁸ The action of Utricularia bladder is one of the fastest movement in plant kingdom. When the trap of Utricularia is set, ready for trapping, it looks shrunken due to negative hydrostatic pressure. When the trapdoor is stimulated by prey it opens, sucks the water with prey and the door rapidly shuts. This firing process takes about 30 ms. Then the bladder restores its negative hydrostatic pressure by the removal of water from trap lumen through the glands. The resetting of bladders is a respiration-dependent process accompanied by the consumption of ATP.^1,19,20 Adamec suggests that the bladders of Utricularia were in post-firing state and were therefore pumping water and is possible that their R_D in this state was much higher than in their resting state.¹⁸ Adaptative changes in cytochrome c oxidase in the genus Utricularia may provide respiratory power for bladder function.²¹ The most famous carnivorous plant the Venus flytrap (Dionaea muscipula) also uses active trapping mechanism for prey capture. Recently, Hájek and Adamec published that the traps of D. muscipula had lower A_N, whereas the R_D in lamina and trap was comparable.¹² This is in accordance with the classical interpretation of cost/benefit model of carnivory. However, in our previous study we have shown that trigger hair irritation in the open as well as in closed trap of Dionaea muscipula resulted in the rapid increase of R_D and decrease of effective quantum yield of photochemical energy conversion in photosystem II (Φ_PSII).¹⁷ We have suggested that this is a result of generation of action potentials upon trigger hair irritation.^22–25The link between electrical signals and inhibition of photosynthesis and stimulation of respiration has been described in several plant species, however it has not been known in carnivorous plants.^26–30 Another genus of carnivorous plants that generates action potentials in response to mechanical irritation is sundew (Drosera). In the Dionaea traps, the action potential originates in any one of the six trigger hair and the potential propagates over the entire trap blade more rapidly across the lower (abaxial) surface. In the Drosera tentacle, action potentials are initiated by a receptor potential just below the swollen head of the tentacle and propagate only to its base and do not reach the leaf lamina.^31–33 This is in accordance with the results that separated D. prolifera tentacles have many times greater R_D in comparison with that of leaf lamina. This proves a very high metabolic and physiological activity of tentacles probably as a results of electrical irritability.¹¹ It has been suggested that at least some of the energy connected with the rise of R_D after action potential is utilized for the restoration of the state of ionic balance (i.e., restore the resting state).²⁶ Except the electrical signals, chemical substances seem to be also effective in effecting photosynthesis in carnivorous plants. This study describes negative impact of ant-derived formic acid on effective quantum yield of photochemical energy conversion in PSII (Φ_PSII), which is a sensitive indicator of plant photosynthetic performance.We measured the chlorophyll fluorescence in response to prey capture (ant Lasius niger L.) by the leaf of Drosera capensis L. Ten one-year-old Drosera capensis L plants were grown in growth chamber at a irradiance 200 µmol m⁻² s⁻¹ photosynthetic active radiation (PAR), 14/10 h day/night cycle and daily temperature ∼25°C. Before the measurement, the plant was adapted to light intensity 100 µmol m⁻² s⁻¹ PAR for 10 minutes (time required for steady state values of chlorophyll fluorescence in light-adapted state, F_t). The actinic light was provided by fluorcam FC-1000 LC (Photon System Instruments, Czech Republic) using red emitting LED diodes (λ = 620 nm). The experiment started by application of first saturation pulse (4,000 µmol m⁻² s⁻¹ PAR, 800 ms duration, λ = 620 nm). Then (after 10 seconds) one ant (Lasius niger) was gently put on the D. capensis leaf. During the first two hours, saturation pulses were applied every three minute, thereafter every hour and later every 24 hour. After each saturation flash the visible pictures were taken by camera Nikon D60 (Nikon, Thailand). The Φ_PSII, which indicates the proportion of the light absorbed by chlorophyll associated with photosystem II that is used in photochemistry, was calculated as (F_m′ - F_t)/F_m′.^34,35 The experiment was repeated without ant''s abdomen (the abdomen was cut by scalpel but ants survive and their moving was not affected). In the last experiment 1 µL 15 M formic acid (Fluka) was dropped on the leaf. All experiments were repeated four times independently and data presented are representative.The inhibition of Φ_PSII occurred within a few minutes after the ant was trapped by Drosera tentacles and then again after 96 hours (Fig. 1). Repeating the experiment without ant''s abdomen had no negative impact on Φ_PSII in spite of ant-induced leaf folding (Fig. 2). The most common substance in ant''s abdomen is formic acid.³⁶ This indicates that the inhibition of Φ_PSII was caused first by the spraying of the formic acid on the leaf by the struggling ant and then by releasing the formic acid after 96 hours from ant''s abdomen as a result of digestion. Therefore, the preliminary observation in Drosera mentioned at the end of discussion of our previous study was not associated with electrical signals.¹⁷ The inhibition was caused by the ant Lasius niger, which inhibits the Φ_PSII in D. capensis by releasing the formic acid from its abdomen. This is consistent with the findings that propagation of action potentials in Drosera is restricted only to the tentacles and therefore had no effect on photosynthesis in leaf blade (Fig. 2). Further, application of 1 µL 15 M formic acid resulted in very similar effect like the living ant with intact abdomen (Fig. 3). The concentration of formic acid was chosen according to data that the venom of Formica rufa contains 5–17 M formic acid.³⁶Open in a separate windowFigure 1The visible response (A) and the response of effective quantum yield of photochemical energy conversion in photosystem II (Φ_PSII, B) of Drosera capensis leaf to prey capture (intact ant Lasius niger). The ant was put on the leaf in time 10 seconds.Open in a separate windowFigure 2The response of effective quantum yield of photochemical energy conversion in photosystem II (Φ_PSII) of Drosera capensis leaf to prey capture (ant Lasius niger without abdomen). The ant without abdomen was put on the leaf in time 10 seconds. Note that no changes in Φ_PSII occurred in spite of leaf folding.Open in a separate windowFigure 3The response of effective quantum yield of photochemical energy conversion in photosystem II (Φ_PSII) of Drosera capensis leaf to 1 µL of 15 M formic acid. The drop of formic acid was put on the leaf in time 10 seconds.The production of formic acid by ants is thought to have evolved to improve capture of invertebrate prey and aid colony defence.³⁷ Some examples document that negative effect of ant-derived formic acid on plant growth is not novel, but it has not been described in carnivorous plants previously. It is known that ants Myrmelachista schumanni use formic acid as a herbicide. The ants live inside the hollow stems of Duroia hirsuta, kill all plants other than their host plant by injecting formic acid into the leaves. By killing these others plants, the ants gain more nest sites and they create a single species stand of plants.³⁸ Also, weaver ants (Oecophylla smaragdina) damage mango fruit by deposition of formic acid as a result of fighting between weaver colonies.³⁹The mechanism of action is very similar to the well known herbicide 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). Formic acid causes significant inhibition of the electron transfer on the acceptor side of photosystem II, particularly from plastoquinone A to plastoquinone B.^40,41 From the data analysis of carnivorous plants published recently the genera with the highest proportions of ants in their diets are Brocchinia (90%), Nepenthes (73%) and Sarracenia (55%).⁴² All the mentioned genera have pitcher traps, with the permanent level of digestive fluid, in which the formic acid is diluted during digestion and thus the pitchers are probably prevented against its toxic effect. Captures of ants is much less frequent for sticky traps of Drosera (3.4%) and Pinguicula (0.5%); however it may have deteriorate effect.Carnivorous plants are not just killers but are a fascinating group of plant. They do not just eat the animals but may form a complicated social network with them. Complicated animal-plant interaction, as has been described e.g. between carnivorous pitcher plant Nepenthes bicalcarata and ants may have direct impact on physiological processes similar as a well known relationship between acacia and ants.⁴³ The possible impact of formic acid of ant species co-occurring with carnivorous plants in their natural habitat on photosynthesis remains to be elucidated.     

Synthesis, characterization, molecular docking and cytotoxic activity of novel plumbagin hydrazones against breast cancer cells

Novel plumbagin hydrazonates were prepared, structurally characterized and evaluated for anti-proliferative activity against estrogen receptor-positive MCF-7 and triple negative MDA-MB-231 and MDA-MB-468 breast cancer cell lines which exhibited superior inhibitory activity than parent plumbagin compound. Molecular docking studies indicated that hydroxyl groups on plumbagin and hydrazonate side chain favor additional hydrogen bonding interactions with amino acid residues in p50-subunit of NF-κB protein and these compounds inhibited NF-κB expression which may be responsible for the enhanced anti-proliferative activity. These compounds were found to be more effective against triple negative breast cancer cells and might serve as a starting point for building future strategies against triple negative breast cancers which are known for their increased drug resistance and poor prognosis of breast cancer patients.     

Behavior of the rhabdocoel flatworm Mesostoma ehrenbergii in prey capture and feeding

The prey-capture and feeding behavior of the rhabdocoel flatworm Mesostoma ehrenbergii (Focke, 1836) was analyzed using a variety of live and dead prey, including Daphnia, mosquito larvae, and tubifex annelids. Prey-capture behavior was broken down into its individual components. Mesostoma could accommodate to and change its behavior depending on the size and type of prey. Mechanical rather than chemical cues were effective in inducing prey-capture behavior. No evidence for a special chemical paralysis as suggested by other workers was found. The apparent paralysis observed in cladocera such as Daphnia and mosquito larvae was, in part a behavioral response of the prey in ‘playing possum’ and also in part due to immobilization of the prey by the flatworm with mucous threads. This revised version was published online in July 2006 with corrections to the Cover Date.     

Foraging behaviour and capture success in perch, pikeperch and pike and the effects of prey density

The effect of school size on capture success in three different piscivores, perch Perca fluviatilis , pikeperch Stizostedion lucioperca and pike Esox lucius , was investigated. Roach Rutilus rutilus were used as prey in a pool experiment where individual predators were presented prey at densities of one, two, four, eight and 16 prey, respectively. Treatments were replicated seven times for each predator species. Perch was at first virtually unable to capture a prey from a school and suffered a significant confusion effect with increasing prey density. The effect, however, was limited in the long run, as the perch was a very effective predator in its hunting strategy where it singled out and repeatedly attacked single prey irrespective of prey density or school size. Pikeperch and pike were able to attack and capture prey at any prey density equally successfully and thus did not suffer from a confusion effect. Neither did these predators receive any apparent advantages from increasing prey density.