Root nutrient uptake enhances photosynthetic assimilation in prey-deprived carnivorous pitcher plant <Emphasis Type="Italic">Nepenthes talangensis</Emphasis>

Carnivorous plants grow in nutrient-poor habitats and obtain substantial amount of nitrogen from prey. Specialization toward carnivory may decrease the ability to utilize soil-derived sources of nutrients in some species. However, no such information exists for pitcher plants of the genus Nepenthes, nor the effect of nutrient uptake via the roots on photosynthesis in carnivorous plants is known. The principal aim of present study was to investigate, whether improved soil nutrient status increases photosynthetic efficiency in prey-deprived pitcher plant Nepenthes talangensis. Gas exchange and chlorophyll (Chl) fluorescence were measured simultaneously and were correlated with Chl and nitrogen concentration as well as with stable carbon isotope abundance (δ¹³C) in control and fertilized N. talangensis plants. Net photosynthetic rate (P _N) and maximum- (F_v/F_m) and effective quantum yield of photosystem II (Φ_PSII) were greater in the plants supplied with nutrients. Biomass, leaf nitrogen, and Chl (a+b) also increased in fertilized plants. In contrast, δ¹³C did not differ significantly between treatments indicating that intercellular concentration of CO₂ did not change. We can conclude that increased root nutrient uptake enhanced photosynthetic efficiency in prey-deprived N. talangensis plants. Thus, the roots of Nepenthes plants are functional and can obtain a substantial amount of nitrogen from the soil.     

Photosynthetic characterization of Australian pitcher plant <Emphasis Type="Italic">Cephalotus follicularis</Emphasis>

Australian carnivorous pitcher plant Cephalotus follicularis Labill. produces two types of leaves. During the spring time, the plant produces a foliage type of noncarnivorous leaf called lamina. Later, the second type of leaf is produced — carnivorous pitcher. Using simultaneous measurements of gas exchange and chlorophyll (Chl) fluorescence photosynthetic efficiency of these two distinct forms of leaves were compared. In addition stomatal density, an important component of gas exchange, and Chl concentration were also determined. Pitcher trap had lower net photosynthetic rate (P _N) in comparison to noncarnivorous lamina, whereas the rate of respiration (R _D) was not significantly different. This was in accordance with lower stomatal density and Chl concentration in the pitcher trap. On the other hand maximum quantum yield of PSII (F_v/F_m) and effective quantum yield of photochemical energy conversion in PSII (Φ_PSII) was not significantly different. Nonphotochemical quenching (NPQ) was significantly higher in the lamina at higher irradiance. These data are in accordance with hypothesis that changing the leaf shape in carnivorous plants to make it a better trap generally makes it less efficient at photosynthesis. However, the pitcher of Cephalotus had much higher P _N than it was expected from the data set of the genus Nepenthes. Because it is not possible to optimize for contrasting function such as photosynthesis and carnivory, it is hypothesized that Cephalotus pitchers are less elaborated for carnivorous function than the pitchers of Nepenthes.     

Feeding on prey increases photosynthetic efficiency in the carnivorous sundew Drosera capensis

Backround and Aims

It has been suggested that the rate of net photosynthesis (A_N) of carnivorous plants increases in response to prey capture and nutrient uptake; however, data confirming the benefit from carnivory in terms of increased A_N are scarce and unclear. The principal aim of our study was to investigate the photosynthetic benefit from prey capture in the carnivorous sundew Drosera capensis.

Methods

Prey attraction experiments were performed, with measurements and visualization of enzyme activities, elemental analysis and pigment quantification together with simultaneous measurements of gas exchange and chlorophyll a fluorescence in D. capensis in response to feeding with fruit flies (Drosophila melanogaster).

Key Results

Red coloration of tentacles did not act as a signal to attract fruit flies onto the traps. Phosphatase, phophodiesterase and protease activities were induced 24 h after prey capture. These activities are consistent with the depletion of phosphorus and nitrogen from digested prey and a significant increase in their content in leaf tissue after 10 weeks. Mechanical stimulation of tentacle glands alone was not sufficient to induce proteolytic activity. Activities of β-D-glucosidases and N-acetyl-β-D-glucosaminidases in the tentacle mucilage were not detected. The uptake of phosphorus from prey was more efficient than that of nitrogen and caused the foliar N:P ratio to decrease; the contents of other elements (K, Ca, Mg) decreased slightly in fed plants. Increased foliar N and P contents resulted in a significant increase in the aboveground plant biomass, the number of leaves and chlorophyll content as well as A_N, maximum quantum yield (F_v/F_m) and effective photochemical quantum yield of photosystem II (Φ_PSII).

Conclusions

According to the stoichiometric relationships among different nutrients, the growth of unfed D. capensis plants was P-limited. This P-limitation was markedly alleviated by feeding on fruit flies and resulted in improved plant nutrient status and photosynthetic performance. This study supports the original cost/benefit model proposed by T. Givnish almost 30 years ago and underlines the importance of plant carnivory for increasing phosphorus, and thereby photosynthesis.     

Tree shrew lavatories: a novel nitrogen sequestration strategy in a tropical pitcher plant

Nepenthes pitcher plants are typically carnivorous, producing pitchers with varying combinations of epicuticular wax crystals, viscoelastic fluids and slippery peristomes to trap arthropod prey, especially ants. However, ant densities are low in tropical montane habitats, thereby limiting the potential benefits of the carnivorous syndrome. Nepenthes lowii, a montane species from Borneo, produces two types of pitchers that differ greatly in form and function. Pitchers produced by immature plants conform to the ‘typical’ Nepenthes pattern, catching arthropod prey. However, pitchers produced by mature N. lowii plants lack the features associated with carnivory and are instead visited by tree shrews, which defaecate into them after feeding on exudates that accumulate on the pitcher lid. We tested the hypothesis that tree shrew faeces represent a significant nitrogen (N) source for N. lowii, finding that it accounts for between 57 and 100 per cent of foliar N in mature N. lowii plants. Thus, N. lowii employs a diversified N sequestration strategy, gaining access to a N source that is not available to sympatric congeners. The interaction between N. lowii and tree shrews appears to be a mutualism based on the exchange of food sources that are scarce in their montane habitat.     

Trap closure and prey retention in Venus flytrap (Dionaea muscipula) temporarily reduces photosynthesis and stimulates respiration

Background and Aims

The carnivorous plant Venus flytrap (Dionaea muscipula) produces a rosette of leaves: each leaf is divided into a lower part called the lamina and an upper part, the trap, with sensory trigger hairs on the adaxial surface. The trap catches prey by very rapid closure, within a fraction of a second of the trigger hairs being touched twice. Generation of action potentials plays an important role in closure. Because electrical signals are involved in reduction of the photosynthetic rate in different plant species, we hypothesized that trap closure and subsequent movement of prey in the trap will result in transient downregulation of photosynthesis, thus representing the energetic costs of carnivory associated with an active trapping mechanism, which has not been previously described.

Methods

Traps were enclosed in a gas exchange cuvette and the trigger hairs irritated with thin wire, thus simulating insect capture and retention. Respiration rate was measured in darkness (R_D). In the light, net photosynthetic rate (A_N), stomatal conductance (g_s) and intercellular CO₂ concentration (c_i) were measured, combined with chlorophyll fluorescence imaging. Responses were monitored in the lamina and trap separately.

Key Results

Irritation of trigger hairs resulted in decreased A_N and increased R_D, not only immediately after trap closure but also during the subsequent period when prey retention was simulated in the closed trap. Stomatal conductance remained stable, indicating no stomatal limitation of A_N, so c_i increased. At the same time, the effective quantum yield of photosystem II (Φ_PSII) decreased transiently. The response was confined mainly to the digestive zone of the trap and was not observed in the lamina. Stopping mechanical irritation resulted in recovery of A_N, R_D and Φ_PSII.

Conclusions

We put forward the first experimental evidence for energetic demands and carbon costs during insect trapping and retention in carnivorous plants, providing a new insight into the cost/benefit model of carnivory.     

The Pitcher Plant Sarracenia purpurea Can Directly Acquire Organic Nitrogen and Short-Circuit the Inorganic Nitrogen Cycle

Background

Despite the large stocks of organic nitrogen in soil, nitrogen availability limits plant growth in many terrestrial ecosystems because most plants take up only inorganic nitrogen, not organic nitrogen. Although some vascular plants can assimilate organic nitrogen directly, only recently has organic nitrogen been found to contribute significantly to the nutrient budget of any plant. Carnivorous plants grow in extremely nutrient-poor environments and carnivory has evolved in these plants as an alternative pathway for obtaining nutrients. We tested if the carnivorous pitcher plant Sarracenia purpurea could directly take up intact amino acids in the field and compared uptake of organic and inorganic forms of nitrogen across a gradient of nitrogen deposition. We hypothesized that the contribution of organic nitrogen to the nitrogen budget of the pitcher plant would decline with increasing nitrogen deposition.

Methodology and Principal Findings

At sites in Canada (low nitrogen deposition) and the United States (high nitrogen deposition), individual pitchers were fed two amino acids, glycine and phenylalanine, and inorganic nitrogen (as ammonium nitrate), individually and in mixture. Plants took up intact amino acids. Acquisition of each form of nitrogen provided in isolation exceeded uptake of the same form in mixture. At the high deposition site, uptake of organic nitrogen was higher than uptake of inorganic nitrogen. At the low deposition site, uptake of all three forms of nitrogen was similar. Completeness of the associated detritus-based food web that inhabits pitcher-plant leaves and breaks down captured prey had no effect on nitrogen uptake.

Conclusions and Significance

By taking up intact amino acids, Sarracenia purpurea can short-circuit the inorganic nitrogen cycle, thus minimizing potential bottlenecks in nitrogen availability that result from the plant''s reliance for nitrogen mineralization on a seasonally reconstructed food web operating on infrequent and irregular prey capture.     

The carnivorous syndrome in Nepenthes pitcher plants: Current state of knowledge and potential future directions

Nepenthes is the largest genus of pitcher plants, with its center of diversity in SE Asia. The plants grow in substrates that are deficient in N and offset this deficiency by trapping animal prey, primarily arthropods. Recent research has provided new insights into the function of the pitchers, particularly with regard to prey tapping and retention. Species examined to date use combinations of wettable peristomes, wax layers and viscoelastic fluid to trap and retain prey. In many respects, this has redefined our understanding of the functioning of Nepenthes pitchers. In addition, recent research has shown that several Nepenthes species target specific groups of prey animals, or are even evolving away from a strictly carnivorous mode of operation. Future research into nutrient sequestration strategies and mechanisms of prey attraction would no doubt further enhance our knowledge of the ecology of this remarkable genus.Key words: carnivory, mutualism, Nepenthes, pitcher plants     

Adaptive significance and ontogenetic variability of the waxy zone in Nepenthes rafflesiana

Background and Aims

The slippery waxy zone in the upper part of pitchers has long been considered the key trapping structure of the Nepenthes carnivorous plants; however, the presence of wax is reported to be variable within and between species of this species-rich genus. This study raises the question of the adaptive significance of the waxy zone and investigates the basis for an ontogenetic cause of its variability and correlation with pitcher shape.

Methods

In Brunei (Borneo) the expression of the waxy zone throughout plant ontogeny was studied in two taxa of the Nepenthes rafflesiana complex, typica and elongata, which differ in pitcher shape and size. We also tested the adaptive significance of this zone by comparing the trapping efficiency and the number of prey captured of wax-bearing and wax-lacking plants.

Key Results

In elongata, the waxy zone is always well expanded and the elongated pitchers change little in form during plant development. Wax efficiently traps experimental ants but the number of captured prey in pitchers is low. In contrast, in typica, the waxy zone is reduced in successively produced pitchers until it is lost at the end of the plant''s juvenile stage. The form of pitchers thus changes continuously throughout plant ontogeny, from elongated to ovoid. In typica, the number of captured prey is greater, but the role of wax in trapping is minor compared with that of the digestive liquid, and waxy plants do not show a higher insect retention and prey abundance as compared with non-waxy plants.

Conclusions

The waxy zone is not always a key trapping structure in Nepenthes and can be lost when supplanted by more efficient features. This study points out how pitcher structure is submitted to selection, and that evolutionary changes in developmental mechanisms could play a role in the morphological diversity of Nepenthes.Key words: Carnivorous plant, developmental evolution, digestive liquid, epicuticular wax, insect trapping, heteroblasty, heterochrony, leaf form, morphological diversity, Nepenthes rafflesiana, ontogenetic change, pitcher plant     

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     

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.     

Secreted pitfall-trap fluid of carnivorous Nepenthes plants is unsuitable for microbial growth

Background and Aims

Carnivorous plants of the genus Nepenthes possess modified leaves that form pitfall traps in order to capture prey, mainly arthropods, to make additional nutrients available for the plant. These pitchers contain a digestive fluid due to the presence of hydrolytic enzymes. In this study, the composition of the digestive fluid was further analysed with regard to mineral nutrients and low molecular-weight compounds. A potential contribution of microbes to the composition of pitcher fluid was investigated.

Methods

Fluids from closed pitchers were harvested and analysed for mineral nutrients using analytical techniques based on ion-chromatography and inductively coupled plasma–optical emission spectroscopy. Secondary metabolites were identified by a combination of LC-MS and NMR. The presence of bacteria in the pitcher fluid was investigated by PCR of 16S-rRNA genes. Growth analyses of bacteria and yeast were performed in vitro with harvested pitcher fluid and in vivo within pitchers with injected microbes.

Key Results

The pitcher fluid from closed pitchers was found to be primarily an approx. 25-mm KCl solution, which is free of bacteria and unsuitable for microbial growth probably due to the lack of essential mineral nutrients such as phosphate and inorganic nitrogen. The fluid also contained antimicrobial naphthoquinones, plumbagin and 7-methyl-juglone, and defensive proteins such as the thaumatin-like protein. Challenging with bacteria or yeast caused bactericide as well as fungistatic properties in the fluid. Our results reveal that Nepenthes pitcher fluids represent a dynamic system that is able to react to the presence of microbes.

Conclusions

The secreted liquid of closed and freshly opened Nepenthes pitchers is exclusively plant-derived. It is unsuitable to serve as an environment for microbial growth. Thus, Nepenthes plants can avoid and control, at least to some extent, the microbial colonization of their pitfall traps and, thereby, reduce the need to vie with microbes for the prey-derived nutrients.     

Quite a few reasons for calling carnivores 'the most wonderful plants in the world'

Background

A plant is considered carnivorous if it receives any noticeable benefit from catching small animals. The morphological and physiological adaptations to carnivorous existence is most complex in plants, thanks to which carnivorous plants have been cited by Darwin as ‘the most wonderful plants in the world’. When considering the range of these adaptations, one realizes that the carnivory is a result of a multitude of different features.

Scope

This review discusses a selection of relevant articles, culled from a wide array of research topics on plant carnivory, and focuses in particular on physiological processes associated with active trapping and digestion of prey. Carnivory offers the plants special advantages in habitats where nutrient supply is scarce. Counterbalancing costs are the investments in synthesis and the maintenance of trapping organs and hydrolysing enzymes. With the progress in genetic, molecular and microscopic techniques, we are well on the way to a full appreciation of various aspects of plant carnivory.

Conclusions

Sufficiently complex to be of scientific interest and finite enough to allow conclusive appraisal, carnivorous plants can be viewed as unique models for the examination of rapid organ movements, plant excitability, enzyme secretion, nutrient absorption, food-web relationships, phylogenetic and intergeneric relationships or structural and mineral investment in carnivory.     

Fenestration: a window of opportunity for carnivorous plants

A long-standing but controversial hypothesis assumes that carnivorous plants employ aggressive mimicry to increase their prey capture success. A possible mechanism is that pitcher plants use aggressive mimicry to deceive prey about the location of the pitcher''s exit. Specifically, species from unrelated families sport fenestration, i.e. transparent windows on the upper surfaces of pitchers which might function to mimic the exit of the pitcher. This hypothesis has not been evaluated against alternative hypotheses predicting that fenestration functions to attract insects from afar. By manipulating fenestration, we show that it does not increase the number of Drosophila flies or of two ant species entering pitchers in Sarracenia minor nor their retention time or a pitcher''s capture success. However, fenestration increased the number of Drosophila flies alighting on the pitcher compared with pitchers of the same plant without fenestration. We thus suggest that fenestration in S. minor is not an example of aggressive mimicry but rather functions in long-range attraction of prey. We highlight the need to evaluate aggressive mimicry relative to alternative concepts of plant–animal communication.     

Rootless Aquatic Plant Aldrovanda Vesiculosa: Physiological Polarity, Mineral Nutrition, and Importance of Carnivory

Various ecophysiological investigations are presented in Aldrovanda vesiculosa, a rootless aquatic carnivorous plant. A distinct polarity of N, P, and Ca tissue content per dry mass (DM) unit was found along Aldrovanda shoots. Due to effective re-utilization, relatively small proportions of N (10 – 13 %) and P (33 – 43 %) are probably lost with senescent leaf whorls, while there is complete loss of all Ca, K, and Mg. The total content of starch and free sugars was 26 – 47 % DM along adult shoots, with the maximum in the 7^th – 10^th whorls. About 30 % of the total maximum sugar content was probably lost with dead whorls. The plant was found to take up 5 – 7 times more NH₄ ⁺ to NO₃ ^– from a mineral medium. Under nearly-natural conditions in an outdoor cultivation container, catching of prey led to significantly more rapid growth than in unfed plants. DM of the fed controls was 48 % higher than in the unfed plants. The controls produced 0.69 branches per plant, while the unfed plants did not produced any. However, the N and P content per DM unit increased by 6 – 25 % in the apices and the first 6 whorls in the unfed variant, as compared to the fed controls. It may be suggested that carnivory is very important for Aldrovanda.     

Plasma-membrane H+-ATPases are expressed in pitchers of the carnivorous plant Nepenthes alata Blanco

Nepenthes is a unique genus of carnivorous plants that can capture insects in trapping organs called pitchers and digest them in pitcher fluid. The pitcher fluid includes digestive enzymes and is strongly acidic. We found that the fluid pH decreased when prey accumulates in the pitcher fluid of Nepenthes alata. The pH decrease may be important for prey digestion and the absorption of prey-derived nutrients. To identify the proton pump involved in the acidification of pitcher fluid, plant proton-pump homologs were cloned and their expressions were examined. In the lower part of pitchers with natural prey, expression of one putative plasma-membrane (PM) H⁺-ATPase gene, NaPHA3, was considerably higher than that of the putative vacuolar H⁺-ATPase (subunit A) gene, NaVHA1, or the putative vacuolar H⁺-pyrophosphatase gene, NaVHP1. Expression of one PM H⁺-ATPase gene, NaPHA1, was detected in the head cells of digestive glands in the lower part of pitchers, where proton extrusion may occur. Involvement of the PM H⁺-ATPase in the acidification of pitcher fluid was also supported by experiments with proton-pump modulators; vanadate inhibited proton extrusion from the inner surface of pitchers, whereas bafilomycin A₁ did not, and fusicoccin induced proton extrusion. These results strongly suggest that the PM H⁺-ATPase is responsible for acidification of the pitcher fluid of Nepenthes. Received: 8 June 2000 / Accepted: 8 August 2000     

Nectar,not colour,may lure insects to their death

We experimentally demonstrate in the field that prey of the carnivorous plant Sarracenia purpurea are attracted to sugar, not to colour. Prey capture (either all taxa summed or individual common taxa considered separately) was not associated with total red area or patterning on pitchers of living pitcher plants. We separated effects of nectar availability and coloration using painted ‘pseudopitchers’, half of which were coated with sugar solution. Unsugared pseudopitchers captured virtually no prey, whereas pseudopitchers with sugar solution captured the same amount of prey as living pitchers. In contrast to a recent study that associated red coloration with prey capture but that lacked controls for nectar availability, we infer that nectar, not colour, is the primary means by which pitcher plants attract prey.     

Pitcher plant facilitates prey capture in a sympatric congener

Carnivorous plants avoid below-ground competition for nitrogen by utilizing an alternative nitrogen resource—invertebrate prey, but it remains unclear if sympatric carnivorous plants compete for prey resources. The aim of this study was to investigate if exploitative prey-resource competition occurs between the two sympatric pitcher plant species, Nepenthes rafflesiana and N. gracilis in Singapore. We first investigated if prey-resource partitioning occurs between these two species, and then investigated niche shift in N. gracilis by examining its pitcher contents along an in situ gradient of N. rafflesiana interspecific competition. Our results showed clear evidence of resource partitioning between the two species, but contrary to the expectation of competition, proximity to N. rafflesiana pitchers correlated with higher total prey numbers in N. gracilis pitchers. Our multivariate model of prey assemblages further suggested that N. rafflesiana facilitates N. gracilis prey capture, especially in several ant taxa that are trapped by both species. Concurrently, we found strong evidence for intraspecific competition between N. gracilis pitchers, suggesting that prey resources are exhaustible by pitcher-predation. Our results show that resource partitioning can be associated with facilitative interactions, instead of competition as is usually assumed. Facilitation is more typically expected between phylogenetically distant species, but divergences in resource acquisition strategies can permit facilitation between congeners.     

Nepenthesin Protease Activity Indicates Digestive Fluid Dynamics in Carnivorous Nepenthes Plants

Carnivorous plants use different morphological features to attract, trap and digest prey, mainly insects. Plants from the genus Nepenthes possess specialized leaves called pitchers that function as pitfall-traps. These pitchers are filled with a digestive fluid that is generated by the plants themselves. In order to digest caught prey in their pitchers, Nepenthes plants produce various hydrolytic enzymes including aspartic proteases, nepenthesins (Nep). Knowledge about the generation and induction of these proteases is limited. Here, by employing a FRET (fluorescent resonance energy transfer)-based technique that uses a synthetic fluorescent substrate an easy and rapid detection of protease activities in the digestive fluids of various Nepenthes species was feasible. Biochemical studies and the heterologously expressed Nep II from Nepenthes mirabilis proved that the proteolytic activity relied on aspartic proteases, however an acid-mediated auto-activation mechanism was necessary. Employing the FRET-based approach, the induction and dynamics of nepenthesin in the digestive pitcher fluid of various Nepenthes plants could be studied directly with insect (Drosophila melanogaster) prey or plant material. Moreover, we observed that proteolytic activity was induced by the phytohormone jasmonic acid but not by salicylic acid suggesting that jasmonate-dependent signaling pathways are involved in plant carnivory.     

Photosynthesis and dark respiration of leaves of terrestrial carnivorous plants

Using CO₂ gasometry, net photosynthetic (P _N) and dark respiration rates (R _D) were measured in leaves or traps of 12 terrestrial carnivorous plant species usually grown in the shade. Generally, mean maximum P _N (60 nmol CO₂ g⁻¹(DM) s⁻¹ or 2.7 μmol m⁻² s⁻¹) was low in comparison with that of vascular non-carnivorous plants but was slightly higher than that reported elsewhere for carnivorous plants. After light saturation, the facultatively heliophytic plants behaved as shade-adapted plants. Mean R _D in leaves and traps of all species reached about 50% of maximum P _N and represents the high photosynthetic (metabolic) cost of carnivory.