Nonvolatile chemicals provide a nest defence mechanism for stingless bees Tetragonula carbonaria (Apidae,Meliponini)

Social insects construct nests that protect their brood and food resources from both the physical environment and natural enemies. Stingless bees use plant‐derived resins, mixed with wax to form propolis, in the construction of their nests, and these products can be effective sources of defense against natural enemies, including ants. However, it is not known whether this defense, in the form of deterring or repelling workers, derives from the physical properties or chemical compounds of these products. The nest entrance of Tetragonula carbonaria is constructed with propolis and Corymbia resins, and we ask whether nonvolatile chemicals present in these products act as a defense against ants. Our field experiments revealed that workers of Iridomyrmex mayri Forel were deterred from crossing a chemical barrier comprising nonvolatile, nonpolar (hexane) extracts of propolis and Corymbia tree resin. However, polar (ethanol) extracts did not have this effect. These data are the first to demonstrate that the chemical components alone of entrance propolis and resins can provide a nest‐defense function against ants.     

Role of social and individual experience in interaction of the meadow ant Formica pratensis (Hymenoptera: Formicidae) with ladybird imagines and hoverfly larvae

The ability to recognize aphidophages is one of the key points in the protection ants provide aphids against their natural enemies. Behavior of honeydew collectors from nature (“field,” control) and laboratory reared “naive” ants of Formica pratensis Retzius, which had never met either “mature” workers or aphids and aphidophages, was observed during their pairwise interactions with ladybird imagines and hoverfly larvae. The majority of the “naive” ants perceived ladybirds as an enemy at their first encounter attacking them immediately without any prior antennation. Ants seem to have a certain innate “enemy image” that lets them react very quickly to protect aphids. Hoverfly larvae were rarely attacked by both “field” and “naive” ants (>15%). During tests with ladybirds ants from nature attacked them and also demonstrated the most aggressive reactions (series of bites and “death grip”) less frequently than the “naive” ants. The percentage of ants avoiding aphidophages after a contact with their chemical defense (reflex bleeding and glue‐like saliva) was significantly higher in the control group. Whereas the “naive” ants did not learn to avoid danger, foragers from nature usually tried to avoid negative experience and used tactics of “short bites.” Overall, experience has been proved to be unimportant for displaying key behavioral reactions underlying ant–ladybird interaction. However, accumulation of experience has been assumed to play an important role in the formation of behavioral strategy that allows honeydew collectors to drive aphidophages away with lower energy costs and avoid or minimize negative consequences of aphidophages’ chemical defense.     

On concept formation in systematics

In his “Grundzüge einer Theorie der phylogenetischen Systematik”, Hennig (1950 ) cited three philosophers: the leading empiricist Rudolf Carnap, the conventionalist Hugo Dingler, and the somewhat more obscure empiricist Theodor Ziehen. David Hull characterized Hennig's “Grundzüge” as one long argument against idealistic morphology. It will here be argued that Hennig attacked idealistic morphology (synonymous with “systematic” morphology) for its mode of concept formation. Building on Carnap and Ziehen, who both looked back on Ernst Cassirer, Hennig argued that the “generic”, “thing” or “class” concept of traditional nomothetic science must be replaced with Cassirer's “relation concept.” According to Hennig, such “emancipation” of systematics from the Aristotelian “species” concept would also allow transcendence from the distinction of idiographic from nomothetic sciences, thus preserving the unity of science. However, the establishment of relations in the construction of a system of order presupposes entities that can be, or are, related. Relations presuppose relata, which in modern systematics are best conceptualized (at least at the supraspecific level) not as Aristotelian classes, nor as individuals as was argued by Hennig and Ziehen, but as tokens of natural kinds. © The Willi Hennig Society 2006.     

Natural product inhibitors of ovarian neoplasia.

The present work constitutes a review of the literature on natural products with potential antitumor activity against ovarian neoplasias. The review refers to five plant extracts and sixty-nine compounds isolated from higher plants and microorganisms, which are classified in appropriate chemical groups and model tested, and cites their activity. Some aspects of recent research with natural products directed to ward producing drugs which are inhibitors of ovarian neoplasia are discussed.     

Natural products targeting the synthesis of β(1,3)-D-glucan and chitin of the fungal cell wall. Existing drugs and recent findings

Background: During the last three decades systemic fungal infections associated to immunosuppressive therapies have become a serious healthcare problem. Clinical development of new antifungals is an urgent requirement. Since fungal but not mammalian cells are encased in a carbohydrate-containing cell wall, which is required for the growth and viability of fungi, the inhibition of cell wall synthesizing machinery, such as β(1,3)-D-glucan synthases (GS) and chitin synthases (CS) that catalyze the synthesis of β(1-3)-D-glucan and chitin, respectively, represent an ideal mode of action of antifungal agents. Although the echinocandins anidulafungin, caspofungin and micafungin are clinically well-established GS inhibitors for the treatment of invasive fungal infections, much effort must still be made to identify inhibitors of other enzymes and processes involved in the synthesis of the fungal cell wall.Purpose: Since natural products (NPs) have been the source of several antifungals in clinical use and also have provided important scaffolds for the development of semisynthetic analogues, this review was devoted to investigate the advances made to date in the discovery of NPs from plants that showed capacity of inhibiting cell wall synthesis targets. The chemical characterization, specific target, discovery process, along with the stage of development are provided here.Methods: An extensive systematic search for NPs against the cell wall was performed considering all the articles published until the end of 2020 through the following scientific databases: NCBI PubMed, Scopus and Google Scholar and using the combination of the terms “natural antifungals” and “plant extracts” with “fungal cell wall”.Results: The first part of this review introduces the state of the art of the structure and biosynthesis of the fungal cell wall and considers exclusively those naturally produced GS antifungals that have given rise to both existing semisynthetic approved drugs and those derivatives currently in clinical trials. According to their chemical structure, natural GS inhibitors can be classified as 1) cyclic lipopeptides, 2) glycolipids and 3) acidic terpenoids. We also included nikkomycins and polyoxins, NPs that inhibit the CS, which have traditionally been considered good candidates for antifungal drug development but have finally been discarded after enduring unsuccessful clinical trials. Finally, the review focuses in the most recent findings about the growing field of plant-derived molecules and extracts that exhibit activity against the fungal cell wall. Thus, this search yielded sixteen articles, nine of which deal with pure compounds and seven with plant extracts or fractions with proven activity against the fungal cell wall. Regarding the mechanism of action, seven (44%) produced GS inhibition while five (31%) inhibited CS. Some of them (56%) interfered with other components of the cell wall. Most of the analyzed articles refer to tests carried out in vitro and therefore are in early stages of development.Conclusion: This report delivers an overview about both existing natural antifungals targeting GS and CS activities and their mechanisms of action. It also presents recent discoveries on natural products that may be used as starting points for the development of potential selective and non-toxic antifungal drugs.     

The defense hypothesis of elemental hyperaccumulation: status,challenges and new directions

Elemental hyperaccumulation may have several functions, including plant defense against natural enemies. A total of 34 studies, including 72 experimental tests, have been conducted to date. At least some tests have demonstrated defense by hyperaccumulated As, Cd, Ni, Se and Zn, but relatively few plant taxa and natural enemies have been investigated. Defense by hyperaccumulated Ni has been shown for most leaf/root chewing herbivores and pathogens tested (20 of 26 tests) but not for herbivores of other feeding modes (1 of 8 tests). Most tests (5 of 6) using Ni concentrations below accumulator levels found no defensive effect, and the single test using plants in the accumulator range also found no effect. For Zn, mixed results have been reported for both hyperaccumulator (3 of 6 tests showed defense) and accumulator levels (3 of 4 tests showed defense). These tests have focused exclusively on leaf chewing/scraping herbivores: no herbivores of other feeding modes, or pathogens, have been tested. Both hyperaccumulator and accumulator concentrations of Se generally have shown defensive effects (12 of 14 tests). Most (75%) of these positive results used plants with accumulator Se concentrations. The three tests of Cd showed defensive effects in two cases, one for hyperaccumulator and one for sub-accumulator Cd concentrations. Arsenic has been tested only once, and was found effective against a leaf-chewing herbivore at a concentration much less than the hyperaccumulator level. Defense studies have used a variety of experimental approaches, including choice and no-choice experiments as well as experiments that use artificial diet or growth media. Investigations of hyperaccumulation as a defense against natural enemies have led to two emerging questions. First, what is the minimum concentration of an element sufficient for defense? Evidence suggests that plants other than hyperaccumulators (such as accumulators) may be defended by elements against some natural enemies. Second, do the effects of an element combine with the effects of organic defensive compounds in plants to produce enhanced joint defensive effects? Recent investigation of this “joint effects hypothesis,” using Ni and secondary plant compounds in artificial insect diet, has demonstrated joint effects. Initial answers to both these questions suggest that defensive effects of elements in plants are more widespread than previously believed. These results also suggest an evolutionary pathway by which elemental hyperaccumulation may have evolved from accumulation. In this “defensive enhancement” scenario, defensive benefits of elevated levels of elements may have led to stepwise increases in element concentrations that further magnified these benefits. This series of steps could have led to increased accumulation, and ultimately hyperaccumulation, of elements by plants.     

Development of the epiphyllous inflorescence of Phyllonoma integerrima (Turcz.) Loes.: implications for comparative morphology*

The inflorescence primordium of Phyllonoma integerrima (Turcz.) Loes. is initiated on the adaxial side of the leaf primordium. At about the same time, a vegetative bud is formed at the base of the same leaf primordium. The vascular anatomy is the same in the fertile and sterile leaves, except that in the fertile leaf an inflorescence trace departs from the midvein of the leaf at the point where the inflorescence is inserted. Neither the inception nor the procambial supply of the inflorescence provide evidence of “congenital fusion”of inflorescence and leaf. It is also argued that the idea of an “adventitious”origin of the inflorescence is not useful in this case. Consequences for our conception of shoot construction are pointed out. It is argued that positional changes in the initiation of organs is an evolutionary process that may have remarkable effects on plant construction.     

microRNA-mediated <Emphasis Type="Italic">R</Emphasis> gene regulation: molecular scabbards for double-edged swords

Plant resistance (R) proteins are immune receptors that recognize pathogen effectors and trigger rapid defense responses, namely effector-triggered immunity. R protein-mediated pathogen resistance is usually race specific. During plant-pathogen coevolution, plant genomes accumulated large numbers of R genes. Even though plant R genes provide important natural resources for breeding disease-resistant crops, their presence in the plant genome comes at a cost. Misregulation of R genes leads to developmental defects, such as stunted growth and reduced fertility. In the past decade, many microRNAs (miRNAs) have been identified to target various R genes in plant genomes. miRNAs reduce R gene levels under normal conditions and allow induction of R gene expression under various stresses. For these reasons, we consider R genes to be double-edged “swords” and miRNAs as molecular “scabbards”. In the present review, we summarize the contributions and potential problems of these “swords” and discuss the features and production of the “scabbards”, as well as the mechanisms used to pull the “sword” from the “scabbard” when needed.     

Rapid,gregarious settlement of the larvae of the marine echiuran Urechis caupo Fisher & MacGinitie 1928

Larvae of Urechis caupo Fisher & MacGinitie, reared in the laboratory, were exposed to potential settlement stimuli, including natural sediment from adult burrows, and “scent” obtained from the skin of adult animals. Competent larvae settled rapidly and specifically in response to adult burrow sediment when compared with their responses to other natural and abiotic sediments. Larvae also responded specifically to chemical “scent” from adult animals when the “scent” of another echiuran worm, Listriolobus pelodes Fisher served as a control. Larval responses to chemical “scent” were as great as their responses to natural burrow sediment. Hence, it is likely that larvae settle gregariously in nature in response to “scent” on sediment grains of adult burrows. The chemical “scent” had a molecular weight between ≈3500 and 14000 daltons, as determined by dialysis. It quickly lost its effectiveness in promoting settlement after it was heated to 80 °C, but was relatively stable at ambient ocean temperatures, retaining its effectiveness for several days. It was soluble in sea water. However, larvae did not respond to the chemical “scent”, unless it was adsorbed onto a surface. Purely tactile stimuli, such as the shape, texture, and size-distribution of particles, were not important settlement cues during these experiments.     

Distinct antimicrobial activities in aphid galls on Pistacia atlantica

Gall-formers are parasitic organisms that manipulate plant traits for their own benefit. Galls have been shown to protect their inhabitants from natural enemies such as predators and parasitoids by various chemical and mechanical means. Much less attention, however, has been given to the possibility of defense against microbial pathogens in the humid and nutrient-rich gall environment. We found that the large, cauliflower-shaped, galls induced by the aphid Slavum wertheimae on buds of Pistacia atlantica trees express antibacterial and antifungal activities distinct from those found in leaves. Antibacterial activity was especially profound against Bacillus spp (a genus of many known insect pathogen) and against Pseudomonas aeruginosa (a known plant pathogen). Antifungal activity was also demonstrated against multiple filamentous fungi. Our results provide evidence for the protective antimicrobial role of galls. This remarkable antibacterial and antifungal activity in the galls of S. wertheimae may be of agricultural and pharmaceutical value.     

Intragroup and intragenomic conflict over chemical defense against predators

Insects are often chemically defended against predators. There is considerable evidence for a group‐beneficial element to their defenses, and an associated potential for individuals to curtail their own investment in costly defense while benefitting from the investments of others, termed “automimicry.” Although females in chemically defended taxa often lay their eggs in clusters, leading to siblings living in close proximity, current models of automimicry have neglected kin‐selection effects, which may be expected to curb the evolution of such selfishness. Here, we develop a general theory of automimicry that explicitly incorporates kin selection. We investigate how female promiscuity modulates intragroup and intragenomic conflicts overinvestment into chemical defense, finding that individuals are favored to invest less than is optimal for their group, and that maternal‐origin genes favor greater investment than do paternal‐origin genes. We translate these conflicts into readily testable predictions concerning gene expression patterns and the phenotypic consequences of genomic perturbations, and discuss how our results may inform gene discovery in relation to economically important agricultural products.     

Orphan selenoproteins

Selenoproteins contain selenium in stoichiometric amounts. Most are synthesized by a process that decodes UGA codons as selenocysteine. Twelve animal selenoproteins have been characterized, and biochemical functions have been described for all but three. Two of these “orphan” selenoproteins are discussed in this paper. Selenoprotein P is an extracellular glycoprotein that contains multiple selenocysteines. It binds heparin and associates with endothelial cells. Two isoforms have been identified. Plasma concentration of selenoprotein P correlates with protection against diquat liver injury, suggesting that the protein protects against oxidant injury. Selenoprotein W is a small intracellular protein that contains one selenocysteine. It binds glutathione and has been suggested to function in oxidant defense. The postulated oxidant defense properties of these selenoproteins are consistent with the facile thiol-redox properties of selenocysteine. It can be predicted that more proteins will be discovered that take advantage of the chemical properties of selenium. BioEssays 21:231–237, 1999. © 1999 John Wiley & Sons, Inc.     

Induction of resistance against pathogens by β-aminobutyric acid

Among the many types of plant stressors, pathogen attack, mainly fungi and bacteria can cause particularly severe damage both to individual plants and, on a wider scale, to agricultural productivity. The magnitude of these pathogen-induced problems has stimulated rapid progress in green biotechnology research into plant defense mechanisms. Plants can develop local and systemic wide-spectrum resistance induced by their exposure to virulent (systemic acquired resistance—SAR) or non-pathogenic microbes and various chemical elicitors (induced systemic resistance—ISR). β-Aminobutyric acid (BABA), non-protein amino acid, is though to be important component of the signaling pathway regulating ISR response in plants. After treatment with BABA or various chemicals, after infection by a necrotizing pathogen, colonization of the roots by beneficial microbes many plants establish a unique physiological state that is called the “primed” state of the plant. This review will focus on the recent knowledge about the role of BABA in the induction of ISR against pathogens mainly against fungi.     

Host plant and the predator Podisus nigrispinus: when the defense compounds of the plant affect the third trophic level

Many herbivorous insects can overcome chemical plant defenses, using the plant's defensive products for their own good, as a defense against predators. Eucalyptus spp. (Myrtaceae), recently introduced in Brazil, are rich in secondary compounds; however, there are reports that these plants have been suffering from population outbreaks of defoliating Lepidoptera in Brazil. The predator Podisus nigrispinus (Dallas) (Hemiptera: Pentatomidae) has been used against herbivorous insects in eucalyptus plantations, but little is known about its establishment in the field. This study aims to investigate whether the effectiveness of this predator may be affected indirectly by compounds of eucalyptus plants, when compared to guava, Psidium guajava L., a Brazilian native species of Myrtaceae. Thus, we evaluated the performance of P. nigrispinus on larvae of Thyrinteina arnobia (Stoll) (Lepidoptera: Geometridae) reared on eucalyptus (exotic species) or guava plants (native species). Podisus nigrispinus performance (reproduction and survival) was better on larvae fed on guava than on larvae fed on eucalyptus. It is possible that the negative effect on the predator's development occurred because of the plants’ secondary compounds appropriated by caterpillars, due to the short coevolutionary history between eucalyptus and the predator. The data suggest that the chemical compounds that could help the plant's defenses against herbivores may also affect their natural enemies, especially when the interaction between plant and natural enemy involves an exotic plant recently introduced into the insect's habitat.     

Evaluation of the antimicrobial activities of plant oxylipins supports their involvement in defense against pathogens

Plant oxylipins are a large family of metabolites derived from polyunsaturated fatty acids. The characterization of mutants or transgenic plants affected in the biosynthesis or perception of oxylipins has recently emphasized the role of the so-called oxylipin pathway in plant defense against pests and pathogens. In this context, presumed functions of oxylipins include direct antimicrobial effect, stimulation of plant defense gene expression, and regulation of plant cell death. However, the precise contribution of individual oxylipins to plant defense remains essentially unknown. To get a better insight into the biological activities of oxylipins, in vitro growth inhibition assays were used to investigate the direct antimicrobial activities of 43 natural oxylipins against a set of 13 plant pathogenic microorganisms including bacteria, oomycetes, and fungi. This study showed unequivocally that most oxylipins are able to impair growth of some plant microbial pathogens, with only two out of 43 oxylipins being completely inactive against all the tested organisms, and 26 oxylipins showing inhibitory activity toward at least three different microbes. Six oxylipins strongly inhibited mycelial growth and spore germination of eukaryotic microbes, including compounds that had not previously been ascribed an antimicrobial activity, such as 13-keto-9(Z),11(E),15(Z)-octadecatrienoic acid and 12-oxo-10,15(Z)-phytodienoic acid. Interestingly, this first large-scale comparative assessment of the antimicrobial effects of oxylipins reveals that regulators of plant defense responses are also the most active oxylipins against eukaryotic microorganisms, suggesting that such oxylipins might contribute to plant defense through their effects both on the plant and on pathogens, possibly through related mechanisms.     

Plant immunization

Plant immunization is the process of activating natural defense system present in plant induced by biotic or abiotic factors. Plants are pre-treated with inducing agents stimulate plant defense responses that form chemical or physical barriers that are used against the pathogen invasion. Inducers used usually give the signals to rouse the plant defense genes ultimately resulting into induced systemic resistance. In many plant-pathogen interactions, R-Avr gene interactions results in localized acquired resistance or hypersensitive response and at distal ends of plant, a broad spectrum resistance is induced known as systemic acquired resistance (SAR). Various biotic or abiotic factors induce systemic resistance in plants that is phenotypically similar to pathogen-induced systemic acquired resistance (SAR). Some of the biotic or abiotic determinants induce systemic resistance in plants through salicylic acid (SA) dependent SAR pathway, others require jasmonic acid (JA) or ethylene. Host plant remains in induced condition for a period of time, and upon challenge inoculation, resistance responses are accelerated and enhanced. Induced systemic resistance (ISR) is effective under field conditions and offers a natural mechanism for biological control of plant disease.