摘要:

SummaryA number of lines of evidence (Mr, number of ‐OH groups, measured fluxes at inner mitochondrial membranes) suggest the intrinsic PSi(OH)4of about 10‐10m s‐1in the plant cell plasmalemma. While relatively low, such a PSi(OH)4could maintain the intracellular concentration of Si(OH)4equal to that in the medium for a phytoplankton cell of 5 μm radius growing with a generation time of 24 h. Such passive entry could not account for SiO, precipitation such as is required for scale (Chrysophyceae) or wall (Bacillariophyceae) production in terms of either the generation of a super‐saturated solution or the quantity of SiO2required; active transport occurs at the plasmalemma (and possibly at an internal membrane) of such cells. The energy required for silicification, even in a diatom with an Si/C ratio of 0.25, is only some 2% of the total energy (as NADPH and ATP) needed for growth; the energy cost of leakage of Si(OH)4due to the intrinsic permeability of lipid bilayers to Si(OH)4is never more than 10% of the cost of silicification.In vascular land plants the entry of Si from the soil into the xylem can involve a flux ratio (mol Si/m3water) that is less than (e.g. Leguminoseae) equal to (e.g. many Gramineae) or greater than (e.g.Oryza, Equisetum) the concentration (mol m‐3) in the bathing solution. Even the low influx of the Leguminoseae cannot be accounted for by the ‘lipid solution’ value of PS(OH)4, but requires entry coupled (phenomenologically) to water influx with a reflexion coefficient of about 0.9. The situation in most Gramineae is described by such a coupling with a reflexion coefficient near O, while the accumulation of Si (relative to water) inOryzaandEquisetuminvolves an apparent reflexion coefficient which is negative, i.e. an active transport system stoichiometrically related to water flux. Even in Leguminoseae with a transpiration‐stream concentration of Si(OH)4of only 20 mmol m‐3(cf. the soil solution at 200 mmol m‐3), the fact that only I % of the water in the xylem is retained in the plant means that Si(OH)4at transpirational termini approaches saturation; super‐saturation, and precipitation of SiO, occurs in Gramineae andEquisetum.SiO2precipitation occurs mainly near transpirational termini but can also occur in the xylem vessels and endodermis of roots, for example. Si(OH)2mobility in the phloem seems to be very restricted.The energy costs of SiO2relative to organic compounds as structural and defensive materials are in the ratio of 1:10‐1:20 (on the basis of weight of material). The relative rarity of SiO2as a structural material is discussed in the context of the evolution of Si(O

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1983.tb00385.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1983.tb00386.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SummaryThe byssus is a structure produced by marine bivalve molluscs to adhere, usually permanently, to substrata under water. As the adhesion of synthetic polymers to surfaces is predictably compromised by the presence of water, particularly bulk water, it is of particular interest to discover the mechanism of byssal adhesion. In most species, the byssus consists of at least four essential components: acid mucopolysaccharides, adhesive protein, fibrous proteins, and an oxidative enzyme, polyphenoloxidase. The function of the mucopolysaccharide component is still uncertain, but it can conceivably be used by the animal as a temporary adhesive, a surface modifying agent, and/or a stabilizing filler for the permanent adhesive. The adhesive protein known as the polyphenolic protein inMytilusis but a thin plaque applied to the substrate surface by the foot of the animal. The molecular and physical properties of this adhesive protein conform remarkably well to what one expects of an ideal synthetic polymer, i.e. high molecular weight, abundance of large and polar side chains, near‐zero surface contact angle, and total water‐insolubility after setting. The fibrous proteins constitute the major portion of the thread or ribbon‐like material connecting the animal to the adhesive plaque on the substrate surface. These proteins are packed in ordered crystalline arrays, e.g. β‐pleated sheet and collagen helix (in mytilids) as is to be expected from structural tensile elements of Nature. The enzyme polyphenoloxidase is presumed to induce intermolecular cross‐linking of proteins in the fibrousandadhesive portions of the byssus. InMytilusthe natural substrates of the enzymc may be the dopa‐containing polyphenolic protein and accessory g

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1983.tb00387.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1983.tb00388.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Summary(1) The assumption that the circulatory system of the insect is instrumental in transporting insecticides to their site of action appeared not to be based on good evidence. On the contrary, experiments specifically designed to test the hypothesis provided ample evidence to refute the idea. Salient points to disprove the haemolymph route of entry can be summed up as follows: (a) A topically applied dose of insecticide does not readily penetrate the insect and the minor fraction that does so is largely retained in the body wall. The small amount that actually passes into the blood is too small to cause symptoms of toxicity if injected into the haemocoel. (b) The amount of insecticide present in the haemolymph (and CNS) does not appear to have any bearing on toxicity ‐ internally introduced insecticides are, in fact, basically very much less toxic than those externally applied. Where injected doses appear to be more toxic than equal amounts topically applied, this is due to the boosting effect of organic solvent carriers. Tests with parabiotically joined insects provide support for the view that haemolymph‐borne insecticide is of no consequence. (c) The topographical proximity of the locus of external application with the site of action (the thoracic ganglia) seems to be important irrespective of the general direction of the blood flow, and this should not be so if the circulatory system was instrumental in the transport of insecticide. (d) The introduction into the haemocoel of material such as olive oil, which is an excellent absorbent for insecticides, does not affect the toxicity (speed of action) of externally applied compounds to a significant extent. It should have a pronounced effect if haemolymph‐borne insecticide were an essential element in the process of poisoning. (e) As judged by speed of action, blocking of the blood circulation does not hamper the insecticide's movement to the site of action.(2) Only two other feasible routes remain. (a) The insecticide might reach the CNS via peripheral nerves and nerve cord, but the results of histochemical assays of cholinesterase inhibition in the insect's CNS make the idea improbable for organo‐phosphates. The nerve route is also incompatible with the observation that a wax barrier blocked the movement in and over the body wall so as to delay the onset of symptoms of toxicity, as such a barrier would not hinder movement into lateral nerves near the locus of application. (6) The only other feasible alternative, i.e. entry by means of lateral transport via the integument of the body wall and tracheae, is supported by autoradiographic and other evidence which showed the insecticide to accumulate in the tracheal system. It is further supported by the fact that inter‐tracheal introduction is faster acting than topical treatment, indicating that the tracheal system offers a very effective pathway to the internal organs.(3) Regarding the mechanism of entry, earlier reviews and text books maintain this to be associated exclusively with penetration into and through the integument by a physicochemical process. However, there is good evidence to show that an active process (requiring metabolic activity as the driving force) plays an essential part in lateral movement in the integument ‐ the epidermis, being the only living tissue continuous throughout the general integument, must perform this function.(4) As to the mode of action, the new hypothesis expounded here implies a single mode based on the fact that insecticides cause the extrusion of fluid from the epidermis into the cuticle and beyond, fluid lost from the epidermal cell layer being replaced from haemolymph and internal tissues. The precise mechanism is not clear but could conceivably involve an as yet hypothetical local endocrine system designed to keep the water content in the integument within certain limits. It is suggested that water extrusion affects the integument's permeability to respiratory gases, resulting in a rate of respiration not commensurate with metabolic need, and that the insecticide's arrival in the trachea (tracheoles) of the CNS leads to excitation and knockdown. Death is thought most likely to be due to dehydration of the CNS and subsequent histological d

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1983.tb00389.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Summary1. The elements that make up the courtship behaviour of males and of females are briefly described. It is pointed out that some of the terms used, such as female ‘repelling’ behaviour, are misleading as they do not reflect the known functions of the behaviours.2. Evidence has been presented for a number of distinct pheromones with different functions during courtship. These claims are critically examined as the evidence is incomplete and at times conflicting. It seems unlikely that any pheromones other than those acting over a very short distance are involved in courtship. There is sound evidence for an aphrodisiac pheromone produced by all females which stimulates male courtship. A pheromone, which may be the same one, is produced by males less than 12 h old, which also stimulates male courtship. No function is ascribed to this pheromone. Fertilized females either produce less aphrodisiac pheromone or they may, in addition, produce one that inhibits male courtship. Mature males may also produce an inhibitory pheromone. Females produce a contact pheromone which is species‐specific and involved in sexual isolation. It is not at present clear whether this is different from the aphrodisiac pheromone.3. There is considerable variability in the importance of vision in courtship. Many species will mate satisfactorily in the dark, suggesting that visual stimuli are not critical. Most species use vision to orient towards one another and for males to track and follow females. Even in light‐independent species such asD. melanogaster, specific visual signals may be used in courtship although they are not obligatory. Thus the red eye of the male is a sexual signal for females. Conversely, some light‐dependent species do not appear to make use of visual signals as a major factor in courtship. Some, however, do perform behaviours that are clearly visual and which may act to emphasize markings on wings, head or body.4. The majority ofDrosophilaspecies perform courtship songs by vibrating one or both wings. The songs produced by males sexually stimulate the females. They are species specific and there is considerable indirect and some direct evidence that the songs are involved in sexual isolation. Males of many species produce two different songs during courtship and it is probable that one is concerned mainly with sexual stimulation and the other with species recognition. Females of certain species ofDrosophilaandZaprionusalso sing during courtship and these songs may aid species recognition by males. In addition males and unreceptive females perform ‘aggressive’ songs.5. Almost all studies ofDrosophilacourtship have been made in very confined conditions in the laboratory. Interpretation of some of the results obtained in this way may require modification in the light of ecological research and observation of courtships under more natur

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1983.tb00390.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Summary(I). Gastropods use chemoreception for a wide variety of behaviours including feeding, homing, escape from predators and a variety of social and reproductive behaviours. Chemoreception is used to locate distant food sources, and to discriminate between potential foods. Responses to chemical food stimuli result from a combination of innate and experiential factors. Gastropods use chemical cues in mucus trails to home. They also home by direct olfactory orientation. Reproductive behaviour in a variety of gastropods appears to involve chemical cues. Evidence exists for pheromones controlling aggregation and mating. Numerous gastropods use chemical cues to avoid or escape from predators.(2). Amino acids appear as likely candidates for attractants and phagostimulants for gastropod feeding. Macromolecules are probably also involved. Amino acids have also been shown to stimulate reproductive behaviours in certain gastropods, thus suggesting a pheromonal function. However, the significance of this finding to the behaviour of the organisms in the field has yet to be evaluated. Saponins have been implicated as the active substances found in sea stars that elicit escape responses of marine gastropods. Choline esters may play a homologous role in gastropod—prey and gastropod‐predator interactions.(3). Gastropods can apparently use a number of different methods to orient to olfactory cues. These include anemotaxis or rheotaxis, klinotaxis and tropotaxis.(4). The major chemosensory organs of gastropods have been identified. They include the anterior and posterior tentacles and lips of terrestrial pulmonates; the cephalic tentacles, the lips and buccal cavity lining, and possibly the osphradium of aquatic pulmonates; the cephalic and mantle tentacles, the anterior margin of the foot, the siphon tip, and the osphradium of prosobranchs; and the rhinophores, tentacles, oral veil and osphradium of opisthobranchs.(5). Many of the organs named above have been examined by both light and electron microscopy. The most common anatomical organization includes bipolar primary sensory cells with cell bodies located subepithelially, and a distal dendrite extending to the free surface. Often a peripheral ganglion is located deep to the sensory epithelium. It is unclear whether axons of the sensory cells project directly to the central ganglion or by way of interneurones located in the peripheral ganglia.(6). The dendritic specializations of the sensory cells vary considerably. Most bear cilia or a combination of cilia and microvilli. The functional significance of the variation in the types of sensory endings is unknown, although the chemosensory epithelia also respond to other sensory modalities, and it is often difficult to ascribe any one cell type to any one modality. Species‐specific variations may also complicate the picture.(7). Prospects for and importance of future studies on gastropod chemoreception are disc

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1983.tb00391.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1983.tb00392.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY