盐生草(Halogeton glomeratus)二型种子的休眠与萌发

盐生草的果实和种子存在二型性,这两种类型的种子在形状、大小、颜色及包被其花被片背部是否具翅上均有显著差异.绿色种子,圆形,直径为(1.552±0.116) mm,宿存花被革质,背部有紫红色翅状附属物,单粒重为(0.808±0.033)mg;黄色种子,椭圆形,长为(1.752±0.155) mm,宽为(1.146±0.088) mm,宿存花被革质,背部无翅状附属物,单粒重为(0.568±0.011) mg.两种种子在3个变温条件(5/25℃、5/25℃、15/25℃,暗12 h /光12 h)下的萌发率均较低,绿色种子为36%,而黄色种子为17%(15℃/25℃).延长储藏时间和划破种皮均能显著提高绿色种子的萌发率,表明绿色种子属于非深度生理休眠.随着储藏时间的延长,黄色种子的萌发率也能缓慢提高,但不显著,而划破种皮能够显著促进其萌发,表明黄色种子属于深度生理休眠.     

Nestmate recognition in burying beetles: the "breeder's badge" as a cue used by females to distinguish their mates from male intruders

Burying beetles use small vertebrate carcasses as food for theirlarvae and defend these carcasses against intra- and interspecificcompetitors. Breeding associations on carcasses can consistof single females, heterosexual pairs, or various combinationsof males and females. When a heterosexual pair collaborate ina breeding attempt, they do not typically exhibit aggressivebehavior toward each other, but do attack newly arrived conspecificsthat attempt to usurp the carcass. We investigated the cuesinvolved in discrimination between breeding partners and intrudersby female burying beetles. We found that resident females toleratemales that have cared for a brood, as well as males that havenot cared for a brood but have been on a carcass for a day ortwo. Males that have had no prior contact with a carcass areattacked. Females appear to use a chemical cue, the "breeder'sbadge," an apolar substance on the male's cuticle that can beremoved by washing with pentane. This cue is reliably correlatedwith recent male experience with a carcass that is suitablefor reproduction. The breeder's badge develops as a result ofprolonged contact with such a carcass, and disappears on removalfrom the carcass; its presence does not require contact witha female or with larvae. Female recognition of their male partnersin burying beetles thus does not involve individual recognition,but rather recognition of reproductive condition.     

The Effect of Changes in Organic Nitrogen Concentration of Rumex obtusifolius L. on the Population Dynamics of Aphis rumicis L. (Homoptera: Aphididae)

ABSTRACT The study of plant-herbivore dynamics was carried out using Aphis rumicis L. The insect is oligophagous to the genus Rumex. It utilizes its food plant by means of phloem sucking. Here, in this study, organic nitrogen as a form of a pellet fertilizer was used as a limiting factor. The major aim of the study is to find out the tripartite relationship among soil nitrogen concentration, the plant, and the insect. Observations were made from both the natural habitat site and the manipulated field site. The result shows that Aphis rumicis responded positively to increased N concentration of leaves (p< 0.005). The application of organic nitrogen did not alter the pattern of the population dynamics of Aphis rumicis over the study period. However, it may determine the time for the optimal exploitation of resources by the insect. It is also suggested that the growth efficiency of the insect relates to the C: N ratio in the phloem.     

Identification of thioredoxin h-reducible disulphides in proteomes by differential labelling of cysteines: insight into recognition and regulation of proteins in barley seeds by thioredoxin h

Using thiol-specific fluorescence labelling, over 30 putative target proteins of thioredoxin h with diverse structures and functions have been identified in seeds of barley and other plants. To gain insight at the structural level into the specificity of target protein reduction by thioredoxin h, thioredoxin h-reducible disulphide bonds in individual target proteins are identified using a novel strategy based on differential alkylation of cysteine thiol groups by iodoacetamide and 4-vinylpyridine. This method enables the accessible cysteine side chains in the thiol form (carbamidomethylated) to be distinguished from those inaccessible or disulphide bound form (pyridylethylated) according to the mass difference in the peptide mass maps obtained by matrix-assistend laser desorption/ionisation-time of flight mass spectrometry. Using this approach, in vitro reduction of disulphides in recombinant barley alpha-amylase/subtilisin inhibitor (BASI) by barley thioredoxin h isoform 1 was analysed. Furthermore, the method was coupled with two-dimensional electrophoresis for convenient thioredoxin h-reducible disulphide identification in barley seed extracts without the need for protein purification or production of recombinant proteins. Mass shifts of 15 peptides, induced by treatment with thioredoxin h and differential alkylation, identified specific reduction of nine disulphides in BASI, four alpha-amylase/trypsin inhibitors and a protein of unknown function. Two specific disulphides, located structurally close to the alpha-amylase binding surfaces of BASI and alpha-amylase inhibitor BMAI-1 were demonstrated to be reduced to a particularly high extent. For the first time, specificity of thioredoxin h for particular disulphide bonds is demonstrated, providing a basis to study structural aspects of the recognition mechanism and regulation of target proteins.     

Kin recognition by larval wood frogs (Rana sylvatica): effects of diet and prior exposure to conspecifics

Summary We investigated kin recognition by larval wood frogs (Rana sylvatica) in blind laboratory experiments using spatial affinity as a recognition assay. Tadpoles reared with full-sibs displayed a significant preference for familiar full-sibs over unfamiliar non-kin, but failed to discriminate between unfamiliar full-sibs and unfamiliar paternal half-sibs. Tadpoles reared in social isolation (with or without maternal egg jelly) from the two-celled embryonic stage displayed a significant preference for unfamiliar full-sibs over unfamiliar non-kin. Tadpoles reared on a meat diet with their full-sibs: 1) exhibited a significant preference for unfamiliar full-sibs fed meat over unfamiliar non-kin fed meat, 2) failed to discriminate between unfamiliar full-sibs fed lettuce and unfamiliar non-kin fed meat, 3) exhibited a significant preference for unfamiliar non-kin fed meat over unfamiliar non-lin fed lettuce, 4) failed to discriminate between unfamiliar full-sibs fed meat and unfamiliar full-sibs fed lettuce, and 5) displayed a significant spatial preference for odors associated with meat (a familiar food) over odors associated with lettuce (an unfamiliar food). Our results, together with those of Cornell et al. (1989), indicate that the recognition cue of larval R. sylvatica has both genetic and environmental (dietary) components. Our findings establish that previous exposure to maternal egg jelly, kin, or conspecifics is not necessary for the development of kin recognition ability in larval R. sylvatica. Our results are more consistent with the self-learning of recognition cues (a form of phenotype matching) than with a recognition mechanism that involves a genetically fixed recognition template. Finally, our results indicate that increasing similarity between the recognition template and perceived cue does not necessarily result in increasing spatial affinity for kin.     

Messages in the mucus: Selection of land snail resting sites based on the presence of mucus from conspecifics and other species

Mucus is applied to substrates as snails move and when they rest. Beyond the use of mucus in movement and adhesion, the wide array of chemicals in mucus allows for supplemental use in communication. This communication is apparent in trail-following behavior. This study addresses the potential communication via mucus in selecting resting sites in a laboratory assay. In a series of six experiments, individuals of Cornu aspersum (which often rest on above-ground surfaces) were placed into lidded plastic containers with three or four sections swabbed with water (the control) or mucus, which included the test snail's own mucus, mucus from conspecifics from the same or a different container holding snails from the same lab colony, or from a different colony, and mucus from three additional snail species. The resting location was recorded on the following day. In two additional experiments, the facultative predator Rumina decollata was tested against conspecific and other snails' mucus. Individuals of C. aspersum preferentially rested in areas with the mucus of familiar conspecifics over mucus of unfamiliar conspecifics, a behavior that may contribute to homing and aggregation behaviors. There was evidence that juveniles may be less selective than adults. The mucus of only one of the three other species was avoided by individuals of C. aspersum. Unlike individuals of C. aspersum, individuals of the predator R. decollata avoided the mucus of conspecifics, which may be associated with less need for mate-finding in this self-fertilizing species. Individuals of R. decollata did not select among potential prey species.     

Germination of annual celery (Apium graveolens) seeds: Inhibition by paclobutrazol and its reversal by gibberellins and benzyladenine

Plants of annual celery ( Apium graveolens L.) were treated with paclobutrazol during anthesis. Seeds collected from the treated plants showed a marked reduction in germination in light and failed to germinate in the dark. Application of GA_4/7 to the imbibition solution reversed the inhibitory effect of paclobutrazol while gibberellic acid (GA₃) was ineffective. Benzyladenine (BA) interaction with GA_4/7 was light and concentration-dependent. At relatively low concentrations in the dark there was a synergistic effect, but at higher concentrations, especially in the light, BA, antagonized the GA_4/7 effect. Seedlings emerging from the seeds from paclobutrazol-treated plants were only slightly shortened. It is suggested that paclobutrazol applied to the mother plants inhibited the biosynthesis of endogenous GAs, which normally enable the germination of annual seeds under unfavorable conditions. Exogenously applied GA_4/7 fulfills the function of the absent endogenous GAs.     

Maternal tissue is involved in stimulant reception by seeds of the parasitic plant Orobanche

Background and Aims

A fundamental element in the evolution of obligate root-parasitic angiosperms is their ability to germinate only in response to chemical stimulation by roots, to ensure contact with a nearby nourishing host. The aim of this study was to explore inheritance of the unique germination control in this group of plants.

Methods

Analysis was made of the segregation of spontaneous (non-induced) germination that appeared in hybrid progenies derived from crosses between Orobanche cernua and O. cumana, which, like all other Orobanche species, are totally dependent on chemical stimulation for the onset of germination, and show negligible spontaneous germination in their natural seed populations.

Key Results and Conclusions

F₁ and F₂ seeds did not germinate in the absence of chemical stimulation, but significant spontaneous germination was found in some F₃ seed families. This indicates that the prevention of non-induced germination in Orobanche seeds, i.e. dependence on an external chemical stimulation for seed germination, is genetically controlled, that this genetic control is expressed in a seed tissue with maternal origin (presumably the perisperm that originates from the nucellus) and that genetic variation for this trait exists in Orobanche species. Similar segregation results were obtained in reciprocal crosses, suggesting that stimulated germination is controlled by nuclear genes.     

Enzyme specificity: base recognition and hydrolysis of RNA by ribonuclease A

The substrate specificity of pancreatic ribonuclease A is discussed in light of observations based on accurate X-ray structure analysis of several enzyme-nucleotide complexes. A hypothesis for protein-nucleic acid recognition is presented which proposes that: (a) pyrimidine bases in RNA are recognised by ribonuclease due to the charge complementarity of two groups (the amide nitrogen and the side chain oxygen (OG) of threonine 45) of the protein and relevant atoms in the heterocyclic base (O2 and N3 in pyrimidine nucleotides); (b) interaction of the protein with the ribose moiety of the nucleotides is non-specific; and (c) conformational flexibility in the region of the scissile P-O bond is provided by different locations of the phosphoryl oxygens, rather than by an overall translation of the phosphate moiety.     

Choosy cannibals: Targeted consumption of conspecific hatchlings by larval cane toads is triggered by species‐specific defensive toxins

In many species, cannibalism is uncommon and involves nonselective consumption of conspecifics as well as heterospecifics. However, within their invasive Australian range, cane toad larvae (Rhinella marina) specifically target and voraciously consume the eggs and hatchlings of conspecifics, often extirpating entire clutches. In contrast, toad larvae rarely consume the eggs and hatchlings of native frogs. Here, we use laboratory studies to demonstrate that this selective consumption is triggered by species‐specific chemical cues: maternally‐invested bufadienolide toxins that otherwise defend cane toad eggs and hatchlings against predators. We find that these cues stimulate feeding behaviors in toad tadpoles, such that the addition of bufadienolide toxins to the water column increases predation on eggs, not only of conspecifics, but also of native anuran species that are otherwise usually ignored. In contrast, we find that cannibalism rates on conspecific hatchlings are high and unaffected by the addition of bufadienolide cues. The maternally‐invested toxins present in conspecific eggs may therefore be more easily detected post‐hatching, at which point tadpole feeding behaviors are induced whether or not additional toxin cues are present. As bufadienolide cues have previously been found to attract toad tadpoles to vulnerable hatchlings, our present findings demonstrate that the same toxin cues that attract cannibalistic tadpoles also induce them to feed, thereby facilitating cannibalism through multiple behavioral effects. Because native fauna do not produce bufadienolide toxins, the species specificity of these chemical cues in the Australian landscape may have facilitated the evolution of targeted (species‐specific) cannibalism in invasive cane toad populations. Thus, these bufadienolide toxins confer cost (increased vulnerability to cannibalism in early life‐stages) as well as benefit (reduced vulnerability to predation by other taxa).     

Role of chemical and visual cues in food recognition by leatherback posthatchlings (Dermochelys coriacea L)

We raised leatherback posthatchlings in the laboratory for up to 7 weeks to study the role of visual and chemical cues in food recognition and food-seeking behavior. Turtles were reared on a formulated (artificial gelatinous) diet and had no contact with test materials until experiments began. Subjects were presented with visual cues (a plastic jellyfish; white plastic shapes [circle, square, diamond] similar in surface area to the plastic model), chemical cues (homogenates of lion's mane jellyfish, Cyanea capillata; moon jellyfish, Aurelia aurita; and a ctenophore, Ocyropsis sp., introduced through a water filter outflow), and visual and chemical cues presented simultaneously. Visual stimuli evoked an increase in swimming activity, biting, diving, and orientation toward the object. Chemical cues elicited an increase in biting, and orientation into water currents (rheotaxis). When chemical and visual stimuli were combined, turtles ignored currents and oriented toward the visual stimuli. We conclude that both cues are used to search for, and locate, food but that visual cues may be of primary importance. We hypothesize that under natural conditions turtles locate food visually, then, as a consequence of feeding, associate chemical with visual cues. Chemical cues then may function alone as a feeding attractant.     

Birds associate species-specific acoustic and visual cues: recognition of heterospecific rivals by male blackcaps

Animals need to be able to identify other species, which iscrucial in competition for ecological resources, for using otherspecies as a cue in habitat selection, and for the establishmentand maintenance of parasite-host species associations in brood-parasiticspecies. The ability to discriminate between conspecifics andheterospecifics may be crucially important also in refinementof mating preferences during speciation and for premating isolationof sympatric species. It has long been hypothesized that speciesidentification ability is based on learned associations betweenmultiple features that distinguish species. Here I test thishypothesis using dual-choice song playback experiments withinterspecifically territorial male blackcaps (Sylvia atricapilla)that defend territories against male garden warblers (Sylviaborin). I show that male blackcaps can associate species-specificsongs with species-specific plumage and also that they retainthe memory of this association for an 8-month period withoutcontact with heterospecific rivals. Apparently, yearling maleblackcaps achieve this ability several months prior to theirfirst breeding attempt. This is the first time a long-term memoryof associations between species-specific signals from two differentsensory modalities (visual and auditory) has been shown to beimportant for distinguishing conspecifics from heterospecifics.     

Factors implicated in determining the structure of zinc tubulin-sheets: Lateral tubulin–tubulin interaction is promoted by the presence of zinc

Addition of increasing amounts of zinc to a cold microtubule protein solution results in the disappearance of 30 S oligomer found in the absence of that cation and in the appearance of new tubulin oligomers, 90 S and 23 S. When a microtubule protein solution is warmed in the presence of zinc, tubulin-sheets are assembled. We have tested the influence of microtubule associated proteins and the zinc:tubulin ratio on the polymerization process. Depletion of microtubule associated proteins results in wider and longer tubulin-sheets than those polymerized in the presence of microtubule associated proteins. However by increasing zinc concentration wider but shorter tubulin-sheets were found. These results suggest that microtubule associated proteins and zinc could promote nucleation of tubulin-sheets, but zinc also promotes lateral tubulin-tubulin interaction. This interpretation was confirmed when microtubule protein was assembled at a low zinctubulin ratio. In such conditions composite structures of microtubules and zinc tubulin-sheets arc formed. These composite structures are consequence of a lateral attachment of a zinc tubulin-sheet on a microtubule protofilament.     

The importance of being familiar: individual recognition and social behavior in sea trout (Salmo trutta)

This study addressed two hypotheses: (1) that individual recognitionis used to reduce the cost of contesting resources in sea troutand (2) that the hatchery environment selects against individualrecognition. Predictions from these hypotheses were tested inlaboratory experiments where behavior and growth were studiedin juvenile sea trout. In tact groups of familiar fish werecompared with groups that contained both familiar and unfamiliarindividuals. In general, the results were in agreement withthe first hypothesis. Familiar fish in intact groups had morestable dominance ranks, higher food intake, and better utilizationof food. Familiarity also reduced the distance to the nearestneighbor. Furthermore, initiators of conflicts were more likelyto win against familiar fish than against strangers. These resultssupport game-theory-based hypotheses explaining the dear-enemyphenomenon as an effect of familiarity A picture emerges inwhich familiarity stabilizes the hierarchical structure of agroup and governs behavioral modifications that will promotefeeding and growth, in turn leading to higher fitness. The secondhypothesis, which predicted a reduced effect of individual recognitionin sea-ranched trout, was not strongly supported because familiarityaffected sea-ranched and wild trout similarly in most respects.However, familiarity was not beneficial for growth in sea-ranchedtrout, whereas it increased growth rate in wild fish. In addition,sea-ranched trout tended to maintain larger distances to theirnearest neighbors than did wild trout.     

Oviposition and mining by Phytobia betulae (Diptera: Agromyzidae) in genotypes of European white birch (Betula pendula)

Abstract 1 The colonization success of herbivorous insects depends partly on the ability of females to choose suitable host plants. Phytobia betulae Kangas (Diptera: Agromyzidae), a miner of differentiating xylem, infests birch (Betula pendula Roth and Betula pubescens Ehrh.) trees. 2 In a field experiment we measured successful ovipositions in the long shoots of eight 5‐year‐old‐birch genotypes. Later in the growing season, in the same experiment, we counted the number of larvae from the same birch genotypes (different replicates). 3 We attempted to determine where Phytobia females lay their eggs in the birch canopy, what kind of shoots Phytobia utilize, whether birch genotypes differ in their susceptibility to Phytobia, and which tree characteristics correlate with successful utilization of birch for oviposition and larval development. 4 The ovipositions were concentrated in fast growing shoots and only 5% of the available shoots were utilized. Usually a shoot contained only one oviposition (80% of the cases). However, oviposition pattern resulted in significant aggregations (two to four ovipositions per shoot): 11% of shoots selected for oviposition contained more than one Phytobia and 22% of larvae shared their shoot with at least one other larva. Although birch shoots were much more abundant than Phytobia, there may be intraspecific competition for host resources among Phytobia. 5 Birch genotypes differed in the number of ovipositions but not in the number of larvae, although in general the number of larvae was correlated positively with the number of ovipositions. There were more ovipositions in the faster growing genotypes.     

Cuticular hydrocarbon dynamics in young adult Polistes dominulus (Hymenoptera: Vespidae) and the role of linear hydrocarbons in nestmate recognition systems

In social insects, cuticular hydrocarbons (CHCs) play an important role in nestmate discrimination processes, but young individuals are usually not discriminated. We studied CHC changes in young workers of the social wasp Polistes dominulus. A quantitative estimation demonstrated that total quantities of CHCs increased after emergence, with branched alkanes increasing drastically when compared with other classes of hydrocarbons. The relative quantity of longer-chain compounds increased with respect to shorter ones; unsaturated compounds decreased. These changes might reduce the capacity of the cuticle to acquire compounds of environmental origin. We then tested whether individuals acquire hydrocarbons from the environment, and whether this capability equally characterises newly emerged and mature wasps. We exposed wasps of two age classes (adults younger or older than 24 h) to four linear hydrocarbons in turn, and observed how nestmates reacted to their re-introduction into the natal colony. Exposed young wasps elicited significantly more aggressive responses than control sisters; but treated wasps older than 24 h were generally accepted by nestmates. Chemical assays showed that exposed young wasps readily absorbed hydrocarbons; older ones did not incorporate hydrocarbons, suggesting that the chemical profiles of mature wasps are less prone to chemical shifts than those of newly emerged wasps.     

Accumulation of phenolic compounds in birch leaves is changed by elevated carbon dioxide and ozone

Atmospheric change may affect plant phenolic compounds, which play an important part in plant survival. Therefore, we studied the impacts of CO₂ and O₃ on the accumulation of 27 phenolic compounds in the short‐shoot leaves of two European silver birch (Betula pendula Roth) clones (clones 4 and 80). Seven‐year‐old soil‐grown trees were exposed in open‐top chambers over three growing seasons to ambient and twice ambient CO₂ and O₃ concentrations singly and in combination in central Finland. Elevated CO₂ increased the concentration of the phenolic acids (+25%), myricetin glycosides (+18%), catechin derivatives (+13%) and soluble condensed tannins (+19%) by increasing their accumulation in the leaves of the silver birch trees, but decreased the flavone aglycons (?7%) by growth dilution. Elevated O₃ increased the concentration of 3,4′‐dihydroxypropiophenone 3‐β‐d ‐glucoside (+22%), chlorogenic acid (+19%) and flavone aglycons (+4%) by inducing their accumulation possibly as a response to increased oxidative stress in the leaf cells. Nevertheless, this induction of antioxidant phenolic compounds did not seem to protect the birch leaves from detrimental O₃ effects on leaf weight and area, but may have even exacerbated them. On the other hand, elevated CO₂ did seem to protect the leaves from elevated O₃ because all the O₃‐derived effects on the leaf phenolics and traits were prevented by elevated CO₂. The effects of the chamber and elevated CO₂ on some compounds changed over time in response to the changes in the leaf traits, which implies that the trees were acclimatizing to the altered environmental conditions. Although the two clones used possessed different composition and concentrations of phenolic compounds, which could be related to their different latitudinal origin and physiological characteristics, they responded similarly to the treatments. However, in some cases the variation in phenolic concentrations caused by genotype or chamber environment was much larger than the changes caused by either elevated CO₂ or O₃.     

The activity of siRNA in mammalian cells is related to the kinetics of siRNA-target recognition in vitro: mechanistic implications

The specificity of siRNA-mediated suppression of gene expression involves base-base recognition between siRNA and its single-stranded RNA target. We investigated the kinetics of this process in vitro by using full-length ICAM-1 target RNA and biologically active and inactive ICAM-1-directed siRNA, respectively. To mimic the situation in living cells we used the well-characterised facilitator of RNA-RNA annealing and strand exchange cetyltrimethylammonium bromide, which increases strongly the kinetics of RNA-RNA interactions at conditions that do not affect RNA structure nor the presumed structure-function relationship. For the biologically active siRNA si2B, we find faster binding, i.e. recognition of the target and a slower backward reaction when compared with the biologically inactive siRNA si1. This is reflected by an approximately 400-fold more favorable equilibrium constant of si2B. Kinetic evidence favors an associative mechanism of recognition of the target strand by the double-stranded siRNA. The minimal model for siRNA-target recognition described here is consistent with the high biological activity of si2B only if one assumes a step subsequent to target recognition, which might be degradation of the target RNA when complexed with the antisense strand of siRNA or when considering rapid destruction of the released sense strand of siRNA.