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1.
A mathematical model is presented for the emergence of perceptual-cognitive-behavioral modes in psychophysical experiments in which participants are confronted with two alternatives. The model is based on the theory of self-organization and, in particular, the order parameter concept such that the emergence of a mode is conceptualized as an instability leading to the emergence of an appropriately defined order parameter. The order parameter model is merged with a second model that describes adaptation in terms of a system parameter dynamics. It is shown that the two-component model predicts hysteretic mode-mode transitions when control parameters are increased or decreased beyond critical values. The two-component model can account for both positive and negative hysteresis effects due to the interaction between order parameter and system parameter dynamics. Moreover, the model-based analysis reveals that response time curves look rather flat when response times are relatively decoupled from the mode-mode transition phenomenon. In general, response time curves exhibit a peaked close to the mode-mode transition point. In this context, the possibility is discussed that such peaked response time curves belong to the class of critical phenomena of self-organizing systems. In order to illustrate the relevance of peaked response time curves for future research and research reported in the past, results from a perceptual judgment experiment are reported, in which participants judged their ability to stand on a tilted slope for various angles of inclination. Response time curves were found that exhibited a peak around the mode-mode-transition points between “yes” and “no” responses.  相似文献   
2.
The primary free polyamines identified during growth and development of strawberry (Fragaria × ananassa Duch.) microcuttings cultivated in vitro were putrescine, spermidine and spermine. Polyamine composition differed according to tissue and stages of development; putrescine was predominant in aerial green tissues and roots. -DL-difluoromethylarginine (DFMA), a specific and irreversible inhibitor of the putrescine-synthesizing enzyme, arginine decarboxylase (ADC), strongly inhibited growth and development. Application of agmatine or putrescine to the inhibited system resulted in a reversal of inhibition, indicating that polyamines are involved in regulating the growth and development of strawberry microcuttings. -DL-difluoromethylornithine (DFMO), a specific and irreversible inhibitor of putrescine biosynthesis by ornithine decarboxylase, promoted growth and development. We propose that ADC regulates putrescine biosynthesis during microcutting development. The application of exogenous polyamines (agmatine, putrescine, spermidine) stimulated development and growth of microcuttings, suggesting that the endogenous concentrations of these polyamines can be growth limiting.Abbreviations ADC arginine decarboxylase - ODC ornithine decarboxylase - DFMA -difluoromethylarginine - DFMO -difluoromethylornithine - Put putrescine - Spd spermidine - Sp spermine - DW dry weight - PA polyamine - PPF photosynthetic photon flux  相似文献   
3.
为探讨中华绒螯蟹(Eriocheir sinensis)蜕壳前后肌肉组织的形态特征变化, 采用石蜡切片、电镜及生物化学方法, 研究了中华绒螯蟹蜕皮过程中步行足和腹部肌肉的组织学、超微结构及主要蛋白质含量的变化。结果显示: 相对于蜕皮间期, 步行足在蜕皮前后组织学形态特征无明显变化; 超微结构在蜕皮前无明显变化, 蜕皮后可见肌原纤维纵裂及肌小节横裂现象, 表明蜕皮后外骨骼硬化的过程伴随着肌肉的生长。相对于蜕皮间期, 腹部肌肉在蜕皮前后组织学特征变化明显: 蜕皮前肌束间隙增大, 蜕皮后肌束内肌纤维间隙增大。电子显微镜观察显示, 蜕皮前肌原纤维在内部降解, 出现空洞, 肌原纤维边缘降解, 导致肌原纤维间隙增大; 蜕皮后肌原纤维重新组装、重建, 恢复到间期正常形态。生物化学研究发现, 蜕皮前后步行足和腹部肌肉中肌原纤维蛋白和可溶性蛋白含量的变化同其结构特征的变化相一致。以上研究结果表明, 中华绒螯蟹肌肉组织的结构特征同蜕皮周期密切相关。  相似文献   
4.
Manduca sexta (tobacco hornworm) chitinase is a molting enzyme that contains several domains including a catalytic domain, a serine/threonine-rich region, and a C-terminal cysteine-rich domain. Previously we showed that this chitinase acts as a biopesticide in transgenic plants where it disrupts gut physiology. To delineate the role of these domains further and to identify and characterize some of the multiple forms produced in molting fluid and in transgenic plants, three different forms with variable lengths of C-terminal deletions were generated. Appropriately truncated forms of the M. sexta chitinase cDNA were generated, introduced into a baculovirus vector, and expressed in insect cells. Two of the truncated chitinases (Chi 1-407 and Chi 1-477) were secreted into the medium, whereas the one with the longest deletion (Chi 1-376) was retained inside the insect cells. The two larger truncated chitinases and the full-length enzyme (Chi 1-535) were purified and their properties were compared. Differences in carbohydrate compositions, pH–activity profiles, and kinetic constants were observed among the different forms of chitinases. All three of these chitinases had some affinity for chitin, and they also exhibited differences in their ability to hydrolyze colloidal chitin. The results support the hypothesis that multiple forms of this enzyme occur in vivo due to proteolytic processing at the C-terminal end and differential glycosylation.  相似文献   
5.
Aim To describe a protocol for incorporating a temporal dimension into historical biogeographical analysis, while maintaining the essential independence of all datasets, involving the generation of general area cladograms. Location Global. Methods General area cladograms (GACs) are a reconstruction of the evolutionary history of a set of areas and unrelated clades within those areas. Nodes on a GAC correspond to speciation events in a group of taxa; general nodes are those at which multiple unrelated clades speciate. We undertake temporal calibration of GACs using molecular clock estimates of splitting events between extant taxa as well as first appearance data from the fossil record. We present two examples based on re‐analysis of previously published data: first, a temporally calibrated GAC generated from secondary Brooks parsimony analysis (BPA) of six extant bird clades from the south‐west of North America using molecular clock estimates of divergence times; and second, an analysis of African Neogene mammals based on a phylogenetic analysis for comparing trees (PACT) analysis. Results A hypothetical example demonstrates how temporal calibration reveals potentially critical information about the timing of both unique and general events, while also illustrating instances of incongruence between dates generated from molecular clock estimates and fossils. For the African Neogene mammal dataset, our analysis reveals that most mammal clades underwent geodispersal associated with the Neogene climatic optimum (c. 16 Ma) and vicariant speciation in central Africa correlated with increased aridity and cooler temperatures around 2.5 Ma. Main conclusions Temporally calibrated GACs are valuable tools for assessing whether coordinated patterns of speciation are associated with large‐scale climatic or tectonic phenomena.  相似文献   
6.
A plant collected in South Africa in the early 1960's has been considered an intergeneric hybrid with the parental taxa beingRuspolia hypocrateriformis (Vahl)Milne-Redhead var.australis Milne-Redhead andRuttya ovata Harv. The intermediate morphology of the plant provided the strongest evidence of its hybrid origin. The natural hybrid, named formally as ×Ruttyruspolia A. Meeuse & de Wet, is highly sterile. Crosses between the two presumed parental taxa produced two plants that are very similar to the putative natural hybrid. We had examined the presumed parental species and the natural and artificial hybrids using enzyme electrophoresis. The two parental species are highly differentiated at genes specifying soluble enzymes; they have a genetic identity of 0.51. They have no common alleles at two genes, and contain alternative alleles in very different frequencies at two loci.Ruttya andRuspolia exhibit both unique and common alleles at two additional genes. The natural and artificially produced plants of ×Ruttyruspolia are identical electrophoretically and contain alleles unique to each of the parental species at two genes. In addition, individuals of ×Ruttyruspolia combine alternative high frequency alleles from each parent at two loci. Allozymes provide strong confirming evidence for the hybrid origin of naturally occurring ×Ruttyruspolia because the products of specific alleles either unique to or highly characteristic of the two putative parental taxa are found combined in ×Ruttyruspolia.  相似文献   
7.
Summary (1) The fine structure of the cercal campaniform sensilla and epidermal cells of Gryllus bimaculatus Deg. (Saltatoria, Gryllidae) was examined, and the ecdysteroid level was monitored throughout the last larval instar. (2) The epidermal cells show changes in shape, cytoplasmic inclusions and differentiation of the apical cell membrane, coupled to the phases of buildup and breakdown of the (cercus) cuticle. (3) The imaginal epicuticle of the epidermal cells begins to form later (by about approximately 6 h) than that of the campaniform sensilla. (4) The campaniform sensilla were studied with respect to (a) the morphogenesis of the cuticular apparatus, (b) the inclusion of phenol oxidases in the cuticular apparatus, and (c) changes in the sensory apparatus preparatory to molting. (5) After apolysis the folding of the tormogen-cell wall into microvilli transiently disappears. Microvilli re-form shortly before imaginai ecdysis, and at the same time an outer receptor-lymph space develops. The role of the tormogen-cell plaques is discussed. (6) The levels of - and -ecdysone were determined separately by radioimmunoassay. (7) At the beginning of the instar the hormone level, especially that of -ecdysone, falls. Prior to apolysis, the concentration of -ecdysone rises, reaching an intermediate peak after apolysis is complete. The maximum hormone concentration (approximately 2,000 ng/g) is reached after the cuticulin layer is deposited, primarily due to the increase in -ecdysone. While the proecdysial cuticle is forming, the hormone titer is reduced; at this time -ecdysone is its chief component. (8) The identification of the ecdysteroids monitored by radioimmunoassay was confirmed by gas chromatography.This paper is dedicated to Professor H. Risler on the occasion of his 65th birthdaySupported by the Deutsche Forschungsgemeinschaft  相似文献   
8.
9.
The development times and survival of immature stages in rockwool and the fecundity and longevity of adult Scatella stagnalis were determined and stage-specific life-tables constructed for the species at constant 20 and 25 °C and at a fluctuating temperature (23–34 °C, mean 28.5 °C). Development time from egg to adult decreased with temperature, being 15.9±0.1 days at 20 °C, 11.4±0.1 days at 25 °C and 10.1±0.2 days at fluctuating temperature with mean of 28.5 °C. The lower threshold for egg-to-adult development was 6.4±2.7 °C and the total quantity of thermal energy required to complete development was 212.8±.0 °C. The proportion of females in two populations studied was 0.521. High temperature increased the mortality of pupae from 7% (20 °C) and 10% (25 °C) to 29% at 28.5 °C. At 25 °C, female longevity was 15.5±0.7 days and fecundity 315±19 eggs/female (20.4 eggs/female/day). Males lived for 22.0±1.1 days. At constant 25 °C, the net reproductive rate was 126.1 female eggs/female, generation time was 18.4 days, the doubling time of the population 5.3 days, and the intrinsic rate of increase (r m) 0.263 day–1.  相似文献   
10.
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