Behavioral Thermoregulation and the "Final Preferendum" Paradigm

Wider attention to Fry's (1947) "final preferendum" paradigmwould facilitate comparative studies of temperature preference(behavioral thermoregulation) among different animal groups.According to Fry's bipartite definition, the final preferendumis that temperature at which preference and acclimation areequal, and to which an animal in a thermal gradient will finallygravitate regardless of its prior thermal experience (acclimation).This paradigm is helpful in distinguishing between acute thermalpreferenda (measured within 2 hr or less after placing an animalin a thermal gradient), which are influenced by acclimationtemperature, and the species-specific final preferendum (measured24–96 hr after placement in the gradient), which is essentiallyindependent of prior acclimation because reacclimation occursduring the gravitation process. The paradigm does not take intoaccount non-thermal acclimatization influences (e.g., season,photoperiod, age, light intensity, salinity, disease, nutrition,pollutants, biotic interactions) which can also affect temperaturepreference. However, a graph of acutely preferred temperaturesversus acclimation temperatures can be employed to determinean equivalent acclimation temperature for any given acclimatizationstate, as a simple means of quantifying acclimatization statesresulting from interactions of many influences. This paradigm,developed for use with fishes, can also be applied to otherectothermic taxa, although it is most easily employed with aquaticorganisms because of the simplicity of specifying aquatic thermalenvironments in terms of water temperature alone. Methodologiesused in studies of behavioral thermoregulation should take theparadigm into account (especially with respect to length oftests) to enhance the comparative value of data across taxa.     

Juvenile Hormone: The Status of "Status Quo"

SYNOPSIS. Cuticular proteins show specificity for stage, age,and anatomical region. Analysis of the cuticular proteins ofsecond pupae created by application of juvenile hormone demonstratesthat the hormone prevents the onset of new sequences of synthesesand favors repetition of the region-specific, temporal patternof syntheses used in the previous stage. The argument made isthat juvenile hormone might exert this "status quo" action bypreventing alterations in chromatin configuration. Evidencefrom a wide variety of systems shows that polyamines might beinvolved in reprogramming chromatin. Ecdysterone induces ornithinedecarboxylase, the rate limiting enzyme in animal polyaminesynthesis. I suggest that juvenile hormone might be exertingits status quo action by inhibiting this induction. Preliminarystudies of ornithine decarboxylase induction support this specifichypothesis; experiments with an inhibitor of this enzyme, -difluoromethylornithine, however, do not show the expected juvenile hormonemimicry. Further studies are needed to define the control ofpolyamine biosynthesis in insects and to discover whether juvenilehormone plays a role in this control.     

The "Lost Year" Question in Young Sea Turtles

An adequate understanding of young sea turtle dispersal patternsis necessary for effective management of threatened or endangeredspecies. Such patterns are poorly understood, and the term "lostyear" has been adopted to emphasize this gap in sea turtle lifehistory information. Tag returns from pen-reared yearling seaturtles indicate ocean current dispersal. Evidence indicateshatchlings would be similarly dispersed by ocean currents. Feedingstudies with tank-held animals suggest that food resources areavailable in ocean currents for long-term sea turtle survival.Green turtle (Chelonia mydas) growth appears slow in nature.     

Feeding of freshwater filter-feeders at very low food concentrations: Poor evidence for "threshold feeding" and "optimal foraging" in Daphnia longispina and Eudiaptomus gracilis

The feeding behaviour of two freshwater zooplankton species,the calanoid copepod Eudiaptomus gracilis and the cladoceranDaphnia longispina, at extremely low food concentrations hasbeen studied in order to test whether the animals react as predictedby the models of optimal foraging. Three different sized algae were offered in concentrations downto 1µg C/litre at 7°C during winter and 19°C duringsummer. Ingestion rates were measured by use of a flow-through¹⁴C-technique In contrast to the findings of several authors working withmarine copepods a threshold concentration where the animalsceased filtering could be detected only in one experiment byregression analysis (Daphnia, 19°C, food: Stichococcus).A depression of the filtering rate at low concentrations wasobserved only in Daphnia at 19°C with Stichococcus and Scenedesmusas food. It is supposed that in this case the reduction of thefiltering rate is not a direct response of the filtrator, butis caused by exhaustion due to the experimental conditions. As freshwater zooplankton is very rarely exposed to food abundancesas low as in the marine environment, there seems to be no selectionpressure favouring the evolution of an "optimal forager" behaviour. ⁽¹⁾Supported by Deutsche Forschungsgemeinschaft     

A Kv channel with an altered activation gate sequence displays both "fast" and "slow" activation kinetics

The Kv1–4 families of K⁺ channels contain a tandem proline motif (PXP) in the S6 helix that is crucial for channel gating. In human Kv1.5, replacing the first proline by an alanine resulted in a nonfunctional channel. This mutant was rescued by introducing another proline at a nearby position, changing the sequence into AVPP. This resulted in a channel that activated quickly (ms range) upon the first depolarization. However, thereafter, the channel became trapped in another gating mode that was characterized by slow activation kinetics (s range) with a shallow voltage dependence. The switch in gating mode was observed even with very short depolarization steps, but recovery to the initial "fast" mode was extremely slow. Computational modeling suggested that switching occurred during channel deactivation. To test the effect of the altered PXP sequence on the mobility of the S6 helix, we used molecular dynamics simulations of the isolated S6 domain of wild type (WT) and mutants starting from either a closed or open conformation. The WT S6 helix displayed movements around the PXP region with simulations starting from either state. However, the S6 with a AVPP sequence displayed flexibility only when started from the closed conformation and was rigid when started from the open state. These results indicate that the region around the PXP motif may serve as a "hinge" and that changing the sequence to AVPP results in channels that deactivate to a state with an alternate configuration that renders them "reluctant" to open subsequently. voltage-gated potassium channel     

Development of Sink Capacity of the "Storage Root" in a Radish Variety with a Low Ratio of "Storage Root" to Shoot

Controling mechanisms of sink capacity are poorly understood.Previously we suggested that sucrose synthase (SuSy), but notinvertase, plays an important role for sink capacity of theradish "storage root" in a variety, Raphanus sativus L. (cv.White Cherish) [plant Cell Physiol. (1999) 40: 369]. With thisvariety about 50% of the total dry weight (DW) was in the "storageroot" at 21 d after sowing (DAS). We investigated the sink capacityof another radish variety, R. sativus L. (cv. Kosena) with alow ratio of "storage root" to shoot. With the latter varietyonly 3% of the total DW was in the "storage root" at 21 DAS.Sink activity (increase in DW of the "storage root" per unitof DW present per unit of time) of the "storage root" in Kosenaas well as White Cherish was strongly related to the level andactivity of SuSy but not to the activity of invertase. Theseresults confirmed that SuSy rather than invertase may be criticalfor the development of the sink activity of the radish "storageroot" and that the reaction products of UDP-glucose and fructoseare utilized for sink growth including biosynthesis of the cellwall. In Kosena photosynthates seemed to be partitioned mainlyinto developing leaves and fibrous roots. Differences in partitioningof photosynthates among various sinks with these two varietiesare discussed including anatomical considerations. (Received July 19, 1999; Accepted September 30, 1999)     

Growth of grana from "primary" thylakoids in Phaseolus vulgaris

The plastids of young dark-grown bean leaves, exposed to periodiclight are agranal, devoid of chlorophyll b and contain primarythylakoids and chlorophyll a. Transfer of these plants to continuousillumination results in synthesis of new chlorophyll a, chlorophyllb and grana. This study was done in order to study whether andhow the grana are formed from preexisting primary thylakoids.¹⁴C--aminolevulinic acid was used to label the chlorophyll aof the primary thylakoids, and its fate was studied after transferof the plants to continuous light. It was found that chlorophyll b and grana become ¹⁴C-labelled.The total radioactivity of chlorophyll b per bean increasedwith the parallel decrease of that of chlorophyll a. All subchloroplastfractions, obtained after digitonin disruption of chloroplasts,contained chlorophyll a of equal specific radioactivity. Thespecific radioactivity of chlorophyll b was lower than thatof chlorophyll a, and, in addition, it was lower in the granathan in the stroma lamellae fraction. The data suggest that chlorophyll b is formed from chlorophylla; the grana are formed by stacking of preexisting primary thylakoids;chlorophyll b is synthesized faster in the grana than the stromalamellae; the newly formed chlorophyll a molecules are distributedat random throughout the developing photosynthetic membraneand not on specific growing sites. (Received April 24, 1976; )     

"GIGANTISM" OF CHLORELLA VULGARIS I. MECHANISM OF INDUCTION OF CIGANTISM

1. Based on the microscopic observations, two stages, "giant cellstage" and the subsequent "palmelloid body stage", were distinguishedin the process of formation of giant Chlorella induced by theaddition of sugars. The "giant cell" is much larger in sizethan the control cell, but the other morphological featuresare the same as those of the latter. The "palmelloid body" isa form composed of many conjoined autospores.
2. When a highconcentration of glucose was maintained in the medium,gigantismwas also maintained. Under this condition, the algashows acyclic transformation between "giant cell" and "palmelloidbody"without returning to the small single cells.
3. Large amountsof carbohydrate composed of hexose were foundto be accumulatedin the giant algal cells, and it was inferredthat this carbohydrateaccumulation causes greater enlargementof cell volume as comparedwith control cells.
4. Uronic acids, which were found to be absentin the control cells,were formed and lost in the cells culturedin the glucose mediumin parallel with the appearance and disappearanceof gigantism.
5. Pectic substances, from which uronic acids areconsidered tobe derived during the extraction procedure, werefound to bepresent only in giant Chlorella.
6. The conjoinedautospores in giant Chlorella (at the palmelloidbody stage)were separated to some extent by the addition ofEDTA, and theresulting cells were similar to control Chlorellacells.
7. Basedon these results it was inferred that inductive formationofthe pectic substances is causally related with the appearanceof "palmelloid body".

¹ Present address: Department of Chemistry, College of GeneralEducation, Osaka University, Toyonaka, Osaka.     

Statistical Studies Using AIC Method to Decide the Question of "Break" or "Straight" in Arrhenius Plots of Water Proton NMR Relaxation Times in Chilling-Sensitive Vigna and Insensitive Pisum Seedlings

The question of "break" or "straight" in Arrhenius plots forthe temperature dependency of NMR relaxation times (T₁) of waterprotons in etiolated intact seedlings for chilling-sensitivetwo Vigna species and chilling-insensitive Pisum was statisticallystudied using the Akaike's Information Criterion (AIC), a versatileprocedure for statistical model identification. Among sevenmodels, the most appropriate was based on the following assumptions:individual k (preparation numbers) two-half lines connectingat the break point (TCB) and imposing no restrictions for thegradient and the break point (Model 7). The worst two modelswere one straight line or one TCB (Model 1 or 4). Thus, thedata obtained from replicated preparations should not be treatedas a whole but as individual in each sample case. Break pointsdetermined with Model 7 ranged around 11-5°C for V. radiataand 17-10°C for V. mungo. The implication of the occurrenceof "break" for Pisum clearly differed from Vigna judging bythe model fitness based on the AIC values. The question of "break"or "straight" in Arrhenius plots is therefore fairly dependenton the validity of the model selection in the statistical analysis,and the AIC method is a useful procedure for the resolutionof the problem of the "use" or "misuse" of Arrhenius plots inplant physiology. (Received November 2, 1988; Accepted January 17, 1989)     

Acetate metabolism in the process of "acetate-bleaching" of Chlorella protothecoides

Green cells of Chlorella protothecoides when incubated in amedium containing acetate but no nitrogen source, have beenshown to be bleached as strongly as in glucose-induced bleaching.Using U-¹⁴C-acetate as tracer, the acetate metabolism of algalcells during the process of acetate-induced bleaching was investigated.Changes in algal cell activities for respiration and assimilationof added ¹⁴C-acetate were followed during bleaching processesin "acetate-adapted" and "non-adapted" green cells. As in glucose-inducedbleaching of algal cells, algal cell activity for incorporating¹⁴C into lipids showed the most characteristic change, suggestingthat lipogenesis is causally related to the occurrence of bleachingin algal cells. (Received March 5, 1969; )     

Ventilation and Its Effect on "Infinite Pool" Exchangers

SYNOPSIS. Unlike internal exchange surfaces, the skin contactsan "infinite pool" of air or water with which exchange of gases,water, ions, and other solutes may occur. Even though the "infinitepool" may be well mixed, an unstirred diffusion boundary layeris always present about the skin and may constitute a significantresistance to exchange. The thickness of the diffusion boundarylayer (as approximated by the fluid dynamic boundary layer)is related to the flow of the respiratory medium, viscosityand density of the medium, and the morphology of the exchangesurface. Oxygen microelectrode studies suggest that, in mostcircumstances, the diffusion boundary layer in water is at leastas thick as the blood-respiratory medium distance in amphibianskin. Accordingly, the movement of water about the skin {i.e.,skin ventilation) should have pronounced effects on cutaneousexchange, especially at low "free stream" velocities. Mountingphysiological evidence suggests that: (1) skin ventilation canaugment cutaneous gas exchange; and (2) some vertebrates activelyventilate their skins, especially in aquatic hypoxia. The ubiquityand significance of diffusion boundary layers are central toa general understanding of cutaneous exchange and all surface-mediatedexchange processes.     

"Living high-training low": effect of moderate-altitude acclimatization with low-altitude training on performance

Levine, Benjamin D., and James Stray-Gundersen."Living high-training low": effect of moderate-altitudeacclimatization with low-altitude training on performance.J. Appl. Physiol. 83(1): 102-112, 1997.The principal objective of this study was to test the hypothesisthat acclimatization to moderate altitude (2,500 m) plus training atlow altitude (1,250 m), "living high-training low," improvessea-level performance in well-trained runners more than an equivalentsea-level or altitude control. Thirty-nine competitive runners (27 men,12 women) completed 1) a 2-wklead-in phase, followed by 2) 4 wkof supervised training at sea level; and3) 4 wk of field training camprandomized to three groups: "high-low"(n = 13), living at moderate altitude(2,500 m) and training at low altitude (1,250 m); "high-high"(n = 13), living and training atmoderate altitude (2,500 m); or "low-low"(n = 13), living and training in amountain environment at sea level (150 m). A 5,000-m time trial was theprimary measure of performance; laboratory outcomes included maximalO₂ uptake(O_{2 max}), anaerobic capacity (accumulated O₂ deficit),maximal steady state (MSS; ventilatory threshold), running economy,velocity at O_{2 max}, and blood compartment volumes. Both altitude groups significantly increased O_{2 max}(5%) in direct proportion to an increase in red cell mass volume(9%; r = 0.37, P < 0.05), neither of which changedin the control. Five-kilometer time was improved by the field trainingcamp only in the high-low group (13.4 ± 10 s), in directproportion to the increase inO_{2 max}(r = 0.65, P < 0.01). Velocity atO_{2 max} andMSS also improved only in the high-low group. Four weeks of livinghigh-training low improves sea-level running performance in trainedrunners due to altitude acclimatization (increase in red cell massvolume and O_{2 max}) and maintenance of sea-level training velocities, mostlikely accounting for the increase in velocity atO_{2 max} and MSS.

     

Challenge to the Specialist: Abraham Trembley's Approach to Research on the Organism--1744 and Today

We define an organismic biologist as one whose research is focusedprimarily on a single organism, or group of related organisms,and who investigates virtually the whole of nature as livedby that organism. We contrast an organismic biologist with aproblem-oriented biologist, that is one who uses an organism,or a group of organisms, in order to investigate a particularquestion. In our view, the consummate organismic biologist hasan outlook that allows her or him to conduct research on organismswith an open eye, to follow the cues offered by the organism,and to switch and learn new disciplines when the challenge tounderstanding the particular organism leads the investigatorin those directions. We provide examples of the organismic approachof Abraham Trembley working in the eighteenth century and ofthe senior author working in the twentieth century. Both focusedtheir investigations mostly on the freshwater hydra. While studyinghydra, Trembley demonstrated that: (a) complete animals canregenerate from small, cut pieces of those animals; (b) animalscan reproduce asexually by budding; (c) tissue sections fromtwo different animals of the same species can be grafted toeach other; (d) the materials oozing out of the edges of cuttissue have properties that fit the definition of protoplasmas described by Dujardin one hundred years later; (e) livingtissues can be stained, and those stained tissues can be usedin experiments; and (f) "eyeless" animals can exhibit a behavioralresponse to light. Some of the topics investigated in hydraby the senior author and his students are: (a) behavioral responsesto the peptide reduced glutathione and to tryosine; (b) mechanismof activation of the receptor to glutathione; (c) migrationof nematocytes; (d) algal-animal endosymbiosis; (e) an unusualdisulfide-linked collagen of nematocyst capsules; (f) componentsand action of nematocyst venom; (g) intracellular digestionof radioactive protein; (h) composition of and role in cellularadhesion of the mesoglea; and, (k) a developmental mutant androle of nerve cells in promoting budding. We conclude with aproposal for one way to train future organismic biologists atthe graduate and post graduate levels. This proposal grew outof our perception of the need to provide environments that nurturescientists who, by studying organisms, will find and definenew experimental systems for the next waves of biological discoveryyet to come when the specialists begin to investigate even moreintensively the interactions between cells, tissues, organisms,and communities. Specifically, we propose that on the campusesof several major universities having a broad range of graduateprograms, there be established year-round Institutes for OrganismicMarine Biology focused on the investigation of organisms notpreviously amenable to systematic experimentation. We believethat if America's biology is to remain vibrant and innovative,organismic biology should be an integral component in any longterm planning for research and training in the biological sciences.     

Difference in nitrate reduction in "light" and "dark" stages of synchronously grown Chlorella pyrenoidosa and resultant metabolic changes

Using synchronized cells of Chlorella pyrenoidosa, the incorporationpatterns of ¹⁴C into various metabolites with and without nitrogensources were studied under steady-state and non steady-stateconditions. From the patterns it was found that the smallestcells which are divided in the dark utilize nitrate and nitritevery little, if at all. The importance of ammonia for regulation of secondary flow forChlorella is discussed and the suggested regulatory points aredescribed. ¹This work was sponsored, in part, by the U.S. Atomic EnergyCommission (Received January 26, 1970; )     

When males and hermaphrodites coexist: a review of androdioecy in animals

Androdioecy (populations consisting of males and hermaphrodites)is a rare mating system in plants and animals: up to 50 plantsand only 36 animals have been described as being androdioecious,with most of the latter being crustaceans. To date, a thoroughcomparative analysis of androdioecy in animals has not beenundertaken. Herein we present such an analysis. Androdioecyhas only been extensively surveyed in 2 animal taxa: the nematodeCaenorhabditis and the clam shrimp Eulimnadia. The other majortaxon having androdioecious species is the Cirripedia (barnacles),but there are only limited studies on androdioecy in this group.In animals, androdioecy is found either in species that havemorphologically and ecologically distinct sexes (that is, hermaphroditesand small, "complemental" males) that are derived from hermaphroditicancestors (that is, the barnacles) or in species that have similarly-sizedmales and hermaphrodites that have been derived from dioeciousancestors (the remaining androdioecious species). We suggestthat the barnacles have evolved a sexual specialization in theform of these complemental males that can more efficiently usethe constrained habitats that these barnacles often experience.For the remaining species, we suggest that androdioecy has evolvedas a response to reproductive assurance in species that experienceepisodic low densities. Additionally, we hypothesize that thedevelopment of mechanisms allowing reproductive assurance inspecies with a number of sexually differentiated traits is mostlikely to result in androdioecy rather than gynodioecy (mixturesof females and hermaphrodites), and that these species may bedevelopmentally constrained to stay androdioecious rather thanbeing capable of evolving into populations solely consistingof efficient, self-compatible hermaphrodites. We conclude bysuggesting several areas in need of further study to understandmore completely the evolution and distribution of this interestingmating system in animals.     

Ecological Bases of Hormone--Behavior Interactions: The "Emergency Life History Stage"

SYNOPSIS. Superimposed upon seasonal changes in morphology,physiology and behavior, are facultative responses to unpredictableevents known as labile (i.e., short-lived) perturbation factors(LPFs). These responses include behavioral and physiologicalchanges that enhance survival and collectively make up the "emergency"life history stage. There is considerable evidence that glucocorticosteroids,and other hormones in the hypothalamo—pituitary—adrenal(HPA) cascade, initiate and orchestrate the emergency life historystage within minutes to hours. This stage has a number of sub—stagesthat promote survival and avoid potential deleterious effectsof stress that may result from chronically elevated levels ofcirculating glucocorticosteroids over days and weeks. Thesesub—stages may include: redirection of behavior from anormal life history stage to increased foraging, irruptivetypemigration during the day, enhanced restfulness at night, andelevated gluconeogenesis. Once the perturbation passes, glucocorticosteroidsmay also promote recovery. Additional evidence from birds indicatesthat glucocorticosteroid responses to a standardized capture,handling and restraint protocol are modulated both on seasonaland individual levels. Field work reveals that these changesin responsiveness to LPFs have ecological bases, such as reproductivestate, body condition etc., that in turn indicate differenthormonal control mechanisms in the HPA cascade.     

Role of Neurochemicals in the Interaction between the Microbiota and the Immune and the Nervous System of the Host Organism

This work is concerned with the role of evolutionary conserved substances, neurotransmitters, and neurohormones, within the complex framework of the microbial consortium–immune system–nervous system axis in the human or animal organism. Although the operation of each of these systems per se is relatively well understood, their combined effects on the host organism still await further research. Drawing on recent research on host-produced and microbial low-molecular-weight neurochemicals such as biogenic amines, amino acids, and short-chain fatty acids (SCFAs), we suggest that these mediators form a part of a universal neurochemical “language.” It mediates the whole gamut of harmonious and disharmonious interactions between (a) the intestinal microbial consortium, (b) local and systemic immune cells, and (c) the central and peripheral nervous system. Importantly, the ongoing microbiota–host interactivity is bidirectional. We present evidence that a large number of microbially produced low-molecular-weight compounds are identical or homologous to mediators that are synthesized by immune or nervous cells and, therefore, can bind to the corresponding host receptors. In addition, microbial cells specifically respond to host-produced neuromediators/neurohormones because they have adapted to them during the course of many millions of years of microbiota–host coevolution. We emphasize that the terms “microbiota” and “microbial consortium” are to be used in the broadest sense, so as to include, apart from bacteria, also eukaryotic microorganisms. These are exemplified by the mycobiota whose role in the microbial consortium–immune system–nervous system axis researchers are only beginning to elucidate. In light of the above, it is imperative to reform the current strategies of using probiotic microorganisms and their metabolites for treating and preventing dysbiosis-related diseases. The review demonstrates, in the example of novel probiotics (psychobiotics), that many target-oriented probiotic preparations produce important side effects on a wide variety of processes in the host organism. In particular, we should take into account probiotics’ capacity to produce mediators that can considerably modify the operation of the microecological, immune, and nervous system of the human organism.     

Chemical Interactions in the Cactus-Microorganism-Drosophila Model System of the Sonoran Desert

The Cactus-Microorganism-Drosophila Model System of the SonoranDesert represents an excellent paradigm of the role of chemistryin plant-animal interactions. In this system, four species ofendemic Drosophila feed and reproduce in necrotic tissue offive species of columnar cacti. Studies over the past 35 yrhave characterized a myriad of interactions between the threemajor components of the model system. The cacti contain a varietyof allelochemicals which are primarily responsible for the highlyspecific pattern of host plant utilization exhibited by thedesert Drosophila. Plant chemistry, through its effect on themicrobially produced volatile patterns, is further involvedin host specificity because the flies use the volatile patternto cue in on necroses in the appropriate species of cactus.The metabolic activities of microorganisms (bacteria and yeasts)living in the necrosis can affect the substrate chemistry inboth positive and negative ways (i.e., acting to increase orto decrease the toxicity of the substrate). Finally, cactuschemistry may affect drosophilid mating behavior since larvalrearing substrate has been shown to influence adult hydrocarbonepicuticular composition. In D. mojavensis, adult hydrocarbonprofile has been implicated as a determinant of mate choiceleading to premating isolation between geographically isolatedpopulations that use chemically different cactus substrates.Current research is focused on the evolution and regulationof genes whose products (cytochrome P450 enzymes) are involvedin the specific insect-host plant relationships which existbetween the Drosophila species and the cactus species. There are many reasons why investigators choose to focus theirresearch efforts on what are referred to as "model systems."Typically included among these would be the idea that modelsystems are easier to study because they are less complex thanother scientific situations. At the same time, model systemsshould be representative of more complex, natural systems sothat information that is obtained from their study is broadlyapplicable. For almost a century, the fruit fly, Drosophilamelanogaster, has served as a model organism for the study ofgenetics. As a genetic paradigm, Drosophila is more tractableto scientific investigation than most organisms and has providedimportant insights into a wide variety of human maladies fromalcohol abuse to neurological brain disorders (Bellen, 1998).Similarly, the interrelationships of the columnar cacti andthe cactophilic Drosophila species of the Sonoran Desert have,for the past 35 yr, provided an excellent model system withwhich to study relevant questions in evolution, ecological genetics,and chemical ecology. The intent of this article is to brieflyreview and characterize the chemical interactions between theplants (cacti) and animals (Drosophila) of this model system,and, in addition, provide some thoughts on possible future directionsfor integrative approaches in this research area.     

DE- AND RE-GENERATION OF CHLOROPLASTS IN THE CELLS OF CHLORELLA PROTOTHECOIDES: II. EFFECTS OF ACTINOMYCIN ON GREENING OF "GLUCOSE-BLEACHED" AND "ETIOLATED" ALGAL CELLS

The "glucose-bleached" and "etiolated" cells of Chlorella protothecoideshaving plastids of different degrees of degeneration were preparedby the methods previously reported, and the effects of actinomycin(C complex) upon the processes of greening of these cells wereinvestigated under various experimental conditions. As has beenshown previously, these cells formed normal chloroplasts onbeing incubated in the light with provision of nitrogen source(urea), but without glucose. The greening process of the glucose-bleachedcells has been found to differ from that of the etiolated cellsin the point that it involves a light-independent phase precedinga light-requiring phase. It was revealed that the greening ofglucose-bleached cells is inhibited by actinomycin much morestrongly than that of etiolated cells. On applying the antibioticat different times during the chloroplast development in glucose-bleachedcells, it was found that the inhibitory effect was remarkablyreduced with the progress of the developmental process. Thisindicated that the antibiotic attacked more strongly the light-independentphase than the light-requiring phase in question. Based on theseobservations it was inferred that, in the process of chloroplastdevelopment in glucose-bleached cells, DNA and RNA are playingimportant roles, especially during the early light-independentphase of chloroplast development. (Received September 18, 1964; )     

Image-analysis-based assessment of the effects of the "Ca2+-jump" technique on sarcomere uniformity

A new imageanalysis-based technique was used to quantitatively examine the effectsof the "Ca²⁺-jump"activation protocol on the maintenance of fiber quality in skinnedrabbit psoas muscle fiber segments. Specifically, contractions in pCa4.6 were preceded by short-duration "preactivation" soaks in asolution in which EGTA was replaced with thelow-Ca²⁺ buffering capacity analoghexamethylenediamine-N, N, N', N'-tetraacetate, which facilitated rapid Ca²⁺equilibration within the fiber segments. Fiber quality was assessed byexamining the Fourier spectra of the muscle fiber images before, during, and after activation. Segment lengths were typically below 500 µm, thus allowing the majority of the sarcomeres to be visualized inthe field of view (×200 and ×400 magnification). Thepreactivation protocol resulted in less deterioration of fiber qualitywith repetitive activation. In addition, there was also a significant reduction in the time required to reach the 50% level of maximum tension, with no significant change in the maximum tension level.