Biogenesis of protein bodies by budding from vacuoles in developing pumpkin cotyledons

Summary Vacuoles were isolated from pumpkin cotyledons at three developmental stages and judged to be pure by light microscopic inspection and marker enzyme assays. The time sequence of structural changes of vacuoles were examined by light microscopic inspection in parallel with their stainability with neutral red. Vacuoles isolated from the early stage of cotyledon development were heterogeneous in size (Ø=2–10 m) but stained uniformly with the dye. In contrast, vacuoles isolated from the middle stage were much larger (Ø=5–15 m), and there exist one to three cores, unstainable with neutral red, within a single vacuole. Electron microscopic observation confirms that vacuoles contain a few protein cores in cotyledon cells at the middle stage. Characteristically at this stage, it was observable that some large cores (Ø=4m) were budding from vacuoles. At the late stage, size of vacuoles becomes much smaller (Ø=6m), nearly equal to that of the protein bodies in dry seeds. Importantly, at this stage most of the volume of each vacuole was occupied by a single core, and only a small matrix space was stainable with neutral red. Suborganellar fractionation indicates that the vacuolar cores were identical to the crystalloids deposited in the protein bodies in dry seeds. Overall results strongly provide the evidence that one crystalloid buds from the vacuole during the later stage of seed maturation, giving rise to a protein body.     

Upper limit on translational diffusion of visual pigment in intact unfixed barnacle photoreceptors

Translational diffusion of pigment molecules in the disc membranes of amphibian rod outer segments is in the range of 10 /10 s. Recently, Goldsmith and Wehner set an upper limit of 10 /20 min to the diffusion in isolated formaldehyde-fixed rhabdoms of crayfish. We have now used the early receptor potential (ERP) to study the diffusion in intact, unfixed barnacle photoreceptors. The ERP from a cell fully adapted to blue light (most of the pigment in the rhodopsin state) was changed by 8–22% of its maximum change when the pigment in a 30 m spot was (almost) completely shifted to the metarhodopsin state by red laser adaptation. Further red illumination of the same spot 30 min later produced only a limited further change in the ERP (attributable to light scatter), showing that R had not migrated into the spot. It is concluded that the visual pigment diffuses by less than 30 /30 min.Based on material presented at the European Neurosciences Meeting, Florence, September 1978     

Hematocrit and hemoglobin levels in some peruvian rodents from high and low altitude

Hematocrit levels in highland (3900–4500 m) AKODON (4 species) showed no change following a month at sea level, but showed a reduction of about 50 ml/1 after an additional 1–2 months. Feral MUS established at 4500 m had more cells(570 vs.470 ml/l) than those from sea level; about half this advantage was lost after a week at sea level. Highland species or races showed no consistent advantage in erythrocyte level over lowland species. The lowland PHYLLOTIS DARWINII LIMATUS actually had a higher hematocrit than any of the highland PHYLLOTIS. Mean cell hemoglobin concentrations ranged from 28 to 33 g/100 ml in rodents, and to 42 g/100 ml in the alpaca.Mean cell volumes ranged from 44 to 65 3 in rodents, and were 25–263 for the alpaca and vicna. The cell hemoglobin mass varied from 13 to 18 g in rodents and was 11.5g in the alpaca and vicuña. None of these values for rodents appear remarkable.

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Zusammenfassung Die HÄmatokrit-Werte von 4 Arten Hochland-AKODON (3900–4500 m) zeigten nach einem Monat Aufenthalt der Tiere auf Meereshöhe keine VerÄnderung; nach 2–3 Monaten waren die Werte 50 ml/l niedriger als der Vorwert. Wilde MUS in 4500 m Höhe hatten 570 ml und wilde MUS auf Meereshöhe 470 ml Erythrozyten/1 Blut. Wurden die Tiere aus der Höhe ins Tal gebracht, verschwand die HÄlfte des Unterschiedes innerhalb einer Woche. Die Erythrozyten-Werte von Hochland-Arten und -Rassen zeigten keine übereinstimmende überlegenheit über die von Tiefland-Arten. Tiefland PHYLLOTIS DARWINII LIMATUS hatten sogar einen höheren HÄmatokrit als Hochland PHYLLOTIS. In Hochland-Nagern betrug der mittlere Zell-HÄmoglobingehalt 28 bis 33 g/100 ml, in Alpaca bis 42 g/100 ml. Das mittlere Zellvolumen war bei Nagern 44–653 und beim Alpaca und Vivuna 25–263. Die Menge HÄmoglobin pro Zelle betrug 13–18g bei Nagern und 11-5g beim Alpaca und Vicuna. Die Werte bei Nagern im Hochland sind in keiner Weise bemerkenswert.

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Résumé Les valeurs hématocrites de 4 sortes d'AKODON de hautes terres (3000 – 4500 m) ne montraient pas de changement après un mois de séjour des animaux au niveau de la mer; après 2–3 mois, les valeurs étaient 50 ml/l plus basses que la valeur précédante. A 4500 m d'altitude les MUS sauvages avaient 570 ml érythrocytes/l sang et au niveau de la mer 470 ml. Les animaux transportés de l'altitude dans la vallée, la moitié de la différence disparut au bout d'une semaine.Les valeurs d'erythrocytes de sortes et rasses de hautes terres ne montraient point de supériorité concordante aux sortes de basses terres. PHYLLOTIS DARWINI LIMATUS de basses terres avaient mÊme un hématocrit plus haut que le PHYLLOTIS de hautes terres. Le contenu moyen de l'hémoglobine cellulaire des rongeurs de hautes terres était de 28 à 33/100 ml,chez Alpaca jusqu'à 429/100 ml. Aux rongeurs, la volume cellulaire moyenne,était 44–653et Alpaca et Vicuna avaient 25–263. Les rongeurs avaient une quantité d'hémoglobine par cellule de 13–18g, les Alpaca et Vicuna avaient 11,5g. Les valeurs aux rongeurs ne sont remarquable en aucun égard.

     

Effects of cytochalasins onNeurospora crassa

Summary Growth of various strains ofNeurospora crassa in the continued presence of cytochalasins A and B results in the following pattern. At low concentration the drugs cause an increase in branching which, depending on the strain, may also reveal an increase in dry weight. Increasing the concentration results in abnormal hyphae (swollen, irregular) and eventually in inhibition of growth. Most strains are inhibited at 10–20 g/ml cytochalasin A. Ultrastructure of hyphae grown in the presence of cytochalasin A reveals the presence of abnormal wall deposits. These deposits are not observed in cultures grown with cytochalasin B which generally causes a lower growth response also.     

Eiwei\kristalloide in Parenchymzell-Plastiden vonMusa

Zusammenfassung Die Piastiden des leitbündelnahen Parenchyms sehr junger BananenblÄtter enthalten neben StÄrke, Prolamellarkörpern und Thylakoiden in ihrem Stroma bis zu l gro\e Eiwei\-kristalloide, die einen regelmÄ\igen Feinbau aus filamentartig angeordneten 50–60 å weiten Untereinheiten erkennen lassen. Die Kristalloide sind von einer Hülle umgeben, die hÄufig mit dichten Thylakoidstapeln in Verbindung steht.

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Protein crystalloids in plastids ofMusa parenchyma cells

Summary In very young banana leaves plastids of the parenchyma cells near the vascular bundles contain about 1 large crystalloids in their stroma, besides starch, prolamellar bodies and thylacoids. The crystalloids have a very regular fine structure consisting of 50–60 å filament-like subunits and are surrounded by a membranous envelope that often is in contact with stacks of thylacoids. Form and array of the crystalloid subunits are finally compared with protein-crystalloids inPhaseolus plastids, intramitochondrial crystals and crystal-containing bodies.

     

Production of dodecaploid plants of Japanese persimmon (Diospyros kaki L.) by colchicine treatment of protoplasts

Summary Dodecaploid plants of Japanese persimmon (Diospyros kaki L.) were obtained by colchicine treatment of protoplasts. Callus protoplasts of Jiro (2n=90, x=15) were cultured in modified KM8p medium with 0.1% colchicine for 3–9 days. After colchicine treatment, they were cultured using agarose bead culture. Microcalli were recovered from the protoplasts after 3 months. Flow cytometric measurement showed that nine of 31 callus lines obtained from 6 days of colchicine treatment had twice the nuclear DNA content as non-treated controls. Plantlets were regenerated from the calli with twice the nuclear DNA content. Microscopic observation of root tip cells showed that their somatic chromosome number was 2n=180 (x=15). Compared with Jiro, dodecaploid plants had longer stomatal guard cells and lower stomatal densities, consistent with increased ploidy.     

A flash-photolysis study of the reactions of acaa 3-ttype cytochrome oxidase with dioxygen and carbon monoxide

The time course of absorbance changes following flash photolysis of the fully-reduced carboxycytochrome oxidase fromBacillus PS3 in the presence of O₂ has been followed at 445, 550, 605, and 830 nm, and the results have been compared with the corresponding changes in bovine cytochrome oxidase. The PS3 enzyme has a covalently bound cytochromec subunit and the fully-reduced species therefore accommodates five electrons instead of four as in the bovine enzyme. In the bovine enzyme, following CO dissociation, four phases were observed with time constants of about 10 s, 30 s, 100 s, and 1 ms at 445 nm. The initial, 10-s absorbance change at 445 nm is similar in the two enzymes. The subsequent phases involving hemea and Cu_A are not seen in the PS3 enzyme at 445 nm, because these redox centers are re-reduced by the covalently bound cytochromec, as indicated by absorbance changes at 550 nm. A reaction scheme consistent with the experimental observations is presented. In addition, internal electron-transfer reactions in the absence of O₂ were studied following flash-induced CO dissociation from the mixed-valence enzyme. Comparisons of the CO recombination rates in the mixed-valence and fully-reduced oxidases indicate that more electrons were transferred from hemea ₃ toa in PS3 oxidase compared to the bovine enzyme.     

The influence of lactation products on the temporal expression of histo-blood group antigens in the intestines of suckling pigs: lectin histochemical and immunohistochemical analysis

Summary Lectins and carbohydrate-specific monoclonal antibodies were used as cytochemical probes to investigate the possible influence of lactation products on the expression of intestinal membrane and secretory glycoconjugates in suckling piglets. Two different lactational regimes were compared; the first involved normal rearing of piglets for 8 weeks on a single dam and the second involved repeated cross-fostering of littermates onto recently farrowed sows, thereby restricting them to early milk. Five histo-blood group phenotypes were recognized within the piglet population: two immature phenotypes, O immature or Oi and A immature or Ai, and three mature forms, O, A and -. Under the normal suckling regime the transition from immature to mature OA phenotypes was evident at the fifth weekpost partum. However, in the repeatedly cross-fostered piglets this transition was evident much earlier at 3 weekspost partum. It is suggested that qualitative or quantitative variations in milk composition during the sow's lactation may significantly influence the expression of intestinal histo-blood group antigens in her suckling young.Abbreviations GalNac N-acetylgalactosamine - Gal Galactose - GlcNac N-acetylglucosamine     

Taxol affects meiotic spindle function in locust spermatocytes

Summary Addition of 0.1 to 10 M taxol to meiotic spindles in locust spermatocytes leads to a concentration dependent promotion of MT assembly at the centrosomes and depletion of MTs at the kinetochores, leading to the formation of prominent asters. In anaphase spindles, the equatorial region of the interzone becomes partly depleted of MTs, too. Microcinematographically, cytostatic effects are highly concentration/time dependent, being most rapid and nearly complete at 10 M taxol, but even in 0.1 M and 1 M taxol anaphase A movement is clearly affected. The drug strongly reduces the rate of chromosome-to-pole movement (anaphase A), leading to an insufficient separation of the chromosomes which indirectly hampers cytokinesis. Obviously, the chromosomal movement seems to be ratelimited by the compactness of the centrosomal asters reaching the equatorial plane in meta- and anaphase. Although the interzonal MT-number has become strongly reduced, anaphase B is not seriously affected but appears even slightly accelerated. Together with an occasional broadening of the cell equator (transverse elongation) instead of normal elongation, these results could be taken as an indication of the previously suggested active role of the cell's cortex in spindle pole separation during anaphase B (Daub andHauser 1986).Prof. Dr. K.-E.Wohlfarth-Bottermann on the occasion of his 65th birthday.     

Permeability change in transformed mouse fibroblasts caused by ionophores,and its relationship to membrane permeabilization by exogenous ATP

Summary Electrogenic ionophores have been found to induce membrane permeabilization in Swiss mouse 3T3 cells that had undergone spontaneous transformation (3T6 cells). Cells attached to plastic dishes were loaded with [³H] uridine, and then the medium was replaced by buffered salt solution at pH 7.8. The enhancement of membrane permeability was assayed by following the efflux of uridine nucleotides, normally impermeant substances. Titration with electrogenic ionophores, such as carbonylcyanidem-chlorophenylhydrazone (CCCP), SF-6847 and gramicidin D, markedly increased the membrane permeability within a very narrow range of ionophore concentration. Nonelectrogenic ionophores, such as monensin and nigericin, did not affect membrane permeability. Measurements of the distribution of the lipophilic cation tetraphenylphosphonium (TPP⁺) between the cells and their environment implied that the remarkable increase in permeability took place within a narrow range of membrane potential (). The data could be explaine by a threshold value, under which aqueous channels are opened in the plasma membrane. The effects exerted by electrogenic ionophores on the plasma membrane were found to be similar to those induced by exogenous ATP. In both cases rapid efflux of K⁺, influx of Na⁺ and reduction of preceded membrane permeabilization to low molecular weight, charged molecules, such as nucleotides. It is suggested that dissipation of induces conformational alterations in membranal components, and/or topological changes, such as aggregation of protein molecules, to form membranal aqueous channels. Electrogenic ionophores permeabilize both normal (3T3) and transformed (3T6) mouse fibroblasts, whereas ATP effects are specific for transformed cells. Thus, it is postulated that ATP actsvia specific sites on the surface of transformed cells.     

Avian smooth muscle: Morphometric analysis and comparison of different types

Summary Smooth muscle from the pigeon gizzard and intestine, and quail gizzard were investigated using ultrastructural morphometric analysis and compared on the basis of volume percent mitochondria, dense bodies, sarcoplasmic reticulum, number of mitochondria/m², and fiber diameter. One-way analysis of variance tests showed significant differences in (1) volume percent mitochondria between pigeon intestine and quail gizzard and between pigeon and quail gizzards; (2) mitochondrial number between all three muscles; and (3) fiber diameter between pigeon gizzard and intestine and pigeon intestine and quail gizzard.     

Coiled mechanoreceptors inAplysia revealed by sensorin immunofluorescence and confocal microscopy

Identified mechanosensory neurons ofAplysia are established model neurons for studies on learning and memory, and for examining responses to axonal injury. Although many characteristics of these sensory neurons have received intensive study, the nature of the peripheral mechanoreceptive endings remains unknown. Identification of a peptide, sensorin, specific inAplysia for mechanosensory neurons, led to the development of an antibody which proved useful in studying the peripheral morphology of these neurons. Immunostaining for sensorin in tail body wall revealed that sensorin is present in peripheral arborizations. Examination of sensorin-positive fibers in the periphery revealed that they terminate as coiled structures in the muscle layer of the body wall. These coiled structures (0.5 m diameter processes, 2–3 m across the coil, 60) m long) run parallel to muscle fibers and have a pitch of about one turn per 4 um. Sensorin immunostaining was particularly intense in varicosities, both along peripheral fibers and along the coiled structure. The localization of sensorin suggests that it may be released peripherally where it could have various paracrine and/or autocrine neuromodulatory actions.     

Spontaneous chlorophyll mutants of Pennisetum americanum: Genetics and chlorophyll quantities

Summary Thirteen spontaneously occurring chlorophyll deficient phenotypes have been described and their genetic basis was established. Ten of these — white, white tipped green, patchy white, white virescent, white striping 1, white striping 2, white striping 4, fine striping, chlorina and yellow virescent showed monogenic recessive inheritance and the remaining three — yellow striping, yellow green and light green seedling phenotypes showed digenic recessive inheritance. The genes for (i) white tipped green (wr) and yellow virescent (yv) and (ii) patchy white (pw) and white striping 1 (wst 1) showed independent assortment. Further, the genes for white (w), white tipped green (wr) and yellow virescent (yv) were inherited independently of the gene for hairy leaf margin (Hm).In the mutants — white tipped green, patchy white, white striping 1, white striping 2, fine striping, chlorina, yellow virescent, yellow striping, yellow green and light green phenotypes total quantity of chlorophyll was significantly less than that in the corresponding controls, while in white virescent there was no reduction in the mature stage. For nine of the mutants the quantity of chlorophyll was also estimated in F₁'s (mutant x control green). In F₁'s of six of the mutants — white tip, patchy white, chlorina, yellow virescent, fine striping and yellow striping the quantity of chlorophyll was almost equal to the wild type. In the F₁'s of three of the mutants — white striping 1, white striping 2 and light green an intermediate value between the mutant and wild types was observed. In yellow virescent retarded synthesis of chlorophyll, particularly chlorophyll a was observed in the juvenile stage. Reduced quantity of chlorophyll was associated with defective chloroplasts. In the mutants — white tipped green, white virescent, fine striping, chlorina, yellow striping, yellow green and light green defective plastids were also observed. In patchy white secondary destruction of chlorophylls and the presence of defective plastids were found to be associated with reduced chlorophyll quantity at maturity.Paper chromatographic studies of leaf flavonoids revealed some variation between the inbreds, but there were three common spots, 7, 8 and 9, except for PDP in which the spot 8 was absent. Chlorophyll deficient mutants differed from their respective controls in the absence of one or more of the spots present in the controls and in the presence of new spots in some of the mutants.Most of the chlorophyll mutants showed higher survival rate in the Kharif season than in Rabi season which was attributed to the higher mean day temperature and longer day light period in the Kharif season than in Rabi season.     

Forskolin increases osmotic water permeability of rabbit cortical collecting tubule

Summary Forskolin is a unique diterpene that may directly activate the catalytic subunit of adenylate cyclase. We therefore examined the effect of 50 m forskohn on osmotic water permeability in rabbit cortical collecting tubules perfusedin vitro. Forskolin increased net volume flux (J _v , from 0.30 to 1.22 nl/mm/min,P<0.02) in all tubules. The hydro-osmotic effect of forskolin was similar with respect to magnitude and time course to that produced by a maximal dose (250 U/ml) of arginine vasopressin. An additive effect onJ _v andL _p was not observed when maximal concentrations of forskolin and arginine vasopressin were given simultaneously. The compound d(CH₂)₅Tyr(Et) VAVP, which noncompetitively inhibits the vasopressin receptor, significantly reduced collecting tubular hydro-osmotic response to arginine vasopressin. In contrast, the hydro-osmotic response to forskolin was maintained in the presence of d(CH₂)₅ Tyr(Et)VAVP. However, the hydro-osmotic response to forskolin could be inhibited by 1.0 m guanine 5-(,-imido) triphosphate (GppNHp) and by the calmodulin inhibitor N-(6-amenohexyl)-5-chloro-1-naphthalenesulfonamide (W-7). These results demonstrate that forskolin exerts an hydro-osmotic effect in the mammalian nephron which occurs independent of the vasopressin receptor. Guanine nucleotide regulatory proteins may modulate the osmotic water permeability effect of forskolin. Finally, calmodulin is required for full expression of the effect of forskolin to increase osmotic water flux.     

The role of glutamate in the locus coeruleus during opioid withdrawal and effects of H-7, a protein kinase inhibitor, on the action of glutamate in rats

To investigate the role of glutamate in the locus coeruleus (LC) during opioid withdrawal, rats were continuously infused with morphine (a -opioid receptor agonist, 26 nmol/µl/h) or butorphanol (a //-mixed opioid receptor agonist, 26 nmol/µl/h) intracerebroventricularly (i.c.v.) via osmotic minipumps for 3 days. A direct LC injection of glutamate (1 or 10 nmol/5 µl) or naloxone (an opioid receptor antagonist, 24 nmol/5 µl) induced withdrawal signs in morphine- or butorphanol-dependent animals. However, these agents failed to precipitate any withdrawal signs in saline-treated control animals. On the other hand, the expression of withdrawal signs precipitated by the administration of glutamate or naloxone in opioid-dependent animals was completely blocked by concomitant infusion with 1 or 10 nmol/µl/h of an inhibitor of adenosine 3,5-cyclic monophosphate (cAMP)-dependent protein kinase and protein kinase C, H-7 [1-(5-isoquinolinesulfonyl)-2-methylpiperazine]. In animals that had been infused with opioids in the same manner, i.c.v. injection of naloxone (48 nmol/5 µl) precipitated withdrawal signs and increased extracellular fluid levels of glutamate in the LC of morphine- or butorphanol-dependent rats measured by in vivo microdialysis method. However, concomitant infusion with H-7 inhibited the increases of glutamate levels in the LC. These results strongly suggest that an expeditious release of glutamate in the LC region plays an important role in the expression of physical dependence on opioids. Furthermore, the action on glutamate release might be increased by the enhancement of cAMP-dependent protein kinase and/or protein kinase C activity.     

The native F0F1-inhibitor protein complex from beef heart mitochondria and its reconstitution in liposomes

A functional F₀F₁ ATP synthase that contains the endogenous inhibitor protein (F₀F₁I) was isolated by the use of two combined techniques [Adolfsen, R., McClung, J.A., and Moudrianakis, E. N. (1975).Biochemistry 14, 1727–1735; Dreyfus, G., Celis, H., and Ramirez, J. (1984).Anal. Biochem. 142, 215–220]. The preparation is composed of 18 subunits as judged by SDS-PAGE. A steady-state kinetic analysis of the latent ATP synthase complex at various concentrations of ATP showed aV _max of 1.28mol min^–1 mg^–1, whereas theV _max of the complex without the inhibitor was 8.3mol min^–1 mg^–1. In contrast, theK _m for Mg-ATP of F₀F₁ I was 148M, comparable to theK _m value of 142M of the F₀F₁ complex devoid of IF₁. The hydrolytic activity of the F₀F₁I increased severalfold by incubation at 60C at pH 6.8, reaching a maximal ATPase activity of 9.5mol min^–1 mg^–1; at pH 9.0 a rapid increase in the specific activity of hydrolysis was followed by a sharp drop in activity. The latent ATP synthase was reconstituted into liposomes by means of a column filtration method. The proteoliposomes showed ATP-Pi exchange activity which responded to phosphate concentration and was sensitive to energy transfer inhibitors like oligomycin and the uncouplerp-trifluoromethoxyphenylhydrazone.     

Holes photogeneration in phthalocyanine-doped polysilane

Polysilane polymers are attractive photoconductive materials, due to the high mobility of the charge carriers (holes). The photoconductivity in the visible region is greatly enhanced by the addition of a phthalocyanine, because the dopant increases the absorption of light and the quantum yield of the holes photogeneration. The quantum yield has been measured by the technique of xerographic discharge at several values of the polarisation field. From these data the intrinsic quantum yield ₀ and the thermalisation distance r ₀ were calculated. r ₀ is similar to the value measured in the trinitrofluorenone doped polyvinylcarbazole system (27.5 ) while ₀ is much lower (2.8·10^–2 compared to 0.11). In fact, r ₀ is assumed to be mainly dependent on the polymeric environment, while ₀ depends on the nature of the coupling between the dopant and the polymer.     

Mitotic disrupter herbicides act by a single mechanism but vary in efficacy

Summary Although there are numerous herbicides that disrupt mitosis as a mechanism of action, to date not one has compared the effects of these disrupters on a single species and over a range of concentrations. Oat seedlings, treated with a range of concentrations of nine different mitotic disrupter herbicides, were examined by immunofluorescence microscopy of tubulin in methacrylate sections. All herbicides caused the same kinds of microtubule disruption, although the concentrations required to cause the effects differed markedly between the herbicides. Effects on spindle and phragmoplast mitotic microtubule arrays were seen at the lowest concentrations and manifested as multipolar spindles and bifurcated phragmoplasts (which subsequently resulted in abnormal cell plate formation). At increasing concentrations, effects on mitotic microtubule arrays manifested as microtubule tufts at kinetochores and reduction of cortical microtubules resulting in arrested prometaphase figures and isodiametric cells. These data indicate that all mitotic disrupter herbicides have a common primary mechanism of action, inhibition of microtubule polymerization, and that marginal effects observed in the past were the result of incomplete inhibition and/or differential sensitivity of the microtubule arrays.Abbreviations DCPA 2,3,5,6-tetrachloroterephthalic acid dimethyl ester - APM amiprophosmethyl - DAPI 4,6-diamidino-2-phenyl indole - MTOC microtubule organizing center     

Intracellular air bubbles and interfacial tension inNicotiana miersii

Summary Air bubbles were introduced into living hair cells ofNicotiana miersii. The air entered through wounds inflicted on slightly flaccid trichomes from the base of a fruiting stem. Protoplasmic streaming often continued normally in the threads that were near or apparently touched the air bubble. When air bubbles were included within a plasmolyzing protoplast, the protoplasm nearest the air bubble appeared and behaved like that further away.The volume of an included air bubble is affected by many factors, but as the bubble gets smaller, the overriding factor determining the rate of decrease in volume is the surface tension. The effect of the surface tension on the pressure within the bubble is such that the slope, in a graph of the radius of the bubble to the third power against time, is a constant. The value of this slope constant varies directly with the surface tension, although the surface tension is not the only factor determining its magnitude. The rate of volume decrease of bubbles both in living and in dead cells tended to be constant for small bubbles, and the value of the slope for radius cubed vs. time ranged from – 5 ³/sec. to –14 ³/sec, with most values near –10 ³/sec. A theoretical value for the slope of a nitrogen bubble in water at 25 C. is calculated to be –94 ³/sec. A minimum estimate of the surface tension of the cell content surrounding the air bubble is therefore 1/10th of the value of water.The relatively high value of the surface tension is interpreted to indicate that the organization of the cell content at the surface of the air bubble is not of the structural complexity assumed for the plasmalemma.A portion of this paper was presented at the annual meeting of the Botanical Society of America, Physiology Section, Lafayette, Indiana, 1961.This investigation was partly supported by a grant (G 8716) from the National Science Foundation.     

Analyzing the “Group effect”: Rheotropic responses of developingFucus eggs

Summary Zygotes of the brown alga speciesFucus furcatus were allowed to differentiate while being subjected to a steady laminar flow of sea water. The cell polarity was found, as a consequence, to be determined rheotropically. At pH 6.5, the cells tend to form their rhizoidal pole downstream, if the flow speeds range from 0.01 to 10 per second. The degree of this downstream orientation increases with flow speed in a way that indicates that it is brought about by convective redistribution of a macromolecular and locally effective growth stimulator with a diffusion constant of the order of 10^–8 cm²/second.Qualitatively, the downstream response concurs with thepositive group effect since both responses are due to a stimulator and are more or less restricted to pH<7.0. At two other pH values tested, 7.1 and 8.1, no relevant downstream orientation was detected. At flow speeds >1/second (pH 7.1 and 8.1) and 100/second (pH 6.5), a very strong upstream orientation of the rhizoid formation was found. This upstream response may be mediated by convective redistribution of a relatively mobile growth inhibitor.

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Zusammenfassung Fucus-Zygoten wurden in der Zeit zwischen 3 und 18 Stdn. nach ihrer Befruchtung konstant und laminar strömendem Seewasser ausgesetzt: Je nach pH-Wert und Strömungsgeschwindigkeit entwickelten daraufhin bis zu 60% einer Zellpopulation ihre Polaritätsachse parallel zur Strömungsrichtung.Bei pH 6,5 und Strömungsgeschwindigkeiten von 0,01 bis zu 10/sec bildeten die Zellen ihren Rhizoidpol stromabwärts. Die quantitative Analyse dieser rheotropischen Reaktion benutzte ein früher entwickeltes Modell, welches beschreibt, wie die Verteilung einer Substanz um ihre kugelförmige Quelle in Abhängigkeit von der Geschwindigkeit eines umgebenden strömenden Mediums zu Konzentrationsunterschieden zwischen Luv- und Leepol der Kugel führt. Nun wächst die gefundene rheotropische Reaktion in gleicher Weise mit der Strömungs-geschwindigkeit und strebt auch dem gleichen Maximalwerte um 25% zu, wie der Konzentrationsunterschied im Modell; vgl. die Spalten 2 und 3 in Tabelle 2. Diese übereinstimmung erlaubt den Schluß, daß die rheotropische Reaktion auf der Umverteilung eines von der Zelle emittierten Wuchsstoffes beruht, dessen Diffusionskonstante 10^–8 cm²/sec beträgt; der unbekannte Wuchsstoff muß daher hochmolekular sein (M>10⁷). Qualitativ entspricht diese rheotropische Reaktion bei pH 6,5 dempositiven Gruppeneffekt; beide Reaktionen sind nur bei pH-Werten <7,0 reproduzierbar. Andererseits spricht die sehr niedrige Diffusionskonstante des rheotropisch wirksamen Stoffes gegen dessen Rolle als Mittler despositiven Gruppeneffektes.Bei Strömungsgeschwindigkeiten > 1/sec (pH 7,1 und 8,1) sowie 100/sec (pH 6,5) treiben die Zellen das Rhizoid am stromaufwärtigen Pol aus. Dabei weicht das Ausmaß der Reaktion so stark vom theoretisch erwartbaren ab, daß der verantwortliche, hier wuchshemmende Stoff nicht näher charakterisiert werden kann; er ist wesentlich beweglicher, somit von viel geringerem Molekulargewicht als sein wuchsförderndes Gegenstück. Ein anderer Mechanismus als das Zusammenspiel von Konvektion und Diffusion kommt auch hier kaum in Frage, da eine Erhöhung der Viskosität des Seewassers (auf das Zwölffache) die rheotropische Reaktion nicht berührt.

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This work was supported by National Science Foundation Grant GD-2446.