Peptide pheromones synchronize crustacean egg hatching and larval release

At the time of egg hatching in the crab Rhithropanopeus harrisii,pheromones are released from the eggs. These pheromones inducea stereotypic larval release behaviour in which the female vigorouslypumps her abdomen. This action breaks open the unhatched eggsand results in the synchronizes release of larvae. A previousstudy suggested the pheromone was composed of a group of smallpeptides. The present study identifies active peptides. Thisbehaiour is evoked by di-and tripeptides, which have a neutralamino acid at the amino terminus and a basic amino acid at thecarboxy terminus. The most effective peptides also have a hydrophohicfunctionality at the amino terminus. The two most active peptidestested were leucylarginine and glycyl-glycyl-arginine, whichhad lower thresholds of 10^–10 and 9.0 x 10^–9 M respectiely.These peptides are predicted to be present in the pheromonemixture, and the concentrations that evoke reponses are consistentwith their predicted aailability in natie material, Free aminoacids composing the active peptides inituate the female's laralrelease behaiour but only at concentrations > 10^–6M. Thus specific small paptides appear to act as crustaeeanpheromones     

Larval release in the crab Rhithropanopeus harrisii (Gould): chemical cues from hatching eggs

Decapod crustaceans have rhythmic larval release patterns. Inthe case of Rhithropanopeus harrisii substances associated withhatching eggs induce ovigerous crabs to exhibit stereotypiclarval release behavior involving vigorous abdomen pumping.In this study, the pumping response of ovigerous crabs was usedto investigate the chemistry of the substances (pumping factor)that evoke larval release behavior. Pumping was induced by polarsubstances released into sea water upon egg hatching. Pumpingfactor was concentrated and desalted by adsorption chromatographywith Amberlite XAD-7 resin. Size fractionation by cascade pressuredialysis indicated that most of the active material had a mol.wt. <500 daltons. Biological activity was destroyed by incubationof pumping factor with a non-specific protease. Amino acid analysisof hydrolyzed factor indicated that arginine comprised –50%of the amino acids. Pumping responses were elicited experimentallyby abnormally high concentrations of mixtures of the two majoramino acids (arginine and glycine) in the hydrolysate. Theseresults suggest that pumping factor is a heterogeneous groupof small peptides each containing arginine.     

Amiloride does not block taste transduction in the mudpuppy, Necturus maculosus

Activity of the glossopharyngeal nerve was recorded with bipolarsilver wire electrodes while taste stimuli were applied to thelingual surface in anesthetized mudpuppies. Taste stimuli wereinjected into a continuous stream of distilled water which wasrunning over the tongue, KCl, CaCl₂ and LiCl₂ at 0.4 M elicitedbrisk responses, as did HCl at 0.2 M and quinine at 6 x 10^–4M. Sucrose, glucose and saccharin did not elicit responses.Twenty amino acids were surveyed for their ability to evokea response at 0.04 M: 1-arginine, 1-valine, 1-phenylalanine,1-tryptophan, 1-tyrosine, 1-glutamic acid, 1-lysine and histidinealways evoked responses, whereas other amino acids either didnot evoke responses or only occasionally evoked responses. Thesupernatants from solutions of minced worms and minnows andPurina Trout Chow were effective taste stimuli. Pre-adaptingthe tongue to Ringer's solution by running a continuous streamof Ringer's solution over it eliminated responses to quinineand decreased responses to NaCl. Pre-adapting the tongue to10^–4 to 10^–3 M amiloride, a potent sodium channelblocker, did not alter the responses to NaCl, LiCl, or othertaste stimuli.     

Characterization, Biosynthesis, and Release of Neuropeptides from the X-Organ-Sinus Gland System of the Crab, Cardisoma carnifex

Separation of neuropeptides by high-pressure liquid chromatographyand proteins by gel electrophoresis has been undertaken forthe X–organ–sinus gland (XOSG) neurosecretory systemof the crab, Cardisoma carnifex. Biosynthetic incorporationof [³H]leucine by isolated XOSG systems confirms synthesis ofthe peptides and certain of the proteins, as well as their calcium-dependentrelease during secretion evoked by elevation of saline potassium.Eleven peptides (mol wt < 7,000) are consistently found insignificant quantities. Characterization of these shows themto represent three groups: 1) red-pigment concentrating hormone(previously sequenced, Fernlund and Josefsson, 1972); 2) 3 hyperglycemicpeptides with amino acid compositions similar to those previouslyreported (Keller, 1981); and 3) 7 novel peptides whose biologicalactivities have not been determined, labelled b, C, D, E, F,H, and I. Peptides b, C, D, E, F, and I can be explained bythe partial proteolysis of peptide H at two internal sites,with non-proteolytic covalent modification of at least one ofthe amino-terminal fragments. Analysis of single glands showsdifferent relative amounts of the b–I peptides in differentanimals, but with precise duplication of relative amounts ofthe b–I peptides in contralateral sinus glands. The datasuggest that mixtures of peptides secreted may vary under physiologicalcontrol and raise the question whether the physiological effectsof such mixtures differ.     

Distinct roles of PMCA isoforms in Ca2+ homeostasis of bladder smooth muscle: evidence from PMCA gene-ablated mice

We previously showed that plasma membrane Ca²⁺-ATPase (PMCA) activity accounted for 25–30% of relaxation in bladder smooth muscle (8). Among the four PMCA isoforms only PMCA1 and PMCA4 are expressed in smooth muscle. To address the role of these isoforms, we measured cytosolic Ca²⁺ ([Ca²⁺]_i) using fura-PE3 and simultaneously measured contractility in bladder smooth muscle from wild-type (WT), Pmca1^+/–, Pmca4^+/–, Pmca4^–/–, and Pmca1^+/–Pmca4^–/– mice. There were no differences in basal [Ca²⁺]_i values between bladder preparations. KCl (80 mM) elicited both larger forces (150–190%) and increases in [Ca²⁺]_i (130–180%) in smooth muscle from Pmca1^+/– and Pmca1^+/–Pmca4^–/– bladders than those in WT or Pmca4^–/–. The responses to carbachol (CCh: 10 µM) were also greater in Pmca1^+/– (120–150%) than in WT bladders. In contrast, the responses in Pmca4^–/– and Pmca1^+/–Pmca4^–/– bladders to CCh were significantly smaller (40–50%) than WT. The rise in half-times of force and [Ca²⁺]_i increases in response to KCl and CCh, and the concomitant half-times of their decrease upon washout of agonist were prolonged in Pmca4^–/– (130–190%) and Pmca1^+/–Pmca4^–/– (120–250%) bladders, but not in Pmca1^+/– bladders with respect to WT. Our evidence indicates distinct isoform functions with the PMCA1 isoform involved in overall Ca²⁺ clearance, while PMCA4 is essential for the [Ca²⁺]_i increase and contractile response to the CCh receptor-mediated signal transduction pathway. PMCA; bladder smooth muscle; gene-altered mice     

Larval Development and Vitellin-like Protein Expression in Palaemon elegans Larvae Following Xeno-oestrogen Exposure

Certain anthropogenic chemicals, most notably xeno-oestrogens,are known to have the potential to disrupt vertebrate endocrinesystems. For example, induction of the female-specific protein,vitellogenin, in male fish is a well-known effect of exposureto xeno-oestrogens and serves as a biomarker of such exposure.There have been few comparable studies of putative biomarkersof endocrine disruption in invertebrates. An exception is theupregulation of vitellin-like larval storage protein (LSP) expressionin the barnacle cypris larva following exposure to oestrogenicchemicals. The current study aimed to establish whether larvaeof the glass prawn, Palaemon elegans, are likewise susceptibleto xeno-oestrogen exposure. Using a polyclonal antiserum toP. elegans apolipovitellin, an 86 kDa polypeptide was detectedby western blotting in the larval and early postlarval stagesof this species. An indirect ELISA applied to the soluble proteinfraction of larval homogenates determined that the titre ofthis putative LSP ranged, depending on larval stage, from 0.48–0.67ng µg^–1. Exposure of P. elegans larvae to the xeno-oestrogen4-n-nonylphenol (4-NP), at 0.2–20 µg L^–1,resulted in a significant, concentration-independent increasein putative LSP levels of 5–18%. Conversely, exposureto the natural oestrogen, 17ß-oestradiol (E₂), at0.2 and 20 µg L^–1, led to a significant concentration-independentdecline (up to 11%) in LSP levels. Whether the effect of 4-NPresults from endocrine disruption is not known, however, anoestrogen receptor-mediated effect is unlikely. Other than aslight increase in larval mortality when exposed to 4-NP at2 µg L^–1, neither 4-NP nor E₂ significantly affecteddevelopment, growth or survival of P. elegans larvae.     

Action Potentials Evoked by Light in Traps of Dionaea muscipula Ellis

At low light intensities (less than 50 µmol m^–2s^–1) illumination evokes transient depolarization of membranepotential in mesophyll cells of the leaf-trap of Dionaea muscipulaEllis. Darkening causes hyperpolarization approximately symmetricto the response to illumination. The amplitude as well as therate of potential changes depend on light intensity. After exceedinga definite threshold (usually between 50 and 80 µmol m^–2s^–1)the depolarization plays the role of a generator potential andan all-or-none action potential (AP) is released. Switchinglight off in a depolarization phase of an AP does not changeits shape and the amplitude. When the light intensity is increasedto 80–150 µmol m^–2 s^–1 a single lightstimulus triggers two successive APs. The time interval betweenthe two APs decreases with increasing stimulus strength andreaches the minimum between 300 and 400 µmol m^–2s^–1. At higher light intensities the interval increasesagain, and finally only a single AP is triggered. It was shownthat the effect was evoked by light but not by temperature changeaccompanying illumination. An inhibitor of the photosyn-theticelectron transport chain, DCMU, blocked the generator potentialsmediating between light absorption and APs. Residual responsesto light stimuli in plants treated with DCMU had reverse polarityand strongly reduced the amplitudes. (Received September 16, 1997; Accepted January 16, 1998)     

Summer coastal zooplankton biomass and copepod community structure near the Italian Terra Nova Base (Terra Nova Bay, Ross Sea, Antarctica)

The structure of the zooplankton biotic community and of copepodpopulation in the coastal area of Terra Nova Bay (Ross Sea,Antarctica) was investigated during the 10th Italian AntarcticExpedition (1994/1995). Zooplankton biotic community consistedmainly of pteropods (Limacina helicina and Clione antarctica),Cyclopoid (Oithona similis), Poecilostomatoid (Oncaea curvata)and Calanoid (Ctenocalanus vanus, Paraeuchaeta antarctica, Metridiagerlachei and Stephos longipes) copepods, ostracods, larvalpolychaetes and larval euphausiids. Zooplankton abundance rangedfrom 48.1 ind m^–3 to 5968.9 ind m^–3, and copepodabundance ranged from 45.2 ind m^–3 to 3965.3 ind m^–3.The highest peak of zooplankton abundance was observed between25 m and the surface and was mainly due to the contributionof O. similis, O. curvata and C. vanus. Zooplankton biomassranged from 5.28 mg m^–3 to 13.04 mg m^–3 dry weight;the maximum value was observed between 25 m and the surface.Total lipid content varied from 216.44 to 460.73 mg g^–1dry weight.     

Vanadate Sensitive ATPase and Phosphatase Activity in Guard Cell Protoplasts of Commelina

Flicker, M. D. and Willmer, C. M. 1986. Vanadate sensitive ATPaseand phosphatase activity in guard cell protoplasts of Commelina.—J.exp. Bot. 38: 642–648. Phosphatase activity was measured in extracts of guard cellprotoplasts of Commelina communis L. using the artificial substratep-nitrophenylphosphate. A pH optimum of 5.8 to 6.3 was determined.Ammonium molybdate (Ol mol m^–3) and sodium vanadate (1–0mol m^–3) gave almost complete inhibition of phosphataseactivity at pH 60. ATPase assays were, therefore, conductedin the presence of 0–2 mol m ^–3 molybdate and vanadatewas used as a specific inhibitor of plasmamembrane ATPase activity.Vanadate sensitive ATPase activity showed a pH optimum of 6.6and activity was stimulated by KC1. These properties are characteristicof plasmamembrane proton pumping ATPases in other systems andsuggest that proton extrusion in guard cells could be mediatedby a similar enzyme. The maximum ATPase activity is sufficientto account for all the proton flux observed during the stomatalopening response. Key words: ATPase, Commelina, guard cell protoplasts, phosphatase, vanadate     

Studies on the Growth and Respiration of Roots: I. THE EFFECTS OF STIMULATORY AND INHIBITORY CONCENTRATIONS OF {beta}-INDOLYLACETIC ACID ON ROOT SECTIONS OF PISUM SATIVUM

Simultaneous observations on extension growth and respirationrate (oxygen consumption) of 2-mm. sections excised from theextension zone of roots of pea (Pisum sativum) growing in distilledwater and 0·5 per cent. sucrose have yielded resultsclosely similar to those of Brown and Sutcliffe (1950). Respirationrate is not obviously correlated with growth rate either inwater or in sucrose, but it is strongly correlated with sectionlength. Respiration rate per unit section length (¬per unitfresh weight) shows a marked downward drift during extensionand is affected little by growth conditions. Tentative suggestionsare advanced to account for the small differences between driftsin o·5 per cent. sucrose and those in distilled water. Medium agitation produces an immediate and sustained stimulationof growth but no stimulation of oxygen uptake until the latergrowth stages. Thus respiration per unit section length is unaffectedby agitation at any stage. A typical growth response to ß-indolylacetic acid(IAA) was obtained, with a maximum stimulation (of about 35per cent.) at 1 part in 10¹¹ and inhibitions increasing progressivelywith concentration beyond the threshold of about i part in 10⁹.Both percentage stimulation and percentage inhibition of growthwere independent of the presence of sucrose. Respiratory responses to ß-indolylacetic acid werecomplex. In water no immediate response could be detected witheither a growth-stimulatory (10^–11) or a growth-inhibitory(10^–-8) concentration, while in 0·5 per cent. sucrosethe inhibitory concentration prevented the small immediate respiratoryrise due to the sucrose, probably by impeding sugar entry. Duringthe subsequent period of rapid growth (up to 36 hours) the smallrespiratory responses observed closely followed the small growthresponses to both concentrations of IAA, suggesting that theformer are the direct result of the differences in section lengthinduced by the auxin. When growth ceases (at 48 hours) sectionswhich have grown considerably in sucrose show respiratory ratesstill closely correlated with section length, whereas in waterboth concentrations of auxin induce marked depressions in respirationrate. It is concluded that ß-indolylacetic acid in bothgrowth-stimulatory and growth- inhibitory concentrations hasno direct effect on the activity of the respiratory enzyme systemof growing root cells. The small respiratory responses are bestexplained as resulting from differential changes in sectionsize and correlated changes in the enzyme complements of thegrowing cell.     

Quantal Response of Seed Germination in Seven Genera of Cruciferae to White Light of Varying Photon Flux Density and Photoperiod

The response of the germination of seeds of Barbarea vema (Mill.)Aschers, Brassica chinensis L., Brassica juncea (L.) Czern.& Coss., Brassica oleracea L. var. gongylodes L., Camelinasaliva (L.) Crantz, Eruca saliva Mill., Lepidium sativum L.,Nasturtium officinale R. Br., and Rorippa palustris (L.) Besserto white fluorescent light of different photon flux densitiesapplied for different daily durations in a diurnal alternatingtemperature regime of 20 °C/30 °C (16 h/8 h) was quantifiedby linear relations between probit percentage germination andthe logarithm of photon dose, the product of photon flux densityand duration. The low energy reaction, in which increasing dosepromotes germination, was detected in all the seed populationsbut in Barbarea vema and Brassica Juncea the lowest photon doseapplied (10^–5–2 and 10^{–5 7} mol m^–2 d^–1,respectively) was sufficient to saturate the response. Comparisons,where possible, between photoperiods demonstrated reciprocity,i.e. germination was proportional to photon dose irrespectiveof photoperiod, for the low energy reaction in Brassica oleracea(1 min d^–1 to 1 h d^–1), Camelina saliva (1 min d^–1to 8 h d^–1), Eruca saliva (1 min d^–1 to 24 h d^–1),Lepidium sativum (I min d^–1 to 8 h d^–1) and Rorippapalustris (1 min d^–1 to 8 h d^–1), but not in Brassicachinensis and Nasturtium officinale. The high irradiance reaction,in which increasing dose inhibits germination, was detectedin Barbarea vema, Brassica chinensis, Brassica juncea, Brassicaoleracea, and Camelina saliva. The minimum dose at which inhibitionwas detected was lO^–0–3 mol m^–2 d^–1.These results are discussed in the context of devising optimallight regimes for laboratory tests intended to maximize germination The response of germination to photon dose was also quantifiedwith 3 x 10^–4 M GA₂, co-applied (Brassica chinensis, Camelinasaliva, and Lepidium sativum) and with 2 x 10^–2 M potassiumnitrate co-applied (Brassica chinensis). In the latter casepotassium nitrate had no effect in the dark and inhibited germinationin the light, but GA₂, promoted germination substantially inall three species. Variation amongst seeds in the minimum photondose required to stimulate germination was not affected by co-applicationof GA₂, in Brassica chinensis and Camelina saliva, whereas seedsof Lepidium salivum showed a narrower distribution of sensitivitiesto the low energy reaction in the presence of GA₂ Barbarea vema (Mill.) Aschers, Brassica chinensis L., Brassica juncea (L.) Czern. & Coss., Brassica oleracea L. var. gongylodes L., Camelina saliva (L.) Crantz, Eruca saliva Mill., Lepidium satiaum L., Nasturtium officinale R. Br., Rorippa palustris (L.) Besser, Cruciferae, light, gibberellic acid, seed germination, seed dormancy     

Growth and ingestion rates of larval fish populations in the coastal waters of Israel

Clupeoid larvae were collected on eight cruises between February1984 and February 1985 in the coastal waters of Israel. Fromanalysis of daily growth increments of otoliths, growth ratesof the abundant clupeoids, Engraulis encrasicolus, Sardina pilchardusand Sardinella aurita were found to be 0.55 mm day^–1,0.67 mm day^–1 and 0.60 mm day^–1, respectively, duringthe first month after hatching. Ingestion rates were estimatedusing an equation from the literature relating ingestion andgrowth of larval fish. Ingestion calculated for populationsof fish larvae in pelagic waters ranged from 0 to >23 mgC m^–2 day^–1 with maximum rates observed in April.Annual ingestion by larval fish at a pelagic station near Haifawas calculated to be 2.2 g C m^–2 year^–1, 10–20%of annual primary production estimated from ¹⁴C uptake.     

DCEBIO stimulates Cl- secretion in the mouse jejunum

We investigated the effects of 5,6-dichloro-1-ethyl-1,3-dihydro-2H-benzimidazol-2-one(DCEBIO) on the Cl^– secretory response of the mouse jejunum using the Ussing short-circuit current (I_sc) technique. DCEBIO stimulated a concentration-dependent, sustained increase in I_sc (EC₅₀ 41 ± 1 µM). Pretreating tissues with 0.25 µM forskolin reduced the concentration-dependent increase in I_sc by DCEBIO and increased the EC₅₀ (53 ± 5 µM). Bumetanide blocked (82 ± 5%) the DCEBIO-stimulated I_sc consistent with Cl^– secretion. DCEBIO was a more potent stimulator of Cl^– secretion than its parent molecule, 1-ethyl-2-benzimidazolinone. Glibenclamide or NPPB reduced the DCEBIO-stimulated I_sc by >80% indicating the participation of CFTR in the DCEBIO-stimulated I_sc response. Clotrimazole reduced DCEBIO-stimulated I_sc by 67 ± 15%, suggesting the participation of the intermediate conductance Ca²⁺-activated K⁺ channel (IK_Ca) in the DCEBIO-activated I_sc response. In the presence of maximum forskolin (10 µM), the DCEBIO response was reduced and biphasic, reaching a peak response of the change in I_sc of 43 ± 5 µA/cm² and then falling to a steady-state response of 17 ± 10 µA/cm² compared with DCEBIO control tissues (61 ± 6 µA/cm²). The forskolin-stimulated I_sc in the presence of DCEBIO was reduced compared with forskolin control tissues. Similar results were observed with DCEBIO and 8-BrcAMP where adenylate cyclase was bypassed. H89, a PKA inhibitor, reduced the DCEBIO-activated I_sc, providing evidence that DCEBIO increased Cl^– secretion via a cAMP/PKA-dependent manner. These data suggest that DCEBIO stimulates Cl^– secretion of the mouse jejunum and that DCEBIO targets components of the Cl^– secretory mechanism. 1-ethyl-2-benzimidazolinone; forskolin; glibenclamide; clotrimazole; H89     

In vitro Regeneration from Excised Leaf Discs of Three Brassica Species

Excised leaf discs of three Brassica species, B. oleracea, B.napus, and B. campestris were induced to produce adventitiousbuds and subsequently entire plants by culture on media withspecific combinations of 6-benzylaminopurine (BAP) and -naphthylaceticacid (NAA). Each species required a particular hormone concentrationfor optimum growth and differentiation: B. oleracea, BAP 10mg^–1 and NAA 1 mg 1^–1; B. napus, BAP 10 mg 1^–1and NAA 10 mg 1^–1; B. campestris, BAP 1 mg 1^–1 andNAA 10 mg 1^–1. In a more detailed study on one of these species, namely B.oleracea, the relative influence of other media components suchas amino acids and other organic additives was examined. Itwas also found that the source and size of the explant greatlyaffected the growth response, as did the size of the culturevessel. The regenerated plants dislayed a range of ploidy as well asphenotypic abnormalities. Findings are discussed in relation to results from other tissueculture systems.     

SOME BEHAVIOURAL AND ELECTRICAL RESPONSES OF SCROBICULARIA PLANA (BIVALVIA:TELLINACEA) TO SIPHONAL WOUNDING

Water pumping, valve movements and heart rate have been recordedfrom Scrobicularia for short periods of normal behaviour andthen after siphonal wounding. Scrobicularia exhibits regularand repetitive pumping periods interrupted for only 2–3s after siphonal wounding, without the regularity of these periodsbeing affected. Wounding does not prevent animals from usingtheir inhalant siphons for deposit feeding. A preliminary investigationof neural responses to stimulation has shown that wounding thesiphon causes minimal disturbance to the animal, a brief (2s)burst of nerve activity occurs, the siphon is retracted, butvalve adduction does not occur. In contrast to this tactilestimulation of the mantle edge always elicits a large burstof impulses in the posterior adductor nerve, valve closure results,usually for 14–15 s. ¹Present address: Dept of Zoology, University of Cape Town,Rondebosch 7700, South Africa. (Received 2 February 1981;     

Nitrate Effects on Pre-emergence Growth and Emergence Percentage of Wheat (Triticum aestivum L.) from Different Sowing Depths

The effects of a range of applied nitrate (NO₃^–) concentrations(0–20 mol m3) on germination and emergence percentageof Triticum aestivum L. cv. Otane were examined at 30, 60, 90and 120 mm sowing depths. Germination percentage was not affectedby either sowing depth or applied NO₃^– concentration whereasemergence percentage decreased with increased sowing depth regardlessof applied NO₃^– concentration. Nitrate did not affectemergence percentage at 30 mm sowing depth, but at 60 to 120mm depth, emergence percentage decreased sharply with an increasedapplied NO₃^– concentration of 0 to 1·0 mol m^–3then decreased only slightly with further increases in appliedNO₃^– of about 5·0 mol m^–3. Root and shoot growth, NO₃^– accumulation and nitrate reductaseactivity (NRA) of plants supplied with 0, 1·0 and 1·0mol m^–3 NO₃^– at a sowing depth of 60 mm were measuredprior to emergence. The coleoptile of all seedlings opened withinthe substrate. Prior to emergence from the substrate, shootextension growth was unaffected by additional NO₃^– butshoot fr. wt. and dry wt. were both greater at 1·0 and1·0 mol m^–3 NO₃^– than with zero NO₃^–.Root dry wt. was unaffected by NO₃^–. Nitrate concentrationand NRA in root and shoot were always low without NO₃^–.At 1·0 and 10 mol m3 NO₃^–, NO₃^– accumulatedin the root and shoot to concentrations substantially greaterthan that applied and caused the induction of NRA. Regardlessof the applied NO₃^– concentration, seedlings which failedto emerge still had substantial seed reserves one month afterplanting. Coleoptile length was substantially less for seedlingswhich did not emerge than for seedlings which emerged, but wasnot affected by NO₃^–. It is proposed that (a) decreasedemergence percentage with increased sowing depth was due tothe emergence of leaf I from the coleoptile within the substrateand (b) decreased emergence percentage with additional NO₃^–was due to the increased expansion of leaf 1 within the substrateresulting in greater folding and damage of the leaf. Key words: Triticum aestivwn L., nitrate, sowing depth, seedling growth, seedling emergence     

Analogue Inhibition of the Active HCO-3 Transport Site in the Characean Plasma Membrane

Competitive inhibition of the HCO^–₃ transport site, atthe plasmalemma of Chara coraUina, by the CO^2–₃ ion isdemonstrated. This CO^2–₃ inhibition was used to demonstratethat HCO^–₃ ions enter the cell by facilitated ‘diffusion’when the HCO^–₃ transport system has been inactivated bytreatment with 10 mM K⁺. Use of CO^2–₃ as a HCO^–₃analogue is limited, however, because of the necessity to employsolutions of high pH. Inhibition was not observed in the presenceof a range of organic and inorganic acid anions. These resultsdemonstrate the stereo-specific nature of the HCO^–₃ bindingsite. A variety of amino compounds were found to inhibit H¹⁴CO^–₃influx. Inhibition appeared to be competitive, being completelyrelieved at higher substrate (HCO^–₃) concentrations. Asimple correlation was not found between the degree of inhibitionand the concentration of neutral base. A combination of thepresence of neutral base and experimental pH values of at least8·0 was required to produce the reactive species thatinhibited HCO^–₃ transport. This species is consideredto be the amino carbamate. These results are discussed withrespect to further HCO^–₃ analogue experiments.     

Synthetic peptide analogs to barnacle settlement pheromone

Barnacle pheromone enhances the rate of settlement and metamorphosis of larvae of Balanus amphitrite Darwin. Analogs to the heterogeneous pheromone peptides were sought. Settlement assays were used to assess both the pheromone and the potential analogs. The pheromone has a lower threshold of activity at a concentration of 0.2 μg BSA protein equivalence l⁻¹. Treatment with carboxypeptidase eliminates biological activity. Series of dipeptides were tested to determine if dipeptides could promote settlement. Combinations of acidic, neutral, and basic amino acids in dipeptides were examined. Specific small peptides can mimic barnacle pheromone. Only peptides with a basic carboxy-terminal amino acid and either a neutral or a basic amino-terminal amino acid enhance settlement. Six peptides were shown to mimic pheromone activity at concentrations comparable to the native molecule. Some peptides were more potent than others. The most effective peptides were L-leucyl-L-arginine and L-histidyl-L-lysine which had a lower threshold of settlement enhancement of 2.0×10⁻¹⁰ M and caused a 130% increase in settlement rate at 2.0×10⁻⁸ M. Glycyl-glycyl-L-arginine, glycyl-L-histidyl-L-lysine, L-leucyl-glycyl-L-arginine and L-tyrosyl-L-arginine had thresholds between 2.0×10⁻⁸ M and 2.0×10⁻⁹ M. Peptide pheromone analogs should be useful in determining the nature and mechanism of barnacle pheromone receptor interactions.     

Responses of CO2 assimilation to changes in irradiance: laboratory and field data and a model for beans (Phaseolus vulgaris L.)

The responses of net CO₂ assimilation to sudden changes in irradiancewere studied in Phaseolus vulgaris L. in the laboratory andthe field. For irradiance changes between 50 µmol m^–2s^–1 to 350 µmol m^–2 s^–1 in the laboratory,assimilation rate increased with half-times of 2.7 and 4.1 minin well-watered and water-stressed plants, respectively. Ina field experiment with a change in irradiance from 400 to 1200µmol m^–2 s^–1 the response was faster (half-time=c.1.2 min). In all cases when irradiance was returned to a lowvalue, assimilation declined rapidly with a half-time of approximately1 min, which approached the time resolution of the gas-exchangesystem. The corresponding changes in stomatal conductance in responseto both increasing and decreasing irradiance were much slowerthan the assimilation responses, indicating that biochemicalprocesses, rather than CO₂ supply, primarily determined theactual rate of assimilation in these experiments. The conceptof stomatal limitation to photosynthesis is discussed in relationto these results. A simple model for assimilation in a fluctuating light environmentis proposed that depends on a steadystate light response curve,an ‘induction lag’ on increasing irradiance, andan induction-state memory. The likely importance of taking accountof such induction lags in natural canopy microclimates is considered. Key words: Models, Phaseolus vulgaris, photosynthetic induction, CO₂ assimilation, stomatal limitation, sunflecks, water stress