Effects of di-n-butyl phthalate on growth and photosynthesis in algae and on isolated organelles from higher plants

Di- n -butyl phthalate (DBF) is widely used as a plasticizer and has been found in all types of ecosystems. It inhibits growth and photosynthesis of green algae ( Chlorella emersonii CCAP strain 211/8 h and Selenastrum capricornutum CCAP strain 278/4) at concentrations higher than 10-⁵ M . The IC₅₀ value for CO₂-dependent oxygen evolution in algae was 3 × 10^-4M. The CO₂-reduction in isolated protoplasts prepared from barley ( Hordeum vulgare L. cv. Simba) was also inhibited by phthalate. The IC₅₀ value was 2 × 10^-4 M . The electron transport in isolated thylakoids prepared from spinach was inhibited with an IC₅₀ value of 3 × 10^-4 M . The IC₅₀ value for uncoupled electron transport extrapolated to zero chlorophyll concentration was 2.5 × 10^-5 M . The effect of di-n-butyl phthalate was localized to reactions in photosystem II. Di-n-butyl phthalate could thus be a pollutant which affects growth and photosynthesis of plants. The reported IC₅₀ values may be underestimated since di- n -butyl phthalate can attach to surfaces. The results are discussed in relation to observed effects of di- n -butyl phthalate on other organisms.     

Interaction of triacontanol with gibberellin in control of lettuce seed germination

Triacontanol at concentrations from 2.3 × 10^-9 M to 2.3 × 10^-7 M did not affect the germination of lettuce ( Lactuca sativa L., cv. Grand Rapids) seeds in darkness, stimulated by light at 25°C or by benzyladenine at 31°C. Stimulation of seed germination by gibberellin A₃ (10^-5 M ) was significantly inhibited by triacontanol; the most effective concentration was 4.6 × 10^-8 M. Pulse experiments demonstrated that triacontanol was ineffective when applied later than gibberellin, whereas an inverse sequence of treatment caused an inhibition comparable to that resulting from continuous treatment of seeds with both factors. Possible interaction of triacontanol with gibberellin receptor is discussed.     

Feeding responses of the horsefly, Tabanus nigrovittatus, to phagostimulants

ABSTRACT. Wild caught horseflies, Tabanus nigrovittatus Macq. (Diptera, Tabanidae), were presented solutions of 0.15 MNaCl at 37°C containing various concentrations of ATP, ADP, AMP, adenosine, phytic acid or 2,3-diphosphoglycerate in an artificial feeding apparatus. The insects fed upward through a Para-film M® membrane. ADP (ED₅₀ 35 μM) was more potent than ATP (ED₅₀ 112 μM) and AMP (ED₅₀ 382 mUM). All of these diets were deposited in the midgut, an indication that the flies were in the 'blood feeding' mode. Adenosine caused only 23% gorging at 1 mM. Phytic acid caused only 10% gorging at 1 mM and 2,3-diphosphoglyceric acid had no activity at 0.6 mM. Flies would feed only in highly reflective cages under high levels of light intensity (1200–1500 lux) at the membrane surface.     

ACCUMULATION OF ADENOSINE 3'',5''-MONOPHOSPHATE IN BRAIN SLICES: INTERACTION OF LOCAL ANAESTHETICS AND DEPOLARIZING AGENTS

Abstract— Membrane depolarizing agents such as veratridine, ouabain and high concentrations of potassium ions elicit a remarkable accumulation of cyclic AMP in brain slices incubated in vitro , and this accumulation, but not that elicited by biogenic amines, is prevented by a membrane stabilizer, cocaine. The effect of various local anaesthetics (compounds which are known to stabilize the membrane of peripheral sensory nerves) on the accumulation of cyclic AMP elicited by depolarizing agents in incubated slices of guinea pig brain has now been examined. At optimal concentrations the anaesthetics inhibited by more than 95 per cent the accumulation of cyclic AMP elicited with veratridine, ouabain, and high concentrations of potassium ions. The order of the inhibitory potency vs. veratridine was: dibucaine (ED₅₀= 9.5 ± 10⁻⁶ M) > tetracaine > cocaine (ED₅₀= 1·3 ± 10⁻⁴ M) > lidocaine > procaine (ED₅₀= 1.7 ± 10⁻³M). This order is consistent with the order of their local anaesthetic potency, but is not consonant with the order of the relative toxicity of these agents when used as spinal anaesthetics.     

Feeding responses of the horsefly, Tabanus nigrovittatus, to physical factors, ATP analogues and blood fractions

ABSTRACT. Wild-caught female horseflies, Tabanus nigrovittatus Macq. (Diptera: Tabanidae), were presented solutions of seven analogues of ATP in 0.15 m NaCl, or various blood fractions, either as free liquids at 22 or 38C or covered with a Parafilm M membrane at 38C. Warming the diet, so that it can stimulate the insects' heat receptors, or presenting it warmed and covered with a membrane, which the flies can pierce and thus deploy their mouthparts as they would when blood-feeding, enhances the response to gorging stimulants. ADP (ED₅₀ 45 μM) was the most potent chemical phagostimulant. There were no significant differences between the potencies of AMP, A(TETRA)P, AMP-PCP, AMP-PNP or AMP-S, which were 3.5-5 times less potent than ADP. Cyclic AMP had no phagostimulatory activity at concentrations of 400 or 1000 μM. The ED₅₀ for washed red blood cells (RBC) in saline was 4.5% (one tenth the concentration found in blood). RBC-free plasma caused only 10% gorging but plasma with 0.5% RBC caused 61% gorging, indicating synergism between RBC and plasma.     

CHARACTERISTICS OF D-GLUCOSAMINE UPTAKE BY RAT BRAIN SYNAPTOSOMES

Abstract— The uptake of D-glucosamine by rat brain synaptosomes is studied as a function of time, temperature and synaptosomal protein and substrate concentrations. The rate of D-glucosamine uptake, after correcting for simple diffusion, obeys Michaelis-Menten kinetics. The apparent kinetic constants for the uptake process are K_m = 2.5 0.8 m m , V_max = 3.7 ± 1.2 nmol/mg protein/min. D-Glucose, D-mannose, 2-deoxy-D-glucose and 3-0-methyl-o-glucose are potent inhibitors of D-glucosamine uptake. 2-Deoxy-D-glucose and D-glucosamine inhibit the uptake of one another in a simple competitive manner, indicating their sharing of a common transport system. Cytochalasin B, phloretin and phloridzin are powerful competitive inhibitors of D-glucosamine uptake with apparent inhibitor constants ( K₁ ) of 7.0 × 10^-5, 2.3 × 10^-3 and 0.4 mM, respectively. The uptake is unaffected by Na⁺, Li⁺ and Mg²⁺, partially inhibited by NH₄⁺, Mn²⁺ and Ca²⁺, and slightly stimulated by PO₄-ions. D-Glucosamine uptake is also sensitive to inhibition by several sulfhydryl reagents, thus implying the involvement of sulfhydryl groups in the transport process. The apparent affinity constants for synaptosomal transport for both D-glucosamine and 2-deoxy-D-glucose are about 4 times greater in 7-day-old than in the adult rat brains.     

Feeding behaviour in response to blood fractions and chemical phagostimulants in the black-fly, Simulium venustum

ABSTRACT. Wild-caught black-flies ( Simulium venustum Say complex) were presented with diets at 37°C in an artificial feeding apparatus. Washed human red cells resuspended 1:1 in Ringer solution were potent phagostimulants, causing 89% of flies to gorge. Whole plasma was more potent (32% gorging) than platelet-poor plasma (2%). The ED₅₀ for red cells was 3.5%. Although ADP, contained in high-concentration in platelets, was confirmed as a more potent phagostimulant than ATP (ED₅₀ of 5πM V. 12μM), red cells were clearly more phagostimulatory than platelets, and with a potency more than adequate to trigger gorging in vivo. A high response to the ATP analogues, β, γ-methylene ATP and adenine phosphosulphate, supports the view that the phosphate chain is relatively unimportant in determining nucleotide potency to simuliids. The compounds phytic acid and 2,3-disphosphoglycerate, potent stimulants to Rhodnius prolixus , produced only moderate and no response, respectively at 1 mM; 5-hydroxytryptamine, another major constituent of platelets, also produced only a moderate response. Only flies caught while showing a characteristic probing behaviour would subsequently probe and feed in vitro; this 'blood-feeding mode' rapidly disappeared in the absence of stimuli eliciting actual probing, but for flies in this state a small temperature rise was sufficient stimulus for probing.     

Enteric Glia Exhibit P2U Receptors that Increase Cytosolic Calcium by a Phospholipase C-Dependent Mechanism

Abstract: Calcium signaling in fura-2 acetoxymethyl ester-loaded enteric glia was investigated in response to neuroligands; responses to ATP were studied in detail. Carbachol (1 m M ), glutamate (100 µ M ), norepinephrine (10 µ M ), and substance P (1 µ M ) did not increase the intracellular calcium concentration ([Ca²⁺]_i) in cultured enteric glia. An increasing percentage of glia responded to serotonin (4%; 100 µ M ), bradykinin (11%; 10 µ M ), and histamine (31%; 100 µ M ), whereas 100% of glia responded to ATP (100 µ M ). ATP-evoked calcium signaling was concentration dependent in terms of the percentage of glia responding and the peak [Ca²⁺]_i achieved; responses were pertussis toxin insensitive. Based on responsiveness of enteric glia to purinergic agonists and peak [Ca²⁺]_i evoked, ATP = UTP > ADP > β,γ-methyleneadenosine 5'-triphosphate ≫ 2-methylthioadenosine 5'-triphosphate = α,β-methyleneadenosine 5'-triphosphate = AMP = adenosine, suggesting a glial P_2U receptor. Depletion of d - myo -inositol 1,4,5-trisphosphate-sensitive calcium stores by thapsigargin (10 µ M ) abolished glial responses to ATP. Similarly, calcium responses were decreased 92% by U-73122 (10 µ M ), an inhibitor of phospholipase C, and 93% by the phorbol ester phorbol 12-myristate 13-acetate (100 n M ), an activator of protein kinase C. Thus, cultured enteric glia can respond to neurotransmitters with increases in [Ca²⁺]_i. Our data suggest that glial responses to ATP are mediated by a P_2U receptor coupled to activation of phospholipase C and release of intracellular calcium stores.     

ADENOSINE KINASE OF MAMMALIAN BRAIN: PARTIAL PURIFICATION AND ITS ROLE FOR THE UPTAKE OF ADENOSINE

Abstract— Adenosine metabolism in the homogenate of brain mainly undergoes deamination to inosine and hypoxanthine, while uniformly labelled [¹⁴C]adenosine injected into the carotid artery or [8-¹⁴C]adenosine incubated with brain slices was mostly phosphorylated to [¹⁴C]adenine nucleotides in brain cells. Adenosine kinase has now been partially purified from homogenates of guinea pig brain. The kinase preparation was free of adenosine deaminase, almost free of adenosine triphosphatase and had a K_m of the order of 2 × 10^-5M for adenosine.
Kinetic studies with brain slices showed that adenosine reached the cells by diffusion and that the diffusion was facilitated by subsequent phosphorylation to adenine nucleotides. From the following experimental results, it is concluded that the phosphorylation is catalysed by adenosine kinase quantitatively. (1) During the uptake and phosphorylation of adenosine by brain slices, the nucleoside did not split to adenine and ribose moieties. (2) The rate of formation of adenine nucleotides in the slices was a hyperbolic function of the concentration of adenosine in the medium, showing an apparent K_m foradenosine of the order of 2 × 10^-5 M. (3) Some analogues of adenosine inhibited both the facilitated diffusion of adenosine and the kinase activity, but ouabain (0.005 mM) did not inhibit either.     

Two Distinct ATP Receptors Activate Calcium Entry and Internal Calcium Release in Bovine Chromaffin Cells

Abstract: ATP, an established neurotransmitter, causes elevation of cytosolic Ca²⁺ and catecholamine secretion when applied to chromaffin cells in the intact adrenal gland. The ATP-induced rise in Ca²⁺ is due both to release from internal stores and to entry across the plasma membrane. The latter source of Ca²⁺ causes secretion; the primary role of Ca²⁺ released from internal stores remains undetermined. In this article, we have studied the nucleotide specificity for activating the two types of Ca²⁺ increases. The agonist potency order for the increase in fluorescence from fura-2-loaded chromaffin cells due to release of Ca²⁺ from internal stores is ATP = UTP > ADP > 2-methylthio-ATP, α,β-methylene ATP, identifying the receptor as a P_2U purinoceptor. The potency order for secretion is 2-methylthio-ATP > ATP > α,β-methylene ATP, ADP, UTP, placing the receptor in the P_2Y subtype. Thus, two distinct receptors are responsible for Ca²⁺ release and secretion. Agonists were more effective in the absence of extracellular Mg²⁺, suggesting that ATP uncomplexed with divalent cations binds preferentially to both receptors. The low response of both receptors to ADP distinguishes them from the ATP receptor on these cells that inhibits voltage-dependent Ca²⁺ current and secretion.     

Interaction of photoperiod and gibberellin on growth and photosynthesis of high-latitude Poa pratensis

The relative growth rate of pot-grown plants of Poa pratensis L. cv. Holt, origin 69s°N, was increased by 20–40% by photoperiod extension with low intensity incandescent light from 8 to 24 h at 9–21°C. The main increase occurred over the 14 to 18 h photoperiod range. The true photoperiodic nature of the response was demonstrated by the effectiveness of night interruption in stimulating growth. Fortnightly sprayings with gibberellic acid (GA₃) (3 × 10^-6 to 3 × 10^-5 M ) mimicked all the effects of long days, whereas (2-chloroethyl)-trimethylammonium chloride (CCC) counteracted the effects of long days. Both growth substances exhibited pronounced interactions with photoperiod, GA₃ being most effective in short days and CCC in long days. The growth stimulation, whether caused by long days or GA₃, was exerted mainly through increases in individual and total leaf area. This was associated with a reduction in CO₂, exchange rate and a parallel fall in specific leaf weight. Proportionally, however, the increase in leaf area was greater than the fall in CO₂ exchange rate, resulting in a 38 to 118% increase in photosynthesis per leaf. No evidence was found of any direct and promotive effect of transition to long days on the CO₂ exchange rate of already expanded leaves.     

Joint action of l-leucine and sodium phosphate buffer solutions as feeding stimulants for protein-deprived females of the house fly Musca domestica

ABSTRACT. Potentiation in joint action was demonstrated between solutions of L-leucine and sodium phosphate buffer (pH 6.3) as feeding stimulants for protein-deprived females of the house fly, Musca domestica L. Both components alone elicited feeding. In two-choice feeding tests, mixtures consisting of equi-stimulating concentrations of the two components were taken in greater quantities than either component alone at twice the concentration in the mixture.
The presence of 1×10^-1 M phosphate buffer markedly lowered the threshold for detection of L-leucine. The presence of phosphate buffer strengthened the preferences shown by flies given choices of concentrations of L-leucine differing by a factor of 2 and enabled them to display preferences at lower concentrations.
The presence of 1×10^-3 M L-leucine increased, somewhat, the ability of flies to detect low concentrations of phosphate buffer. Its presence had relatively little effect on the strength of preference shown between two-fold differences in concentration of phosphate buffer when the higher concentration was 6.3×10^-3 M or less, but markedly strengthened the preferences when the higher concentration was 2.5×10^-2M or greater. Leucine increased the optimal concentration of phosphate buffer by a factor of more than 2 and converted 2×10^-1 M phosphate buffer from a mild feeding deterrent to a powerful feeding stimulant.     

Nitrate and nitrite reduction in the plant fraction of alfalfa root nodules

The plant fraction of alfalfa ( Medicago sativa L. cv. Aragon) nodules contained both nitrate reductase (NR) and nitrite reductase (NiR). Specific activity of NADH-NR from the cytosol of nodules not treated with NO₃- was about 30 nmol (mg protein)^-1-h^-1 and was not basically affected by NO₃ addition. In contrast, typical specific activity for cytosolic NiR was 1.5 umol (mg protein)^-1h^-1 using methyl viologen as electron donor. This activity strongly increased with NO₃ concentration, probably due to substrate induction. Maximal activity was 3.5 μmol (mg protein)^-1h^-1 at 50 to 200 mM NO₃.
Estimates indicate that the contribution of cytosol to the overall NR and NiR activities of alfalfa nodules is distinctly different: less than 10% and about 70%, respectively. The increasing amounts of NO₂ accumulating in the cytosol upon NO₃, supply, and the different response to NO₃ of bacteroid and cytosolic NRs support the concept that most of this NO₂ comes from the bacteroids.     

Stimulation of respiration by Pb2+ in detached leaves and mitochondria of C3 and C4 plants

The exposure of detached leaves of C₃ plants (pea, barley) and C₄ plant (maize) to 5 m M Pb (NO₃)₂ for 24 h caused a reduction of their photosynthetic activity by 40–60%, whereas the respiratory rate was stimulated by 20–50%. Mitochondria isolated from Pb²⁺-treated pea leaves oxidized substrates (glycine, succinate, malate) at higher rates than mitochondria from control leaves. The respiratory control (RCR) and the ADP/O ratio were not affected. Pb²⁺ caused an increase in ATP content and the ATP/ADP ratio in pea and maize leaves. Rapid fractionation of barley protoplasts incubated at low and high CO₂ conditions, indicated that the increased ATP/ADP ratio in Pb²⁺-treated leaves resulted mainly from the production of mitochondrial ATP. The measurements of membrane potential of mitochondria with a TPP⁺-sensitive electrode further showed that mitochondria isolated from Pb²⁺-treated leaves had at least as high membrane potential as mitochondria from control leaves. The activity of NAD-malate dehydrogenase in the protoplasts from barley leaves treated with Pb²⁺ was 3-fold higher than in protoplasts from control leaves. The activities of photorespiratory enzymes NADH-hydroxypyruvate reductase and glycolate oxidase as well as of NAD-malic enzyme were not affected. The presented data indicate that stimulation of respiration in leaves treated by lead is in a close relationship with activation of malate dehydrogenase and stimulation of the mitochondrial ATP production. Thus, respiration might fulfil a protective role during heavy metal exposure.     

Effects of 1-Methyl-4-Phenylpyridinium on Isolated Rat Brain Mitochondria: Evidence for a Primary Involvement of Energy Depletion

Abstract: The effects of 1-methyl-4-phenylpyridinium (MPP⁺) on the oxygen consumption, ATP production, H₂O₂ production, and mitochondrial NADH-CoQ₁ reductase (complex I) activity of isolated rat brain mitochondria were investigated. Using glutamate and malate as substrates, concentrations of 10–100 µ M MPP⁺ had no effect on state 4 (−ADP) respiration but decreased state 3 (+ADP) respiration and ATP production. Incubating mitochondria with ADP for 30 min after loading with varying concentrations of MPP⁺ produced a concentration-dependent decrease in H₂O₂ production. Incubation of mitochondria with ADP for 60 min after loading with 100 µ M MPP⁺ caused no loss of complex I activity after washing of MPP⁺ from the mitochondrial membranes. These data are consistent with MPP⁺ initially binding specifically to complex I and inhibiting both the flow of reducing equivalents and the production of H₂O₂ by the mitochondrial respiratory chain, without irreversibly damaging complex I. However, mitochondria incubated with H₂O₂ in the presence of Cu²⁺ ions showed decreased complex I activity. This study provides additional evidence that cellular damage initiated by MPP⁺ is due primarily to energy depletion caused by specific binding to complex I, any increased damage due to free radical production by mitochondria being a secondary effect.     

Seasonal changes in the response of wood-ants (Formica lugubris) to sucrose baits

Abstract. 1. The acceptability of sucrose solutions to Formica lugubris Zett. in the field was tested by offering droplets of known concentrations to ants tending aphids.
2. A probit model fitted to the data allowed the computation of the Median Effective Concentration (ED₅₀) and its confidence limits.
3. In spring and early summer ED₅₀ was about 0.15 M sucrose, but the ED₅₀ rose in 1 week at the end of June from 0.2 M to 0.9 M. The change was simultaneous on pine and birch trees. The ED₅₀ fell gradually to about 0.4 M in early November.
4. The increase in ED₅₀ is related to the production of the summer apterae in the aphids tended, Cinara pini (L.) on pines and Symydobius oblongus (von Heyden) on birch. This increases the 'quality' of food resource so that low sucrose concentrations can no longer compete for ant attendance.
5. The increase in ED₅₀ may limit the attendance of wood-ants at the nectaries of bracken, Pteridium aquilinum (L.) Kuhn. and at colonies of some other aphid species which are attended only in early summer.     

Evidence for Chromosomal Macronuclear Substructures in Tetrahymena*†

SYNOPSIS.
Under the growth conditions employed, the G₁ macronucleus of Tetrahymena pyriformis HSM contains 7.4 × 10^-12 g DNA, the G₂ micronucleus 0.42 × 10^-12 g. DNA content from the Tetrahymena thermophila macronucleus did not significantly differ from that of HSM, but the micronucleus contained about twice as much DNA as the micronucleus of the HSM cells. The T. thermophila macronucleus contained on average enough DNA for ˜ 35 haploid micronuclear copies. A new spreading technic allowed separation of macronuclear substructures from cells of late G₂ to early G₁. Photometric determination of DNA content of 345 individual structures suggested the existence of 5 different-sized macronuclear structures with a DNA content corresponding to 2, 4, 8, and 16 × the basic values. Comparison of the DNA content of these structures with (a) mitotic micronuclear chromosomes and (b) meiotic micronuclear chromosomes of T. thermophila cells suggests that the 5 basic values of macronuclear structures derive from structures of micronuclear chromosomes. The micronuclear chromosomes of T. pyriformis may be oligotenic. It is suggested that these results further our understanding of macronuclear organization.     

PHOSPHOCHOLINE DIGLYCERIDE TRANSFERASE ACTIVITY DURING DEVELOPMENT OF THE CHICKEN BRAIN

Abstract— The activity of chicken brain phosphocholine diglyceride transferase was followed during pre- and postnatal development. The specific activity of this enzyme increases from the 10th day of embryonic life, reaches a maximum at hatching and decreases thereafter. Total brain activity increases in parallel with the increase of brain lecithins. The apparent K _m of the enzyme for CDP choline is 1.5 × 10^-4 m before the 10th day of embryonic life, 2.5 × 10^-5 m between the 13th day of the embryo and the 10th day after hatching, and finally 1.3 × 10^-4 m after the 38th day of postnatal life. These data suggest the existence of isoenzymes, one of which appears at the beginning of myelination.     

THE UPTAKE OF γ-[3H]AMINOBUTYRIC ACID BY SLICES FROM VARIOUS REGIONS OF RAT BRAIN AND THE EFFECT OF LITHIUM

Abstract— Slices from various regions of rat brain, incubated at 25°C, rapidly accumulate [³H]GABA from the surrounding medium until after 60min tissue:medium ratios as high as 300 may be achieved. Kinetic analysis has demonstrated two distinct uptake systems for GABA in all the brain regions examined. One system has a relatively high substrate affinity ( K_m = 1.2 ± 10^-5 M) while the other has a lower affinity ( K_m = 4 ± 10^-4 M). Studies at low GABA concentration (5 ± 10^-8 M), as well as estimates of maximum velocities, have shown that the distribution of the high affinity uptake system is heterogeneous. Cortex, hypothala mus, midbrain and hippocampus have relatively high uptake rates while the striatum, cerebellum and pons and medulla have a lower uptake rate. Maximum velocities for the low affinity uptake system show much less regional variation.
Lithium, either added to the incubation medium or fed to rats, had no effect on the uptake of GABA by cortical slices.     

Oxygen Perception and O2 Toxicity in the Freshwater Ciliated Protozoon Loxodes

ABSTRACT. Loxodes reached peak abundance close to the oxic-anoxic boundary (O₂ 5% atm) in two lakes, in test tube cultures, and in glass chambers with horizontal O₂ gradients. Vertical profiles of CO₂, pH, sulfide, and Fe²⁺ in a lake were not closely related to Loxodes abundance. In a laboratory experiment, Loxodes followed a retreating source of O₂ and was repelled by a high pO₂. This behavior was sustained when cells simultaneously swam up or down gradients of both CO₂ and pH. Aggregation of cells was abolished by KCN (10^-4-10^-6 M). Sodium azide (10^-1-10^-4 M) had no effect and 2,4-DNP sharpened the aggregation. Rotenone, Antimycin A, and HOQNO had no obvious effect. Cytochrome oxidase is probably the oxygen receptor. Loxodes striatus contained low activities of superoxide dismutase and catalase. Extracellular production of superoxide (O_-²) and hydrogen peroxide (H₂O₂) were probably not responsible for the exclusion of Loxodes from water with a high pO₂. Continuous exposure of Loxodes to oxygen at normal atmospheric pressure at 10°C led to 50% mortality in 10 days. Cells left free to swim in an oxygen gradient doubled their number in the same period. Light exacerbated the toxic effects of O₂. Behavioral responses to the dissolved oxygen tension probably controlled the spatial distribution of Loxodes.